sdk/log: Add altering Processor example (#5550)

Towards #5065

---------

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

sdk/log/example_test.go

@@ -0,0 +1,45 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package log_test
+
+import (
+	"context"
+	"strings"
+
+	"go.opentelemetry.io/otel/log"
+	logsdk "go.opentelemetry.io/otel/sdk/log"
+)
+
+// Use a processor which redacts sensitive data from some attributes.
+func ExampleProcessor_redact() {
+	// Existing processor that emits telemetry.
+	var processor logsdk.Processor = logsdk.NewBatchProcessor(nil)
+
+	// Wrap the processor so that it redacts values from token attributes.
+	processor = &RedactTokensProcessor{processor}
+
+	// The created processor can then be registered with
+	// the OpenTelemetry Logs SDK using the WithProcessor option.
+	_ = logsdk.NewLoggerProvider(
+		logsdk.WithProcessor(processor),
+	)
+}
+
+// RedactTokensProcessor is a [logsdk.Processor] decorator that redacts values
+// from attributes containing "token" in the key.
+type RedactTokensProcessor struct {
+	logsdk.Processor
+}
+
+// OnEmit redacts values from attributes containing "token" in the key
+// by replacing them with a REDACTED value.
+func (s *RedactTokensProcessor) OnEmit(ctx context.Context, record logsdk.Record) error {
+	record.WalkAttributes(func(kv log.KeyValue) bool {
+		if strings.Contains(strings.ToLower(kv.Key), "token") {
+			record.AddAttributes(log.String(kv.Key, "REDACTED"))
+		}
+		return true
+	})
+	return s.Processor.OnEmit(ctx, record)
+}

sdk/log/record.go

@@ -166,6 +166,7 @@ func (r *Record) WalkAttributes(f func(log.KeyValue) bool) {
 }
 
 // AddAttributes adds attributes to the log record.
+// Attributes in attrs will overwrite any attribute already added to r with the same key.
 func (r *Record) AddAttributes(attrs ...log.KeyValue) {
 	n := r.AttributesLen()
 	if n == 0 {