1// Copyright The OpenTelemetry Authors
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//     http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15package propagation // import "go.opentelemetry.io/otel/propagation"
16
17import (
18	"context"
19	"encoding/hex"
20	"fmt"
21	"regexp"
22	"strings"
23
24	"go.opentelemetry.io/otel/attribute"
25	"go.opentelemetry.io/otel/trace"
26)
27
28const (
29	supportedVersion  = 0
30	maxVersion        = 254
31	traceparentHeader = "traceparent"
32	tracestateHeader  = "tracestate"
33)
34
35// TraceContext is a propagator that supports the W3C Trace Context format
36// (https://www.w3.org/TR/trace-context/)
37//
38// This propagator will propagate the traceparent and tracestate headers to
39// guarantee traces are not broken. It is up to the users of this propagator
40// to choose if they want to participate in a trace by modifying the
41// traceparent header and relevant parts of the tracestate header containing
42// their proprietary information.
43type TraceContext struct{}
44
45var _ TextMapPropagator = TraceContext{}
46var traceCtxRegExp = regexp.MustCompile("^(?P<version>[0-9a-f]{2})-(?P<traceID>[a-f0-9]{32})-(?P<spanID>[a-f0-9]{16})-(?P<traceFlags>[a-f0-9]{2})(?:-.*)?$")
47
48// Inject set tracecontext from the Context into the carrier.
49func (tc TraceContext) Inject(ctx context.Context, carrier TextMapCarrier) {
50	sc := trace.SpanContextFromContext(ctx)
51	if !sc.IsValid() {
52		return
53	}
54
55	carrier.Set(tracestateHeader, sc.TraceState().String())
56
57	// Clear all flags other than the trace-context supported sampling bit.
58	flags := sc.TraceFlags() & trace.FlagsSampled
59
60	h := fmt.Sprintf("%.2x-%s-%s-%s",
61		supportedVersion,
62		sc.TraceID(),
63		sc.SpanID(),
64		flags)
65	carrier.Set(traceparentHeader, h)
66}
67
68// Extract reads tracecontext from the carrier into a returned Context.
69//
70// The returned Context will be a copy of ctx and contain the extracted
71// tracecontext as the remote SpanContext. If the extracted tracecontext is
72// invalid, the passed ctx will be returned directly instead.
73func (tc TraceContext) Extract(ctx context.Context, carrier TextMapCarrier) context.Context {
74	sc := tc.extract(carrier)
75	if !sc.IsValid() {
76		return ctx
77	}
78	return trace.ContextWithRemoteSpanContext(ctx, sc)
79}
80
81func (tc TraceContext) extract(carrier TextMapCarrier) trace.SpanContext {
82	h := carrier.Get(traceparentHeader)
83	if h == "" {
84		return trace.SpanContext{}
85	}
86
87	matches := traceCtxRegExp.FindStringSubmatch(h)
88
89	if len(matches) == 0 {
90		return trace.SpanContext{}
91	}
92
93	if len(matches) < 5 { // four subgroups plus the overall match
94		return trace.SpanContext{}
95	}
96
97	if len(matches[1]) != 2 {
98		return trace.SpanContext{}
99	}
100	ver, err := hex.DecodeString(matches[1])
101	if err != nil {
102		return trace.SpanContext{}
103	}
104	version := int(ver[0])
105	if version > maxVersion {
106		return trace.SpanContext{}
107	}
108
109	if version == 0 && len(matches) != 5 { // four subgroups plus the overall match
110		return trace.SpanContext{}
111	}
112
113	if len(matches[2]) != 32 {
114		return trace.SpanContext{}
115	}
116
117	var scc trace.SpanContextConfig
118
119	scc.TraceID, err = trace.TraceIDFromHex(matches[2][:32])
120	if err != nil {
121		return trace.SpanContext{}
122	}
123
124	if len(matches[3]) != 16 {
125		return trace.SpanContext{}
126	}
127	scc.SpanID, err = trace.SpanIDFromHex(matches[3])
128	if err != nil {
129		return trace.SpanContext{}
130	}
131
132	if len(matches[4]) != 2 {
133		return trace.SpanContext{}
134	}
135	opts, err := hex.DecodeString(matches[4])
136	if err != nil || len(opts) < 1 || (version == 0 && opts[0] > 2) {
137		return trace.SpanContext{}
138	}
139	// Clear all flags other than the trace-context supported sampling bit.
140	scc.TraceFlags = trace.TraceFlags(opts[0]) & trace.FlagsSampled
141
142	scc.TraceState = parseTraceState(carrier.Get(tracestateHeader))
143	scc.Remote = true
144
145	sc := trace.NewSpanContext(scc)
146	if !sc.IsValid() {
147		return trace.SpanContext{}
148	}
149
150	return sc
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}
157
158func parseTraceState(in string) trace.TraceState {
159	if in == "" {
160		return trace.TraceState{}
161	}
162
163	kvs := []attribute.KeyValue{}
164	for _, entry := range strings.Split(in, ",") {
165		parts := strings.SplitN(entry, "=", 2)
166		if len(parts) != 2 {
167			// Parse failure, abort!
168			return trace.TraceState{}
169		}
170		kvs = append(kvs, attribute.String(parts[0], parts[1]))
171	}
172
173	// Ignoring error here as "failure to parse tracestate MUST NOT
174	// affect the parsing of traceparent."
175	// https://www.w3.org/TR/trace-context/#tracestate-header
176	ts, _ := trace.TraceStateFromKeyValues(kvs...)
177	return ts
178}
179