snapshot of https://github.com/grpc/grpc-go.git (master, 2026-09-15; blobs > 131072B omitted)

stats/opentelemetry/internal/tracing/carrier.go

@@ -0,0 +1,131 @@
+/*
+ *
+ * Copyright 2024 gRPC 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 tracing implements the OpenTelemetry carrier for context propagation
+// in gRPC tracing.
+package tracing
+
+import (
+	"context"
+
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/metadata"
+)
+
+var logger = grpclog.Component("otel-plugin")
+
+// IncomingCarrier is a TextMapCarrier that uses incoming `context.Context` to
+// retrieve any propagated key-value pairs in text format.
+type IncomingCarrier struct {
+	ctx context.Context
+}
+
+// NewIncomingCarrier creates a new `IncomingCarrier` with the given context.
+// The incoming carrier should be used with propagator's `Extract()` method in
+// the incoming rpc path.
+func NewIncomingCarrier(ctx context.Context) *IncomingCarrier {
+	return &IncomingCarrier{ctx: ctx}
+}
+
+// Get returns the string value associated with the passed key from the
+// carrier's incoming context metadata.
+//
+// It returns an empty string if the key is not present in the carrier's
+// context or if the value associated with the key is empty.
+//
+// If multiple values are present for a key, it returns the last one.
+func (c *IncomingCarrier) Get(key string) string {
+	values := metadata.ValueFromIncomingContext(c.ctx, key)
+	if len(values) == 0 {
+		return ""
+	}
+	return values[len(values)-1]
+}
+
+// Set just logs an error. It implements the `TextMapCarrier` interface but
+// should not be used with `IncomingCarrier`.
+func (c *IncomingCarrier) Set(string, string) {
+	logger.Error("Set() should not be used with IncomingCarrier.")
+}
+
+// Keys returns the keys stored in the carrier's context metadata. It returns
+// keys from incoming context metadata.
+func (c *IncomingCarrier) Keys() []string {
+	md, ok := metadata.FromIncomingContext(c.ctx)
+	if !ok {
+		return nil
+	}
+	keys := make([]string, 0, len(md))
+	for key := range md {
+		keys = append(keys, key)
+	}
+	return keys
+}
+
+// Context returns the underlying context associated with the
+// `IncomingCarrier“.
+func (c *IncomingCarrier) Context() context.Context {
+	return c.ctx
+}
+
+// OutgoingCarrier is a TextMapCarrier that uses outgoing `context.Context` to
+// store any propagated key-value pairs in text format.
+type OutgoingCarrier struct {
+	ctx context.Context
+}
+
+// NewOutgoingCarrier creates a new Carrier with the given context. The
+// outgoing carrier should be used with propagator's `Inject()` method in the
+// outgoing rpc path.
+func NewOutgoingCarrier(ctx context.Context) *OutgoingCarrier {
+	return &OutgoingCarrier{ctx: ctx}
+}
+
+// Get just logs an error and returns an empty string. It implements the
+// `TextMapCarrier` interface but should not be used with `OutgoingCarrier`.
+func (c *OutgoingCarrier) Get(string) string {
+	logger.Error("Get() should not be used with `OutgoingCarrier`")
+	return ""
+}
+
+// Set stores the key-value pair in the carrier's outgoing context metadata.
+//
+// If the key already exists, given value is appended to the last.
+func (c *OutgoingCarrier) Set(key, value string) {
+	c.ctx = metadata.AppendToOutgoingContext(c.ctx, key, value)
+}
+
+// Keys returns the keys stored in the carrier's context metadata. It returns
+// keys from outgoing context metadata.
+func (c *OutgoingCarrier) Keys() []string {
+	md, ok := metadata.FromOutgoingContext(c.ctx)
+	if !ok {
+		return nil
+	}
+	keys := make([]string, 0, len(md))
+	for key := range md {
+		keys = append(keys, key)
+	}
+	return keys
+}
+
+// Context returns the underlying context associated with the
+// `OutgoingCarrier“.
+func (c *OutgoingCarrier) Context() context.Context {
+	return c.ctx
+}