vendor/go.opencensus.io/plugin/ochttp/propagation/b3/b3.go

   1 // Copyright 2018, OpenCensus Authors
   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 // Package b3 contains a propagation.HTTPFormat implementation
  16 // for B3 propagation. See https://github.com/openzipkin/b3-propagation
  17 // for more details.
  18 package b3 // import "go.opencensus.io/plugin/ochttp/propagation/b3"
  19
  20 import (
  21         "encoding/hex"
  22         "net/http"
  23
  24         "go.opencensus.io/trace"
  25         "go.opencensus.io/trace/propagation"
  26 )
  27
  28 // B3 headers that OpenCensus understands.
  29 const (
  30         TraceIDHeader = "X-B3-TraceId"
  31         SpanIDHeader  = "X-B3-SpanId"
  32         SampledHeader = "X-B3-Sampled"
  33 )
  34
  35 // HTTPFormat implements propagation.HTTPFormat to propagate
  36 // traces in HTTP headers in B3 propagation format.
  37 // HTTPFormat skips the X-B3-ParentId and X-B3-Flags headers
  38 // because there are additional fields not represented in the
  39 // OpenCensus span context. Spans created from the incoming
  40 // header will be the direct children of the client-side span.
  41 // Similarly, reciever of the outgoing spans should use client-side
  42 // span created by OpenCensus as the parent.
  43 type HTTPFormat struct{}
  44
  45 var _ propagation.HTTPFormat = (*HTTPFormat)(nil)
  46
  47 // SpanContextFromRequest extracts a B3 span context from incoming requests.
  48 func (f *HTTPFormat) SpanContextFromRequest(req *http.Request) (sc trace.SpanContext, ok bool) {
  49         tid, ok := ParseTraceID(req.Header.Get(TraceIDHeader))
  50         if !ok {
  51                 return trace.SpanContext{}, false
  52         }
  53         sid, ok := ParseSpanID(req.Header.Get(SpanIDHeader))
  54         if !ok {
  55                 return trace.SpanContext{}, false
  56         }
  57         sampled, _ := ParseSampled(req.Header.Get(SampledHeader))
  58         return trace.SpanContext{
  59                 TraceID:      tid,
  60                 SpanID:       sid,
  61                 TraceOptions: sampled,
  62         }, true
  63 }
  64
  65 // ParseTraceID parses the value of the X-B3-TraceId header.
  66 func ParseTraceID(tid string) (trace.TraceID, bool) {
  67         if tid == "" {
  68                 return trace.TraceID{}, false
  69         }
  70         b, err := hex.DecodeString(tid)
  71         if err != nil {
  72                 return trace.TraceID{}, false
  73         }
  74         var traceID trace.TraceID
  75         if len(b) <= 8 {
  76                 // The lower 64-bits.
  77                 start := 8 + (8 - len(b))
  78                 copy(traceID[start:], b)
  79         } else {
  80                 start := 16 - len(b)
  81                 copy(traceID[start:], b)
  82         }
  83
  84         return traceID, true
  85 }
  86
  87 // ParseSpanID parses the value of the X-B3-SpanId or X-B3-ParentSpanId headers.
  88 func ParseSpanID(sid string) (spanID trace.SpanID, ok bool) {
  89         if sid == "" {
  90                 return trace.SpanID{}, false
  91         }
  92         b, err := hex.DecodeString(sid)
  93         if err != nil {
  94                 return trace.SpanID{}, false
  95         }
  96         start := 8 - len(b)
  97         copy(spanID[start:], b)
  98         return spanID, true
  99 }
 100
 101 // ParseSampled parses the value of the X-B3-Sampled header.
 102 func ParseSampled(sampled string) (trace.TraceOptions, bool) {
 103         switch sampled {
 104         case "true", "1":
 105                 return trace.TraceOptions(1), true
 106         default:
 107                 return trace.TraceOptions(0), false
 108         }
 109 }
 110
 111 // SpanContextToRequest modifies the given request to include B3 headers.
 112 func (f *HTTPFormat) SpanContextToRequest(sc trace.SpanContext, req *http.Request) {
 113         req.Header.Set(TraceIDHeader, hex.EncodeToString(sc.TraceID[:]))
 114         req.Header.Set(SpanIDHeader, hex.EncodeToString(sc.SpanID[:]))
 115
 116         var sampled string
 117         if sc.IsSampled() {
 118                 sampled = "1"
 119         } else {
 120                 sampled = "0"
 121         }
 122         req.Header.Set(SampledHeader, sampled)
 123 }