Use iter.Seq to iterate over ScanIterator (#3348)

* Add support for iter.Seq for ScanIterator

* Simplify Vals

* Review fixes

example/del-keys-without-ttl/main.go

@@ -28,8 +28,8 @@ func main() {
 	checker.Start(ctx)
 
 	iter := rdb.Scan(ctx, 0, "", 0).Iterator()
-	for iter.Next(ctx) {
-		checker.Add(iter.Val())
+	for val := range iter.Vals(ctx) {
+		checker.Add(val)
 	}
 	if err := iter.Err(); err != nil {
 		panic(err)

example_test.go

@@ -632,8 +632,8 @@ func Example_customCommand2() {
 
 func ExampleScanIterator() {
 	iter := rdb.Scan(ctx, 0, "", 0).Iterator()
-	for iter.Next(ctx) {
-		fmt.Println(iter.Val())
+	for val := range iter.Vals(ctx) {
+		fmt.Println(val)
 	}
 	if err := iter.Err(); err != nil {
 		panic(err)
@@ -642,8 +642,8 @@ func ExampleScanIterator() {
 
 func ExampleScanCmd_Iterator() {
 	iter := rdb.Scan(ctx, 0, "", 0).Iterator()
-	for iter.Next(ctx) {
-		fmt.Println(iter.Val())
+	for val := range iter.Vals(ctx) {
+		fmt.Println(val)
 	}
 	if err := iter.Err(); err != nil {
 		panic(err)

iterator.go

@@ -2,6 +2,7 @@ package redis
 
 import (
 	"context"
+	"iter"
 )
 
 // ScanIterator is used to incrementally iterate over a collection of elements.
@@ -16,6 +17,8 @@ func (it *ScanIterator) Err() error {
 }
 
 // Next advances the cursor and returns true if more values can be read.
+//
+// Deprecated: support for native iterators has been added in go 1.23. Use Vals instead.
 func (it *ScanIterator) Next(ctx context.Context) bool {
 	// Instantly return on errors.
 	if it.cmd.Err() != nil {
@@ -65,6 +68,8 @@ func (it *ScanIterator) Next(ctx context.Context) bool {
 }
 
 // Val returns the key/field at the current cursor position.
+//
+// Deprecated: support for native iterators has been added in go 1.23. Use Vals instead.
 func (it *ScanIterator) Val() string {
 	var v string
 	if it.cmd.Err() == nil && it.pos > 0 && it.pos <= len(it.cmd.page) {
@@ -72,3 +77,49 @@ func (it *ScanIterator) Val() string {
 	}
 	return v
 }
+
+// Vals returns iterator over key/field at the current cursor position.
+func (it *ScanIterator) Vals(ctx context.Context) iter.Seq[string] {
+	return func(yield func(string) bool) {
+		if it.cmd.Err() != nil {
+			return
+		}
+
+		for {
+			for _, val := range it.cmd.page {
+				if !yield(val) {
+					return
+				}
+			}
+
+			// Return if there is no more data to fetch.
+			if it.cmd.cursor == 0 {
+				return
+			}
+
+			// Fetch next page.
+			var cursorIndex int
+			switch it.cmd.args[0] {
+			case "scan", "qscan":
+				cursorIndex = 1
+			default:
+				cursorIndex = 2
+			}
+
+			it.cmd.args[cursorIndex] = it.cmd.cursor
+
+			err := it.cmd.process(ctx, it.cmd)
+			if err != nil {
+				return
+			}
+			// Await the fetch before reading page/cursor: on the deferred
+			// autopipeline face process() only enqueues, and reading the raw
+			// fields of a not-yet-executed command would spin re-issuing SCANs
+			// with a stale cursor forever. Err() blocks until executed there and
+			// is a no-op read everywhere else.
+			if it.cmd.Err() != nil {
+				return
+			}
+		}
+	}
+}

iterator_test.go

@@ -2,6 +2,7 @@ package redis_test
 
 import (
 	"fmt"
+	"slices"
 
 	. "github.com/bsm/ginkgo/v2"
 	. "github.com/bsm/gomega"
@@ -55,13 +56,20 @@ var _ = Describe("ScanIterator", func() {
 		Expect(closeSubject()).NotTo(HaveOccurred())
 	})
 
-	It("should scan across empty DBs", func() {
+	It("should scan across empty DBs using Next", func() {
 		iter := client.Scan(ctx, 0, "", 10).Iterator()
 		Expect(iter.Next(ctx)).To(BeFalse())
 		Expect(iter.Err()).NotTo(HaveOccurred())
 	})
 
-	It("should scan across one page", func() {
+	It("should scan across empty DBs using Vals", func() {
+		iter := client.Scan(ctx, 0, "", 10).Iterator()
+		vals := slices.Collect(iter.Vals(ctx))
+		Expect(vals).To(BeEmpty())
+		Expect(iter.Err()).NotTo(HaveOccurred())
+	})
+
+	It("should scan across one page using Next", func() {
 		Expect(seed(7)).NotTo(HaveOccurred())
 
 		var vals []string
@@ -73,7 +81,16 @@ var _ = Describe("ScanIterator", func() {
 		Expect(vals).To(ConsistOf([]string{"K01", "K02", "K03", "K04", "K05", "K06", "K07"}))
 	})
 
