package stdcopy import ( "encoding/binary" "errors" "fmt" "io" "github.com/Sirupsen/logrus" ) // StdType is the type of standard stream // a writer can multiplex to. type StdType byte const ( // Stdin represents standard input stream type. Stdin StdType = iota // Stdout represents standard output stream type. Stdout // Stderr represents standard error steam type. Stderr stdWriterPrefixLen = 8 stdWriterFdIndex = 0 stdWriterSizeIndex = 4 startingBufLen = 32*1024 + stdWriterPrefixLen + 1 ) // stdWriter is wrapper of io.Writer with extra customized info. type stdWriter struct { io.Writer prefix byte } // Write sends the buffer to the underneath writer. // It insert the prefix header before the buffer, // so stdcopy.StdCopy knows where to multiplex the output. // It makes stdWriter to implement io.Writer. func (w *stdWriter) Write(buf []byte) (n int, err error) { if w == nil || w.Writer == nil { return 0, errors.New("Writer not instantiated") } if buf == nil { return 0, nil } header := [stdWriterPrefixLen]byte{stdWriterFdIndex: w.prefix} binary.BigEndian.PutUint32(header[stdWriterSizeIndex:], uint32(len(buf))) line := append(header[:], buf...) n, err = w.Writer.Write(line) n -= stdWriterPrefixLen if n < 0 { n = 0 } return } // NewStdWriter instantiates 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 stdcopy.Stdin, stdcopy.Stdout, stdcopy.Stderr. func NewStdWriter(w io.Writer, t StdType) io.Writer { return &stdWriter{ Writer: w, prefix: byte(t), } } // 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, startingBufLen) 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 StdType(buf[stdWriterFdIndex]) { case Stdin: fallthrough case Stdout: // Write on stdout out = dstout case Stderr: // Write on stderr out = dsterr default: logrus.Debugf("Error selecting output fd: (%d)", buf[stdWriterFdIndex]) return 0, fmt.Errorf("Unrecognized input header: %d", buf[stdWriterFdIndex]) } // 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 } }