[github/fretlink/terraform-provider-statuscake.git] / vendor / golang.org / x / net / http2 / transport.go

// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Transport code.

package http2

import (
        "bufio"
        "bytes"
        "compress/gzip"
        "context"
        "crypto/rand"
        "crypto/tls"
        "errors"
        "fmt"
        "io"
        "io/ioutil"
        "log"
        "math"
        mathrand "math/rand"
        "net"
        "net/http"
        "net/http/httptrace"
        "net/textproto"
        "sort"
        "strconv"
        "strings"
        "sync"
        "time"

        "golang.org/x/net/http/httpguts"
        "golang.org/x/net/http2/hpack"
        "golang.org/x/net/idna"
)

const (
        // transportDefaultConnFlow is how many connection-level flow control
        // tokens we give the server at start-up, past the default 64k.
        transportDefaultConnFlow = 1 << 30

        // transportDefaultStreamFlow is how many stream-level flow
        // control tokens we announce to the peer, and how many bytes
        // we buffer per stream.
        transportDefaultStreamFlow = 4 << 20

        // transportDefaultStreamMinRefresh is the minimum number of bytes we'll send
        // a stream-level WINDOW_UPDATE for at a time.
        transportDefaultStreamMinRefresh = 4 << 10

        defaultUserAgent = "Go-http-client/2.0"
)

// Transport is an HTTP/2 Transport.
//
// A Transport internally caches connections to servers. It is safe
// for concurrent use by multiple goroutines.
type Transport struct {
        // DialTLS specifies an optional dial function for creating
        // TLS connections for requests.
        //
        // If DialTLS is nil, tls.Dial is used.
        //
        // If the returned net.Conn has a ConnectionState method like tls.Conn,
        // it will be used to set http.Response.TLS.
        DialTLS func(network, addr string, cfg *tls.Config) (net.Conn, error)

        // TLSClientConfig specifies the TLS configuration to use with
        // tls.Client. If nil, the default configuration is used.
        TLSClientConfig *tls.Config

        // ConnPool optionally specifies an alternate connection pool to use.
        // If nil, the default is used.
        ConnPool ClientConnPool

        // DisableCompression, if true, prevents the Transport from
        // requesting compression with an "Accept-Encoding: gzip"
        // request header when the Request contains no existing
        // Accept-Encoding value. If the Transport requests gzip on
        // its own and gets a gzipped response, it's transparently
        // decoded in the Response.Body. However, if the user
        // explicitly requested gzip it is not automatically
        // uncompressed.
        DisableCompression bool

        // AllowHTTP, if true, permits HTTP/2 requests using the insecure,
        // plain-text "http" scheme. Note that this does not enable h2c support.
        AllowHTTP bool

        // MaxHeaderListSize is the http2 SETTINGS_MAX_HEADER_LIST_SIZE to
        // send in the initial settings frame. It is how many bytes
        // of response headers are allowed. Unlike the http2 spec, zero here
        // means to use a default limit (currently 10MB). If you actually
        // want to advertise an ulimited value to the peer, Transport
        // interprets the highest possible value here (0xffffffff or 1<<32-1)
        // to mean no limit.
        MaxHeaderListSize uint32

        // StrictMaxConcurrentStreams controls whether the server's
        // SETTINGS_MAX_CONCURRENT_STREAMS should be respected
        // globally. If false, new TCP connections are created to the
        // server as needed to keep each under the per-connection
        // SETTINGS_MAX_CONCURRENT_STREAMS limit. If true, the
        // server's SETTINGS_MAX_CONCURRENT_STREAMS is interpreted as
        // a global limit and callers of RoundTrip block when needed,
        // waiting for their turn.
        StrictMaxConcurrentStreams bool

        // t1, if non-nil, is the standard library Transport using
        // this transport. Its settings are used (but not its
        // RoundTrip method, etc).
        t1 *http.Transport

        connPoolOnce  sync.Once
        connPoolOrDef ClientConnPool // non-nil version of ConnPool
}

func (t *Transport) maxHeaderListSize() uint32 {
        if t.MaxHeaderListSize == 0 {
                return 10 << 20
        }
        if t.MaxHeaderListSize == 0xffffffff {
                return 0
        }
        return t.MaxHeaderListSize
}

func (t *Transport) disableCompression() bool {
        return t.DisableCompression || (t.t1 != nil && t.t1.DisableCompression)
}

// ConfigureTransport configures a net/http HTTP/1 Transport to use HTTP/2.
// It returns an error if t1 has already been HTTP/2-enabled.
func ConfigureTransport(t1 *http.Transport) error {
        _, err := configureTransport(t1)
        return err
}

func configureTransport(t1 *http.Transport) (*Transport, error) {
        connPool := new(clientConnPool)
        t2 := &Transport{
                ConnPool: noDialClientConnPool{connPool},
                t1:       t1,
        }
        connPool.t = t2
        if err := registerHTTPSProtocol(t1, noDialH2RoundTripper{t2}); err != nil {
                return nil, err
        }
        if t1.TLSClientConfig == nil {
                t1.TLSClientConfig = new(tls.Config)
        }
        if !strSliceContains(t1.TLSClientConfig.NextProtos, "h2") {
                t1.TLSClientConfig.NextProtos = append([]string{"h2"}, t1.TLSClientConfig.NextProtos...)
        }
        if !strSliceContains(t1.TLSClientConfig.NextProtos, "http/1.1") {
                t1.TLSClientConfig.NextProtos = append(t1.TLSClientConfig.NextProtos, "http/1.1")
        }
        upgradeFn := func(authority string, c *tls.Conn) http.RoundTripper {
                addr := authorityAddr("https", authority)
                if used, err := connPool.addConnIfNeeded(addr, t2, c); err != nil {
                        go c.Close()
                        return erringRoundTripper{err}
                } else if !used {
                        // Turns out we don't need this c.
                        // For example, two goroutines made requests to the same host
                        // at the same time, both kicking off TCP dials. (since protocol
                        // was unknown)
                        go c.Close()
                }
                return t2
        }
        if m := t1.TLSNextProto; len(m) == 0 {
                t1.TLSNextProto = map[string]func(string, *tls.Conn) http.RoundTripper{
                        "h2": upgradeFn,
                }
        } else {
                m["h2"] = upgradeFn
        }
        return t2, nil
}

func (t *Transport) connPool() ClientConnPool {
        t.connPoolOnce.Do(t.initConnPool)
        return t.connPoolOrDef
}

func (t *Transport) initConnPool() {
        if t.ConnPool != nil {
                t.connPoolOrDef = t.ConnPool
        } else {
                t.connPoolOrDef = &clientConnPool{t: t}
        }
}

// ClientConn is the state of a single HTTP/2 client connection to an
// HTTP/2 server.
type ClientConn struct {
        t         *Transport
        tconn     net.Conn             // usually *tls.Conn, except specialized impls
        tlsState  *tls.ConnectionState // nil only for specialized impls
        singleUse bool                 // whether being used for a single http.Request

        // readLoop goroutine fields:
        readerDone chan struct{} // closed on error
        readerErr  error         // set before readerDone is closed

        idleTimeout time.Duration // or 0 for never
        idleTimer   *time.Timer

        mu              sync.Mutex // guards following
        cond            *sync.Cond // hold mu; broadcast on flow/closed changes
        flow            flow       // our conn-level flow control quota (cs.flow is per stream)
        inflow          flow       // peer's conn-level flow control
        closing         bool
        closed          bool
        wantSettingsAck bool                     // we sent a SETTINGS frame and haven't heard back
        goAway          *GoAwayFrame             // if non-nil, the GoAwayFrame we received
        goAwayDebug     string                   // goAway frame's debug data, retained as a string
        streams         map[uint32]*clientStream // client-initiated
        nextStreamID    uint32
        pendingRequests int                       // requests blocked and waiting to be sent because len(streams) == maxConcurrentStreams
        pings           map[[8]byte]chan struct{} // in flight ping data to notification channel
        bw              *bufio.Writer
        br              *bufio.Reader
        fr              *Framer
        lastActive      time.Time
        // Settings from peer: (also guarded by mu)
        maxFrameSize          uint32
        maxConcurrentStreams  uint32
        peerMaxHeaderListSize uint64
        initialWindowSize     uint32

        hbuf    bytes.Buffer // HPACK encoder writes into this
        henc    *hpack.Encoder
        freeBuf [][]byte

        wmu  sync.Mutex // held while writing; acquire AFTER mu if holding both
        werr error      // first write error that has occurred
}

// clientStream is the state for a single HTTP/2 stream. One of these
// is created for each Transport.RoundTrip call.
type clientStream struct {
        cc            *ClientConn
        req           *http.Request
        trace         *httptrace.ClientTrace // or nil
        ID            uint32
        resc          chan resAndError
        bufPipe       pipe // buffered pipe with the flow-controlled response payload
        startedWrite  bool // started request body write; guarded by cc.mu
        requestedGzip bool
        on100         func() // optional code to run if get a 100 continue response

        flow        flow  // guarded by cc.mu
        inflow      flow  // guarded by cc.mu
        bytesRemain int64 // -1 means unknown; owned by transportResponseBody.Read
        readErr     error // sticky read error; owned by transportResponseBody.Read
        stopReqBody error // if non-nil, stop writing req body; guarded by cc.mu
        didReset    bool  // whether we sent a RST_STREAM to the server; guarded by cc.mu

        peerReset chan struct{} // closed on peer reset
        resetErr  error         // populated before peerReset is closed

        done chan struct{} // closed when stream remove from cc.streams map; close calls guarded by cc.mu

        // owned by clientConnReadLoop:
        firstByte    bool  // got the first response byte
        pastHeaders  bool  // got first MetaHeadersFrame (actual headers)
        pastTrailers bool  // got optional second MetaHeadersFrame (trailers)
        num1xx       uint8 // number of 1xx responses seen

        trailer    http.Header  // accumulated trailers
        resTrailer *http.Header // client's Response.Trailer
}

// awaitRequestCancel waits for the user to cancel a request or for the done
// channel to be signaled. A non-nil error is returned only if the request was
// canceled.
func awaitRequestCancel(req *http.Request, done <-chan struct{}) error {
        ctx := req.Context()
        if req.Cancel == nil && ctx.Done() == nil {
                return nil
        }
        select {
        case <-req.Cancel:
                return errRequestCanceled
        case <-ctx.Done():
                return ctx.Err()
        case <-done:
                return nil
        }
}

var got1xxFuncForTests func(int, textproto.MIMEHeader) error

// get1xxTraceFunc returns the value of request's httptrace.ClientTrace.Got1xxResponse func,
// if any. It returns nil if not set or if the Go version is too old.
func (cs *clientStream) get1xxTraceFunc() func(int, textproto.MIMEHeader) error {
        if fn := got1xxFuncForTests; fn != nil {
                return fn
        }
        return traceGot1xxResponseFunc(cs.trace)
}

