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|
package helper
import (
"fmt"
"io"
"os"
"sync"
)
type WriteFlusher interface {
io.Writer
Flush() error
}
// Couple r and w so that until r has been drained (before r.Read() has
// returned some error), all writes to w are sent to a tempfile first.
// The caller must call Flush() on the returned WriteFlusher to ensure
// all data is propagated to w.
func NewWriteAfterReader(r io.Reader, w io.Writer) (io.Reader, WriteFlusher) {
br := &busyReader{Reader: r}
return br, &coupledWriter{Writer: w, busyReader: br}
}
type busyReader struct {
io.Reader
error
errorMutex sync.RWMutex
}
func (r *busyReader) Read(p []byte) (int, error) {
if err := r.getError(); err != nil {
return 0, err
}
n, err := r.Reader.Read(p)
if err != nil {
if err != io.EOF {
err = fmt.Errorf("busyReader: %w", err)
}
r.setError(err)
}
return n, err
}
func (r *busyReader) IsBusy() bool {
return r.getError() == nil
}
func (r *busyReader) getError() error {
r.errorMutex.RLock()
defer r.errorMutex.RUnlock()
return r.error
}
func (r *busyReader) setError(err error) {
if err == nil {
panic("busyReader: attempt to reset error to nil")
}
r.errorMutex.Lock()
defer r.errorMutex.Unlock()
r.error = err
}
type coupledWriter struct {
io.Writer
*busyReader
tempfile *os.File
tempfileMutex sync.Mutex
writeError error
}
func (w *coupledWriter) Write(data []byte) (int, error) {
if w.writeError != nil {
return 0, w.writeError
}
if w.busyReader.IsBusy() {
n, err := w.tempfileWrite(data)
if err != nil {
w.writeError = fmt.Errorf("coupledWriter: %w", err)
}
return n, w.writeError
}
if err := w.Flush(); err != nil {
w.writeError = fmt.Errorf("coupledWriter: %w", err)
return 0, w.writeError
}
return w.Writer.Write(data)
}
func (w *coupledWriter) Flush() error {
w.tempfileMutex.Lock()
defer w.tempfileMutex.Unlock()
tempfile := w.tempfile
if tempfile == nil {
return nil
}
w.tempfile = nil
defer tempfile.Close()
if _, err := tempfile.Seek(0, 0); err != nil {
return err
}
if _, err := io.Copy(w.Writer, tempfile); err != nil {
return err
}
return nil
}
func (w *coupledWriter) tempfileWrite(data []byte) (int, error) {
w.tempfileMutex.Lock()
defer w.tempfileMutex.Unlock()
if w.tempfile == nil {
tempfile, err := w.newTempfile()
if err != nil {
return 0, err
}
w.tempfile = tempfile
}
return w.tempfile.Write(data)
}
func (*coupledWriter) newTempfile() (tempfile *os.File, err error) {
tempfile, err = os.CreateTemp("", "gitlab-workhorse-coupledWriter")
if err != nil {
return nil, err
}
if err := os.Remove(tempfile.Name()); err != nil {
tempfile.Close()
return nil, err
}
return tempfile, nil
}
|
