First draft. One metric - command duration.

Signed-off-by: Elena Kolevska <elena@kolevska.com>

internal/otel/metrics.go

@@ -0,0 +1,47 @@
+package otel
+
+import (
+	"context"
+	"time"
+
+	"github.com/redis/go-redis/v9/internal/pool"
+)
+
+// Cmder is a minimal interface for command information needed for metrics.
+// This avoids circular dependencies with the main redis package.
+type Cmder interface {
+	Name() string
+	FullName() string
+	Args() []interface{}
+	Err() error
+}
+
+// Recorder is the interface for recording metrics.
+// Implementations are provided by extra/redisotel-native package.
+type Recorder interface {
+	// RecordOperationDuration records the total operation duration (including all retries)
+	RecordOperationDuration(ctx context.Context, duration time.Duration, cmd Cmder, attempts int, cn *pool.Conn)
+}
+
+// Global recorder instance (initialized by extra/redisotel-native)
+var globalRecorder Recorder = noopRecorder{}
+
+// SetGlobalRecorder sets the global recorder (called by Init() in extra/redisotel-native)
+func SetGlobalRecorder(r Recorder) {
+	if r == nil {
+		globalRecorder = noopRecorder{}
+		return
+	}
+	globalRecorder = r
+}
+
+// RecordOperationDuration records the total operation duration.
+// This is called from redis.go after command execution completes.
+func RecordOperationDuration(ctx context.Context, duration time.Duration, cmd Cmder, attempts int, cn *pool.Conn) {
+	globalRecorder.RecordOperationDuration(ctx, duration, cmd, attempts, cn)
+}
+
+// noopRecorder is a no-op implementation (zero overhead when metrics disabled)
+type noopRecorder struct{}
+
+func (noopRecorder) RecordOperationDuration(context.Context, time.Duration, Cmder, int, *pool.Conn) {}