trace_context.go raw

   1  // Copyright The OpenTelemetry Authors
   2  // SPDX-License-Identifier: Apache-2.0
   3  
   4  package propagation // import "go.opentelemetry.io/otel/propagation"
   5  
   6  import (
   7  	"context"
   8  	"encoding/hex"
   9  	"fmt"
  10  	"strings"
  11  
  12  	"go.opentelemetry.io/otel/trace"
  13  )
  14  
  15  const (
  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.
  31  type TraceContext struct{}
  32  
  33  var (
  34  	_           TextMapPropagator = TraceContext{}
  35  	versionPart                   = fmt.Sprintf("%.2X", supportedVersion)
  36  )
  37  
  38  // Inject injects the trace context from ctx into carrier.
  39  func (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.
  72  func (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  
  80  func (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.
 131  func 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  
 140  func 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.
 154  func (TraceContext) Fields() []string {
 155  	return []string{traceparentHeader, tracestateHeader}
 156  }
 157