// awaitRequestCancel waits for the user to cancel a request, its context to
// expire, or for the request to be done (any way it might be removed from the
// cc.streams map: peer reset, successful completion, TCP connection breakage,
// etc). If the request is canceled, then cs will be canceled and closed.
func (cs *clientStream) awaitRequestCancel(req *http.Request) {
        if err := awaitRequestCancel(req, cs.done); err != nil {
                cs.cancelStream()
                cs.bufPipe.CloseWithError(err)
        }
}

func (cs *clientStream) cancelStream() {
        cc := cs.cc
        cc.mu.Lock()
        didReset := cs.didReset
        cs.didReset = true
        cc.mu.Unlock()

        if !didReset {
                cc.writeStreamReset(cs.ID, ErrCodeCancel, nil)
                cc.forgetStreamID(cs.ID)
        }
}

// checkResetOrDone reports any error sent in a RST_STREAM frame by the
// server, or errStreamClosed if the stream is complete.
func (cs *clientStream) checkResetOrDone() error {
        select {
        case <-cs.peerReset:
                return cs.resetErr
        case <-cs.done:
                return errStreamClosed
        default:
                return nil
        }
}

func (cs *clientStream) getStartedWrite() bool {
        cc := cs.cc
        cc.mu.Lock()
        defer cc.mu.Unlock()
        return cs.startedWrite
}

func (cs *clientStream) abortRequestBodyWrite(err error) {
        if err == nil {
                panic("nil error")
        }
        cc := cs.cc
        cc.mu.Lock()
        cs.stopReqBody = err
        cc.cond.Broadcast()
        cc.mu.Unlock()
}

type stickyErrWriter struct {
        w   io.Writer
        err *error
}

func (sew stickyErrWriter) Write(p []byte) (n int, err error) {
        if *sew.err != nil {
                return 0, *sew.err
        }
        n, err = sew.w.Write(p)
        *sew.err = err
        return
}

// noCachedConnError is the concrete type of ErrNoCachedConn, which
// needs to be detected by net/http regardless of whether it's its
// bundled version (in h2_bundle.go with a rewritten type name) or
// from a user's x/net/http2. As such, as it has a unique method name
// (IsHTTP2NoCachedConnError) that net/http sniffs for via func
// isNoCachedConnError.
type noCachedConnError struct{}

func (noCachedConnError) IsHTTP2NoCachedConnError() {}
func (noCachedConnError) Error() string             { return "http2: no cached connection was available" }

// isNoCachedConnError reports whether err is of type noCachedConnError
// or its equivalent renamed type in net/http2's h2_bundle.go. Both types
// may coexist in the same running program.
func isNoCachedConnError(err error) bool {
        _, ok := err.(interface{ IsHTTP2NoCachedConnError() })
        return ok
}

var ErrNoCachedConn error = noCachedConnError{}

// RoundTripOpt are options for the Transport.RoundTripOpt method.
type RoundTripOpt struct {
        // OnlyCachedConn controls whether RoundTripOpt may
        // create a new TCP connection. If set true and
        // no cached connection is available, RoundTripOpt
        // will return ErrNoCachedConn.
        OnlyCachedConn bool
}

func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
        return t.RoundTripOpt(req, RoundTripOpt{})
}

// authorityAddr returns a given authority (a host/IP, or host:port / ip:port)
// and returns a host:port. The port 443 is added if needed.
func authorityAddr(scheme string, authority string) (addr string) {
        host, port, err := net.SplitHostPort(authority)
        if err != nil { // authority didn't have a port
                port = "443"
                if scheme == "http" {
                        port = "80"
                }
                host = authority
        }
        if a, err := idna.ToASCII(host); err == nil {
                host = a
        }
        // IPv6 address literal, without a port:
        if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") {
                return host + ":" + port
        }
        return net.JoinHostPort(host, port)
}

// RoundTripOpt is like RoundTrip, but takes options.
func (t *Transport) RoundTripOpt(req *http.Request, opt RoundTripOpt) (*http.Response, error) {
        if !(req.URL.Scheme == "https" || (req.URL.Scheme == "http" && t.AllowHTTP)) {
                return nil, errors.New("http2: unsupported scheme")
        }

        addr := authorityAddr(req.URL.Scheme, req.URL.Host)
        for retry := 0; ; retry++ {
                cc, err := t.connPool().GetClientConn(req, addr)
                if err != nil {
                        t.vlogf("http2: Transport failed to get client conn for %s: %v", addr, err)
                        return nil, err
                }
                traceGotConn(req, cc)
                res, gotErrAfterReqBodyWrite, err := cc.roundTrip(req)
                if err != nil && retry <= 6 {
                        if req, err = shouldRetryRequest(req, err, gotErrAfterReqBodyWrite); err == nil {
                                // After the first retry, do exponential backoff with 10% jitter.
                                if retry == 0 {
                                        continue
                                }
                                backoff := float64(uint(1) << (uint(retry) - 1))
                                backoff += backoff * (0.1 * mathrand.Float64())
                                select {
                                case <-time.After(time.Second * time.Duration(backoff)):
                                        continue
                                case <-req.Context().Done():
                                        return nil, req.Context().Err()
                                }
                        }
                }
                if err != nil {
                        t.vlogf("RoundTrip failure: %v", err)
                        return nil, err
                }
                return res, nil
        }
}

// CloseIdleConnections closes any connections which were previously
// connected from previous requests but are now sitting idle.
// It does not interrupt any connections currently in use.
func (t *Transport) CloseIdleConnections() {
        if cp, ok := t.connPool().(clientConnPoolIdleCloser); ok {
                cp.closeIdleConnections()
        }
}

var (
        errClientConnClosed    = errors.New("http2: client conn is closed")
        errClientConnUnusable  = errors.New("http2: client conn not usable")
        errClientConnGotGoAway = errors.New("http2: Transport received Server's graceful shutdown GOAWAY")
)

// shouldRetryRequest is called by RoundTrip when a request fails to get
// response headers. It is always called with a non-nil error.
// It returns either a request to retry (either the same request, or a
// modified clone), or an error if the request can't be replayed.
func shouldRetryRequest(req *http.Request, err error, afterBodyWrite bool) (*http.Request, error) {
        if !canRetryError(err) {
                return nil, err
        }
        // If the Body is nil (or http.NoBody), it's safe to reuse
        // this request and its Body.
        if req.Body == nil || req.Body == http.NoBody {
                return req, nil
        }

        // If the request body can be reset back to its original
        // state via the optional req.GetBody, do that.
        if req.GetBody != nil {
                // TODO: consider a req.Body.Close here? or audit that all caller paths do?
                body, err := req.GetBody()
                if err != nil {
                        return nil, err
                }
                newReq := *req
                newReq.Body = body
                return &newReq, nil
        }

        // The Request.Body can't reset back to the beginning, but we
        // don't seem to have started to read from it yet, so reuse
        // the request directly. The "afterBodyWrite" means the
        // bodyWrite process has started, which becomes true before
        // the first Read.
        if !afterBodyWrite {
                return req, nil
        }

        return nil, fmt.Errorf("http2: Transport: cannot retry err [%v] after Request.Body was written; define Request.GetBody to avoid this error", err)
}

func canRetryError(err error) bool {
        if err == errClientConnUnusable || err == errClientConnGotGoAway {
                return true
        }
        if se, ok := err.(StreamError); ok {
                return se.Code == ErrCodeRefusedStream
        }
        return false
}

func (t *Transport) dialClientConn(addr string, singleUse bool) (*ClientConn, error) {
        host, _, err := net.SplitHostPort(addr)
        if err != nil {
                return nil, err
        }
        tconn, err := t.dialTLS()("tcp", addr, t.newTLSConfig(host))
        if err != nil {
                return nil, err
        }
        return t.newClientConn(tconn, singleUse)
}

func (t *Transport) newTLSConfig(host string) *tls.Config {
        cfg := new(tls.Config)
        if t.TLSClientConfig != nil {
                *cfg = *t.TLSClientConfig.Clone()
        }
        if !strSliceContains(cfg.NextProtos, NextProtoTLS) {
                cfg.NextProtos = append([]string{NextProtoTLS}, cfg.NextProtos...)
        }
        if cfg.ServerName == "" {
                cfg.ServerName = host
        }
        return cfg
}

func (t *Transport) dialTLS() func(string, string, *tls.Config) (net.Conn, error) {
        if t.DialTLS != nil {
                return t.DialTLS
        }
        return t.dialTLSDefault
}

func (t *Transport) dialTLSDefault(network, addr string, cfg *tls.Config) (net.Conn, error) {
        cn, err := tls.Dial(network, addr, cfg)
        if err != nil {
                return nil, err
        }
        if err := cn.Handshake(); err != nil {
                return nil, err
        }
        if !cfg.InsecureSkipVerify {
                if err := cn.VerifyHostname(cfg.ServerName); err != nil {
                        return nil, err
                }
        }
        state := cn.ConnectionState()
        if p := state.NegotiatedProtocol; p != NextProtoTLS {
                return nil, fmt.Errorf("http2: unexpected ALPN protocol %q; want %q", p, NextProtoTLS)
        }
        if !state.NegotiatedProtocolIsMutual {
                return nil, errors.New("http2: could not negotiate protocol mutually")
        }
        return cn, nil
}

// disableKeepAlives reports whether connections should be closed as
// soon as possible after handling the first request.
func (t *Transport) disableKeepAlives() bool {
        return t.t1 != nil && t.t1.DisableKeepAlives
}

func (t *Transport) expectContinueTimeout() time.Duration {
        if t.t1 == nil {
                return 0
        }
        return t.t1.ExpectContinueTimeout
}

func (t *Transport) NewClientConn(c net.Conn) (*ClientConn, error) {
        return t.newClientConn(c, false)
}

func (t *Transport) newClientConn(c net.Conn, singleUse bool) (*ClientConn, error) {
        cc := &ClientConn{
                t:                     t,
                tconn:                 c,
                readerDone:            make(chan struct{}),
                nextStreamID:          1,
                maxFrameSize:          16 << 10,           // spec default
                initialWindowSize:     65535,              // spec default
                maxConcurrentStreams:  1000,               // "infinite", per spec. 1000 seems good enough.
                peerMaxHeaderListSize: 0xffffffffffffffff, // "infinite", per spec. Use 2^64-1 instead.
                streams:               make(map[uint32]*clientStream),
                singleUse:             singleUse,
                wantSettingsAck:       true,
                pings:                 make(map[[8]byte]chan struct{}),
        }
        if d := t.idleConnTimeout(); d != 0 {
                cc.idleTimeout = d
                cc.idleTimer = time.AfterFunc(d, cc.onIdleTimeout)
        }
        if VerboseLogs {
                t.vlogf("http2: Transport creating client conn %p to %v", cc, c.RemoteAddr())
        }

        cc.cond = sync.NewCond(&cc.mu)
        cc.flow.add(int32(initialWindowSize))