-	It("should scan across multiple pages", func() {
+	It("should scan across one page using Vals", func() {
+		Expect(seed(7)).NotTo(HaveOccurred())
+
+		iter := client.Scan(ctx, 0, "", 0).Iterator()
+		vals := slices.Collect(iter.Vals(ctx))
+		Expect(iter.Err()).NotTo(HaveOccurred())
+		Expect(vals).To(ConsistOf([]string{"K01", "K02", "K03", "K04", "K05", "K06", "K07"}))
+	})
+
+	It("should scan across multiple pages using Next", func() {
 		Expect(seed(71)).NotTo(HaveOccurred())
 
 		var vals []string
@@ -87,7 +104,18 @@ var _ = Describe("ScanIterator", func() {
 		Expect(vals).To(ContainElement("K71"))
 	})
 
-	It("should hscan across multiple pages", func() {
+	It("should scan across multiple pages using Vals", func() {
+		Expect(seed(71)).NotTo(HaveOccurred())
+
+		iter := client.Scan(ctx, 0, "", 10).Iterator()
+		vals := slices.Collect(iter.Vals(ctx))
+		Expect(iter.Err()).NotTo(HaveOccurred())
+		Expect(vals).To(HaveLen(71))
+		Expect(vals).To(ContainElement("K01"))
+		Expect(vals).To(ContainElement("K71"))
+	})
+
+	It("should hscan across multiple pages using Next", func() {
 		SkipBeforeRedisVersion("7.4", "doesn't work with older redis stack images")
 		Expect(hashSeed(71)).NotTo(HaveOccurred())
 
@@ -103,7 +131,20 @@ var _ = Describe("ScanIterator", func() {
 		Expect(vals).To(ContainElement("x"))
 	})
 
-	It("should hscan without values across multiple pages", Label("NonRedisEnterprise"), func() {
+	It("should hscan across multiple pages using Vals", func() {
+		SkipBeforeRedisVersion("7.4", "doesn't work with older redis stack images")
+		Expect(hashSeed(71)).NotTo(HaveOccurred())
+
+		iter := client.HScan(ctx, hashKey, 0, "", 10).Iterator()
+		vals := slices.Collect(iter.Vals(ctx))
+		Expect(iter.Err()).NotTo(HaveOccurred())
+		Expect(vals).To(HaveLen(71 * 2))
+		Expect(vals).To(ContainElement("K01"))
+		Expect(vals).To(ContainElement("K71"))
+		Expect(vals).To(ContainElement("x"))
+	})
+
+	It("should hscan without values across multiple pages using Next", Label("NonRedisEnterprise"), func() {
 		SkipBeforeRedisVersion("7.4", "doesn't work with older redis stack images")
 		Expect(hashSeed(71)).NotTo(HaveOccurred())
 
@@ -119,7 +160,20 @@ var _ = Describe("ScanIterator", func() {
 		Expect(vals).NotTo(ContainElement("x"))
 	})
 
-	It("should scan to page borders", func() {
+	It("should hscan without values across multiple pages using Vals", Label("NonRedisEnterprise"), func() {
+		SkipBeforeRedisVersion("7.4", "doesn't work with older redis stack images")
+		Expect(hashSeed(71)).NotTo(HaveOccurred())
+
+		iter := client.HScanNoValues(ctx, hashKey, 0, "", 10).Iterator()
+		vals := slices.Collect(iter.Vals(ctx))
+		Expect(iter.Err()).NotTo(HaveOccurred())
+		Expect(vals).To(HaveLen(71))
+		Expect(vals).To(ContainElement("K01"))
+		Expect(vals).To(ContainElement("K71"))
+		Expect(vals).NotTo(ContainElement("x"))
+	})
+
+	It("should scan to page borders using Next", func() {
 		Expect(seed(20)).NotTo(HaveOccurred())
 
 		var vals []string
@@ -131,7 +185,16 @@ var _ = Describe("ScanIterator", func() {
 		Expect(vals).To(HaveLen(20))
 	})
 
-	It("should scan with match", func() {
+	It("should scan to page borders using Vals", func() {
+		Expect(seed(20)).NotTo(HaveOccurred())
+
+		iter := client.Scan(ctx, 0, "", 10).Iterator()
+		vals := slices.Collect(iter.Vals(ctx))
+		Expect(iter.Err()).NotTo(HaveOccurred())
+		Expect(vals).To(HaveLen(20))
+	})
+
+	It("should scan with match using Next", func() {
 		Expect(seed(33)).NotTo(HaveOccurred())
 
 		var vals []string
@@ -143,7 +206,16 @@ var _ = Describe("ScanIterator", func() {
 		Expect(vals).To(HaveLen(13))
 	})
 
-	It("should scan with match across empty pages", func() {
+	It("should scan with match using Vals", func() {
+		Expect(seed(33)).NotTo(HaveOccurred())
+
+		iter := client.Scan(ctx, 0, "K*2*", 10).Iterator()
+		vals := slices.Collect(iter.Vals(ctx))
+		Expect(iter.Err()).NotTo(HaveOccurred())
+		Expect(vals).To(HaveLen(13))
+	})
+
+	It("should scan with match across empty pages using Next", func() {
 		Expect(extraSeed(2, 10)).NotTo(HaveOccurred())
 
 		var vals []string
@@ -154,4 +226,13 @@ var _ = Describe("ScanIterator", func() {
 		Expect(iter.Err()).NotTo(HaveOccurred())
 		Expect(vals).To(HaveLen(2))
 	})
+
+	It("should scan with match across empty pages using Vals", func() {
+		Expect(extraSeed(2, 10)).NotTo(HaveOccurred())
+
+		iter := client.Scan(ctx, 0, "K*", 1).Iterator()
+		vals := slices.Collect(iter.Vals(ctx))
+		Expect(iter.Err()).NotTo(HaveOccurred())
+		Expect(vals).To(HaveLen(2))
+	})
 })