Cap the amount of buffering done by BytesPipe

Turn BytesPipe's Read and Write functions into blocking, goroutine-safe
functions. Add a CloseWithError function to propagate an error code to
the Read function.

Adjust tests to work with the blocking Read and Write functions.

Remove BufReader, since now its users can use BytesPipe directly.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

ioutils/readers.go

@@ -4,7 +4,6 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"io"
-	"sync"
 )
 
 type readCloserWrapper struct {
@@ -45,92 +44,6 @@ func NewReaderErrWrapper(r io.Reader, closer func()) io.Reader {
 	}
 }
 
-// bufReader allows the underlying reader to continue to produce
-// output by pre-emptively reading from the wrapped reader.
-// This is achieved by buffering this data in bufReader's
-// expanding buffer.
-type bufReader struct {
-	sync.Mutex
-	buf      io.ReadWriter
-	reader   io.Reader
-	err      error
-	wait     sync.Cond
-	drainBuf []byte
-}
-
-// NewBufReader returns a new bufReader.
-func NewBufReader(r io.Reader) io.ReadCloser {
-	reader := &bufReader{
-		buf:      NewBytesPipe(nil),
-		reader:   r,
-		drainBuf: make([]byte, 1024),
-	}
-	reader.wait.L = &reader.Mutex
-	go reader.drain()
-	return reader
-}
-
-// NewBufReaderWithDrainbufAndBuffer returns a BufReader with drainBuffer and buffer.
-func NewBufReaderWithDrainbufAndBuffer(r io.Reader, drainBuffer []byte, buffer io.ReadWriter) io.ReadCloser {
-	reader := &bufReader{
-		buf:      buffer,
-		drainBuf: drainBuffer,
-		reader:   r,
-	}
-	reader.wait.L = &reader.Mutex
-	go reader.drain()
-	return reader
-}
-
-func (r *bufReader) drain() {
-	for {
-		//Call to scheduler is made to yield from this goroutine.
-		//This avoids goroutine looping here when n=0,err=nil, fixes code hangs when run with GCC Go.
-		callSchedulerIfNecessary()
-		n, err := r.reader.Read(r.drainBuf)
-		r.Lock()
-		if err != nil {
-			r.err = err
-		} else {
-			if n == 0 {
-				// nothing written, no need to signal
-				r.Unlock()
-				continue
-			}
-			r.buf.Write(r.drainBuf[:n])
-		}
-		r.wait.Signal()
-		r.Unlock()
-		if err != nil {
-			break
-		}
-	}
-}
-
-func (r *bufReader) Read(p []byte) (n int, err error) {
-	r.Lock()
-	defer r.Unlock()
-	for {
-		n, err = r.buf.Read(p)
-		if n > 0 {
-			return n, err
-		}
-		if r.err != nil {
-			return 0, r.err
-		}
-		r.wait.Wait()
-	}
-}
-
-// Close closes the bufReader
-func (r *bufReader) Close() error {
-	closer, ok := r.reader.(io.ReadCloser)
-	if !ok {
-		return nil
-	}
-	return closer.Close()
-}
-
 // HashData returns the sha256 sum of src.
 func HashData(src io.Reader) (string, error) {
 	h := sha256.New()