Source: correlation_context_propagator.go in package go.opentelemetry.io/otel/api/correlation

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 correlation

import (
	"context"
	"net/url"
	"strings"

	"go.opentelemetry.io/otel/api/propagation"
	"go.opentelemetry.io/otel/label"
)

Temporary header name until W3C finalizes format. https://github.com/open-telemetry/opentelemetry-specification/blob/18b2752ebe6c7f0cdd8c7b2bcbdceb0ae3f5ad95/specification/correlationcontext/api.md#header-name

const correlationContextHeader = "otcorrelations"

CorrelationContext propagates Key:Values in W3C CorrelationContext format. nolint:golint

type CorrelationContext struct{}

var _ propagation.HTTPPropagator = CorrelationContext{}

DefaultHTTPPropagator returns the default context correlation HTTP propagator.

func DefaultHTTPPropagator() propagation.HTTPPropagator {
	return CorrelationContext{}
}

Inject implements HTTPInjector.

func (CorrelationContext) Inject(ctx context.Context, supplier propagation.HTTPSupplier) {
	correlationCtx := MapFromContext(ctx)
	firstIter := true
	var headerValueBuilder strings.Builder
	correlationCtx.Foreach(func(kv label.KeyValue) bool {
		if !firstIter {
			headerValueBuilder.WriteRune(',')
		}
		firstIter = false
		headerValueBuilder.WriteString(url.QueryEscape(strings.TrimSpace((string)(kv.Key))))
		headerValueBuilder.WriteRune('=')
		headerValueBuilder.WriteString(url.QueryEscape(strings.TrimSpace(kv.Value.Emit())))
		return true
	})
	if headerValueBuilder.Len() > 0 {
		headerString := headerValueBuilder.String()
		supplier.Set(correlationContextHeader, headerString)
	}
}

Extract implements HTTPExtractor.

func (CorrelationContext) Extract(ctx context.Context, supplier propagation.HTTPSupplier) context.Context {
	correlationContext := supplier.Get(correlationContextHeader)
	if correlationContext == "" {
		return ctx
	}

	contextValues := strings.Split(correlationContext, ",")
	keyValues := make([]label.KeyValue, 0, len(contextValues))
	for _, contextValue := range contextValues {
		valueAndProps := strings.Split(contextValue, ";")
		if len(valueAndProps) < 1 {
			continue
		}
		nameValue := strings.Split(valueAndProps[0], "=")
		if len(nameValue) < 2 {
			continue
		}
		name, err := url.QueryUnescape(nameValue[0])
		if err != nil {
			continue
		}
		trimmedName := strings.TrimSpace(name)
		value, err := url.QueryUnescape(nameValue[1])
		if err != nil {
			continue
		}
		trimmedValue := strings.TrimSpace(value)

TODO (skaris): properties defiend https://w3c.github.io/correlation-context/, are currently just put as part of the value.

		var trimmedValueWithProps strings.Builder
		trimmedValueWithProps.WriteString(trimmedValue)
		for _, prop := range valueAndProps[1:] {
			trimmedValueWithProps.WriteRune(';')
			trimmedValueWithProps.WriteString(prop)
		}

		keyValues = append(keyValues, label.String(trimmedName, trimmedValueWithProps.String()))
	}

Only update the context if valid values were found

		return ContextWithMap(ctx, NewMap(MapUpdate{
			MultiKV: keyValues,
		}))
	}

	return ctx
}

GetAllKeys implements HTTPPropagator.

func (CorrelationContext) GetAllKeys() []string {
	return []string{correlationContextHeader}