        // TODO: adjust this writer size to account for frame size +
        // MTU + crypto/tls record padding.
        cc.bw = bufio.NewWriter(stickyErrWriter{c, &cc.werr})
        cc.br = bufio.NewReader(c)
        cc.fr = NewFramer(cc.bw, cc.br)
        cc.fr.ReadMetaHeaders = hpack.NewDecoder(initialHeaderTableSize, nil)
        cc.fr.MaxHeaderListSize = t.maxHeaderListSize()

        // TODO: SetMaxDynamicTableSize, SetMaxDynamicTableSizeLimit on
        // henc in response to SETTINGS frames?
        cc.henc = hpack.NewEncoder(&cc.hbuf)

        if t.AllowHTTP {
                cc.nextStreamID = 3
        }

        if cs, ok := c.(connectionStater); ok {
                state := cs.ConnectionState()
                cc.tlsState = &state
        }

        initialSettings := []Setting{
                {ID: SettingEnablePush, Val: 0},
                {ID: SettingInitialWindowSize, Val: transportDefaultStreamFlow},
        }
        if max := t.maxHeaderListSize(); max != 0 {
                initialSettings = append(initialSettings, Setting{ID: SettingMaxHeaderListSize, Val: max})
        }

        cc.bw.Write(clientPreface)
        cc.fr.WriteSettings(initialSettings...)
        cc.fr.WriteWindowUpdate(0, transportDefaultConnFlow)
        cc.inflow.add(transportDefaultConnFlow + initialWindowSize)
        cc.bw.Flush()
        if cc.werr != nil {
                return nil, cc.werr
        }

        go cc.readLoop()
        return cc, nil
}

func (cc *ClientConn) setGoAway(f *GoAwayFrame) {
        cc.mu.Lock()
        defer cc.mu.Unlock()

        old := cc.goAway
        cc.goAway = f

        // Merge the previous and current GoAway error frames.
        if cc.goAwayDebug == "" {
                cc.goAwayDebug = string(f.DebugData())
        }
        if old != nil && old.ErrCode != ErrCodeNo {
                cc.goAway.ErrCode = old.ErrCode
        }
        last := f.LastStreamID
        for streamID, cs := range cc.streams {
                if streamID > last {
                        select {
                        case cs.resc <- resAndError{err: errClientConnGotGoAway}:
                        default:
                        }
                }
        }
}

// CanTakeNewRequest reports whether the connection can take a new request,
// meaning it has not been closed or received or sent a GOAWAY.
func (cc *ClientConn) CanTakeNewRequest() bool {
        cc.mu.Lock()
        defer cc.mu.Unlock()
        return cc.canTakeNewRequestLocked()
}

// clientConnIdleState describes the suitability of a client
// connection to initiate a new RoundTrip request.
type clientConnIdleState struct {
        canTakeNewRequest bool
        freshConn         bool // whether it's unused by any previous request
}

func (cc *ClientConn) idleState() clientConnIdleState {
        cc.mu.Lock()
        defer cc.mu.Unlock()
        return cc.idleStateLocked()
}

func (cc *ClientConn) idleStateLocked() (st clientConnIdleState) {
        if cc.singleUse && cc.nextStreamID > 1 {
                return
        }
        var maxConcurrentOkay bool
        if cc.t.StrictMaxConcurrentStreams {
                // We'll tell the caller we can take a new request to
                // prevent the caller from dialing a new TCP
                // connection, but then we'll block later before
                // writing it.
                maxConcurrentOkay = true
        } else {
                maxConcurrentOkay = int64(len(cc.streams)+1) < int64(cc.maxConcurrentStreams)
        }

        st.canTakeNewRequest = cc.goAway == nil && !cc.closed && !cc.closing && maxConcurrentOkay &&
                int64(cc.nextStreamID)+2*int64(cc.pendingRequests) < math.MaxInt32
        st.freshConn = cc.nextStreamID == 1 && st.canTakeNewRequest
        return
}

func (cc *ClientConn) canTakeNewRequestLocked() bool {
        st := cc.idleStateLocked()
        return st.canTakeNewRequest
}

// onIdleTimeout is called from a time.AfterFunc goroutine. It will
// only be called when we're idle, but because we're coming from a new
// goroutine, there could be a new request coming in at the same time,
// so this simply calls the synchronized closeIfIdle to shut down this
// connection. The timer could just call closeIfIdle, but this is more
// clear.
func (cc *ClientConn) onIdleTimeout() {
        cc.closeIfIdle()
}

func (cc *ClientConn) closeIfIdle() {
        cc.mu.Lock()
        if len(cc.streams) > 0 {
                cc.mu.Unlock()
                return
        }
        cc.closed = true
        nextID := cc.nextStreamID
        // TODO: do clients send GOAWAY too? maybe? Just Close:
        cc.mu.Unlock()

        if VerboseLogs {
                cc.vlogf("http2: Transport closing idle conn %p (forSingleUse=%v, maxStream=%v)", cc, cc.singleUse, nextID-2)
        }
        cc.tconn.Close()
}

var shutdownEnterWaitStateHook = func() {}

// Shutdown gracefully close the client connection, waiting for running streams to complete.
func (cc *ClientConn) Shutdown(ctx context.Context) error {
        if err := cc.sendGoAway(); err != nil {
                return err
        }
        // Wait for all in-flight streams to complete or connection to close
        done := make(chan error, 1)
        cancelled := false // guarded by cc.mu
        go func() {
                cc.mu.Lock()
                defer cc.mu.Unlock()
                for {
                        if len(cc.streams) == 0 || cc.closed {
                                cc.closed = true
                                done <- cc.tconn.Close()
                                break
                        }
                        if cancelled {
                                break
                        }
                        cc.cond.Wait()
                }
        }()
        shutdownEnterWaitStateHook()
        select {
        case err := <-done:
                return err
        case <-ctx.Done():
                cc.mu.Lock()
                // Free the goroutine above
                cancelled = true
                cc.cond.Broadcast()
                cc.mu.Unlock()
                return ctx.Err()
        }
}

func (cc *ClientConn) sendGoAway() error {
        cc.mu.Lock()
        defer cc.mu.Unlock()
        cc.wmu.Lock()
        defer cc.wmu.Unlock()
        if cc.closing {
                // GOAWAY sent already
                return nil
        }
        // Send a graceful shutdown frame to server
        maxStreamID := cc.nextStreamID
        if err := cc.fr.WriteGoAway(maxStreamID, ErrCodeNo, nil); err != nil {
                return err
        }
        if err := cc.bw.Flush(); err != nil {
                return err
        }
        // Prevent new requests
        cc.closing = true
        return nil
}

// Close closes the client connection immediately.
//
// In-flight requests are interrupted. For a graceful shutdown, use Shutdown instead.
func (cc *ClientConn) Close() error {
        cc.mu.Lock()
        defer cc.cond.Broadcast()
        defer cc.mu.Unlock()
        err := errors.New("http2: client connection force closed via ClientConn.Close")
        for id, cs := range cc.streams {
                select {
                case cs.resc <- resAndError{err: err}:
                default:
                }
                cs.bufPipe.CloseWithError(err)
                delete(cc.streams, id)
        }
        cc.closed = true
        return cc.tconn.Close()
}

const maxAllocFrameSize = 512 << 10

// frameBuffer returns a scratch buffer suitable for writing DATA frames.
// They're capped at the min of the peer's max frame size or 512KB
// (kinda arbitrarily), but definitely capped so we don't allocate 4GB
// bufers.
func (cc *ClientConn) frameScratchBuffer() []byte {
        cc.mu.Lock()
        size := cc.maxFrameSize
        if size > maxAllocFrameSize {
                size = maxAllocFrameSize
        }
        for i, buf := range cc.freeBuf {
                if len(buf) >= int(size) {
                        cc.freeBuf[i] = nil
                        cc.mu.Unlock()
                        return buf[:size]
                }
        }
        cc.mu.Unlock()
        return make([]byte, size)
}

func (cc *ClientConn) putFrameScratchBuffer(buf []byte) {
        cc.mu.Lock()
        defer cc.mu.Unlock()
        const maxBufs = 4 // arbitrary; 4 concurrent requests per conn? investigate.
        if len(cc.freeBuf) < maxBufs {
                cc.freeBuf = append(cc.freeBuf, buf)
                return
        }
        for i, old := range cc.freeBuf {
                if old == nil {
                        cc.freeBuf[i] = buf
                        return
                }
        }
        // forget about it.
}

// errRequestCanceled is a copy of net/http's errRequestCanceled because it's not
// exported. At least they'll be DeepEqual for h1-vs-h2 comparisons tests.
var errRequestCanceled = errors.New("net/http: request canceled")

func commaSeparatedTrailers(req *http.Request) (string, error) {
        keys := make([]string, 0, len(req.Trailer))
        for k := range req.Trailer {
                k = http.CanonicalHeaderKey(k)
                switch k {
                case "Transfer-Encoding", "Trailer", "Content-Length":
                        return "", &badStringError{"invalid Trailer key", k}
                }
                keys = append(keys, k)
        }
        if len(keys) > 0 {
                sort.Strings(keys)
                return strings.Join(keys, ","), nil
        }
        return "", nil
}

func (cc *ClientConn) responseHeaderTimeout() time.Duration {
        if cc.t.t1 != nil {
                return cc.t.t1.ResponseHeaderTimeout
        }
        // No way to do this (yet?) with just an http2.Transport. Probably
        // no need. Request.Cancel this is the new way. We only need to support
        // this for compatibility with the old http.Transport fields when
        // we're doing transparent http2.
        return 0
}

// checkConnHeaders checks whether req has any invalid connection-level headers.
// per RFC 7540 section 8.1.2.2: Connection-Specific Header Fields.
// Certain headers are special-cased as okay but not transmitted later.
func checkConnHeaders(req *http.Request) error {
        if v := req.Header.Get("Upgrade"); v != "" {
                return fmt.Errorf("http2: invalid Upgrade request header: %q", req.Header["Upgrade"])
        }
        if vv := req.Header["Transfer-Encoding"]; len(vv) > 0 && (len(vv) > 1 || vv[0] != "" && vv[0] != "chunked") {
                return fmt.Errorf("http2: invalid Transfer-Encoding request header: %q", vv)
        }
        if vv := req.Header["Connection"]; len(vv) > 0 && (len(vv) > 1 || vv[0] != "" && !strings.EqualFold(vv[0], "close") && !strings.EqualFold(vv[0], "keep-alive")) {
                return fmt.Errorf("http2: invalid Connection request header: %q", vv)
        }
        return nil
}

