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// Copyright 2018 Google LLC
//
// 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.
// +build go1.8
// Package propagation implements X-Cloud-Trace-Context header propagation used
// by Google Cloud products.
package propagation
import (
"encoding/binary"
"encoding/hex"
"fmt"
"net/http"
"strconv"
"strings"
"go.opencensus.io/trace"
"go.opencensus.io/trace/propagation"
)
const (
httpHeaderMaxSize = 200
httpHeader = `X-Cloud-Trace-Context`
)
var _ propagation.HTTPFormat = (*HTTPFormat)(nil)
// HTTPFormat implements propagation.HTTPFormat to propagate
// traces in HTTP headers for Google Cloud Platform and Stackdriver Trace.
type HTTPFormat struct{}
// SpanContextFromRequest extracts a Stackdriver Trace span context from incoming requests.
func (f *HTTPFormat) SpanContextFromRequest(req *http.Request) (sc trace.SpanContext, ok bool) {
h := req.Header.Get(httpHeader)
// See https://cloud.google.com/trace/docs/faq for the header HTTPFormat.
// Return if the header is empty or missing, or if the header is unreasonably
// large, to avoid making unnecessary copies of a large string.
if h == "" || len(h) > httpHeaderMaxSize {
return trace.SpanContext{}, false
}
// Parse the trace id field.
slash := strings.Index(h, `/`)
if slash == -1 {
return trace.SpanContext{}, false
}
tid, h := h[:slash], h[slash+1:]
buf, err := hex.DecodeString(tid)
if err != nil {
return trace.SpanContext{}, false
}
copy(sc.TraceID[:], buf)
// Parse the span id field.
spanstr := h
semicolon := strings.Index(h, `;`)
if semicolon != -1 {
spanstr, h = h[:semicolon], h[semicolon+1:]
}
sid, err := strconv.ParseUint(spanstr, 10, 64)
if err != nil {
return trace.SpanContext{}, false
}
binary.BigEndian.PutUint64(sc.SpanID[:], sid)
// Parse the options field, options field is optional.
if !strings.HasPrefix(h, "o=") {
return sc, true
}
o, err := strconv.ParseUint(h[2:], 10, 64)
if err != nil {
return trace.SpanContext{}, false
}
sc.TraceOptions = trace.TraceOptions(o)
return sc, true
}
// SpanContextToRequest modifies the given request to include a Stackdriver Trace header.
func (f *HTTPFormat) SpanContextToRequest(sc trace.SpanContext, req *http.Request) {
sid := binary.BigEndian.Uint64(sc.SpanID[:])
header := fmt.Sprintf("%s/%d;o=%d", hex.EncodeToString(sc.TraceID[:]), sid, int64(sc.TraceOptions))
req.Header.Set(httpHeader, header)
}
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