fix(cli): write pls -p playlist output to stdout (#5996)

The export path used the `println` builtin, which writes to stderr, so
`navidrome pls -p X > playlist.m3u8` produced an empty file while the M3U
body was interleaved with the startup logs on stderr.

`println` also appended a newline that `ToM3U8` already provides, so the
piped output had a stray trailing blank line that `-o file` did not. Both
destinations are now byte-identical.

The stdout/file choice moved into a `writePlaylist` helper shared by
`pls -p` and `pls export -p`, which both had the same bug. It takes the
destination as an `io.Writer`, matching the existing convention in
cmd/artwork.go.

cmd/pls.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
 	"strconv"
@@ -141,14 +142,16 @@ func findPlaylist(ctx context.Context, ds model.DataStore, nameOrID string) *mod
 func runExporter(ctx context.Context) {
 	ds, ctx := getAdminContext(ctx)
 	playlist := findPlaylist(ctx, ds, playlistID)
-	pls := playlist.ToM3U8()
-	if outputFile == "-" || outputFile == "" {
-		println(pls)
+	writePlaylist(playlist.ToM3U8(), os.Stdout, outputFile)
+}
+
+func writePlaylist(m3u string, out io.Writer, file string) {
+	if file == "" || file == "-" {
+		fmt.Fprint(out, m3u)
 		return
 	}
-	err := os.WriteFile(outputFile, []byte(pls), 0600)
-	if err != nil {
-		log.Fatal("Error writing to the output file", "file", outputFile, err)
+	if err := os.WriteFile(file, []byte(m3u), 0600); err != nil {
+		log.Fatal("Error writing to the output file", "file", file, err)
 	}
 }
 
@@ -157,7 +160,7 @@ func runExport(ctx context.Context) {
 
 	if playlistID != "" && outputFile == "" {
 		playlist := findPlaylist(ctx, ds, playlistID)
-		println(playlist.ToM3U8())
+		writePlaylist(playlist.ToM3U8(), os.Stdout, outputFile)
 		return
 	}
 

cmd/pls_test.go

@@ -0,0 +1,35 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("writePlaylist", func() {
+	const m3u = "#EXTM3U\n#PLAYLIST:DJ Wave\n#EXTINF:364,Bel Canto - Dreaming Girl\n"
+	plsFile := filepath.Join(os.TempDir(), fmt.Sprintf("navidrome-pls-%d.m3u8", os.Getpid()))
+
+	BeforeEach(func() {
+		DeferCleanup(func() { _ = os.Remove(plsFile) })
+	})
+
+	DescribeTable("writes the playlist to exactly one destination",
+		func(file, wantStream, wantFile string) {
+			var out strings.Builder
+
+			writePlaylist(m3u, &out, file)
+
+			written, _ := os.ReadFile(plsFile)
+			Expect(out.String()).To(Equal(wantStream))
+			Expect(string(written)).To(Equal(wantFile))
+		},
+		Entry("no file name writes to the stream", "", m3u, ""),
+		Entry("a dash writes to the stream", "-", m3u, ""),
+		Entry("a path writes to the file", plsFile, "", m3u),
+	)
+})