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/
propagation.go
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/
propagation.go
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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 tracecontext contains HTTP propagator for TraceContext standard.
// See https://github.com/w3c/distributed-tracing for more information.
package tracecontext // import "go.opencensus.io/plugin/ochttp/propagation/tracecontext"
import (
"encoding/hex"
"fmt"
"net/http"
"net/textproto"
"regexp"
"strings"
"go.opencensus.io/trace"
"go.opencensus.io/trace/propagation"
"go.opencensus.io/trace/tracestate"
)
const (
supportedVersion = 0
maxVersion = 254
maxTracestateLen = 512
traceparentHeader = "traceparent"
tracestateHeader = "tracestate"
trimOWSRegexFmt = `^[\x09\x20]*(.*[^\x20\x09])[\x09\x20]*$`
)
var trimOWSRegExp = regexp.MustCompile(trimOWSRegexFmt)
var _ propagation.HTTPFormat = (*HTTPFormat)(nil)
// HTTPFormat implements the TraceContext trace propagation format.
type HTTPFormat struct{}
// SpanContextFromRequest extracts a span context from incoming requests.
func (f *HTTPFormat) SpanContextFromRequest(req *http.Request) (sc trace.SpanContext, ok bool) {
h, ok := getRequestHeader(req, traceparentHeader, false)
if !ok {
return trace.SpanContext{}, false
}
sections := strings.Split(h, "-")
if len(sections) < 4 {
return trace.SpanContext{}, false
}
if len(sections[0]) != 2 {
return trace.SpanContext{}, false
}
ver, err := hex.DecodeString(sections[0])
if err != nil {
return trace.SpanContext{}, false
}
version := int(ver[0])
if version > maxVersion {
return trace.SpanContext{}, false
}
if version == 0 && len(sections) != 4 {
return trace.SpanContext{}, false
}
if len(sections[1]) != 32 {
return trace.SpanContext{}, false
}
tid, err := hex.DecodeString(sections[1])
if err != nil {
return trace.SpanContext{}, false
}
copy(sc.TraceID[:], tid)
if len(sections[2]) != 16 {
return trace.SpanContext{}, false
}
sid, err := hex.DecodeString(sections[2])
if err != nil {
return trace.SpanContext{}, false
}
copy(sc.SpanID[:], sid)
opts, err := hex.DecodeString(sections[3])
if err != nil || len(opts) < 1 {
return trace.SpanContext{}, false
}
sc.TraceOptions = trace.TraceOptions(opts[0])
// Don't allow all zero trace or span ID.
if sc.TraceID == [16]byte{} || sc.SpanID == [8]byte{} {
return trace.SpanContext{}, false
}
sc.Tracestate = tracestateFromRequest(req)
return sc, true
}
// getRequestHeader returns a combined header field according to RFC7230 section 3.2.2.
// If commaSeparated is true, multiple header fields with the same field name using be
// combined using ",".
// If no header was found using the given name, "ok" would be false.
// If more than one headers was found using the given name, while commaSeparated is false,
// "ok" would be false.
func getRequestHeader(req *http.Request, name string, commaSeparated bool) (hdr string, ok bool) {
v := req.Header[textproto.CanonicalMIMEHeaderKey(name)]
switch len(v) {
case 0:
return "", false
case 1:
return v[0], true
default:
return strings.Join(v, ","), commaSeparated
}
}
// TODO(rghetia): return an empty Tracestate when parsing tracestate header encounters an error.
// Revisit to return additional boolean value to indicate parsing error when following issues
// are resolved.
// https://github.com/w3c/distributed-tracing/issues/172
// https://github.com/w3c/distributed-tracing/issues/175
func tracestateFromRequest(req *http.Request) *tracestate.Tracestate {
h, _ := getRequestHeader(req, tracestateHeader, true)
if h == "" {
return nil
}
var entries []tracestate.Entry
pairs := strings.Split(h, ",")
hdrLenWithoutOWS := len(pairs) - 1 // Number of commas
for _, pair := range pairs {
matches := trimOWSRegExp.FindStringSubmatch(pair)
if matches == nil {
return nil
}
pair = matches[1]
hdrLenWithoutOWS += len(pair)
if hdrLenWithoutOWS > maxTracestateLen {
return nil
}
kv := strings.Split(pair, "=")
if len(kv) != 2 {
return nil
}
entries = append(entries, tracestate.Entry{Key: kv[0], Value: kv[1]})
}
ts, err := tracestate.New(nil, entries...)
if err != nil {
return nil
}
return ts
}
func tracestateToRequest(sc trace.SpanContext, req *http.Request) {
var pairs = make([]string, 0, len(sc.Tracestate.Entries()))
if sc.Tracestate != nil {
for _, entry := range sc.Tracestate.Entries() {
pairs = append(pairs, strings.Join([]string{entry.Key, entry.Value}, "="))
}
h := strings.Join(pairs, ",")
if h != "" && len(h) <= maxTracestateLen {
req.Header.Set(tracestateHeader, h)
}
}
}
// SpanContextToRequest modifies the given request to include traceparent and tracestate headers.
func (f *HTTPFormat) SpanContextToRequest(sc trace.SpanContext, req *http.Request) {
h := fmt.Sprintf("%x-%x-%x-%x",
[]byte{supportedVersion},
sc.TraceID[:],
sc.SpanID[:],
[]byte{byte(sc.TraceOptions)})
req.Header.Set(traceparentHeader, h)
tracestateToRequest(sc, req)
}