// actualContentLength returns a sanitized version of
// req.ContentLength, where 0 actually means zero (not unknown) and -1
// means unknown.
func actualContentLength(req *http.Request) int64 {
        if req.Body == nil || req.Body == http.NoBody {
                return 0
        }
        if req.ContentLength != 0 {
                return req.ContentLength
        }
        return -1
}

func (cc *ClientConn) RoundTrip(req *http.Request) (*http.Response, error) {
        resp, _, err := cc.roundTrip(req)
        return resp, err
}

func (cc *ClientConn) roundTrip(req *http.Request) (res *http.Response, gotErrAfterReqBodyWrite bool, err error) {
        if err := checkConnHeaders(req); err != nil {
                return nil, false, err
        }
        if cc.idleTimer != nil {
                cc.idleTimer.Stop()
        }

        trailers, err := commaSeparatedTrailers(req)
        if err != nil {
                return nil, false, err
        }
        hasTrailers := trailers != ""

        cc.mu.Lock()
        if err := cc.awaitOpenSlotForRequest(req); err != nil {
                cc.mu.Unlock()
                return nil, false, err
        }

        body := req.Body
        contentLen := actualContentLength(req)
        hasBody := contentLen != 0

        // TODO(bradfitz): this is a copy of the logic in net/http. Unify somewhere?
        var requestedGzip bool
        if !cc.t.disableCompression() &&
                req.Header.Get("Accept-Encoding") == "" &&
                req.Header.Get("Range") == "" &&
                req.Method != "HEAD" {
                // Request gzip only, not deflate. Deflate is ambiguous and
                // not as universally supported anyway.
                // See: http://www.gzip.org/zlib/zlib_faq.html#faq38
                //
                // Note that we don't request this for HEAD requests,
                // due to a bug in nginx:
                //   http://trac.nginx.org/nginx/ticket/358
                //   https://golang.org/issue/5522
                //
                // We don't request gzip if the request is for a range, since
                // auto-decoding a portion of a gzipped document will just fail
                // anyway. See https://golang.org/issue/8923
                requestedGzip = true
        }

        // we send: HEADERS{1}, CONTINUATION{0,} + DATA{0,} (DATA is
        // sent by writeRequestBody below, along with any Trailers,
        // again in form HEADERS{1}, CONTINUATION{0,})
        hdrs, err := cc.encodeHeaders(req, requestedGzip, trailers, contentLen)
        if err != nil {
                cc.mu.Unlock()
                return nil, false, err
        }

        cs := cc.newStream()
        cs.req = req
        cs.trace = httptrace.ContextClientTrace(req.Context())
        cs.requestedGzip = requestedGzip
        bodyWriter := cc.t.getBodyWriterState(cs, body)
        cs.on100 = bodyWriter.on100

        cc.wmu.Lock()
        endStream := !hasBody && !hasTrailers
        werr := cc.writeHeaders(cs.ID, endStream, int(cc.maxFrameSize), hdrs)
        cc.wmu.Unlock()
        traceWroteHeaders(cs.trace)
        cc.mu.Unlock()

        if werr != nil {
                if hasBody {
                        req.Body.Close() // per RoundTripper contract
                        bodyWriter.cancel()
                }
                cc.forgetStreamID(cs.ID)
                // Don't bother sending a RST_STREAM (our write already failed;
                // no need to keep writing)
                traceWroteRequest(cs.trace, werr)
                return nil, false, werr
        }

        var respHeaderTimer <-chan time.Time
        if hasBody {
                bodyWriter.scheduleBodyWrite()
        } else {
                traceWroteRequest(cs.trace, nil)
                if d := cc.responseHeaderTimeout(); d != 0 {
                        timer := time.NewTimer(d)
                        defer timer.Stop()
                        respHeaderTimer = timer.C
                }
        }

        readLoopResCh := cs.resc
        bodyWritten := false
        ctx := req.Context()

        handleReadLoopResponse := func(re resAndError) (*http.Response, bool, error) {
                res := re.res
                if re.err != nil || res.StatusCode > 299 {
                        // On error or status code 3xx, 4xx, 5xx, etc abort any
                        // ongoing write, assuming that the server doesn't care
                        // about our request body. If the server replied with 1xx or
                        // 2xx, however, then assume the server DOES potentially
                        // want our body (e.g. full-duplex streaming:
                        // golang.org/issue/13444). If it turns out the server
                        // doesn't, they'll RST_STREAM us soon enough. This is a
                        // heuristic to avoid adding knobs to Transport. Hopefully
                        // we can keep it.
                        bodyWriter.cancel()
                        cs.abortRequestBodyWrite(errStopReqBodyWrite)
                }
                if re.err != nil {
                        cc.forgetStreamID(cs.ID)
                        return nil, cs.getStartedWrite(), re.err
                }
                res.Request = req
                res.TLS = cc.tlsState
                return res, false, nil
        }

        for {
                select {
                case re := <-readLoopResCh:
                        return handleReadLoopResponse(re)
                case <-respHeaderTimer:
                        if !hasBody || bodyWritten {
                                cc.writeStreamReset(cs.ID, ErrCodeCancel, nil)
                        } else {
                                bodyWriter.cancel()
                                cs.abortRequestBodyWrite(errStopReqBodyWriteAndCancel)
                        }
                        cc.forgetStreamID(cs.ID)
                        return nil, cs.getStartedWrite(), errTimeout
                case <-ctx.Done():
                        if !hasBody || bodyWritten {
                                cc.writeStreamReset(cs.ID, ErrCodeCancel, nil)
                        } else {
                                bodyWriter.cancel()
                                cs.abortRequestBodyWrite(errStopReqBodyWriteAndCancel)
                        }
                        cc.forgetStreamID(cs.ID)
                        return nil, cs.getStartedWrite(), ctx.Err()
                case <-req.Cancel:
                        if !hasBody || bodyWritten {
                                cc.writeStreamReset(cs.ID, ErrCodeCancel, nil)
                        } else {
                                bodyWriter.cancel()
                                cs.abortRequestBodyWrite(errStopReqBodyWriteAndCancel)
                        }
                        cc.forgetStreamID(cs.ID)
                        return nil, cs.getStartedWrite(), errRequestCanceled
                case <-cs.peerReset:
                        // processResetStream already removed the
                        // stream from the streams map; no need for
                        // forgetStreamID.
                        return nil, cs.getStartedWrite(), cs.resetErr
                case err := <-bodyWriter.resc:
                        // Prefer the read loop's response, if available. Issue 16102.
                        select {
                        case re := <-readLoopResCh:
                                return handleReadLoopResponse(re)
                        default:
                        }
                        if err != nil {
                                cc.forgetStreamID(cs.ID)
                                return nil, cs.getStartedWrite(), err
                        }
                        bodyWritten = true
                        if d := cc.responseHeaderTimeout(); d != 0 {
                                timer := time.NewTimer(d)
                                defer timer.Stop()
                                respHeaderTimer = timer.C
                        }
                }
        }
}

// awaitOpenSlotForRequest waits until len(streams) < maxConcurrentStreams.
// Must hold cc.mu.
func (cc *ClientConn) awaitOpenSlotForRequest(req *http.Request) error {
        var waitingForConn chan struct{}
        var waitingForConnErr error // guarded by cc.mu
        for {
                cc.lastActive = time.Now()
                if cc.closed || !cc.canTakeNewRequestLocked() {
                        if waitingForConn != nil {
                                close(waitingForConn)
                        }
                        return errClientConnUnusable
                }
                if int64(len(cc.streams))+1 <= int64(cc.maxConcurrentStreams) {
                        if waitingForConn != nil {
                                close(waitingForConn)
                        }
                        return nil
                }
                // Unfortunately, we cannot wait on a condition variable and channel at
                // the same time, so instead, we spin up a goroutine to check if the
                // request is canceled while we wait for a slot to open in the connection.
                if waitingForConn == nil {
                        waitingForConn = make(chan struct{})
                        go func() {
                                if err := awaitRequestCancel(req, waitingForConn); err != nil {
                                        cc.mu.Lock()
                                        waitingForConnErr = err
                                        cc.cond.Broadcast()
                                        cc.mu.Unlock()
                                }
                        }()
                }
                cc.pendingRequests++
                cc.cond.Wait()
                cc.pendingRequests--
                if waitingForConnErr != nil {
                        return waitingForConnErr
                }
        }
}

// requires cc.wmu be held
func (cc *ClientConn) writeHeaders(streamID uint32, endStream bool, maxFrameSize int, hdrs []byte) error {
        first := true // first frame written (HEADERS is first, then CONTINUATION)
        for len(hdrs) > 0 && cc.werr == nil {
                chunk := hdrs
                if len(chunk) > maxFrameSize {
                        chunk = chunk[:maxFrameSize]
                }
                hdrs = hdrs[len(chunk):]
                endHeaders := len(hdrs) == 0
                if first {
                        cc.fr.WriteHeaders(HeadersFrameParam{
                                StreamID:      streamID,
                                BlockFragment: chunk,
                                EndStream:     endStream,
                                EndHeaders:    endHeaders,
                        })
                        first = false
                } else {
                        cc.fr.WriteContinuation(streamID, endHeaders, chunk)
                }
        }
        // TODO(bradfitz): this Flush could potentially block (as
        // could the WriteHeaders call(s) above), which means they
        // wouldn't respond to Request.Cancel being readable. That's
        // rare, but this should probably be in a goroutine.
        cc.bw.Flush()
        return cc.werr
}

// internal error values; they don't escape to callers
var (
        // abort request body write; don't send cancel
        errStopReqBodyWrite = errors.New("http2: aborting request body write")

