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- // 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 b3 contains a propagation.HTTPFormat implementation
- // for B3 propagation. See https://github.com/openzipkin/b3-propagation
- // for more details.
- package b3 // import "go.opencensus.io/plugin/ochttp/propagation/b3"
-
- import (
- "encoding/hex"
- "net/http"
-
- "go.opencensus.io/trace"
- "go.opencensus.io/trace/propagation"
- )
-
- // B3 headers that OpenCensus understands.
- const (
- TraceIDHeader = "X-B3-TraceId"
- SpanIDHeader = "X-B3-SpanId"
- SampledHeader = "X-B3-Sampled"
- )
-
- // HTTPFormat implements propagation.HTTPFormat to propagate
- // traces in HTTP headers in B3 propagation format.
- // HTTPFormat skips the X-B3-ParentId and X-B3-Flags headers
- // because there are additional fields not represented in the
- // OpenCensus span context. Spans created from the incoming
- // header will be the direct children of the client-side span.
- // Similarly, receiver of the outgoing spans should use client-side
- // span created by OpenCensus as the parent.
- type HTTPFormat struct{}
-
- var _ propagation.HTTPFormat = (*HTTPFormat)(nil)
-
- // SpanContextFromRequest extracts a B3 span context from incoming requests.
- func (f *HTTPFormat) SpanContextFromRequest(req *http.Request) (sc trace.SpanContext, ok bool) {
- tid, ok := ParseTraceID(req.Header.Get(TraceIDHeader))
- if !ok {
- return trace.SpanContext{}, false
- }
- sid, ok := ParseSpanID(req.Header.Get(SpanIDHeader))
- if !ok {
- return trace.SpanContext{}, false
- }
- sampled, _ := ParseSampled(req.Header.Get(SampledHeader))
- return trace.SpanContext{
- TraceID: tid,
- SpanID: sid,
- TraceOptions: sampled,
- }, true
- }
-
- // ParseTraceID parses the value of the X-B3-TraceId header.
- func ParseTraceID(tid string) (trace.TraceID, bool) {
- if tid == "" {
- return trace.TraceID{}, false
- }
- b, err := hex.DecodeString(tid)
- if err != nil {
- return trace.TraceID{}, false
- }
- var traceID trace.TraceID
- if len(b) <= 8 {
- // The lower 64-bits.
- start := 8 + (8 - len(b))
- copy(traceID[start:], b)
- } else {
- start := 16 - len(b)
- copy(traceID[start:], b)
- }
-
- return traceID, true
- }
-
- // ParseSpanID parses the value of the X-B3-SpanId or X-B3-ParentSpanId headers.
- func ParseSpanID(sid string) (spanID trace.SpanID, ok bool) {
- if sid == "" {
- return trace.SpanID{}, false
- }
- b, err := hex.DecodeString(sid)
- if err != nil {
- return trace.SpanID{}, false
- }
- start := 8 - len(b)
- copy(spanID[start:], b)
- return spanID, true
- }
-
- // ParseSampled parses the value of the X-B3-Sampled header.
- func ParseSampled(sampled string) (trace.TraceOptions, bool) {
- switch sampled {
- case "true", "1":
- return trace.TraceOptions(1), true
- default:
- return trace.TraceOptions(0), false
- }
- }
-
- // SpanContextToRequest modifies the given request to include B3 headers.
- func (f *HTTPFormat) SpanContextToRequest(sc trace.SpanContext, req *http.Request) {
- req.Header.Set(TraceIDHeader, hex.EncodeToString(sc.TraceID[:]))
- req.Header.Set(SpanIDHeader, hex.EncodeToString(sc.SpanID[:]))
-
- var sampled string
- if sc.IsSampled() {
- sampled = "1"
- } else {
- sampled = "0"
- }
- req.Header.Set(SampledHeader, sampled)
- }
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