Merge pull request #1631 from knadh/feat-decoder

Add redis.Scan() to scan results from redis maps into structs.

Author: vmihailenco

command.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/go-redis/redis/v8/internal"
+	"github.com/go-redis/redis/v8/internal/hscan"
 	"github.com/go-redis/redis/v8/internal/proto"
 	"github.com/go-redis/redis/v8/internal/util"
 )
@@ -371,6 +372,26 @@ func (cmd *SliceCmd) String() string {
 	return cmdString(cmd, cmd.val)
 }
 
+// Scan scans the results from the map into a destination struct. The map keys
+// are matched in the Redis struct fields by the `redis:"field"` tag.
+func (cmd *SliceCmd) Scan(dst interface{}) error {
+	if cmd.err != nil {
+		return cmd.err
+	}
+
+	// Pass the list of keys and values.
+	// Skip the first two args for: HMGET key
+	var args []interface{}
+	if cmd.args[0] == "hmget" {
+		args = cmd.args[2:]
+	} else {
+		// Otherwise, it's: MGET field field ...
+		args = cmd.args[1:]
+	}
+
+	return hscan.Scan(dst, args, cmd.val)
+}
+
 func (cmd *SliceCmd) readReply(rd *proto.Reader) error {
 	v, err := rd.ReadArrayReply(sliceParser)
 	if err != nil {
@@ -917,6 +938,27 @@ func (cmd *StringStringMapCmd) String() string {
 	return cmdString(cmd, cmd.val)
 }
 
+// Scan scans the results from the map into a destination struct. The map keys
+// are matched in the Redis struct fields by the `redis:"field"` tag.
+func (cmd *StringStringMapCmd) Scan(dst interface{}) error {
+	if cmd.err != nil {
+		return cmd.err
+	}
+
+	strct, err := hscan.Struct(dst)
+	if err != nil {
+		return err
+	}
+
+	for k, v := range cmd.val {
+		if err := strct.Scan(k, v); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 func (cmd *StringStringMapCmd) readReply(rd *proto.Reader) error {
 	_, err := rd.ReadArrayReply(func(rd *proto.Reader, n int64) (interface{}, error) {
 		cmd.val = make(map[string]string, n/2)

commands_test.go

@@ -1134,6 +1134,22 @@ var _ = Describe("Commands", func() {
 			Expect(mGet.Val()).To(Equal([]interface{}{"hello1", "hello2", nil}))
 		})
 
+		It("should scan Mget", func() {
+			err := client.MSet(ctx, "key1", "hello1", "key2", 123).Err()
+			Expect(err).NotTo(HaveOccurred())
+
+			res := client.MGet(ctx, "key1", "key2", "_")
+			Expect(res.Err()).NotTo(HaveOccurred())
+
+			type data struct {
+				Key1 string `redis:"key1"`
+				Key2 int    `redis:"key2"`
+			}
+			var d data
+			Expect(res.Scan(&d)).NotTo(HaveOccurred())
+			Expect(d).To(Equal(data{Key1: "hello1", Key2: 123}))
+		})
+
 		It("should MSetNX", func() {
 			mSetNX := client.MSetNX(ctx, "key1", "hello1", "key2", "hello2")
 			Expect(mSetNX.Err()).NotTo(HaveOccurred())
@@ -1375,6 +1391,22 @@ var _ = Describe("Commands", func() {
 			Expect(m).To(Equal(map[string]string{"key1": "hello1", "key2": "hello2"}))
 		})
 
+		It("should scan", func() {
+			err := client.HMSet(ctx, "hash", "key1", "hello1", "key2", 123).Err()
+			Expect(err).NotTo(HaveOccurred())
+
+			res := client.HGetAll(ctx, "hash")
+			Expect(res.Err()).NotTo(HaveOccurred())
+
+			type data struct {
+				Key1 string `redis:"key1"`
+				Key2 int    `redis:"key2"`
+			}
+			var d data
+			Expect(res.Scan(&d)).NotTo(HaveOccurred())
+			Expect(d).To(Equal(data{Key1: "hello1", Key2: 123}))
+		})
+
 		It("should HIncrBy", func() {
 			hSet := client.HSet(ctx, "hash", "key", "5")
 			Expect(hSet.Err()).NotTo(HaveOccurred())

example_test.go

@@ -276,6 +276,73 @@ func ExampleClient_ScanType() {
 	// Output: found 33 keys
 }
 
+// ExampleStringStringMapCmd_Scan shows how to scan the results of a map fetch
+// into a struct.
+func ExampleStringStringMapCmd_Scan() {
+	rdb.FlushDB(ctx)
+	err := rdb.HMSet(ctx, "map",
+		"name", "hello",
+		"count", 123,
+		"correct", true).Err()
+	if err != nil {
+		panic(err)
+	}
+
+	// Get the map. The same approach works for HmGet().
+	res := rdb.HGetAll(ctx, "map")
+	if res.Err() != nil {
+		panic(err)
+	}
+
+	type data struct {
+		Name    string `redis:"name"`
+		Count   int    `redis:"count"`
+		Correct bool   `redis:"correct"`
+	}
+
+	// Scan the results into the struct.
+	var d data
+	if err := res.Scan(&d); err != nil {
+		panic(err)
+	}
+
+	fmt.Println(d)
+	// Output: {hello 123 true}
+}
+
+// ExampleSliceCmd_Scan shows how to scan the results of a multi key fetch
+// into a struct.
+func ExampleSliceCmd_Scan() {
+	rdb.FlushDB(ctx)
+	err := rdb.MSet(ctx,
+		"name", "hello",
+		"count", 123,
+		"correct", true).Err()
+	if err != nil {
+		panic(err)
+	}
+
+	res := rdb.MGet(ctx, "name", "count", "empty", "correct")
+	if res.Err() != nil {
+		panic(err)
+	}
+
+	type data struct {
+		Name    string `redis:"name"`
+		Count   int    `redis:"count"`
+		Correct bool   `redis:"correct"`
+	}
+
+	// Scan the results into the struct.
+	var d data
+	if err := res.Scan(&d); err != nil {
+		panic(err)
+	}
+
+	fmt.Println(d)
+	// Output: {hello 123 true}
+}
+
 func ExampleClient_Pipelined() {
 	var incr *redis.IntCmd
 	_, err := rdb.Pipelined(ctx, func(pipe redis.Pipeliner) error {

