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writebuffer.go
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writebuffer.go
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package core
import (
"bytes"
"io"
"net/http"
"sync"
)
// WriteBuffer by defaul Write(s) to bytes.Buffer.
// But after WriteTo to new io.Writer - calls Reset.
// Reset will flush current buffer data to new writer and starts to Write to new io.Writer
// WriteTo will be locked until Write fails or Close will be called.
type WriteBuffer struct {
io.Writer
err error
mu sync.Mutex
wg sync.WaitGroup
state byte
}
func NewWriteBuffer(wr io.Writer) *WriteBuffer {
if wr == nil {
wr = bytes.NewBuffer(nil)
}
return &WriteBuffer{Writer: wr}
}
func (w *WriteBuffer) Write(p []byte) (n int, err error) {
w.mu.Lock()
if w.err != nil {
err = w.err
} else if n, err = w.Writer.Write(p); err != nil {
w.err = err
w.done()
} else if f, ok := w.Writer.(http.Flusher); ok {
f.Flush()
}
w.mu.Unlock()
return
}
func (w *WriteBuffer) WriteTo(wr io.Writer) (n int64, err error) {
w.Reset(wr)
w.wg.Wait()
return 0, w.err // TODO: fix counter
}
func (w *WriteBuffer) Close() error {
if closer, ok := w.Writer.(io.Closer); ok {
return closer.Close()
}
w.mu.Lock()
w.done()
w.mu.Unlock()
return nil
}
func (w *WriteBuffer) Reset(wr io.Writer) {
w.mu.Lock()
w.add()
if buf, ok := w.Writer.(*bytes.Buffer); ok && buf.Len() != 0 {
if _, err := io.Copy(wr, buf); err != nil {
w.err = err
w.done()
}
}
w.Writer = wr
w.mu.Unlock()
}
const (
none = iota
start
end
)
func (w *WriteBuffer) add() {
if w.state == none {
w.state = start
w.wg.Add(1)
}
}
func (w *WriteBuffer) done() {
if w.state == start {
w.state = end
w.wg.Done()
}
}
// OnceBuffer will catch only first message
type OnceBuffer struct {
buf []byte
}
func (o *OnceBuffer) Write(p []byte) (n int, err error) {
if o.buf == nil {
o.buf = p
}
return 0, io.EOF
}
func (o *OnceBuffer) WriteTo(w io.Writer) (n int64, err error) {
return io.Copy(w, bytes.NewReader(o.buf))
}
func (o *OnceBuffer) Buffer() []byte {
return o.buf
}
func (o *OnceBuffer) Len() int {
return len(o.buf)
}