From ba5d7979312030fc28e7b57e2f558940987504d0 Mon Sep 17 00:00:00 2001 From: Alan Donovan Date: Tue, 29 Sep 2015 15:04:07 -0400 Subject: [PATCH] ch13: add bzip --- ch13/bzip/bzip2.c | 20 ++++++++++ ch13/bzip/bzip2.go | 88 +++++++++++++++++++++++++++++++++++++++++ ch13/bzip/bzip2_test.go | 39 ++++++++++++++++++ ch13/bzipper/main.go | 25 ++++++++++++ 4 files changed, 172 insertions(+) create mode 100644 ch13/bzip/bzip2.c create mode 100644 ch13/bzip/bzip2.go create mode 100644 ch13/bzip/bzip2_test.go create mode 100644 ch13/bzipper/main.go diff --git a/ch13/bzip/bzip2.c b/ch13/bzip/bzip2.c new file mode 100644 index 0000000..3c77f0d --- /dev/null +++ b/ch13/bzip/bzip2.c @@ -0,0 +1,20 @@ +// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan. + +//!+ +/* This file is gopl.io/ch13/bzip/bzip2.c, */ +/* a simple wrapper for libbzip2 suitable for cgo. */ +#include + +int bz2compress(bz_stream *s, int action, + char *in, unsigned *inlen, char *out, unsigned *outlen) { + s->next_in = in; + s->avail_in = *inlen; + s->next_out = out; + s->avail_out = *outlen; + int r = BZ2_bzCompress(s, action); + *inlen -= s->avail_in; + *outlen -= s->avail_out; + return r; +} + +//!- diff --git a/ch13/bzip/bzip2.go b/ch13/bzip/bzip2.go new file mode 100644 index 0000000..e357622 --- /dev/null +++ b/ch13/bzip/bzip2.go @@ -0,0 +1,88 @@ +// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan. +//!+ + +// Package bzip provides a writer that uses bzip2 compression (bzip.org). +package bzip + +/* +#cgo CFLAGS: -I/usr/include +#cgo LDFLAGS: -L/usr/lib -lbz2 +#include +int bz2compress(bz_stream *s, int action, + char *in, unsigned *inlen, char *out, unsigned *outlen); +*/ +import "C" + +import ( + "io" + "unsafe" +) + +type writer struct { + w io.Writer // underlying output stream + stream *C.bz_stream + outbuf [64 * 1024]byte +} + +// NewWriter returns a writer for bzip2-compressed streams. +func NewWriter(out io.Writer) io.WriteCloser { + const ( + blockSize = 9 + verbosity = 0 + workFactor = 30 + ) + w := &writer{w: out, stream: new(C.bz_stream)} + C.BZ2_bzCompressInit(w.stream, blockSize, verbosity, workFactor) + return w +} + +//!- + +//!+write +func (w *writer) Write(data []byte) (int, error) { + if w.stream == nil { + panic("closed") + } + var total int // uncompressed bytes written + + for len(data) > 0 { + inlen, outlen := C.uint(len(data)), C.uint(cap(w.outbuf)) + C.bz2compress(w.stream, C.BZ_RUN, + (*C.char)(unsafe.Pointer(&data[0])), &inlen, + (*C.char)(unsafe.Pointer(&w.outbuf)), &outlen) + total += int(inlen) + data = data[inlen:] + if _, err := w.w.Write(w.outbuf[:outlen]); err != nil { + return total, err + } + } + return total, nil +} + +//!-write + +//!+close +// Close flushes the compressed data and closes the stream. +// It does not close the underlying io.Writer. +func (w *writer) Close() error { + if w.stream == nil { + panic("closed") + } + defer func() { + C.BZ2_bzCompressEnd(w.stream) + w.stream = nil + }() + for { + inlen, outlen := C.uint(0), C.uint(cap(w.outbuf)) + r := C.bz2compress(w.stream, C.BZ_FINISH, nil, &inlen, + (*C.char)(unsafe.Pointer(&w.outbuf)), &outlen) + if _, err := w.w.Write(w.outbuf[:outlen]); err != nil { + return err + } + if r == C.BZ_STREAM_END { + return nil + } + } +} + +//!-close diff --git a/ch13/bzip/bzip2_test.go b/ch13/bzip/bzip2_test.go new file mode 100644 index 0000000..a7f88da --- /dev/null +++ b/ch13/bzip/bzip2_test.go @@ -0,0 +1,39 @@ +// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan. + +package bzip_test + +import ( + "bytes" + "compress/bzip2" // reader + "io" + "testing" + + "gopl.io/ch13/bzip" // writer +) + +func TestBzip2(t *testing.T) { + var compressed, uncompressed bytes.Buffer + w := bzip.NewWriter(&compressed) + + // Write a repetitive message in a million pieces, + // compressing one copy but not the other. + tee := io.MultiWriter(w, &uncompressed) + for i := 0; i < 1000000; i++ { + io.WriteString(tee, "hello") + } + if err := w.Close(); err != nil { + t.Fatal(err) + } + + // Check the size of the compressed stream. + if got, want := compressed.Len(), 255; got != want { + t.Errorf("1 million hellos compressed to %d bytes, want %d", got, want) + } + + // Decompress and compare with original. + var decompressed bytes.Buffer + io.Copy(&decompressed, bzip2.NewReader(&compressed)) + if !bytes.Equal(uncompressed.Bytes(), decompressed.Bytes()) { + t.Error("decompression yielded a different message") + } +} diff --git a/ch13/bzipper/main.go b/ch13/bzipper/main.go new file mode 100644 index 0000000..dd705c2 --- /dev/null +++ b/ch13/bzipper/main.go @@ -0,0 +1,25 @@ +// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan. +//!+ + +// Bzipper reads input, bzip2-compresses it, and writes it out. +package main + +import ( + "io" + "log" + "os" + + "gopl.io/ch13/bzip" +) + +func main() { + w := bzip.NewWriter(os.Stdout) + if _, err := io.Copy(w, os.Stdin); err != nil { + log.Fatalf("bzipper: %v\n", err) + } + if err := w.Close(); err != nil { + log.Fatalf("bzipper: close: %v\n", err) + } +} + +//!-