Make fingerprinting faster

By using a buffer of the fingerprint's size. This descreases the
amount of syscalls for reading the file.

Also added the benchmark for tracking the function's performance.

filebeat/input/filestream/fswatch.go

@@ -18,6 +18,7 @@
 package filestream
 
 import (
+ "bufio"
  "crypto/sha256"
  "encoding/hex"
  "fmt"
@@ -453,7 +454,6 @@ func (s *fileScanner) toFileDescriptor(it *ingestTarget) (fd loginp.FileDescript
  return fd, fmt.Errorf("filesize of %q is %d bytes, expected at least %d bytes for fingerprinting", fd.Filename, fileSize, minSize)
  }
 
- h := sha256.New()
  file, err := os.Open(it.originalFilename)
  if err != nil {
  return fd, fmt.Errorf("failed to open %q for fingerprinting: %w", it.originalFilename, err)
@@ -467,9 +467,10 @@ func (s *fileScanner) toFileDescriptor(it *ingestTarget) (fd loginp.FileDescript
  }
  }
 
- r := io.LimitReader(file, s.cfg.Fingerprint.Length)
- buf := make([]byte, h.BlockSize())
- written, err := io.CopyBuffer(h, r, buf)
+ bfile := bufio.NewReaderSize(file, int(s.cfg.Fingerprint.Length))
+ r := io.LimitReader(bfile, s.cfg.Fingerprint.Length)
+ h := sha256.New()
+ written, err := io.Copy(h, r)
  if err != nil {
  return fd, fmt.Errorf("failed to compute hash for first %d bytes of %q: %w", s.cfg.Fingerprint.Length, fd.Filename, err)
  }

filebeat/input/filestream/fswatch_test.go

@@ -757,3 +757,31 @@ func filenames(m map[string]loginp.FileDescriptor) (result string) {
  }
  return result
 }
+
+func BenchmarkToFileDescriptor(b *testing.B) {
+ dir := b.TempDir()
+ basename := "created.log"
+ filename := filepath.Join(dir, basename)
+ err := os.WriteFile(filename, []byte(strings.Repeat("a", 1024)), 0777)
+ require.NoError(b, err)
+
+ s := fileScanner{
+ paths: []string{filename},
+ cfg: fileScannerConfig{
+ Fingerprint: fingerprintConfig{
+ Enabled: true,
+ Offset: 0,
+ Length: 1024,
+ },
+ },
+ }
+
+ it, err := s.getIngestTarget(filename)
+ require.NoError(b, err)
+
+ for i := 0; i < b.N; i++ {
+ fd, err := s.toFileDescriptor(&it)
+ require.NoError(b, err)
+ require.Equal(b, "2edc986847e209b4016e141a6dc8716d3207350f416969382d431539bf292e4a", fd.Fingerprint)
+ }
+}