package stdcopy import ( "encoding/binary" "errors" "io" "github.com/Sirupsen/logrus" ) const ( StdWriterPrefixLen = 8 StdWriterFdIndex = 0 StdWriterSizeIndex = 4 ) type StdType [StdWriterPrefixLen]byte var ( Stdin StdType = StdType{0: 0} Stdout StdType = StdType{0: 1} Stderr StdType = StdType{0: 2} ) type StdWriter struct { io.Writer prefix StdType sizeBuf []byte } func (w *StdWriter) Write(buf []byte) (n int, err error) { var n1, n2 int if w == nil || w.Writer == nil { return 0, errors.New("Writer not instanciated") } binary.BigEndian.PutUint32(w.prefix[4:], uint32(len(buf))) n1, err = w.Writer.Write(w.prefix[:]) if err != nil { n = n1 - StdWriterPrefixLen } else { n2, err = w.Writer.Write(buf) n = n1 + n2 - StdWriterPrefixLen } if n < 0 { n = 0 } return } // NewStdWriter instanciates a new Writer. // Everything written to it will be encapsulated using a custom format, // and written to the underlying `w` stream. // This allows multiple write streams (e.g. stdout and stderr) to be muxed into a single connection. // `t` indicates the id of the stream to encapsulate. // It can be utils.Stdin, utils.Stdout, utils.Stderr. func NewStdWriter(w io.Writer, t StdType) *StdWriter { if len(t) != StdWriterPrefixLen { return nil } return &StdWriter{ Writer: w, prefix: t, sizeBuf: make([]byte, 4), } } var ErrInvalidStdHeader = errors.New("Unrecognized input header") // StdCopy is a modified version of io.Copy. // // StdCopy will demultiplex `src`, assuming that it contains two streams, // previously multiplexed together using a StdWriter instance. // As it reads from `src`, StdCopy will write to `dstout` and `dsterr`. // // StdCopy will read until it hits EOF on `src`. It will then return a nil error. // In other words: if `err` is non nil, it indicates a real underlying error. // // `written` will hold the total number of bytes written to `dstout` and `dsterr`. func StdCopy(dstout, dsterr io.Writer, src io.Reader) (written int64, err error) { var ( buf = make([]byte, 32*1024+StdWriterPrefixLen+1) bufLen = len(buf) nr, nw int er, ew error out io.Writer frameSize int ) for { // Make sure we have at least a full header for nr < StdWriterPrefixLen { var nr2 int nr2, er = src.Read(buf[nr:]) nr += nr2 if er == io.EOF { if nr < StdWriterPrefixLen { logrus.Debugf("Corrupted prefix: %v", buf[:nr]) return written, nil } break } if er != nil { logrus.Debugf("Error reading header: %s", er) return 0, er } } // Check the first byte to know where to write switch buf[StdWriterFdIndex] { case 0: fallthrough case 1: // Write on stdout out = dstout case 2: // Write on stderr out = dsterr default: logrus.Debugf("Error selecting output fd: (%d)", buf[StdWriterFdIndex]) return 0, ErrInvalidStdHeader } // Retrieve the size of the frame frameSize = int(binary.BigEndian.Uint32(buf[StdWriterSizeIndex : StdWriterSizeIndex+4])) logrus.Debugf("framesize: %d", frameSize) // Check if the buffer is big enough to read the frame. // Extend it if necessary. if frameSize+StdWriterPrefixLen > bufLen { logrus.Debugf("Extending buffer cap by %d (was %d)", frameSize+StdWriterPrefixLen-bufLen+1, len(buf)) buf = append(buf, make([]byte, frameSize+StdWriterPrefixLen-bufLen+1)...) bufLen = len(buf) } // While the amount of bytes read is less than the size of the frame + header, we keep reading for nr < frameSize+StdWriterPrefixLen { var nr2 int nr2, er = src.Read(buf[nr:]) nr += nr2 if er == io.EOF { if nr < frameSize+StdWriterPrefixLen { logrus.Debugf("Corrupted frame: %v", buf[StdWriterPrefixLen:nr]) return written, nil } break } if er != nil { logrus.Debugf("Error reading frame: %s", er) return 0, er } } // Write the retrieved frame (without header) nw, ew = out.Write(buf[StdWriterPrefixLen : frameSize+StdWriterPrefixLen]) if ew != nil { logrus.Debugf("Error writing frame: %s", ew) return 0, ew } // If the frame has not been fully written: error if nw != frameSize { logrus.Debugf("Error Short Write: (%d on %d)", nw, frameSize) return 0, io.ErrShortWrite } written += int64(nw) // Move the rest of the buffer to the beginning copy(buf, buf[frameSize+StdWriterPrefixLen:]) // Move the index nr -= frameSize + StdWriterPrefixLen } }