1// Copyright The OpenTelemetry Authors
2// SPDX-License-Identifier: Apache-2.0
3
4package propagation // import "go.opentelemetry.io/otel/propagation"
5
6import (
7 "context"
8 "encoding/hex"
9 "fmt"
10 "strings"
11
12 "go.opentelemetry.io/otel/trace"
13)
14
15const (
16 supportedVersion = 0
17 maxVersion = 254
18 traceparentHeader = "traceparent"
19 tracestateHeader = "tracestate"
20 delimiter = "-"
21)
22
23// TraceContext is a propagator that supports the W3C Trace Context format
24// (https://www.w3.org/TR/trace-context/)
25//
26// This propagator will propagate the traceparent and tracestate headers to
27// guarantee traces are not broken. It is up to the users of this propagator
28// to choose if they want to participate in a trace by modifying the
29// traceparent header and relevant parts of the tracestate header containing
30// their proprietary information.
31type TraceContext struct{}
32
33var (
34 _ TextMapPropagator = TraceContext{}
35 versionPart = fmt.Sprintf("%.2X", supportedVersion)
36)
37
38// Inject injects the trace context from ctx into carrier.
39func (tc TraceContext) Inject(ctx context.Context, carrier TextMapCarrier) {
40 sc := trace.SpanContextFromContext(ctx)
41 if !sc.IsValid() {
42 return
43 }
44
45 if ts := sc.TraceState().String(); ts != "" {
46 carrier.Set(tracestateHeader, ts)
47 }
48
49 // Clear all flags other than the trace-context supported sampling bit.
50 flags := sc.TraceFlags() & trace.FlagsSampled
51
52 var sb strings.Builder
53 sb.Grow(2 + 32 + 16 + 2 + 3)
54 _, _ = sb.WriteString(versionPart)
55 traceID := sc.TraceID()
56 spanID := sc.SpanID()
57 flagByte := [1]byte{byte(flags)}
58 var buf [32]byte
59 for _, src := range [][]byte{traceID[:], spanID[:], flagByte[:]} {
60 _ = sb.WriteByte(delimiter[0])
61 n := hex.Encode(buf[:], src)
62 _, _ = sb.Write(buf[:n])
63 }
64 carrier.Set(traceparentHeader, sb.String())
65}
66
67// Extract reads tracecontext from the carrier into a returned Context.
68//
69// The returned Context will be a copy of ctx and contain the extracted
70// tracecontext as the remote SpanContext. If the extracted tracecontext is
71// invalid, the passed ctx will be returned directly instead.
72func (tc TraceContext) Extract(ctx context.Context, carrier TextMapCarrier) context.Context {
73 sc := tc.extract(carrier)
74 if !sc.IsValid() {
75 return ctx
76 }
77 return trace.ContextWithRemoteSpanContext(ctx, sc)
78}
79
80func (tc TraceContext) extract(carrier TextMapCarrier) trace.SpanContext {
81 h := carrier.Get(traceparentHeader)
82 if h == "" {
83 return trace.SpanContext{}
84 }
85
86 var ver [1]byte
87 if !extractPart(ver[:], &h, 2) {
88 return trace.SpanContext{}
89 }
90 version := int(ver[0])
91 if version > maxVersion {
92 return trace.SpanContext{}
93 }
94
95 var scc trace.SpanContextConfig
96 if !extractPart(scc.TraceID[:], &h, 32) {
97 return trace.SpanContext{}
98 }
99 if !extractPart(scc.SpanID[:], &h, 16) {
100 return trace.SpanContext{}
101 }
102
103 var opts [1]byte
104 if !extractPart(opts[:], &h, 2) {
105 return trace.SpanContext{}
106 }
107 if version == 0 && (h != "" || opts[0] > 2) {
108 // version 0 not allow extra
109 // version 0 not allow other flag
110 return trace.SpanContext{}
111 }
112
113 // Clear all flags other than the trace-context supported sampling bit.
114 scc.TraceFlags = trace.TraceFlags(opts[0]) & trace.FlagsSampled
115
116 // Ignore the error returned here. Failure to parse tracestate MUST NOT
117 // affect the parsing of traceparent according to the W3C tracecontext
118 // specification.
119 scc.TraceState, _ = trace.ParseTraceState(carrier.Get(tracestateHeader))
120 scc.Remote = true
121
122 sc := trace.NewSpanContext(scc)
123 if !sc.IsValid() {
124 return trace.SpanContext{}
125 }
126
127 return sc
128}
129
130// upperHex detect hex is upper case Unicode characters.
131func upperHex(v string) bool {
132 for _, c := range v {
133 if c >= 'A' && c <= 'F' {
134 return true
135 }
136 }
137 return false
138}
139
140func extractPart(dst []byte, h *string, n int) bool {
141 part, left, _ := strings.Cut(*h, delimiter)
142 *h = left
143 // hex.Decode decodes unsupported upper-case characters, so exclude explicitly.
144 if len(part) != n || upperHex(part) {
145 return false
146 }
147 if p, err := hex.Decode(dst, []byte(part)); err != nil || p != n/2 {
148 return false
149 }
150 return true
151}
152
153// Fields returns the keys who's values are set with Inject.
154func (tc TraceContext) Fields() []string {
155 return []string{traceparentHeader, tracestateHeader}
156}