        // abort request body write, but send stream reset of cancel.
        errStopReqBodyWriteAndCancel = errors.New("http2: canceling request")
)

func (cs *clientStream) writeRequestBody(body io.Reader, bodyCloser io.Closer) (err error) {
        cc := cs.cc
        sentEnd := false // whether we sent the final DATA frame w/ END_STREAM
        buf := cc.frameScratchBuffer()
        defer cc.putFrameScratchBuffer(buf)

        defer func() {
                traceWroteRequest(cs.trace, err)
                // TODO: write h12Compare test showing whether
                // Request.Body is closed by the Transport,
                // and in multiple cases: server replies <=299 and >299
                // while still writing request body
                cerr := bodyCloser.Close()
                if err == nil {
                        err = cerr
                }
        }()

        req := cs.req
        hasTrailers := req.Trailer != nil

        var sawEOF bool
        for !sawEOF {
                n, err := body.Read(buf)
                if err == io.EOF {
                        sawEOF = true
                        err = nil
                } else if err != nil {
                        cc.writeStreamReset(cs.ID, ErrCodeCancel, err)
                        return err
                }

                remain := buf[:n]
                for len(remain) > 0 && err == nil {
                        var allowed int32
                        allowed, err = cs.awaitFlowControl(len(remain))
                        switch {
                        case err == errStopReqBodyWrite:
                                return err
                        case err == errStopReqBodyWriteAndCancel:
                                cc.writeStreamReset(cs.ID, ErrCodeCancel, nil)
                                return err
                        case err != nil:
                                return err
                        }
                        cc.wmu.Lock()
                        data := remain[:allowed]
                        remain = remain[allowed:]
                        sentEnd = sawEOF && len(remain) == 0 && !hasTrailers
                        err = cc.fr.WriteData(cs.ID, sentEnd, data)
                        if err == nil {
                                // TODO(bradfitz): this flush is for latency, not bandwidth.
                                // Most requests won't need this. Make this opt-in or
                                // opt-out?  Use some heuristic on the body type? Nagel-like
                                // timers?  Based on 'n'? Only last chunk of this for loop,
                                // unless flow control tokens are low? For now, always.
                                // If we change this, see comment below.
                                err = cc.bw.Flush()
                        }
                        cc.wmu.Unlock()
                }
                if err != nil {
                        return err
                }
        }

        if sentEnd {
                // Already sent END_STREAM (which implies we have no
                // trailers) and flushed, because currently all
                // WriteData frames above get a flush. So we're done.
                return nil
        }

        var trls []byte
        if hasTrailers {
                cc.mu.Lock()
                trls, err = cc.encodeTrailers(req)
                cc.mu.Unlock()
                if err != nil {
                        cc.writeStreamReset(cs.ID, ErrCodeInternal, err)
                        cc.forgetStreamID(cs.ID)
                        return err
                }
        }

        cc.mu.Lock()
        maxFrameSize := int(cc.maxFrameSize)
        cc.mu.Unlock()

        cc.wmu.Lock()
        defer cc.wmu.Unlock()

        // Two ways to send END_STREAM: either with trailers, or
        // with an empty DATA frame.
        if len(trls) > 0 {
                err = cc.writeHeaders(cs.ID, true, maxFrameSize, trls)
        } else {
                err = cc.fr.WriteData(cs.ID, true, nil)
        }
        if ferr := cc.bw.Flush(); ferr != nil && err == nil {
                err = ferr
        }
        return err
}

// awaitFlowControl waits for [1, min(maxBytes, cc.cs.maxFrameSize)] flow
// control tokens from the server.
// It returns either the non-zero number of tokens taken or an error
// if the stream is dead.
func (cs *clientStream) awaitFlowControl(maxBytes int) (taken int32, err error) {
        cc := cs.cc
        cc.mu.Lock()
        defer cc.mu.Unlock()
        for {
                if cc.closed {
                        return 0, errClientConnClosed
                }
                if cs.stopReqBody != nil {
                        return 0, cs.stopReqBody
                }
                if err := cs.checkResetOrDone(); err != nil {
                        return 0, err
                }
                if a := cs.flow.available(); a > 0 {
                        take := a
                        if int(take) > maxBytes {

                                take = int32(maxBytes) // can't truncate int; take is int32
                        }
                        if take > int32(cc.maxFrameSize) {
                                take = int32(cc.maxFrameSize)
                        }
                        cs.flow.take(take)
                        return take, nil
                }
                cc.cond.Wait()
        }
}

type badStringError struct {
        what string
        str  string
}

func (e *badStringError) Error() string { return fmt.Sprintf("%s %q", e.what, e.str) }

// requires cc.mu be held.
func (cc *ClientConn) encodeHeaders(req *http.Request, addGzipHeader bool, trailers string, contentLength int64) ([]byte, error) {
        cc.hbuf.Reset()

        host := req.Host
        if host == "" {
                host = req.URL.Host
        }
        host, err := httpguts.PunycodeHostPort(host)
        if err != nil {
                return nil, err
        }

        var path string
        if req.Method != "CONNECT" {
                path = req.URL.RequestURI()
                if !validPseudoPath(path) {
                        orig := path
                        path = strings.TrimPrefix(path, req.URL.Scheme+"://"+host)
                        if !validPseudoPath(path) {
                                if req.URL.Opaque != "" {
                                        return nil, fmt.Errorf("invalid request :path %q from URL.Opaque = %q", orig, req.URL.Opaque)
                                } else {
                                        return nil, fmt.Errorf("invalid request :path %q", orig)
                                }
                        }
                }
        }

        // Check for any invalid headers and return an error before we
        // potentially pollute our hpack state. (We want to be able to
        // continue to reuse the hpack encoder for future requests)
        for k, vv := range req.Header {
                if !httpguts.ValidHeaderFieldName(k) {
                        return nil, fmt.Errorf("invalid HTTP header name %q", k)
                }
                for _, v := range vv {
                        if !httpguts.ValidHeaderFieldValue(v) {
                                return nil, fmt.Errorf("invalid HTTP header value %q for header %q", v, k)
                        }
                }
        }

        enumerateHeaders := func(f func(name, value string)) {
                // 8.1.2.3 Request Pseudo-Header Fields
                // The :path pseudo-header field includes the path and query parts of the
                // target URI (the path-absolute production and optionally a '?' character
                // followed by the query production (see Sections 3.3 and 3.4 of
                // [RFC3986]).
                f(":authority", host)
                m := req.Method
                if m == "" {
                        m = http.MethodGet
                }
                f(":method", m)
                if req.Method != "CONNECT" {
                        f(":path", path)
                        f(":scheme", req.URL.Scheme)
                }
                if trailers != "" {
                        f("trailer", trailers)
                }

                var didUA bool
                for k, vv := range req.Header {
                        if strings.EqualFold(k, "host") || strings.EqualFold(k, "content-length") {
                                // Host is :authority, already sent.
                                // Content-Length is automatic, set below.
                                continue
                        } else if strings.EqualFold(k, "connection") || strings.EqualFold(k, "proxy-connection") ||
                                strings.EqualFold(k, "transfer-encoding") || strings.EqualFold(k, "upgrade") ||
                                strings.EqualFold(k, "keep-alive") {
                                // Per 8.1.2.2 Connection-Specific Header
                                // Fields, don't send connection-specific
                                // fields. We have already checked if any
                                // are error-worthy so just ignore the rest.
                                continue
                        } else if strings.EqualFold(k, "user-agent") {
                                // Match Go's http1 behavior: at most one
                                // User-Agent. If set to nil or empty string,
                                // then omit it. Otherwise if not mentioned,
                                // include the default (below).
                                didUA = true
                                if len(vv) < 1 {
                                        continue
                                }
                                vv = vv[:1]
                                if vv[0] == "" {
                                        continue
                                }

                        }

                        for _, v := range vv {
                                f(k, v)
                        }
                }
                if shouldSendReqContentLength(req.Method, contentLength) {
                        f("content-length", strconv.FormatInt(contentLength, 10))
                }
                if addGzipHeader {
                        f("accept-encoding", "gzip")
                }
                if !didUA {
                        f("user-agent", defaultUserAgent)
                }
        }

        // Do a first pass over the headers counting bytes to ensure
        // we don't exceed cc.peerMaxHeaderListSize. This is done as a
        // separate pass before encoding the headers to prevent
        // modifying the hpack state.
        hlSize := uint64(0)
        enumerateHeaders(func(name, value string) {
                hf := hpack.HeaderField{Name: name, Value: value}
                hlSize += uint64(hf.Size())
        })

        if hlSize > cc.peerMaxHeaderListSize {
                return nil, errRequestHeaderListSize
        }

        trace := httptrace.ContextClientTrace(req.Context())
        traceHeaders := traceHasWroteHeaderField(trace)

        // Header list size is ok. Write the headers.
        enumerateHeaders(func(name, value string) {
                name = strings.ToLower(name)
                cc.writeHeader(name, value)
                if traceHeaders {
                        traceWroteHeaderField(trace, name, value)
                }
        })

        return cc.hbuf.Bytes(), nil
}

// shouldSendReqContentLength reports whether the http2.Transport should send
// a "content-length" request header. This logic is basically a copy of the net/http
// transferWriter.shouldSendContentLength.
// The contentLength is the corrected contentLength (so 0 means actually 0, not unknown).
// -1 means unknown.
func shouldSendReqContentLength(method string, contentLength int64) bool {
        if contentLength > 0 {
                return true
        }
        if contentLength < 0 {
                return false
        }
        // For zero bodies, whether we send a content-length depends on the method.
        // It also kinda doesn't matter for http2 either way, with END_STREAM.
        switch method {
        case "POST", "PUT", "PATCH":
                return true
        default:
                return false
        }
}

// requires cc.mu be held.
func (cc *ClientConn) encodeTrailers(req *http.Request) ([]byte, error) {
        cc.hbuf.Reset()

        hlSize := uint64(0)
        for k, vv := range req.Trailer {
                for _, v := range vv {
                        hf := hpack.HeaderField{Name: k, Value: v}
                        hlSize += uint64(hf.Size())
                }
        }
        if hlSize > cc.peerMaxHeaderListSize {
                return nil, errRequestHeaderListSize
        }

        for k, vv := range req.Trailer {
                // Transfer-Encoding, etc.. have already been filtered at the
                // start of RoundTrip
                lowKey := strings.ToLower(k)
                for _, v := range vv {
                        cc.writeHeader(lowKey, v)
                }
        }
        return cc.hbuf.Bytes(), nil
}

func (cc *ClientConn) writeHeader(name, value string) {
        if VerboseLogs {
                log.Printf("http2: Transport encoding header %q = %q", name, value)
        }
        cc.henc.WriteField(hpack.HeaderField{Name: name, Value: value})
}

type resAndError struct {
        res *http.Response
        err error
}

// requires cc.mu be held.
func (cc *ClientConn) newStream() *clientStream {
        cs := &clientStream{
                cc:        cc,
                ID:        cc.nextStreamID,
                resc:      make(chan resAndError, 1),
                peerReset: make(chan struct{}),
                done:      make(chan struct{}),
        }
        cs.flow.add(int32(cc.initialWindowSize))
        cs.flow.setConnFlow(&cc.flow)
        cs.inflow.add(transportDefaultStreamFlow)
        cs.inflow.setConnFlow(&cc.inflow)
        cc.nextStreamID += 2
        cc.streams[cs.ID] = cs
        return cs
}

func (cc *ClientConn) forgetStreamID(id uint32) {
        cc.streamByID(id, true)
}

func (cc *ClientConn) streamByID(id uint32, andRemove bool) *clientStream {
        cc.mu.Lock()
        defer cc.mu.Unlock()
        cs := cc.streams[id]
        if andRemove && cs != nil && !cc.closed {
                cc.lastActive = time.Now()
                delete(cc.streams, id)
                if len(cc.streams) == 0 && cc.idleTimer != nil {
                        cc.idleTimer.Reset(cc.idleTimeout)
                }
                close(cs.done)
                // Wake up checkResetOrDone via clientStream.awaitFlowControl and
                // wake up RoundTrip if there is a pending request.
                cc.cond.Broadcast()
        }
        return cs
}

