propagation.go

// Copyright (c) 2017 Uber Technologies, Inc.
//
// 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 zipkin

import (
	"strconv"
	"strings"

	opentracing "github.com/opentracing/opentracing-go"

	"github.com/uber/jaeger-client-go"
)

// Option is a function that sets an option on Propagator
type Option func(propagator *Propagator)

// BaggagePrefix is a function that sets baggage prefix on Propagator
func BaggagePrefix(prefix string) Option {
	return func(propagator *Propagator) {
		propagator.baggagePrefix = prefix
	}
}

// Propagator is an Injector and Extractor
type Propagator struct {
	baggagePrefix string
}

// NewZipkinB3HTTPHeaderPropagator creates a Propagator for extracting and injecting
// Zipkin HTTP B3 headers into SpanContexts. Baggage is by default enabled and uses prefix
// 'baggage-'.
func NewZipkinB3HTTPHeaderPropagator(opts ...Option) Propagator {
	p := Propagator{baggagePrefix: "baggage-"}
	for _, opt := range opts {
		opt(&p)
	}
	return p
}

// Inject conforms to the Injector interface for decoding Zipkin HTTP B3 headers
func (p Propagator) Inject(
	sc jaeger.SpanContext,
	abstractCarrier interface{},
) error {
	textMapWriter, ok := abstractCarrier.(opentracing.TextMapWriter)
	if !ok {
		return opentracing.ErrInvalidCarrier
	}

	textMapWriter.Set("x-b3-traceid", sc.TraceID().String())
	if sc.ParentID() != 0 {
		textMapWriter.Set("x-b3-parentspanid", sc.ParentID().String())
	}
	textMapWriter.Set("x-b3-spanid", sc.SpanID().String())
	if sc.IsSampled() {
		textMapWriter.Set("x-b3-sampled", "1")
	} else {
		textMapWriter.Set("x-b3-sampled", "0")
	}
	sc.ForeachBaggageItem(func(k, v string) bool {
		textMapWriter.Set(p.baggagePrefix+k, v)
		return true
	})
	return nil
}

// Extract conforms to the Extractor interface for encoding Zipkin HTTP B3 headers
func (p Propagator) Extract(abstractCarrier interface{}) (jaeger.SpanContext, error) {
	textMapReader, ok := abstractCarrier.(opentracing.TextMapReader)
	if !ok {
		return jaeger.SpanContext{}, opentracing.ErrInvalidCarrier
	}
	var traceID jaeger.TraceID
	var spanID uint64
	var parentID uint64
	sampled := false
	var baggage map[string]string
	err := textMapReader.ForeachKey(func(rawKey, value string) error {
		key := strings.ToLower(rawKey) // TODO not necessary for plain TextMap
		var err error
		if key == "x-b3-traceid" {
			traceID, err = jaeger.TraceIDFromString(value)
		} else if key == "x-b3-parentspanid" {
			parentID, err = strconv.ParseUint(value, 16, 64)
		} else if key == "x-b3-spanid" {
			spanID, err = strconv.ParseUint(value, 16, 64)
		} else if key == "x-b3-sampled" && (value == "1" || value == "true") {
			sampled = true
		} else if strings.HasPrefix(key, p.baggagePrefix) {
			if baggage == nil {
				baggage = make(map[string]string)
			}
			baggage[key[len(p.baggagePrefix):]] = value
		}
		return err
	})

	if err != nil {
		return jaeger.SpanContext{}, err
	}
	if !traceID.IsValid() {
		return jaeger.SpanContext{}, opentracing.ErrSpanContextNotFound
	}
	return jaeger.NewSpanContext(
		traceID,
		jaeger.SpanID(spanID),
		jaeger.SpanID(parentID),
		sampled, baggage), nil
}