// Copyright 2018, OpenCensus Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package ochttp
import (
"net/http"
"net/http/httptrace"
"go.opencensus.io/trace"
"go.opencensus.io/trace/propagation"
)
// Transport is an http.RoundTripper that instruments all outgoing requests with
// OpenCensus stats and tracing.
//
// The zero value is intended to be a useful default, but for
// now it's recommended that you explicitly set Propagation, since the default
// for this may change.
type Transport struct {
// Base may be set to wrap another http.RoundTripper that does the actual
// requests. By default http.DefaultTransport is used.
//
// If base HTTP roundtripper implements CancelRequest,
// the returned round tripper will be cancelable.
Base http.RoundTripper
// Propagation defines how traces are propagated. If unspecified, a default
// (currently B3 format) will be used.
Propagation propagation.HTTPFormat
// StartOptions are applied to the span started by this Transport around each
// request.
//
// StartOptions.SpanKind will always be set to trace.SpanKindClient
// for spans started by this transport.
StartOptions trace.StartOptions
// GetStartOptions allows to set start options per request. If set,
// StartOptions is going to be ignored.
GetStartOptions func(*http.Request) trace.StartOptions
// NameFromRequest holds the function to use for generating the span name
// from the information found in the outgoing HTTP Request. By default the
// name equals the URL Path.
FormatSpanName func(*http.Request) string
// NewClientTrace may be set to a function allowing the current *trace.Span
// to be annotated with HTTP request event information emitted by the
// httptrace package.
NewClientTrace func(*http.Request, *trace.Span) *httptrace.ClientTrace
// TODO: Implement tag propagation for HTTP.
}
// RoundTrip implements http.RoundTripper, delegating to Base and recording stats and traces for the request.
func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
rt := t.base()
if isHealthEndpoint(req.URL.Path) {
return rt.RoundTrip(req)
}
// TODO: remove excessive nesting of http.RoundTrippers here.
format := t.Propagation
if format == nil {
format = defaultFormat
}
spanNameFormatter := t.FormatSpanName
if spanNameFormatter == nil {
spanNameFormatter = spanNameFromURL
}
startOpts := t.StartOptions
if t.GetStartOptions != nil {
startOpts = t.GetStartOptions(req)
}
rt = &traceTransport{
base: rt,
format: format,
startOptions: trace.StartOptions{
Sampler: startOpts.Sampler,
SpanKind: trace.SpanKindClient,
},
formatSpanName: spanNameFormatter,
newClientTrace: t.NewClientTrace,
}
rt = statsTransport{base: rt}
return rt.RoundTrip(req)
}
func (t *Transport) base() http.RoundTripper {
if t.Base != nil {
return t.Base
}
return http.DefaultTransport
}
// CancelRequest cancels an in-flight request by closing its connection.
func (t *Transport) CancelRequest(req *http.Request) {
type canceler interface {
CancelRequest(*http.Request)
}
if cr, ok := t.base().(canceler); ok {
cr.CancelRequest(req)
}
}