// clientConnReadLoop is the state owned by the clientConn's frame-reading readLoop.
type clientConnReadLoop struct {
        cc            *ClientConn
        closeWhenIdle bool
}

// readLoop runs in its own goroutine and reads and dispatches frames.
func (cc *ClientConn) readLoop() {
        rl := &clientConnReadLoop{cc: cc}
        defer rl.cleanup()
        cc.readerErr = rl.run()
        if ce, ok := cc.readerErr.(ConnectionError); ok {
                cc.wmu.Lock()
                cc.fr.WriteGoAway(0, ErrCode(ce), nil)
                cc.wmu.Unlock()
        }
}

// GoAwayError is returned by the Transport when the server closes the
// TCP connection after sending a GOAWAY frame.
type GoAwayError struct {
        LastStreamID uint32
        ErrCode      ErrCode
        DebugData    string
}

func (e GoAwayError) Error() string {
        return fmt.Sprintf("http2: server sent GOAWAY and closed the connection; LastStreamID=%v, ErrCode=%v, debug=%q",
                e.LastStreamID, e.ErrCode, e.DebugData)
}

func isEOFOrNetReadError(err error) bool {
        if err == io.EOF {
                return true
        }
        ne, ok := err.(*net.OpError)
        return ok && ne.Op == "read"
}

func (rl *clientConnReadLoop) cleanup() {
        cc := rl.cc
        defer cc.tconn.Close()
        defer cc.t.connPool().MarkDead(cc)
        defer close(cc.readerDone)

        if cc.idleTimer != nil {
                cc.idleTimer.Stop()
        }

        // Close any response bodies if the server closes prematurely.
        // TODO: also do this if we've written the headers but not
        // gotten a response yet.
        err := cc.readerErr
        cc.mu.Lock()
        if cc.goAway != nil && isEOFOrNetReadError(err) {
                err = GoAwayError{
                        LastStreamID: cc.goAway.LastStreamID,
                        ErrCode:      cc.goAway.ErrCode,
                        DebugData:    cc.goAwayDebug,
                }
        } else if err == io.EOF {
                err = io.ErrUnexpectedEOF
        }
        for _, cs := range cc.streams {
                cs.bufPipe.CloseWithError(err) // no-op if already closed
                select {
                case cs.resc <- resAndError{err: err}:
                default:
                }
                close(cs.done)
        }
        cc.closed = true
        cc.cond.Broadcast()
        cc.mu.Unlock()
}

func (rl *clientConnReadLoop) run() error {
        cc := rl.cc
        rl.closeWhenIdle = cc.t.disableKeepAlives() || cc.singleUse
        gotReply := false // ever saw a HEADERS reply
        gotSettings := false
        for {
                f, err := cc.fr.ReadFrame()
                if err != nil {
                        cc.vlogf("http2: Transport readFrame error on conn %p: (%T) %v", cc, err, err)
                }
                if se, ok := err.(StreamError); ok {
                        if cs := cc.streamByID(se.StreamID, false); cs != nil {
                                cs.cc.writeStreamReset(cs.ID, se.Code, err)
                                cs.cc.forgetStreamID(cs.ID)
                                if se.Cause == nil {
                                        se.Cause = cc.fr.errDetail
                                }
                                rl.endStreamError(cs, se)
                        }
                        continue
                } else if err != nil {
                        return err
                }
                if VerboseLogs {
                        cc.vlogf("http2: Transport received %s", summarizeFrame(f))
                }
                if !gotSettings {
                        if _, ok := f.(*SettingsFrame); !ok {
                                cc.logf("protocol error: received %T before a SETTINGS frame", f)
                                return ConnectionError(ErrCodeProtocol)
                        }
                        gotSettings = true
                }
                maybeIdle := false // whether frame might transition us to idle

                switch f := f.(type) {
                case *MetaHeadersFrame:
                        err = rl.processHeaders(f)
                        maybeIdle = true
                        gotReply = true
                case *DataFrame:
                        err = rl.processData(f)
                        maybeIdle = true
                case *GoAwayFrame:
                        err = rl.processGoAway(f)
                        maybeIdle = true
                case *RSTStreamFrame:
                        err = rl.processResetStream(f)
                        maybeIdle = true
                case *SettingsFrame:
                        err = rl.processSettings(f)
                case *PushPromiseFrame:
                        err = rl.processPushPromise(f)
                case *WindowUpdateFrame:
                        err = rl.processWindowUpdate(f)
                case *PingFrame:
                        err = rl.processPing(f)
                default:
                        cc.logf("Transport: unhandled response frame type %T", f)
                }
                if err != nil {
                        if VerboseLogs {
                                cc.vlogf("http2: Transport conn %p received error from processing frame %v: %v", cc, summarizeFrame(f), err)
                        }
                        return err
                }
                if rl.closeWhenIdle && gotReply && maybeIdle {
                        cc.closeIfIdle()
                }
        }
}

func (rl *clientConnReadLoop) processHeaders(f *MetaHeadersFrame) error {
        cc := rl.cc
        cs := cc.streamByID(f.StreamID, false)
        if cs == nil {
                // We'd get here if we canceled a request while the
                // server had its response still in flight. So if this
                // was just something we canceled, ignore it.
                return nil
        }
        if f.StreamEnded() {
                // Issue 20521: If the stream has ended, streamByID() causes
                // clientStream.done to be closed, which causes the request's bodyWriter
                // to be closed with an errStreamClosed, which may be received by
                // clientConn.RoundTrip before the result of processing these headers.
                // Deferring stream closure allows the header processing to occur first.
                // clientConn.RoundTrip may still receive the bodyWriter error first, but
                // the fix for issue 16102 prioritises any response.
                //
                // Issue 22413: If there is no request body, we should close the
                // stream before writing to cs.resc so that the stream is closed
                // immediately once RoundTrip returns.
                if cs.req.Body != nil {
                        defer cc.forgetStreamID(f.StreamID)
                } else {
                        cc.forgetStreamID(f.StreamID)
                }
        }
        if !cs.firstByte {
                if cs.trace != nil {
                        // TODO(bradfitz): move first response byte earlier,
                        // when we first read the 9 byte header, not waiting
                        // until all the HEADERS+CONTINUATION frames have been
                        // merged. This works for now.
                        traceFirstResponseByte(cs.trace)
                }
                cs.firstByte = true
        }
        if !cs.pastHeaders {
                cs.pastHeaders = true
        } else {
                return rl.processTrailers(cs, f)
        }

        res, err := rl.handleResponse(cs, f)
        if err != nil {
                if _, ok := err.(ConnectionError); ok {
                        return err
                }
                // Any other error type is a stream error.
                cs.cc.writeStreamReset(f.StreamID, ErrCodeProtocol, err)
                cc.forgetStreamID(cs.ID)
                cs.resc <- resAndError{err: err}
                return nil // return nil from process* funcs to keep conn alive
        }
        if res == nil {
                // (nil, nil) special case. See handleResponse docs.
                return nil
        }
        cs.resTrailer = &res.Trailer
        cs.resc <- resAndError{res: res}
        return nil
}

// may return error types nil, or ConnectionError. Any other error value
// is a StreamError of type ErrCodeProtocol. The returned error in that case
// is the detail.
//
// As a special case, handleResponse may return (nil, nil) to skip the
// frame (currently only used for 1xx responses).
func (rl *clientConnReadLoop) handleResponse(cs *clientStream, f *MetaHeadersFrame) (*http.Response, error) {
        if f.Truncated {
                return nil, errResponseHeaderListSize
        }

        status := f.PseudoValue("status")
        if status == "" {
                return nil, errors.New("malformed response from server: missing status pseudo header")
        }
        statusCode, err := strconv.Atoi(status)
        if err != nil {
                return nil, errors.New("malformed response from server: malformed non-numeric status pseudo header")
        }

        header := make(http.Header)
        res := &http.Response{
                Proto:      "HTTP/2.0",
                ProtoMajor: 2,
                Header:     header,
                StatusCode: statusCode,
                Status:     status + " " + http.StatusText(statusCode),
        }
        for _, hf := range f.RegularFields() {
                key := http.CanonicalHeaderKey(hf.Name)
                if key == "Trailer" {
                        t := res.Trailer
                        if t == nil {
                                t = make(http.Header)
                                res.Trailer = t
                        }
                        foreachHeaderElement(hf.Value, func(v string) {
                                t[http.CanonicalHeaderKey(v)] = nil
                        })
                } else {
                        header[key] = append(header[key], hf.Value)
                }
        }

        if statusCode >= 100 && statusCode <= 199 {
                cs.num1xx++
                const max1xxResponses = 5 // arbitrary bound on number of informational responses, same as net/http
                if cs.num1xx > max1xxResponses {
                        return nil, errors.New("http2: too many 1xx informational responses")
                }
                if fn := cs.get1xxTraceFunc(); fn != nil {
                        if err := fn(statusCode, textproto.MIMEHeader(header)); err != nil {
                                return nil, err
                        }
                }
                if statusCode == 100 {
                        traceGot100Continue(cs.trace)
                        if cs.on100 != nil {
                                cs.on100() // forces any write delay timer to fire
                        }
                }
                cs.pastHeaders = false // do it all again
                return nil, nil
        }

        streamEnded := f.StreamEnded()
        isHead := cs.req.Method == "HEAD"
        if !streamEnded || isHead {
                res.ContentLength = -1
                if clens := res.Header["Content-Length"]; len(clens) == 1 {
                        if clen64, err := strconv.ParseInt(clens[0], 10, 64); err == nil {
                                res.ContentLength = clen64
                        } else {
                                // TODO: care? unlike http/1, it won't mess up our framing, so it's
                                // more safe smuggling-wise to ignore.
                        }
                } else if len(clens) > 1 {
                        // TODO: care? unlike http/1, it won't mess up our framing, so it's
                        // more safe smuggling-wise to ignore.
                }
        }

        if streamEnded || isHead {
                res.Body = noBody
                return res, nil
        }

        cs.bufPipe = pipe{b: &dataBuffer{expected: res.ContentLength}}
        cs.bytesRemain = res.ContentLength
        res.Body = transportResponseBody{cs}
        go cs.awaitRequestCancel(cs.req)

        if cs.requestedGzip && res.Header.Get("Content-Encoding") == "gzip" {
                res.Header.Del("Content-Encoding")
                res.Header.Del("Content-Length")
                res.ContentLength = -1
                res.Body = &gzipReader{body: res.Body}
                res.Uncompressed = true
        }
        return res, nil
}

