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// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0
package autoprop // import "go.opentelemetry.io/contrib/propagators/autoprop"
import (
"errors"
"os"
"strings"
"go.opentelemetry.io/otel"
"go.opentelemetry.io/otel/propagation"
)
// otelPropagatorsEnvKey is the environment variable name identifying
// propagators to use.
const otelPropagatorsEnvKey = "OTEL_PROPAGATORS"
// NewTextMapPropagator returns a new TextMapPropagator composited by props or
// one defined by the OTEL_PROPAGATORS environment variable. The
// TextMapPropagator defined by OTEL_PROPAGATORS, if set, will take precedence
// to the once composited by props.
//
// The propagators supported with the OTEL_PROPAGATORS environment variable by
// default are: tracecontext, baggage, b3, b3multi, jaeger, xray, ottrace, and
// none. Each of these values, and their combination, are supported in
// conformance with the OpenTelemetry specification. See
// https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/sdk-environment-variables.md#general-sdk-configuration
// for more information.
//
// The supported environment variable propagators can be extended to include
// custom 3rd-party TextMapPropagator. See the RegisterTextMapPropagator
// function for more information.
//
// If OTEL_PROPAGATORS is not defined and props is no provided, the returned
// TextMapPropagator will be a composite of the TraceContext and Baggage
// propagators.
func NewTextMapPropagator(props ...propagation.TextMapPropagator) propagation.TextMapPropagator {
// Environment variable defined propagator has precedence over arguments.
envProp, err := parseEnv()
if err != nil {
// Communicate to the user their supplied value will not be used.
otel.Handle(err)
}
if envProp != nil {
return envProp
}
switch len(props) {
case 0:
// Default to TraceContext and Baggage.
return propagation.NewCompositeTextMapPropagator(
propagation.TraceContext{}, propagation.Baggage{},
)
case 1:
// Do not add overhead with a composite propagator wrapping a single
// propagator, return it directly.
return props[0]
default:
return propagation.NewCompositeTextMapPropagator(props...)
}
}
// errUnknownPropagator is returned when an unknown propagator name is used in
// the OTEL_PROPAGATORS environment variable.
var errUnknownPropagator = errors.New("unknown propagator")
// parseEnv returns the composite TextMapPropagators defined by the
// OTEL_PROPAGATORS environment variable. A nil TextMapPropagator is returned
// if no propagator is defined for the environment variable. A no-op
// TextMapPropagator will be returned if "none" is defined anywhere in the
// environment variable.
func parseEnv() (propagation.TextMapPropagator, error) {
propStrs := os.Getenv(otelPropagatorsEnvKey)
if propStrs == "" {
return nil, nil
}
return TextMapPropagator(strings.Split(propStrs, ",")...)
}
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