fix(scanner): improve M3U playlist import times (#2706)

utils/slice/slice.go

@@ -1,5 +1,12 @@
 package slice
 
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"iter"
+)
+
 func Map[T any, R any](t []T, mapFunc func(T) R) []R {
 	r := make([]R, len(t))
 	for i, e := range t {
@@ -79,3 +86,57 @@ func RangeByChunks[T any](items []T, chunkSize int, cb func([]T) error) error {
 	}
 	return nil
 }
+
+func LinesFrom(reader io.Reader) iter.Seq[string] {
+	return func(yield func(string) bool) {
+		scanner := bufio.NewScanner(reader)
+		scanner.Split(scanLines)
+		for scanner.Scan() {
+			if !yield(scanner.Text()) {
+				return
+			}
+		}
+	}
+}
+
+// From https://stackoverflow.com/a/41433698
+func scanLines(data []byte, atEOF bool) (advance int, token []byte, err error) {
+	if atEOF && len(data) == 0 {
+		return 0, nil, nil
+	}
+	if i := bytes.IndexAny(data, "\r\n"); i >= 0 {
+		if data[i] == '\n' {
+			// We have a line terminated by single newline.
+			return i + 1, data[0:i], nil
+		}
+		advance = i + 1
+		if len(data) > i+1 && data[i+1] == '\n' {
+			advance += 1
+		}
+		return advance, data[0:i], nil
+	}
+	// If we're at EOF, we have a final, non-terminated line. Return it.
+	if atEOF {
+		return len(data), data, nil
+	}
+	// Request more data.
+	return 0, nil, nil
+}
+
+func CollectChunks[T any](n int, it iter.Seq[T]) iter.Seq[[]T] {
+	return func(yield func([]T) bool) {
+		var s []T
+		for x := range it {
+			s = append(s, x)
+			if len(s) >= n {
+				if !yield(s) {
+					return
+				}
+				s = nil
+			}
+		}
+		if len(s) > 0 {
+			yield(s)
+		}
+	}
+}

utils/slice/slice_test.go

@@ -1,15 +1,19 @@
 package slice_test
 
 import (
+	"os"
+	"slices"
 	"strconv"
 	"testing"
 
+	"github.com/navidrome/navidrome/tests"
 	"github.com/navidrome/navidrome/utils/slice"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
 
 func TestSlice(t *testing.T) {
+	tests.Init(t, false)
 	RegisterFailHandler(Fail)
 	RunSpecs(t, "Slice Suite")
 }
@@ -90,4 +94,32 @@ var _ = Describe("Slice Utils", func() {
 			Expect(chunks[1]).To(HaveExactElements("d", "e"))
 		})
 	})
+
+	DescribeTable("LinesFrom",
+		func(path string, expected int) {
+			count := 0
+			file, _ := os.Open(path)
+			defer file.Close()
+			for _ = range slice.LinesFrom(file) {
+				count++
+			}
+			Expect(count).To(Equal(expected))
+		},
+		Entry("returns empty slice for an empty input", "tests/fixtures/empty.txt", 0),
+		Entry("returns the lines of a file", "tests/fixtures/playlists/pls1.m3u", 3),
+		Entry("returns empty if file does not exist", "tests/fixtures/NON-EXISTENT", 0),
+	)
+
+	DescribeTable("CollectChunks",
+		func(input []int, n int, expected [][]int) {
+			result := [][]int{}
+			for chunks := range slice.CollectChunks[int](n, slices.Values(input)) {
+				result = append(result, chunks)
+			}
+			Expect(result).To(Equal(expected))
+		},
+		Entry("returns empty slice for an empty input", []int{}, 1, [][]int{}),
+		Entry("returns the slice in one chunk if len < chunkSize", []int{1, 2, 3}, 10, [][]int{{1, 2, 3}}),
+		Entry("breaks up the slice if len > chunkSize", []int{1, 2, 3, 4, 5}, 3, [][]int{{1, 2, 3}, {4, 5}}),
+	)
 })