diff options
Diffstat (limited to 'vendor/github.com/philhofer/fwd/writer.go')
-rw-r--r-- | vendor/github.com/philhofer/fwd/writer.go | 224 |
1 files changed, 224 insertions, 0 deletions
diff --git a/vendor/github.com/philhofer/fwd/writer.go b/vendor/github.com/philhofer/fwd/writer.go new file mode 100644 index 000000000..2dc392a91 --- /dev/null +++ b/vendor/github.com/philhofer/fwd/writer.go @@ -0,0 +1,224 @@ +package fwd + +import "io" + +const ( + // DefaultWriterSize is the + // default write buffer size. + DefaultWriterSize = 2048 + + minWriterSize = minReaderSize +) + +// Writer is a buffered writer +type Writer struct { + w io.Writer // writer + buf []byte // 0:len(buf) is bufered data +} + +// NewWriter returns a new writer +// that writes to 'w' and has a buffer +// that is `DefaultWriterSize` bytes. +func NewWriter(w io.Writer) *Writer { + if wr, ok := w.(*Writer); ok { + return wr + } + return &Writer{ + w: w, + buf: make([]byte, 0, DefaultWriterSize), + } +} + +// NewWriterSize returns a new writer +// that writes to 'w' and has a buffer +// that is 'size' bytes. +func NewWriterSize(w io.Writer, size int) *Writer { + if wr, ok := w.(*Writer); ok && cap(wr.buf) >= size { + return wr + } + return &Writer{ + w: w, + buf: make([]byte, 0, max(size, minWriterSize)), + } +} + +// Buffered returns the number of buffered bytes +// in the reader. +func (w *Writer) Buffered() int { return len(w.buf) } + +// BufferSize returns the maximum size of the buffer. +func (w *Writer) BufferSize() int { return cap(w.buf) } + +// Flush flushes any buffered bytes +// to the underlying writer. +func (w *Writer) Flush() error { + l := len(w.buf) + if l > 0 { + n, err := w.w.Write(w.buf) + + // if we didn't write the whole + // thing, copy the unwritten + // bytes to the beginnning of the + // buffer. + if n < l && n > 0 { + w.pushback(n) + if err == nil { + err = io.ErrShortWrite + } + } + if err != nil { + return err + } + w.buf = w.buf[:0] + return nil + } + return nil +} + +// Write implements `io.Writer` +func (w *Writer) Write(p []byte) (int, error) { + c, l, ln := cap(w.buf), len(w.buf), len(p) + avail := c - l + + // requires flush + if avail < ln { + if err := w.Flush(); err != nil { + return 0, err + } + l = len(w.buf) + } + // too big to fit in buffer; + // write directly to w.w + if c < ln { + return w.w.Write(p) + } + + // grow buf slice; copy; return + w.buf = w.buf[:l+ln] + return copy(w.buf[l:], p), nil +} + +// WriteString is analogous to Write, but it takes a string. +func (w *Writer) WriteString(s string) (int, error) { + c, l, ln := cap(w.buf), len(w.buf), len(s) + avail := c - l + + // requires flush + if avail < ln { + if err := w.Flush(); err != nil { + return 0, err + } + l = len(w.buf) + } + // too big to fit in buffer; + // write directly to w.w + // + // yes, this is unsafe. *but* + // io.Writer is not allowed + // to mutate its input or + // maintain a reference to it, + // per the spec in package io. + // + // plus, if the string is really + // too big to fit in the buffer, then + // creating a copy to write it is + // expensive (and, strictly speaking, + // unnecessary) + if c < ln { + return w.w.Write(unsafestr(s)) + } + + // grow buf slice; copy; return + w.buf = w.buf[:l+ln] + return copy(w.buf[l:], s), nil +} + +// WriteByte implements `io.ByteWriter` +func (w *Writer) WriteByte(b byte) error { + if len(w.buf) == cap(w.buf) { + if err := w.Flush(); err != nil { + return err + } + } + w.buf = append(w.buf, b) + return nil +} + +// Next returns the next 'n' free bytes +// in the write buffer, flushing the writer +// as necessary. Next will return `io.ErrShortBuffer` +// if 'n' is greater than the size of the write buffer. +// Calls to 'next' increment the write position by +// the size of the returned buffer. +func (w *Writer) Next(n int) ([]byte, error) { + c, l := cap(w.buf), len(w.buf) + if n > c { + return nil, io.ErrShortBuffer + } + avail := c - l + if avail < n { + if err := w.Flush(); err != nil { + return nil, err + } + l = len(w.buf) + } + w.buf = w.buf[:l+n] + return w.buf[l:], nil +} + +// take the bytes from w.buf[n:len(w.buf)] +// and put them at the beginning of w.buf, +// and resize to the length of the copied segment. +func (w *Writer) pushback(n int) { + w.buf = w.buf[:copy(w.buf, w.buf[n:])] +} + +// ReadFrom implements `io.ReaderFrom` +func (w *Writer) ReadFrom(r io.Reader) (int64, error) { + // anticipatory flush + if err := w.Flush(); err != nil { + return 0, err + } + + w.buf = w.buf[0:cap(w.buf)] // expand buffer + + var nn int64 // written + var err error // error + var x int // read + + // 1:1 reads and writes + for err == nil { + x, err = r.Read(w.buf) + if x > 0 { + n, werr := w.w.Write(w.buf[:x]) + nn += int64(n) + + if err != nil { + if n < x && n > 0 { + w.pushback(n - x) + } + return nn, werr + } + if n < x { + w.pushback(n - x) + return nn, io.ErrShortWrite + } + } else if err == nil { + err = io.ErrNoProgress + break + } + } + if err != io.EOF { + return nn, err + } + + // we only clear here + // because we are sure + // the writes have + // succeeded. otherwise, + // we retain the data in case + // future writes succeed. + w.buf = w.buf[0:0] + + return nn, nil +} |