| package utils |
| |
| import ( |
| "encoding/binary" |
| "errors" |
| "io" |
| ) |
| |
| 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) { |
| if w == nil || w.Writer == nil { |
| return 0, errors.New("Writer not instanciated") |
| } |
| binary.BigEndian.PutUint32(w.prefix[4:], uint32(len(buf))) |
| buf = append(w.prefix[:], buf...) |
| |
| n, err = w.Writer.Write(buf) |
| return n - StdWriterPrefixLen, err |
| } |
| |
| // 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:]) |
| if er == io.EOF { |
| return written, nil |
| } |
| if er != nil { |
| return 0, er |
| } |
| nr += nr2 |
| } |
| |
| // 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: |
| 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])) |
| Debugf("framesize: %d", frameSize) |
| |
| // Check if the buffer is big enough to read the frame. |
| // Extend it if necessary. |
| if frameSize+StdWriterPrefixLen > bufLen { |
| 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:]) |
| if er == io.EOF { |
| return written, nil |
| } |
| if er != nil { |
| Debugf("Error reading frame: %s", er) |
| return 0, er |
| } |
| nr += nr2 |
| } |
| |
| // Write the retrieved frame (without header) |
| nw, ew = out.Write(buf[StdWriterPrefixLen : frameSize+StdWriterPrefixLen]) |
| if nw > 0 { |
| written += int64(nw) |
| } |
| if ew != nil { |
| Debugf("Error writing frame: %s", ew) |
| return 0, ew |
| } |
| // If the frame has not been fully written: error |
| if nw != frameSize { |
| Debugf("Error Short Write: (%d on %d)", nw, frameSize) |
| return 0, io.ErrShortWrite |
| } |
| |
| // Move the rest of the buffer to the beginning |
| copy(buf, buf[frameSize+StdWriterPrefixLen:]) |
| // Move the index |
| nr -= frameSize + StdWriterPrefixLen |
| } |
| } |