vendor/google.golang.org/api/transport/http/internal/propagation/http.go

   1 // Copyright 2018 Google LLC
   2 //
   3 // Licensed under the Apache License, Version 2.0 (the "License");
   4 // you may not use this file except in compliance with the License.
   5 // You may obtain a copy of the License at
   6 //
   7 //      http://www.apache.org/licenses/LICENSE-2.0
   8 //
   9 // Unless required by applicable law or agreed to in writing, software
  10 // distributed under the License is distributed on an "AS IS" BASIS,
  11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12 // See the License for the specific language governing permissions and
  13 // limitations under the License.
  14
  15 // +build go1.8
  16
  17 // Package propagation implements X-Cloud-Trace-Context header propagation used
  18 // by Google Cloud products.
  19 package propagation
  20
  21 import (
  22         "encoding/binary"
  23         "encoding/hex"
  24         "fmt"
  25         "net/http"
  26         "strconv"
  27         "strings"
  28
  29         "go.opencensus.io/trace"
  30         "go.opencensus.io/trace/propagation"
  31 )
  32
  33 const (
  34         httpHeaderMaxSize = 200
  35         httpHeader        = `X-Cloud-Trace-Context`
  36 )
  37
  38 var _ propagation.HTTPFormat = (*HTTPFormat)(nil)
  39
  40 // HTTPFormat implements propagation.HTTPFormat to propagate
  41 // traces in HTTP headers for Google Cloud Platform and Stackdriver Trace.
  42 type HTTPFormat struct{}
  43
  44 // SpanContextFromRequest extracts a Stackdriver Trace span context from incoming requests.
  45 func (f *HTTPFormat) SpanContextFromRequest(req *http.Request) (sc trace.SpanContext, ok bool) {
  46         h := req.Header.Get(httpHeader)
  47         // See https://cloud.google.com/trace/docs/faq for the header HTTPFormat.
  48         // Return if the header is empty or missing, or if the header is unreasonably
  49         // large, to avoid making unnecessary copies of a large string.
  50         if h == "" || len(h) > httpHeaderMaxSize {
  51                 return trace.SpanContext{}, false
  52         }
  53
  54         // Parse the trace id field.
  55         slash := strings.Index(h, `/`)
  56         if slash == -1 {
  57                 return trace.SpanContext{}, false
  58         }
  59         tid, h := h[:slash], h[slash+1:]
  60
  61         buf, err := hex.DecodeString(tid)
  62         if err != nil {
  63                 return trace.SpanContext{}, false
  64         }
  65         copy(sc.TraceID[:], buf)
  66
  67         // Parse the span id field.
  68         spanstr := h
  69         semicolon := strings.Index(h, `;`)
  70         if semicolon != -1 {
  71                 spanstr, h = h[:semicolon], h[semicolon+1:]
  72         }
  73         sid, err := strconv.ParseUint(spanstr, 10, 64)
  74         if err != nil {
  75                 return trace.SpanContext{}, false
  76         }
  77         binary.BigEndian.PutUint64(sc.SpanID[:], sid)
  78
  79         // Parse the options field, options field is optional.
  80         if !strings.HasPrefix(h, "o=") {
  81                 return sc, true
  82         }
  83         o, err := strconv.ParseUint(h[2:], 10, 64)
  84         if err != nil {
  85                 return trace.SpanContext{}, false
  86         }
  87         sc.TraceOptions = trace.TraceOptions(o)
  88         return sc, true
  89 }
  90
  91 // SpanContextToRequest modifies the given request to include a Stackdriver Trace header.
  92 func (f *HTTPFormat) SpanContextToRequest(sc trace.SpanContext, req *http.Request) {
  93         sid := binary.BigEndian.Uint64(sc.SpanID[:])
  94         header := fmt.Sprintf("%s/%d;o=%d", hex.EncodeToString(sc.TraceID[:]), sid, int64(sc.TraceOptions))
  95         req.Header.Set(httpHeader, header)
  96 }