/
propagator.go
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/
propagator.go
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// Copyright The OpenTelemetry 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 xray
import (
"context"
"errors"
"strings"
"go.opentelemetry.io/otel/propagation"
"go.opentelemetry.io/otel/trace"
)
const (
traceHeaderKey = "X-Amzn-Trace-Id"
traceHeaderDelimiter = ";"
kvDelimiter = "="
traceIDKey = "Root"
sampleFlagKey = "Sampled"
parentIDKey = "Parent"
traceIDVersion = "1"
traceIDDelimiter = "-"
isSampled = "1"
notSampled = "0"
traceFlagNone = 0x0
traceFlagSampled = 0x1 << 0
traceIDLength = 35
traceIDDelimitterIndex1 = 1
traceIDDelimitterIndex2 = 10
traceIDFirstPartLength = 8
sampledFlagLength = 1
)
var (
empty = trace.SpanContext{}
errInvalidTraceHeader = errors.New("invalid X-Amzn-Trace-Id header value, should contain 3 different part separated by ;")
errMalformedTraceID = errors.New("cannot decode trace ID from header")
errLengthTraceIDHeader = errors.New("incorrect length of X-Ray trace ID found, 35 character length expected")
errInvalidTraceIDVersion = errors.New("invalid X-Ray trace ID header found, does not have valid trace ID version")
errInvalidSpanIDLength = errors.New("invalid span ID length, must be 16")
)
// Propagator serializes Span Context to/from AWS X-Ray headers.
//
// Example AWS X-Ray format:
//
// X-Amzn-Trace-Id: Root={traceId};Parent={parentId};Sampled={samplingFlag}
type Propagator struct{}
// Asserts that the propagator implements the otel.TextMapPropagator interface at compile time.
var _ propagation.TextMapPropagator = &Propagator{}
// Inject injects a context to the carrier following AWS X-Ray format.
func (xray Propagator) Inject(ctx context.Context, carrier propagation.TextMapCarrier) {
sc := trace.SpanFromContext(ctx).SpanContext()
if !sc.TraceID.IsValid() || !sc.SpanID.IsValid() {
return
}
otTraceID := sc.TraceID.String()
xrayTraceID := traceIDVersion + traceIDDelimiter + otTraceID[0:traceIDFirstPartLength] +
traceIDDelimiter + otTraceID[traceIDFirstPartLength:]
parentID := sc.SpanID
samplingFlag := notSampled
if sc.TraceFlags == traceFlagSampled {
samplingFlag = isSampled
}
headers := []string{traceIDKey, kvDelimiter, xrayTraceID, traceHeaderDelimiter, parentIDKey,
kvDelimiter, parentID.String(), traceHeaderDelimiter, sampleFlagKey, kvDelimiter, samplingFlag}
carrier.Set(traceHeaderKey, strings.Join(headers, ""))
}
// Extract gets a context from the carrier if it contains AWS X-Ray headers.
func (xray Propagator) Extract(ctx context.Context, carrier propagation.TextMapCarrier) context.Context {
// extract tracing information
if header := carrier.Get(traceHeaderKey); header != "" {
sc, err := extract(header)
if err == nil && sc.IsValid() {
return trace.ContextWithRemoteSpanContext(ctx, sc)
}
}
return ctx
}
// extract extracts Span Context from context.
func extract(headerVal string) (trace.SpanContext, error) {
var (
sc = trace.SpanContext{}
err error
delimiterIndex int
part string
)
pos := 0
for pos < len(headerVal) {
delimiterIndex = indexOf(headerVal, traceHeaderDelimiter, pos)
if delimiterIndex >= 0 {
part = headerVal[pos:delimiterIndex]
pos = delimiterIndex + 1
} else {
//last part
part = strings.TrimSpace(headerVal[pos:])
pos = len(headerVal)
}
equalsIndex := strings.Index(part, kvDelimiter)
if equalsIndex < 0 {
return empty, errInvalidTraceHeader
}
value := part[equalsIndex+1:]
if strings.HasPrefix(part, traceIDKey) {
sc.TraceID, err = parseTraceID(value)
if err != nil {
return empty, err
}
} else if strings.HasPrefix(part, parentIDKey) {
//extract parentId
sc.SpanID, err = trace.SpanIDFromHex(value)
if err != nil {
return empty, errInvalidSpanIDLength
}
} else if strings.HasPrefix(part, sampleFlagKey) {
//extract traceflag
sc.TraceFlags = parseTraceFlag(value)
}
}
return sc, nil
}
// indexOf returns position of the first occurrence of a substr in str starting at pos index.
func indexOf(str string, substr string, pos int) int {
index := strings.Index(str[pos:], substr)
if index > -1 {
index += pos
}
return index
}
// parseTraceID returns trace ID if valid else return invalid trace ID.
func parseTraceID(xrayTraceID string) (trace.TraceID, error) {
if len(xrayTraceID) != traceIDLength {
return empty.TraceID, errLengthTraceIDHeader
}
if !strings.HasPrefix(xrayTraceID, traceIDVersion) {
return empty.TraceID, errInvalidTraceIDVersion
}
if xrayTraceID[traceIDDelimitterIndex1:traceIDDelimitterIndex1+1] != traceIDDelimiter ||
xrayTraceID[traceIDDelimitterIndex2:traceIDDelimitterIndex2+1] != traceIDDelimiter {
return empty.TraceID, errMalformedTraceID
}
epochPart := xrayTraceID[traceIDDelimitterIndex1+1 : traceIDDelimitterIndex2]
uniquePart := xrayTraceID[traceIDDelimitterIndex2+1 : traceIDLength]
result := epochPart + uniquePart
return trace.TraceIDFromHex(result)
}
// parseTraceFlag returns a parsed trace flag.
func parseTraceFlag(xraySampledFlag string) byte {
if len(xraySampledFlag) == sampledFlagLength && xraySampledFlag != isSampled {
return traceFlagNone
}
return trace.FlagsSampled
}
// Fields returns list of fields used by HTTPTextFormat.
func (xray Propagator) Fields() []string {
return []string{traceHeaderKey}
}