From a4144ea98eb00abe3eb5f78621d93c1c8c229493 Mon Sep 17 00:00:00 2001
From: Kailash Nadh <kailash@nadh.in>
Date: Tue, 2 Feb 2021 13:04:52 +0530
Subject: [PATCH] Add SliceCmd.Scan() (hscan pkg) and tests

---
 command.go                   |   8 +++
 internal/hscan/hscan.go      |   2 +-
 internal/hscan/hscan_test.go | 125 +++++++++++++++++++++++++++++++++++
 internal/hscan/structmap.go  |   2 +-
 4 files changed, 135 insertions(+), 2 deletions(-)
 create mode 100644 internal/hscan/hscan_test.go

diff --git a/command.go b/command.go
index 5dd553325..602ff61b6 100644
--- a/command.go
+++ b/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 +372,13 @@ func (cmd *SliceCmd) String() string {
 	return cmdString(cmd, cmd.val)
 }
 
+// Scan scans the results from a key-value Redis map result set ([]interface{})
+// like HMGET and HGETALL to a destination struct.
+// The Redis keys are matched to the struct's field with the `redis` tag.
+func (cmd *SliceCmd) Scan(val interface{}) error {
+	return hscan.Scan(cmd.val, val)
+}
+
 func (cmd *SliceCmd) readReply(rd *proto.Reader) error {
 	v, err := rd.ReadArrayReply(sliceParser)
 	if err != nil {
diff --git a/internal/hscan/hscan.go b/internal/hscan/hscan.go
index 1c46f2cd4..51346b831 100644
--- a/internal/hscan/hscan.go
+++ b/internal/hscan/hscan.go
@@ -11,7 +11,7 @@ import (
 type decoderFunc func(reflect.Value, string) error
 
 var (
-	// List of built-in decoders indexed by their numeric constant values (eg: reflect.Bool = 1)
+	// List of built-in decoders indexed by their numeric constant values (eg: reflect.Bool = 1).
 	decoders = []decoderFunc{
 		reflect.Bool:          decodeBool,
 		reflect.Int:           decodeInt,
diff --git a/internal/hscan/hscan_test.go b/internal/hscan/hscan_test.go
new file mode 100644
index 000000000..7a4d0f5b8
--- /dev/null
+++ b/internal/hscan/hscan_test.go
@@ -0,0 +1,125 @@
+package hscan
+
+import (
+	"testing"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+type data struct {
+	Omit  string `redis:"-"`
+	Empty string
+
+	String string  `redis:"string"`
+	Bytes  []byte  `redis:"byte"`
+	Int    int     `redis:"int"`
+	Uint   uint    `redis:"uint"`
+	Float  float32 `redis:"float"`
+	Bool   bool    `redis:"bool"`
+}
+
+func TestGinkgoSuite(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "hscan")
+}
+
+var _ = Describe("Scan", func() {
+	It("catches bad args", func() {
+		var d data
+
+		Expect(Scan([]interface{}{}, &d)).NotTo(HaveOccurred())
+		Expect(d).To(Equal(data{}))
+
+		Expect(Scan([]interface{}{"key"}, &d)).To(HaveOccurred())
+		Expect(Scan([]interface{}{"key", "1", "2"}, &d)).To(HaveOccurred())
+		Expect(Scan([]interface{}{"key", "1"}, nil)).To(HaveOccurred())
+
+		var i map[string]interface{}
+		Expect(Scan([]interface{}{"key", "1"}, &i)).To(HaveOccurred())
+		Expect(Scan([]interface{}{"key", "1"}, data{})).To(HaveOccurred())
+		Expect(Scan([]interface{}{"key", nil, "string", nil}, data{})).To(HaveOccurred())
+	})
+
+	It("scans good values", func() {
+		var d data
+
+		// non-tagged fields.
+		Expect(Scan([]interface{}{"key", "value"}, &d)).NotTo(HaveOccurred())
+		Expect(d).To(Equal(data{}))
+
+		res := []interface{}{"string", "str!",
+			"byte", "bytes!",
+			"int", "123",
+			"uint", "456",
+			"float", "123.456",
+			"bool", "1"}
+		Expect(Scan(res, &d)).NotTo(HaveOccurred())
+		Expect(d).To(Equal(data{
+			String: "str!",
+			Bytes:  []byte("bytes!"),
+			Int:    123,
+			Uint:   456,
+			Float:  123.456,
+			Bool:   true,
+		}))
+
+		// Scan a different type with the same values to test that
+		// the struct spec maps don't conflict.
+		type data2 struct {
+			String string  `redis:"string"`
+			Bytes  []byte  `redis:"byte"`
+			Int    int     `redis:"int"`
+			Uint   uint    `redis:"uint"`
+			Float  float32 `redis:"float"`
+			Bool   bool    `redis:"bool"`
+		}
+		var d2 data2
+		Expect(Scan(res, &d2)).NotTo(HaveOccurred())
+		Expect(d2).To(Equal(data2{
+			String: "str!",
+			Bytes:  []byte("bytes!"),
+			Int:    123,
+			Uint:   456,
+			Float:  123.456,
+			Bool:   true,
+		}))
+
+		Expect(Scan([]interface{}{
+			"string", "",
+			"float", "1",
+			"bool", "t"}, &d)).NotTo(HaveOccurred())
+		Expect(d).To(Equal(data{
+			String: "",
+			Bytes:  []byte("bytes!"),
+			Int:    123,
+			Uint:   456,
+			Float:  1.0,
+			Bool:   true,
+		}))
+	})
+
+	It("omits untagged fields", func() {
+		var d data
+
+		Expect(Scan([]interface{}{
+			"empty", "value",
+			"omit", "value",
+			"string", "str!"}, &d)).NotTo(HaveOccurred())
+		Expect(d).To(Equal(data{
+			String: "str!",
+		}))
+	})
+
+	It("catches bad values", func() {
+		var d data
+
+		Expect(Scan([]interface{}{"int", "a"}, &d)).To(HaveOccurred())
+		Expect(Scan([]interface{}{"uint", "a"}, &d)).To(HaveOccurred())
+		Expect(Scan([]interface{}{"uint", ""}, &d)).To(HaveOccurred())
+		Expect(Scan([]interface{}{"float", "b"}, &d)).To(HaveOccurred())
+		Expect(Scan([]interface{}{"bool", "-1"}, &d)).To(HaveOccurred())
+		Expect(Scan([]interface{}{"bool", ""}, &d)).To(HaveOccurred())
+		Expect(Scan([]interface{}{"bool", "123"}, &d)).To(HaveOccurred())
+	})
+})
diff --git a/internal/hscan/structmap.go b/internal/hscan/structmap.go
index 06d5d2fe1..da97f907d 100644
--- a/internal/hscan/structmap.go
+++ b/internal/hscan/structmap.go
@@ -61,7 +61,7 @@ func getStructFields(t reflect.Type, fieldTag string) *structFields {
 	for i := 0; i < num; i++ {
 		f := t.Field(i)
 
-		tag := t.Field(i).Tag.Get(fieldTag)
+		tag := f.Tag.Get(fieldTag)
 		if tag == "" || tag == "-" {
 			continue
 		}