func (rl *clientConnReadLoop) processTrailers(cs *clientStream, f *MetaHeadersFrame) error {
        if cs.pastTrailers {
                // Too many HEADERS frames for this stream.
                return ConnectionError(ErrCodeProtocol)
        }
        cs.pastTrailers = true
        if !f.StreamEnded() {
                // We expect that any headers for trailers also
                // has END_STREAM.
                return ConnectionError(ErrCodeProtocol)
        }
        if len(f.PseudoFields()) > 0 {
                // No pseudo header fields are defined for trailers.
                // TODO: ConnectionError might be overly harsh? Check.
                return ConnectionError(ErrCodeProtocol)
        }

        trailer := make(http.Header)
        for _, hf := range f.RegularFields() {
                key := http.CanonicalHeaderKey(hf.Name)
                trailer[key] = append(trailer[key], hf.Value)
        }
        cs.trailer = trailer

        rl.endStream(cs)
        return nil
}

// transportResponseBody is the concrete type of Transport.RoundTrip's
// Response.Body. It is an io.ReadCloser. On Read, it reads from cs.body.
// On Close it sends RST_STREAM if EOF wasn't already seen.
type transportResponseBody struct {
        cs *clientStream
}

func (b transportResponseBody) Read(p []byte) (n int, err error) {
        cs := b.cs
        cc := cs.cc

        if cs.readErr != nil {
                return 0, cs.readErr
        }
        n, err = b.cs.bufPipe.Read(p)
        if cs.bytesRemain != -1 {
                if int64(n) > cs.bytesRemain {
                        n = int(cs.bytesRemain)
                        if err == nil {
                                err = errors.New("net/http: server replied with more than declared Content-Length; truncated")
                                cc.writeStreamReset(cs.ID, ErrCodeProtocol, err)
                        }
                        cs.readErr = err
                        return int(cs.bytesRemain), err
                }
                cs.bytesRemain -= int64(n)
                if err == io.EOF && cs.bytesRemain > 0 {
                        err = io.ErrUnexpectedEOF
                        cs.readErr = err
                        return n, err
                }
        }
        if n == 0 {
                // No flow control tokens to send back.
                return
        }

        cc.mu.Lock()
        defer cc.mu.Unlock()

        var connAdd, streamAdd int32
        // Check the conn-level first, before the stream-level.
        if v := cc.inflow.available(); v < transportDefaultConnFlow/2 {
                connAdd = transportDefaultConnFlow - v
                cc.inflow.add(connAdd)
        }
        if err == nil { // No need to refresh if the stream is over or failed.
                // Consider any buffered body data (read from the conn but not
                // consumed by the client) when computing flow control for this
                // stream.
                v := int(cs.inflow.available()) + cs.bufPipe.Len()
                if v < transportDefaultStreamFlow-transportDefaultStreamMinRefresh {
                        streamAdd = int32(transportDefaultStreamFlow - v)
                        cs.inflow.add(streamAdd)
                }
        }
        if connAdd != 0 || streamAdd != 0 {
                cc.wmu.Lock()
                defer cc.wmu.Unlock()
                if connAdd != 0 {
                        cc.fr.WriteWindowUpdate(0, mustUint31(connAdd))
                }
                if streamAdd != 0 {
                        cc.fr.WriteWindowUpdate(cs.ID, mustUint31(streamAdd))
                }
                cc.bw.Flush()
        }
        return
}

var errClosedResponseBody = errors.New("http2: response body closed")

func (b transportResponseBody) Close() error {
        cs := b.cs
        cc := cs.cc

        serverSentStreamEnd := cs.bufPipe.Err() == io.EOF
        unread := cs.bufPipe.Len()

        if unread > 0 || !serverSentStreamEnd {
                cc.mu.Lock()
                cc.wmu.Lock()
                if !serverSentStreamEnd {
                        cc.fr.WriteRSTStream(cs.ID, ErrCodeCancel)
                        cs.didReset = true
                }
                // Return connection-level flow control.
                if unread > 0 {
                        cc.inflow.add(int32(unread))
                        cc.fr.WriteWindowUpdate(0, uint32(unread))
                }
                cc.bw.Flush()
                cc.wmu.Unlock()
                cc.mu.Unlock()
        }

        cs.bufPipe.BreakWithError(errClosedResponseBody)
        cc.forgetStreamID(cs.ID)
        return nil
}

func (rl *clientConnReadLoop) processData(f *DataFrame) error {
        cc := rl.cc
        cs := cc.streamByID(f.StreamID, f.StreamEnded())
        data := f.Data()
        if cs == nil {
                cc.mu.Lock()
                neverSent := cc.nextStreamID
                cc.mu.Unlock()
                if f.StreamID >= neverSent {
                        // We never asked for this.
                        cc.logf("http2: Transport received unsolicited DATA frame; closing connection")
                        return ConnectionError(ErrCodeProtocol)
                }
                // We probably did ask for this, but canceled. Just ignore it.
                // TODO: be stricter here? only silently ignore things which
                // we canceled, but not things which were closed normally
                // by the peer? Tough without accumulating too much state.

                // But at least return their flow control:
                if f.Length > 0 {
                        cc.mu.Lock()
                        cc.inflow.add(int32(f.Length))
                        cc.mu.Unlock()

                        cc.wmu.Lock()
                        cc.fr.WriteWindowUpdate(0, uint32(f.Length))
                        cc.bw.Flush()
                        cc.wmu.Unlock()
                }
                return nil
        }
        if !cs.firstByte {
                cc.logf("protocol error: received DATA before a HEADERS frame")
                rl.endStreamError(cs, StreamError{
                        StreamID: f.StreamID,
                        Code:     ErrCodeProtocol,
                })
                return nil
        }
        if f.Length > 0 {
                if cs.req.Method == "HEAD" && len(data) > 0 {
                        cc.logf("protocol error: received DATA on a HEAD request")
                        rl.endStreamError(cs, StreamError{
                                StreamID: f.StreamID,
                                Code:     ErrCodeProtocol,
                        })
                        return nil
                }
                // Check connection-level flow control.
                cc.mu.Lock()
                if cs.inflow.available() >= int32(f.Length) {
                        cs.inflow.take(int32(f.Length))
                } else {
                        cc.mu.Unlock()
                        return ConnectionError(ErrCodeFlowControl)
                }
                // Return any padded flow control now, since we won't
                // refund it later on body reads.
                var refund int
                if pad := int(f.Length) - len(data); pad > 0 {
                        refund += pad
                }
                // Return len(data) now if the stream is already closed,
                // since data will never be read.
                didReset := cs.didReset
                if didReset {
                        refund += len(data)
                }
                if refund > 0 {
                        cc.inflow.add(int32(refund))
                        cc.wmu.Lock()
                        cc.fr.WriteWindowUpdate(0, uint32(refund))
                        if !didReset {
                                cs.inflow.add(int32(refund))
                                cc.fr.WriteWindowUpdate(cs.ID, uint32(refund))
                        }
                        cc.bw.Flush()
                        cc.wmu.Unlock()
                }
                cc.mu.Unlock()

                if len(data) > 0 && !didReset {
                        if _, err := cs.bufPipe.Write(data); err != nil {
                                rl.endStreamError(cs, err)
                                return err
                        }
                }
        }

        if f.StreamEnded() {
                rl.endStream(cs)
        }
        return nil
}

var errInvalidTrailers = errors.New("http2: invalid trailers")

func (rl *clientConnReadLoop) endStream(cs *clientStream) {
        // TODO: check that any declared content-length matches, like
        // server.go's (*stream).endStream method.
        rl.endStreamError(cs, nil)
}

func (rl *clientConnReadLoop) endStreamError(cs *clientStream, err error) {
        var code func()
        if err == nil {
                err = io.EOF
                code = cs.copyTrailers
        }
        if isConnectionCloseRequest(cs.req) {
                rl.closeWhenIdle = true
        }
        cs.bufPipe.closeWithErrorAndCode(err, code)

        select {
        case cs.resc <- resAndError{err: err}:
        default:
        }
}

func (cs *clientStream) copyTrailers() {
        for k, vv := range cs.trailer {
                t := cs.resTrailer
                if *t == nil {
                        *t = make(http.Header)
                }
                (*t)[k] = vv
        }
}

func (rl *clientConnReadLoop) processGoAway(f *GoAwayFrame) error {
        cc := rl.cc
        cc.t.connPool().MarkDead(cc)
        if f.ErrCode != 0 {
                // TODO: deal with GOAWAY more. particularly the error code
                cc.vlogf("transport got GOAWAY with error code = %v", f.ErrCode)
        }
        cc.setGoAway(f)
        return nil
}

func (rl *clientConnReadLoop) processSettings(f *SettingsFrame) error {
        cc := rl.cc
        cc.mu.Lock()
        defer cc.mu.Unlock()

        if f.IsAck() {
                if cc.wantSettingsAck {
                        cc.wantSettingsAck = false
                        return nil
                }
                return ConnectionError(ErrCodeProtocol)
        }

        err := f.ForeachSetting(func(s Setting) error {
                switch s.ID {
                case SettingMaxFrameSize:
                        cc.maxFrameSize = s.Val
                case SettingMaxConcurrentStreams:
                        cc.maxConcurrentStreams = s.Val
                case SettingMaxHeaderListSize:
                        cc.peerMaxHeaderListSize = uint64(s.Val)
                case SettingInitialWindowSize:
                        // Values above the maximum flow-control
                        // window size of 2^31-1 MUST be treated as a
                        // connection error (Section 5.4.1) of type
                        // FLOW_CONTROL_ERROR.
                        if s.Val > math.MaxInt32 {
                                return ConnectionError(ErrCodeFlowControl)
                        }

                        // Adjust flow control of currently-open
                        // frames by the difference of the old initial
                        // window size and this one.
                        delta := int32(s.Val) - int32(cc.initialWindowSize)
                        for _, cs := range cc.streams {
                                cs.flow.add(delta)
                        }
                        cc.cond.Broadcast()

                        cc.initialWindowSize = s.Val
                default:
                        // TODO(bradfitz): handle more settings? SETTINGS_HEADER_TABLE_SIZE probably.
                        cc.vlogf("Unhandled Setting: %v", s)
                }
                return nil
        })
        if err != nil {
                return err
        }

        cc.wmu.Lock()
        defer cc.wmu.Unlock()

        cc.fr.WriteSettingsAck()
        cc.bw.Flush()
        return cc.werr
}

func (rl *clientConnReadLoop) processWindowUpdate(f *WindowUpdateFrame) error {
        cc := rl.cc
        cs := cc.streamByID(f.StreamID, false)
        if f.StreamID != 0 && cs == nil {
                return nil
        }

        cc.mu.Lock()
        defer cc.mu.Unlock()

        fl := &cc.flow
        if cs != nil {
                fl = &cs.flow
        }
        if !fl.add(int32(f.Increment)) {
                return ConnectionError(ErrCodeFlowControl)
        }
        cc.cond.Broadcast()
        return nil
}

func (rl *clientConnReadLoop) processResetStream(f *RSTStreamFrame) error {
        cs := rl.cc.streamByID(f.StreamID, true)
        if cs == nil {
                // TODO: return error if server tries to RST_STEAM an idle stream
                return nil
        }
        select {
        case <-cs.peerReset:
                // Already reset.
                // This is the only goroutine
                // which closes this, so there
                // isn't a race.
        default:
                err := streamError(cs.ID, f.ErrCode)
                cs.resetErr = err
                close(cs.peerReset)
                cs.bufPipe.CloseWithError(err)
                cs.cc.cond.Broadcast() // wake up checkResetOrDone via clientStream.awaitFlowControl
        }
        return nil
}

