111 lines
2.8 KiB
Go
111 lines
2.8 KiB
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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// See page 362.
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// The version of this file that appears in the book does not comply
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// with the proposed rules for passing pointers between Go and C.
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// (https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md)
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// The rules forbid a C function like bz2compress from storing 'in' and
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// 'out' (pointers to variables allocated by Go) into the Go variable 's',
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// even temporarily.
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//
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// To comply with the rules, the bz_stream variable must be allocated
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// by C code. We have introduced two C functions, bz2alloc and
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// bz2free, to allocate and free instances of the bz_stream type.
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// Also, we have changed bz2compress so that before it returns, it
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// clears the fields of the bz_stream that contain point to Go
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// variables.
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//!+
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// Package bzip provides a writer that uses bzip2 compression (bzip.org).
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package bzip
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/*
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#cgo CFLAGS: -I/usr/include
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#cgo LDFLAGS: -L/usr/lib -lbz2
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#include <bzlib.h>
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#include <stdlib.h>
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bz_stream* bz2alloc() { return calloc(1, sizeof(bz_stream)); }
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int bz2compress(bz_stream *s, int action,
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char *in, unsigned *inlen, char *out, unsigned *outlen);
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void bz2free(bz_stream* s) { return free(s); }
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*/
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import "C"
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import (
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"io"
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"unsafe"
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)
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type writer struct {
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w io.Writer // underlying output stream
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stream *C.bz_stream
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outbuf [64 * 1024]byte
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}
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// NewWriter returns a writer for bzip2-compressed streams.
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func NewWriter(out io.Writer) io.WriteCloser {
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const (
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blockSize = 9
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verbosity = 0
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workFactor = 30
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)
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w := &writer{w: out, stream: C.bz2alloc()}
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C.BZ2_bzCompressInit(w.stream, blockSize, verbosity, workFactor)
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return w
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}
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//!-
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//!+write
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func (w *writer) Write(data []byte) (int, error) {
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if w.stream == nil {
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panic("closed")
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}
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var total int // uncompressed bytes written
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for len(data) > 0 {
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inlen, outlen := C.uint(len(data)), C.uint(cap(w.outbuf))
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C.bz2compress(w.stream, C.BZ_RUN,
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(*C.char)(unsafe.Pointer(&data[0])), &inlen,
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(*C.char)(unsafe.Pointer(&w.outbuf)), &outlen)
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total += int(inlen)
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data = data[inlen:]
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if _, err := w.w.Write(w.outbuf[:outlen]); err != nil {
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return total, err
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}
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}
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return total, nil
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}
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//!-write
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//!+close
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// Close flushes the compressed data and closes the stream.
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// It does not close the underlying io.Writer.
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func (w *writer) Close() error {
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if w.stream == nil {
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panic("closed")
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}
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defer func() {
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C.BZ2_bzCompressEnd(w.stream)
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C.bz2free(w.stream)
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w.stream = nil
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}()
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for {
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inlen, outlen := C.uint(0), C.uint(cap(w.outbuf))
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r := C.bz2compress(w.stream, C.BZ_FINISH, nil, &inlen,
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(*C.char)(unsafe.Pointer(&w.outbuf)), &outlen)
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if _, err := w.w.Write(w.outbuf[:outlen]); err != nil {
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return err
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}
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if r == C.BZ_STREAM_END {
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return nil
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}
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}
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}
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//!-close
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