120 lines
3.2 KiB
Go
120 lines
3.2 KiB
Go
package brotli
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import (
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"errors"
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"io"
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)
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const (
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BestSpeed = 0
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BestCompression = 11
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DefaultCompression = 6
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)
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// WriterOptions configures Writer.
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type WriterOptions struct {
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// Quality controls the compression-speed vs compression-density trade-offs.
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// The higher the quality, the slower the compression. Range is 0 to 11.
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Quality int
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// LGWin is the base 2 logarithm of the sliding window size.
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// Range is 10 to 24. 0 indicates automatic configuration based on Quality.
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LGWin int
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}
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var (
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errEncode = errors.New("brotli: encode error")
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errWriterClosed = errors.New("brotli: Writer is closed")
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)
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// Writes to the returned writer are compressed and written to dst.
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// It is the caller's responsibility to call Close on the Writer when done.
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// Writes may be buffered and not flushed until Close.
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func NewWriter(dst io.Writer) *Writer {
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return NewWriterLevel(dst, DefaultCompression)
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}
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// NewWriterLevel is like NewWriter but specifies the compression level instead
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// of assuming DefaultCompression.
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// The compression level can be DefaultCompression or any integer value between
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// BestSpeed and BestCompression inclusive.
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func NewWriterLevel(dst io.Writer, level int) *Writer {
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return NewWriterOptions(dst, WriterOptions{
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Quality: level,
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})
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}
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// NewWriterOptions is like NewWriter but specifies WriterOptions
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func NewWriterOptions(dst io.Writer, options WriterOptions) *Writer {
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w := new(Writer)
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w.options = options
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w.Reset(dst)
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return w
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}
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// Reset discards the Writer's state and makes it equivalent to the result of
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// its original state from NewWriter or NewWriterLevel, but writing to dst
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// instead. This permits reusing a Writer rather than allocating a new one.
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func (w *Writer) Reset(dst io.Writer) {
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encoderInitState(w)
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w.params.quality = w.options.Quality
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if w.options.LGWin > 0 {
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w.params.lgwin = uint(w.options.LGWin)
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}
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w.dst = dst
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w.err = nil
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}
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func (w *Writer) writeChunk(p []byte, op int) (n int, err error) {
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if w.dst == nil {
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return 0, errWriterClosed
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}
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if w.err != nil {
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return 0, w.err
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}
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for {
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availableIn := uint(len(p))
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nextIn := p
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success := encoderCompressStream(w, op, &availableIn, &nextIn)
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bytesConsumed := len(p) - int(availableIn)
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p = p[bytesConsumed:]
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n += bytesConsumed
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if !success {
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return n, errEncode
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}
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if len(p) == 0 || w.err != nil {
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return n, w.err
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}
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}
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}
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// Flush outputs encoded data for all input provided to Write. The resulting
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// output can be decoded to match all input before Flush, but the stream is
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// not yet complete until after Close.
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// Flush has a negative impact on compression.
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func (w *Writer) Flush() error {
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_, err := w.writeChunk(nil, operationFlush)
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return err
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}
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// Close flushes remaining data to the decorated writer.
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func (w *Writer) Close() error {
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// If stream is already closed, it is reported by `writeChunk`.
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_, err := w.writeChunk(nil, operationFinish)
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w.dst = nil
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return err
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}
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// Write implements io.Writer. Flush or Close must be called to ensure that the
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// encoded bytes are actually flushed to the underlying Writer.
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func (w *Writer) Write(p []byte) (n int, err error) {
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return w.writeChunk(p, operationProcess)
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}
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type nopCloser struct {
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io.Writer
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}
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func (nopCloser) Close() error { return nil }
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