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io_utils.go
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/
io_utils.go
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package common
import (
"io"
"sync"
)
// NoopReadWriteCloser implements io.ReadWriteCloser, discarding all bytes, Read always returns EOF
type NoopReadWriteCloser struct{}
var _ io.ReadWriteCloser = NoopReadWriteCloser{}
// Read implements io.Reader
func (n NoopReadWriteCloser) Read(b []byte) (int, error) { return 0, io.EOF }
// Write implements io.Writer
func (n NoopReadWriteCloser) Write(b []byte) (int, error) { return len(b), nil }
// Close implements io.Closer
func (n NoopReadWriteCloser) Close() error { return nil }
type clampWriter struct {
w io.Writer
remaining int64
overflowErr error
}
func NewClampWriter(buf io.Writer, max uint64, overflowErr error) io.Writer {
if max != 0 {
return &clampWriter{w: buf, remaining: int64(max), overflowErr: overflowErr}
}
return buf
}
func (g *clampWriter) Write(p []byte) (int, error) {
if g.remaining <= 0 {
return 0, g.overflowErr
}
if int64(len(p)) > g.remaining {
p = p[0:g.remaining]
}
n, err := g.w.Write(p)
g.remaining -= int64(n)
if g.remaining <= 0 {
err = g.overflowErr
}
return n, err
}
type clampReadCloser struct {
r io.ReadCloser
remaining int64
overflowErr error
}
func NewClampReadCloser(buf io.ReadCloser, max uint64, overflowErr error) io.ReadCloser {
if max != 0 {
return &clampReadCloser{r: buf, remaining: int64(max), overflowErr: overflowErr}
}
return buf
}
func (g *clampReadCloser) Close() error {
return g.r.Close()
}
func (g *clampReadCloser) Read(p []byte) (int, error) {
if g.remaining <= 0 {
return 0, g.overflowErr
}
if int64(len(p)) > g.remaining {
p = p[0:g.remaining]
}
n, err := g.r.Read(p)
g.remaining -= int64(n)
return n, err
}
type GhostWriter interface {
io.Writer
io.Closer
Swap(r io.Writer) io.Writer
}
// ghostWriter is an io.Writer who will pass writes to an inner writer
// that may be changed at will. it is thread safe to swap or write.
type ghostWriter struct {
cond *sync.Cond
inner io.Writer
closed bool
}
func NewGhostWriter() GhostWriter {
return &ghostWriter{cond: sync.NewCond(new(sync.Mutex)), inner: new(waitWriter)}
}
func (g *ghostWriter) Swap(w io.Writer) (old io.Writer) {
g.cond.L.Lock()
old = g.inner
g.inner = w
g.cond.L.Unlock()
g.cond.Broadcast()
return old
}
func (g *ghostWriter) Close() error {
g.cond.L.Lock()
g.closed = true
g.cond.L.Unlock()
g.cond.Broadcast()
return nil
}
func (g *ghostWriter) awaitRealWriter() (io.Writer, bool) {
// wait for a real writer
g.cond.L.Lock()
for {
if g.closed { // check this first
g.cond.L.Unlock()
return nil, false
}
if _, ok := g.inner.(*waitWriter); ok || g.inner == nil {
g.cond.Wait()
} else {
break
}
}
// we don't need to serialize writes but swapping g.inner could be a race if unprotected
w := g.inner
g.cond.L.Unlock()
return w, true
}
func (g *ghostWriter) Write(b []byte) (int, error) {
w, ok := g.awaitRealWriter()
if !ok {
return 0, io.EOF
}
n, err := w.Write(b)
if err == io.ErrClosedPipe {
// NOTE: we need to mask this error so that docker does not get an error
// from writing the input stream and shut down the container.
err = nil
}
return n, err
}
type GhostReader interface {
io.Reader
io.Closer
Swap(r io.Reader) io.Reader
}
// ghostReader is an io.ReadCloser who will pass reads to an inner reader
// that may be changed at will. it is thread safe to swap or read.
// Read will wait for a 'real' reader if inner is of type *waitReader.
// Close must be called to prevent any pending readers from leaking.
type ghostReader struct {
cond *sync.Cond
inner io.Reader
closed bool
}
func NewGhostReader() GhostReader {
return &ghostReader{cond: sync.NewCond(new(sync.Mutex)), inner: new(waitReader)}
}
func (g *ghostReader) Swap(r io.Reader) (old io.Reader) {
g.cond.L.Lock()
old = g.inner
g.inner = r
g.cond.L.Unlock()
g.cond.Broadcast()
return old
}
func (g *ghostReader) Close() error {
g.cond.L.Lock()
g.closed = true
g.cond.L.Unlock()
g.cond.Broadcast()
return nil
}
func (g *ghostReader) awaitRealReader() (io.Reader, bool) {
// wait for a real reader
g.cond.L.Lock()
for {
if g.closed { // check this first
g.cond.L.Unlock()
return nil, false
}
if _, ok := g.inner.(*waitReader); ok || g.inner == nil {
g.cond.Wait()
} else {
break
}
}
// we don't need to serialize reads but swapping g.inner could be a race if unprotected
r := g.inner
g.cond.L.Unlock()
return r, true
}
func (g *ghostReader) Read(b []byte) (int, error) {
r, ok := g.awaitRealReader()
if !ok {
return 0, io.EOF
}
n, err := r.Read(b)
if err == io.ErrClosedPipe {
// NOTE: we need to mask this error so that docker does not get an error
// from reading the input stream and shut down the container.
err = nil
}
return n, err
}
// waitReader returns io.EOF if anyone calls Read. don't call Read, this is a sentinel type
type waitReader struct{}
func (e *waitReader) Read([]byte) (int, error) {
panic("read on waitReader should not happen")
}
// waitWriter returns io.EOF if anyone calls Write. don't call Write, this is a sentinel type
type waitWriter struct{}
func (e *waitWriter) Write([]byte) (int, error) {
panic("write on waitWriter should not happen")
}