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@ -17,8 +17,11 @@ import (
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var stderrFD = 2 // a variable for testing
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const defaultMaxFileSize = 50 << 20
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type Options struct {
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ReplaceStderr bool // dup over fd 2 so everything written to stderr comes here
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MaxFileSize int
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}
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// A Filch uses two alternating files as a simplistic ring buffer.
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@ -30,6 +33,10 @@ type Filch struct {
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alt *os.File
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altscan *bufio.Scanner
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recovered int64
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maxFileSize int64
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writeCounter int
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// buf is an initial buffer for altscan.
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// As of August 2021, 99.96% of all log lines
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// are below 4096 bytes in length.
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@ -38,7 +45,7 @@ type Filch struct {
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// so that the whole struct takes 4096 bytes
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// (less on 32 bit platforms).
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// This reduces allocation waste.
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buf [4096 - 48]byte
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buf [4096 - 64]byte
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}
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// TryReadline implements the logtail.Buffer interface.
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@ -91,6 +98,22 @@ func (f *Filch) scan() ([]byte, error) {
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func (f *Filch) Write(b []byte) (int, error) {
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f.mu.Lock()
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defer f.mu.Unlock()
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if f.writeCounter == 100 {
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// Check the file size every 100 writes.
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f.writeCounter = 0
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fi, err := f.cur.Stat()
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if err != nil {
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return 0, err
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}
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if fi.Size() >= f.maxFileSize {
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// This most likely means we are not draining.
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// To limit the amount of space we use, throw away the old logs.
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if err := moveContents(f.alt, f.cur); err != nil {
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return 0, err
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}
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}
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}
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f.writeCounter++
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if len(b) == 0 || b[len(b)-1] != '\n' {
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bnl := make([]byte, len(b)+1)
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@ -159,8 +182,13 @@ func New(filePrefix string, opts Options) (f *Filch, err error) {
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return nil, err
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}
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mfs := defaultMaxFileSize
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if opts.MaxFileSize > 0 {
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mfs = opts.MaxFileSize
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}
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f = &Filch{
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OrigStderr: os.Stderr, // temporary, for past logs recovery
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OrigStderr: os.Stderr, // temporary, for past logs recovery
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maxFileSize: int64(mfs),
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}
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// Neither, either, or both files may exist and contain logs from
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@ -234,6 +262,9 @@ func moveContents(dst, src *os.File) (err error) {
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if _, err := src.Seek(0, io.SeekStart); err != nil {
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return err
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}
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if _, err := dst.Seek(0, io.SeekStart); err != nil {
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return err
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}
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if _, err := io.Copy(dst, src); err != nil {
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return err
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}
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