internal/hscan/hscan.go

@@ -0,0 +1,151 @@
+package hscan
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+	"strconv"
+)
+
+// decoderFunc represents decoding functions for default built-in types.
+type decoderFunc func(reflect.Value, string) error
+
+var (
+	// List of built-in decoders indexed by their numeric constant values (eg: reflect.Bool = 1).
+	decoders = []decoderFunc{
+		reflect.Bool:          decodeBool,
+		reflect.Int:           decodeInt,
+		reflect.Int8:          decodeInt,
+		reflect.Int16:         decodeInt,
+		reflect.Int32:         decodeInt,
+		reflect.Int64:         decodeInt,
+		reflect.Uint:          decodeUint,
+		reflect.Uint8:         decodeUint,
+		reflect.Uint16:        decodeUint,
+		reflect.Uint32:        decodeUint,
+		reflect.Uint64:        decodeUint,
+		reflect.Float32:       decodeFloat,
+		reflect.Float64:       decodeFloat,
+		reflect.Complex64:     decodeUnsupported,
+		reflect.Complex128:    decodeUnsupported,
+		reflect.Array:         decodeUnsupported,
+		reflect.Chan:          decodeUnsupported,
+		reflect.Func:          decodeUnsupported,
+		reflect.Interface:     decodeUnsupported,
+		reflect.Map:           decodeUnsupported,
+		reflect.Ptr:           decodeUnsupported,
+		reflect.Slice:         decodeSlice,
+		reflect.String:        decodeString,
+		reflect.Struct:        decodeUnsupported,
+		reflect.UnsafePointer: decodeUnsupported,
+	}
+
+	// Global map of struct field specs that is populated once for every new
+	// struct type that is scanned. This caches the field types and the corresponding
+	// decoder functions to avoid iterating through struct fields on subsequent scans.
+	globalStructMap = newStructMap()
+)
+
+func Struct(dst interface{}) (StructValue, error) {
+	v := reflect.ValueOf(dst)
+
+	// The dstination to scan into should be a struct pointer.
+	if v.Kind() != reflect.Ptr || v.IsNil() {
+		return StructValue{}, fmt.Errorf("redis.Scan(non-pointer %T)", dst)
+	}
+
+	v = v.Elem()
+	if v.Kind() != reflect.Struct {
+		return StructValue{}, fmt.Errorf("redis.Scan(non-struct %T)", dst)
+	}
+
+	return StructValue{
+		spec:  globalStructMap.get(v.Type()),
+		value: v,
+	}, nil
+}
+
+// Scan scans the results from a key-value Redis map result set to a destination struct.
+// The Redis keys are matched to the struct's field with the `redis` tag.
+func Scan(dst interface{}, keys []interface{}, vals []interface{}) error {
+	if len(keys) != len(vals) {
+		return errors.New("args should have the same number of keys and vals")
+	}
+
+	strct, err := Struct(dst)
+	if err != nil {
+		return err
+	}
+
+	// Iterate through the (key, value) sequence.
+	for i := 0; i < len(vals); i++ {
+		key, ok := keys[i].(string)
+		if !ok {
+			continue
+		}
+
+		val, ok := vals[i].(string)
+		if !ok {
+			continue
+		}
+
+		if err := strct.Scan(key, val); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func decodeBool(f reflect.Value, s string) error {
+	b, err := strconv.ParseBool(s)
+	if err != nil {
+		return err
+	}
+	f.SetBool(b)
+	return nil
+}
+
+func decodeInt(f reflect.Value, s string) error {
+	v, err := strconv.ParseInt(s, 10, 0)
+	if err != nil {
+		return err
+	}
+	f.SetInt(v)
+	return nil
+}
+
+func decodeUint(f reflect.Value, s string) error {
+	v, err := strconv.ParseUint(s, 10, 0)
+	if err != nil {
+		return err
+	}
+	f.SetUint(v)
+	return nil
+}
+
+func decodeFloat(f reflect.Value, s string) error {
+	v, err := strconv.ParseFloat(s, 0)
+	if err != nil {
+		return err
+	}
+	f.SetFloat(v)
+	return nil
+}
+
+func decodeString(f reflect.Value, s string) error {
+	f.SetString(s)
+	return nil
+}
+
+func decodeSlice(f reflect.Value, s string) error {
+	// []byte slice ([]uint8).
+	if f.Type().Elem().Kind() == reflect.Uint8 {
+		f.SetBytes([]byte(s))
+	}
+	return nil
+}
+
+func decodeUnsupported(v reflect.Value, s string) error {
+	return fmt.Errorf("redis.Scan(unsupported %s)", v.Type())
+}