// Ping sends a PING frame to the server and waits for the ack.
func (cc *ClientConn) Ping(ctx context.Context) error {
        c := make(chan struct{})
        // Generate a random payload
        var p [8]byte
        for {
                if _, err := rand.Read(p[:]); err != nil {
                        return err
                }
                cc.mu.Lock()
                // check for dup before insert
                if _, found := cc.pings[p]; !found {
                        cc.pings[p] = c
                        cc.mu.Unlock()
                        break
                }
                cc.mu.Unlock()
        }
        cc.wmu.Lock()
        if err := cc.fr.WritePing(false, p); err != nil {
                cc.wmu.Unlock()
                return err
        }
        if err := cc.bw.Flush(); err != nil {
                cc.wmu.Unlock()
                return err
        }
        cc.wmu.Unlock()
        select {
        case <-c:
                return nil
        case <-ctx.Done():
                return ctx.Err()
        case <-cc.readerDone:
                // connection closed
                return cc.readerErr
        }
}

func (rl *clientConnReadLoop) processPing(f *PingFrame) error {
        if f.IsAck() {
                cc := rl.cc
                cc.mu.Lock()
                defer cc.mu.Unlock()
                // If ack, notify listener if any
                if c, ok := cc.pings[f.Data]; ok {
                        close(c)
                        delete(cc.pings, f.Data)
                }
                return nil
        }
        cc := rl.cc
        cc.wmu.Lock()
        defer cc.wmu.Unlock()
        if err := cc.fr.WritePing(true, f.Data); err != nil {
                return err
        }
        return cc.bw.Flush()
}

func (rl *clientConnReadLoop) processPushPromise(f *PushPromiseFrame) error {
        // We told the peer we don't want them.
        // Spec says:
        // "PUSH_PROMISE MUST NOT be sent if the SETTINGS_ENABLE_PUSH
        // setting of the peer endpoint is set to 0. An endpoint that
        // has set this setting and has received acknowledgement MUST
        // treat the receipt of a PUSH_PROMISE frame as a connection
        // error (Section 5.4.1) of type PROTOCOL_ERROR."
        return ConnectionError(ErrCodeProtocol)
}

func (cc *ClientConn) writeStreamReset(streamID uint32, code ErrCode, err error) {
        // TODO: map err to more interesting error codes, once the
        // HTTP community comes up with some. But currently for
        // RST_STREAM there's no equivalent to GOAWAY frame's debug
        // data, and the error codes are all pretty vague ("cancel").
        cc.wmu.Lock()
        cc.fr.WriteRSTStream(streamID, code)
        cc.bw.Flush()
        cc.wmu.Unlock()
}

var (
        errResponseHeaderListSize = errors.New("http2: response header list larger than advertised limit")
        errRequestHeaderListSize  = errors.New("http2: request header list larger than peer's advertised limit")
        errPseudoTrailers         = errors.New("http2: invalid pseudo header in trailers")
)

func (cc *ClientConn) logf(format string, args ...interface{}) {
        cc.t.logf(format, args...)
}

func (cc *ClientConn) vlogf(format string, args ...interface{}) {
        cc.t.vlogf(format, args...)
}

func (t *Transport) vlogf(format string, args ...interface{}) {
        if VerboseLogs {
                t.logf(format, args...)
        }
}

func (t *Transport) logf(format string, args ...interface{}) {
        log.Printf(format, args...)
}

var noBody io.ReadCloser = ioutil.NopCloser(bytes.NewReader(nil))

func strSliceContains(ss []string, s string) bool {
        for _, v := range ss {
                if v == s {
                        return true
                }
        }
        return false
}

type erringRoundTripper struct{ err error }

func (rt erringRoundTripper) RoundTrip(*http.Request) (*http.Response, error) { return nil, rt.err }

// gzipReader wraps a response body so it can lazily
// call gzip.NewReader on the first call to Read
type gzipReader struct {
        body io.ReadCloser // underlying Response.Body
        zr   *gzip.Reader  // lazily-initialized gzip reader
        zerr error         // sticky error
}

func (gz *gzipReader) Read(p []byte) (n int, err error) {
        if gz.zerr != nil {
                return 0, gz.zerr
        }
        if gz.zr == nil {
                gz.zr, err = gzip.NewReader(gz.body)
                if err != nil {
                        gz.zerr = err
                        return 0, err
                }
        }
        return gz.zr.Read(p)
}

func (gz *gzipReader) Close() error {
        return gz.body.Close()
}

type errorReader struct{ err error }

func (r errorReader) Read(p []byte) (int, error) { return 0, r.err }

// bodyWriterState encapsulates various state around the Transport's writing
// of the request body, particularly regarding doing delayed writes of the body
// when the request contains "Expect: 100-continue".
type bodyWriterState struct {
        cs     *clientStream
        timer  *time.Timer   // if non-nil, we're doing a delayed write
        fnonce *sync.Once    // to call fn with
        fn     func()        // the code to run in the goroutine, writing the body
        resc   chan error    // result of fn's execution
        delay  time.Duration // how long we should delay a delayed write for
}

func (t *Transport) getBodyWriterState(cs *clientStream, body io.Reader) (s bodyWriterState) {
        s.cs = cs
        if body == nil {
                return
        }
        resc := make(chan error, 1)
        s.resc = resc
        s.fn = func() {
                cs.cc.mu.Lock()
                cs.startedWrite = true
                cs.cc.mu.Unlock()
                resc <- cs.writeRequestBody(body, cs.req.Body)
        }
        s.delay = t.expectContinueTimeout()
        if s.delay == 0 ||
                !httpguts.HeaderValuesContainsToken(
                        cs.req.Header["Expect"],
                        "100-continue") {
                return
        }
        s.fnonce = new(sync.Once)

        // Arm the timer with a very large duration, which we'll
        // intentionally lower later. It has to be large now because
        // we need a handle to it before writing the headers, but the
        // s.delay value is defined to not start until after the
        // request headers were written.
        const hugeDuration = 365 * 24 * time.Hour
        s.timer = time.AfterFunc(hugeDuration, func() {
                s.fnonce.Do(s.fn)
        })
        return
}

func (s bodyWriterState) cancel() {
        if s.timer != nil {
                s.timer.Stop()
        }
}

func (s bodyWriterState) on100() {
        if s.timer == nil {
                // If we didn't do a delayed write, ignore the server's
                // bogus 100 continue response.
                return
        }
        s.timer.Stop()
        go func() { s.fnonce.Do(s.fn) }()
}

// scheduleBodyWrite starts writing the body, either immediately (in
// the common case) or after the delay timeout. It should not be
// called until after the headers have been written.
func (s bodyWriterState) scheduleBodyWrite() {
        if s.timer == nil {
                // We're not doing a delayed write (see
                // getBodyWriterState), so just start the writing
                // goroutine immediately.
                go s.fn()
                return
        }
        traceWait100Continue(s.cs.trace)
        if s.timer.Stop() {
                s.timer.Reset(s.delay)
        }
}

// isConnectionCloseRequest reports whether req should use its own
// connection for a single request and then close the connection.
func isConnectionCloseRequest(req *http.Request) bool {
        return req.Close || httpguts.HeaderValuesContainsToken(req.Header["Connection"], "close")
}

// registerHTTPSProtocol calls Transport.RegisterProtocol but
// converting panics into errors.
func registerHTTPSProtocol(t *http.Transport, rt noDialH2RoundTripper) (err error) {
        defer func() {
                if e := recover(); e != nil {
                        err = fmt.Errorf("%v", e)
                }
        }()
        t.RegisterProtocol("https", rt)
        return nil
}

// noDialH2RoundTripper is a RoundTripper which only tries to complete the request
// if there's already has a cached connection to the host.
// (The field is exported so it can be accessed via reflect from net/http; tested
// by TestNoDialH2RoundTripperType)
type noDialH2RoundTripper struct{ *Transport }

func (rt noDialH2RoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
        res, err := rt.Transport.RoundTrip(req)
        if isNoCachedConnError(err) {
                return nil, http.ErrSkipAltProtocol
        }
        return res, err
}

func (t *Transport) idleConnTimeout() time.Duration {
        if t.t1 != nil {
                return t.t1.IdleConnTimeout
        }
        return 0
}

func traceGetConn(req *http.Request, hostPort string) {
        trace := httptrace.ContextClientTrace(req.Context())
        if trace == nil || trace.GetConn == nil {
                return
        }
        trace.GetConn(hostPort)
}

func traceGotConn(req *http.Request, cc *ClientConn) {
        trace := httptrace.ContextClientTrace(req.Context())
        if trace == nil || trace.GotConn == nil {
                return
        }
        ci := httptrace.GotConnInfo{Conn: cc.tconn}
        cc.mu.Lock()
        ci.Reused = cc.nextStreamID > 1
        ci.WasIdle = len(cc.streams) == 0 && ci.Reused
        if ci.WasIdle && !cc.lastActive.IsZero() {
                ci.IdleTime = time.Now().Sub(cc.lastActive)
        }
        cc.mu.Unlock()

        trace.GotConn(ci)
}

func traceWroteHeaders(trace *httptrace.ClientTrace) {
        if trace != nil && trace.WroteHeaders != nil {
                trace.WroteHeaders()
        }
}

func traceGot100Continue(trace *httptrace.ClientTrace) {
        if trace != nil && trace.Got100Continue != nil {
                trace.Got100Continue()
        }
}

func traceWait100Continue(trace *httptrace.ClientTrace) {
        if trace != nil && trace.Wait100Continue != nil {
                trace.Wait100Continue()
        }
}

func traceWroteRequest(trace *httptrace.ClientTrace, err error) {
        if trace != nil && trace.WroteRequest != nil {
                trace.WroteRequest(httptrace.WroteRequestInfo{Err: err})
        }
}

func traceFirstResponseByte(trace *httptrace.ClientTrace) {
        if trace != nil && trace.GotFirstResponseByte != nil {
                trace.GotFirstResponseByte()
        }
}