Improve x-subrip detection performance

internal/magic/text.go

@@ -302,19 +302,21 @@ func Svg(raw []byte, limit uint32) bool {
 
 // Srt matches a SubRip file.
 func Srt(in []byte, _ uint32) bool {
- s := bufio.NewScanner(bytes.NewReader(in))
- if !s.Scan() {
+ line, in, found := scanLine(in)
+ if !found {
  return false
  }
+
  // First line must be 1.
- if s.Text() != "1" {
+ if string(line) != "1" {
  return false
  }
-
- if !s.Scan() {
+ line, in, found = scanLine(in)
+ if !found {
  return false
  }
- secondLine := s.Text()
+
+ secondLine := string(line)
  // Timestamp format (e.g: 00:02:16,612 --> 00:02:19,376) limits secondLine
  // length to exactly 29 characters.
  if len(secondLine) != 29 {
@@ -325,14 +327,12 @@ func Srt(in []byte, _ uint32) bool {
  if strings.Contains(secondLine, ".") {
  return false
  }
- // For Go <1.17, comma is not recognised as a decimal separator by `time.Parse`.
- secondLine = strings.ReplaceAll(secondLine, ",", ".")
  // Second line must be a time range.
  ts := strings.Split(secondLine, " --> ")
  if len(ts) != 2 {
  return false
  }
- const layout = "15:04:05.000"
+ const layout = "15:04:05,000"
  t0, err := time.Parse(layout, ts[0])
  if err != nil {
  return false
@@ -345,8 +345,9 @@ func Srt(in []byte, _ uint32) bool {
  return false
  }
 
+ line, _, found = scanLine(in)
  // A third line must exist and not be empty. This is the actual subtitle text.
- return s.Scan() && len(s.Bytes()) != 0
+ return found && len(line) != 0
 }
 
 // Vtt matches a Web Video Text Tracks (WebVTT) file. See
@@ -373,3 +374,16 @@ func Vtt(raw []byte, limit uint32) bool {
  return bytes.Equal(raw, []byte{0xEF, 0xBB, 0xBF, 0x57, 0x45, 0x42, 0x56, 0x54, 0x54}) || // UTF-8 BOM and "WEBVTT"
  bytes.Equal(raw, []byte{0x57, 0x45, 0x42, 0x56, 0x54, 0x54}) // "WEBVTT"
 }
+
+func scanLine(in []byte) (line, remainder []byte, found bool) {
+ line, remainder, found = bytes.Cut(in, []byte("\n"))
+ if !found {
+ return
+ }
+
+ // Drop off any \r before \n.
+ if lenLine := len(line); lenLine > 0 && line[lenLine-1] == '\r' {
+ line = line[:lenLine-1]
+ }
+ return
+}

mimetype_test.go

@@ -176,18 +176,13 @@ var files = map[string]string{
  "so.so": "application/x-sharedlib",
  "sqlite.sqlite": "application/vnd.sqlite3",
  "srt.srt": "application/x-subrip",
- // not.srt.txt uses periods instead of commas for the decimal separators of
- // the timestamps.
- "not.srt.txt": "text/plain; charset=utf-8",
- // not.srt.2.txt does not specify milliseconds.
- "not.srt.2.txt": "text/plain; charset=utf-8",
- "svg.1.svg": "image/svg+xml",
- "svg.svg": "image/svg+xml",
- "swf.swf": "application/x-shockwave-flash",
- "tar.tar": "application/x-tar",
- "tar.gnu.tar": "application/x-tar",
- "tar.oldgnu.tar": "application/x-tar",
- "tar.posix.tar": "application/x-tar",
+ "svg.1.svg": "image/svg+xml",
+ "svg.svg": "image/svg+xml",
+ "swf.swf": "application/x-shockwave-flash",
+ "tar.tar": "application/x-tar",
+ "tar.gnu.tar": "application/x-tar",
+ "tar.oldgnu.tar": "application/x-tar",
+ "tar.posix.tar": "application/x-tar",
  // tar.star.tar was generated with star 1.6.
  "tar.star.tar": "application/x-tar",
  "tar.ustar.tar": "application/x-tar",
@@ -491,6 +486,7 @@ func BenchmarkSliceRand(b *testing.B) {
  }
 
  b.ResetTimer()
+ b.ReportAllocs()
 
  b.RunParallel(func(pb *testing.PB) {
  for pb.Next() {
@@ -499,6 +495,24 @@ func BenchmarkSliceRand(b *testing.B) {
  })
 }
 
+func BenchmarkAll(b *testing.B) {
+ r := rand.New(rand.NewSource(0))
+ data := make([]byte, 3072)
+ if _, err := io.ReadFull(r, data); err != io.ErrUnexpectedEOF && err != nil {
+ b.Fatal(err)
+ }
+ for _, m := range root.flatten() {
+ b.Run(m.String(), func(b *testing.B) {
+ b.ReportAllocs()
+ b.ResetTimer()
+ for n := 0; n < b.N; n++ {
+ m.detector(data, uint32(len(data)))
+ }
+ })
+ }
+
+}
+
 func BenchmarkCommon(b *testing.B) {
  commonFiles := []string{
  "xlsx.xlsx",
@@ -512,13 +526,15 @@ func BenchmarkCommon(b *testing.B) {
  "gif.gif",
  "xls.xls",
  "webm.webm",
+ "csv.csv",
  }
  for _, file := range commonFiles {
+ f, err := os.ReadFile(filepath.Join(testDataDir, file))
+ if err != nil {
+ b.Fatal(err)
+ }
  b.Run(filepath.Ext(file), func(b *testing.B) {
- f, err := os.ReadFile(testDataDir + file)
- if err != nil {
- b.Fatal(err)
- }
+ b.ReportAllocs()
  b.ResetTimer()
  for n := 0; n < b.N; n++ {
  Detect(f)