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// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0
package propagation // import "go.opentelemetry.io/otel/propagation"
import (
"context"
"encoding/hex"
"fmt"
"strings"
"go.opentelemetry.io/otel/trace"
)
const (
supportedVersion = 0
maxVersion = 254
traceparentHeader = "traceparent"
tracestateHeader = "tracestate"
delimiter = "-"
)
// TraceContext is a propagator that supports the W3C Trace Context format
// (https://www.w3.org/TR/trace-context/)
//
// This propagator will propagate the traceparent and tracestate headers to
// guarantee traces are not broken. It is up to the users of this propagator
// to choose if they want to participate in a trace by modifying the
// traceparent header and relevant parts of the tracestate header containing
// their proprietary information.
type TraceContext struct{}
var (
_ TextMapPropagator = TraceContext{}
versionPart = fmt.Sprintf("%.2X", supportedVersion)
)
// Inject injects the trace context from ctx into carrier.
func (tc TraceContext) Inject(ctx context.Context, carrier TextMapCarrier) {
sc := trace.SpanContextFromContext(ctx)
if !sc.IsValid() {
return
}
if ts := sc.TraceState().String(); ts != "" {
carrier.Set(tracestateHeader, ts)
}
// Clear all flags other than the trace-context supported sampling bit.
flags := sc.TraceFlags() & trace.FlagsSampled
var sb strings.Builder
sb.Grow(2 + 32 + 16 + 2 + 3)
_, _ = sb.WriteString(versionPart)
traceID := sc.TraceID()
spanID := sc.SpanID()
flagByte := [1]byte{byte(flags)}
var buf [32]byte
for _, src := range [][]byte{traceID[:], spanID[:], flagByte[:]} {
_ = sb.WriteByte(delimiter[0])
n := hex.Encode(buf[:], src)
_, _ = sb.Write(buf[:n])
}
carrier.Set(traceparentHeader, sb.String())
}
// Extract reads tracecontext from the carrier into a returned Context.
//
// The returned Context will be a copy of ctx and contain the extracted
// tracecontext as the remote SpanContext. If the extracted tracecontext is
// invalid, the passed ctx will be returned directly instead.
func (tc TraceContext) Extract(ctx context.Context, carrier TextMapCarrier) context.Context {
sc := tc.extract(carrier)
if !sc.IsValid() {
return ctx
}
return trace.ContextWithRemoteSpanContext(ctx, sc)
}
func (tc TraceContext) extract(carrier TextMapCarrier) trace.SpanContext {
h := carrier.Get(traceparentHeader)
if h == "" {
return trace.SpanContext{}
}
var ver [1]byte
if !extractPart(ver[:], &h, 2) {
return trace.SpanContext{}
}
version := int(ver[0])
if version > maxVersion {
return trace.SpanContext{}
}
var scc trace.SpanContextConfig
if !extractPart(scc.TraceID[:], &h, 32) {
return trace.SpanContext{}
}
if !extractPart(scc.SpanID[:], &h, 16) {
return trace.SpanContext{}
}
var opts [1]byte
if !extractPart(opts[:], &h, 2) {
return trace.SpanContext{}
}
if version == 0 && (h != "" || opts[0] > 2) {
// version 0 not allow extra
// version 0 not allow other flag
return trace.SpanContext{}
}
// Clear all flags other than the trace-context supported sampling bit.
scc.TraceFlags = trace.TraceFlags(opts[0]) & trace.FlagsSampled
// Ignore the error returned here. Failure to parse tracestate MUST NOT
// affect the parsing of traceparent according to the W3C tracecontext
// specification.
scc.TraceState, _ = trace.ParseTraceState(carrier.Get(tracestateHeader))
scc.Remote = true
sc := trace.NewSpanContext(scc)
if !sc.IsValid() {
return trace.SpanContext{}
}
return sc
}
// upperHex detect hex is upper case Unicode characters.
func upperHex(v string) bool {
for _, c := range v {
if c >= 'A' && c <= 'F' {
return true
}
}
return false
}
func extractPart(dst []byte, h *string, n int) bool {
part, left, _ := strings.Cut(*h, delimiter)
*h = left
// hex.Decode decodes unsupported upper-case characters, so exclude explicitly.
if len(part) != n || upperHex(part) {
return false
}
if p, err := hex.Decode(dst, []byte(part)); err != nil || p != n/2 {
return false
}
return true
}
// Fields returns the keys who's values are set with Inject.
func (tc TraceContext) Fields() []string {
return []string{traceparentHeader, tracestateHeader}
}
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