feat(cache): add support for Redis MGET

Tried to keep the change minimal:

* Follows existing precedent of using first key for errors (Delete)
* Result[V] type which propagates redis.Miss errors

Author: odsod

runtimes/go/storage/cache/basic.go

@@ -37,6 +37,16 @@ func (s *StringKeyspace[K]) Get(ctx context.Context, key K) (string, error) {
 	return s.basicKeyspace.Get(ctx, key)
 }
 
+// MultiGet gets the values stored at multiple keys.
+// For each key, the result contains an Err field indicating success or failure.
+// If Err is nil, Value contains the cached value.
+// If Err matches Miss, the key was not found.
+//
+// See https://redis.io/commands/mget/ for more information.
+func (s *StringKeyspace[K]) MultiGet(ctx context.Context, keys ...K) ([]Result[string], error) {
+	return s.basicKeyspace.MultiGet(ctx, keys...)
+}
+
 // Set updates the value stored at key to val.
 //
 // See https://redis.io/commands/set/ for more information.
@@ -230,6 +240,16 @@ func (s *IntKeyspace[K]) Get(ctx context.Context, key K) (int64, error) {
 	return s.basicKeyspace.Get(ctx, key)
 }
 
+// MultiGet gets the values stored at multiple keys.
+// For each key, the result contains an Err field indicating success or failure.
+// If Err is nil, Value contains the cached value.
+// If Err matches Miss, the key was not found.
+//
+// See https://redis.io/commands/mget/ for more information.
+func (s *IntKeyspace[K]) MultiGet(ctx context.Context, keys ...K) ([]Result[int64], error) {
+	return s.basicKeyspace.MultiGet(ctx, keys...)
+}
+
 // Set updates the value stored at key to val.
 //
 // See https://redis.io/commands/set/ for more information.
@@ -371,6 +391,16 @@ func (s *FloatKeyspace[K]) Get(ctx context.Context, key K) (float64, error) {
 	return s.basicKeyspace.Get(ctx, key)
 }
 
+// MultiGet gets the values stored at multiple keys.
+// For each key, the result contains an Err field indicating success or failure.
+// If Err is nil, Value contains the cached value.
+// If Err matches Miss, the key was not found.
+//
+// See https://redis.io/commands/mget/ for more information.
+func (s *FloatKeyspace[K]) MultiGet(ctx context.Context, keys ...K) ([]Result[float64], error) {
+	return s.basicKeyspace.MultiGet(ctx, keys...)
+}
+
 // Set updates the value stored at key to val.
 //
 // See https://redis.io/commands/set/ for more information.
@@ -498,6 +528,43 @@ func (s *basicKeyspace[K, V]) Get(ctx context.Context, key K) (val V, err error)
 	return val, err
 }
 
+func (s *basicKeyspace[K, V]) MultiGet(ctx context.Context, keys ...K) ([]Result[V], error) {
+	const op = "multi get"
+	ks, err := s.keys(keys, op)
+	endTrace := s.doTrace(op, false, ks...)
+	defer func() { endTrace(err) }()
+	if err != nil {
+		return nil, err
+	}
+	var firstKey string
+	if len(ks) > 0 {
+		firstKey = ks[0]
+	}
+	res, err := s.redis.MGet(ctx, ks...).Result()
+	if err != nil {
+		return nil, toErr(err, op, firstKey)
+	}
+	results := make([]Result[V], 0, len(res))
+	for i, r := range res {
+		if r == nil {
+			results = append(results, Result[V]{Err: toErr(Miss, op, ks[i])})
+			continue
+		}
+		strVal, ok := r.(string)
+		if !ok {
+			results = append(results, Result[V]{Err: toErr(errors.New("invalid redis value type"), op, ks[i])})
+			continue
+		}
+		val, fromRedisErr := s.fromRedis(strVal)
+		if fromRedisErr != nil {
+			results = append(results, Result[V]{Err: toErr(fromRedisErr, op, ks[i])})
+			continue
+		}
+		results = append(results, Result[V]{Value: val})
+	}
+	return results, nil
+}
+
 func (s *basicKeyspace[K, V]) Set(ctx context.Context, key K, val V) error {
 	_, _, err := s.set(ctx, key, val, 0, "set")
 	return err

runtimes/go/storage/cache/basic_test.go

@@ -131,6 +131,30 @@ func TestFloatKeyspace(t *testing.T) {
 	}
 }
 
+func TestMultiGet(t *testing.T) {
+	kt := newStringTest(t)
+	ks, ctx := kt.ks, kt.ctx
+
+	// Set up test data
+	kt.Set("key1", "value1")
+	kt.Set("key2", "value2")
+
+	results := must(ks.MultiGet(ctx, "key1", "key2", "missing"))
+	if len(results) != 3 {
+		t.Fatalf("expected 3 results, got %d", len(results))
+	}
+
+	if results[0].Err != nil || results[0].Value != "value1" {
+		t.Errorf("key1: got Err=%v, Value=%q, want Err=nil, Value=%q", results[0].Err, results[0].Value, "value1")
+	}
+	if results[1].Err != nil || results[1].Value != "value2" {
+		t.Errorf("key2: got Err=%v, Value=%q, want Err=nil, Value=%q", results[1].Err, results[1].Value, "value2")
+	}
+	if !errors.Is(results[2].Err, Miss) {
+		t.Errorf("missing: got Err=%v, want Miss", results[2].Err)
+	}
+}
+
 func newStringTest(t *testing.T) *stringTester {
 	cluster, srv := newTestCluster(t)
 	ks := NewStringKeyspace[string](cluster, KeyspaceConfig{

runtimes/go/storage/cache/cache.go

@@ -135,6 +135,17 @@ var Miss = errors.New("cache miss")
 // It must be checked against with errors.Is.
 var KeyExists = errors.New("key already exists")
 
+// Result represents the result of a cache operation that may or may not have found a value.
+// If Err is nil, Value contains the cached value.
+// If Err matches Miss, the key was not found in the cache.
+// Otherwise Err contains the error that occurred.
+type Result[V any] struct {
+	// Value holds the cached value if Err is nil, otherwise the zero value.
+	Value V
+	// Err is nil on success, Miss if the key was not found, or another error.
+	Err error
+}
+
 // An WriteOption customizes the behavior of a single cache write operation.
 type WriteOption interface {
 	//publicapigen:keep

runtimes/go/storage/cache/struct.go

@@ -49,6 +49,16 @@ func (s *StructKeyspace[K, V]) Get(ctx context.Context, key K) (V, error) {
 	return s.basicKeyspace.Get(ctx, key)
 }
 
+// MultiGet gets the values stored at multiple keys.
+// For each key, the result contains an Err field indicating success or failure.
+// If Err is nil, Value contains the cached value.
+// If Err matches Miss, the key was not found.
+//
+// See https://redis.io/commands/mget/ for more information.
+func (s *StructKeyspace[K, V]) MultiGet(ctx context.Context, keys ...K) ([]Result[V], error) {
+	return s.basicKeyspace.MultiGet(ctx, keys...)
+}
+
 // Set updates the value stored at key to val.
 //
 // See https://redis.io/commands/set/ for more information.