Update to gobook@0a3e8d997823052c6a8575feca6e515ac6f8299d

ch13/bzip-print/bzip2.c

@@ -0,0 +1,28 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 362.
+// This is the version that appears in print,
+// but it does not comply with the proposed
+// rules for passing pointers between Go and C.
+// (https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md)
+// See gopl.io/ch13/bzip for an updated version.
+
+//!+
+/* This file is gopl.io/ch13/bzip/bzip2.c,         */
+/* a simple wrapper for libbzip2 suitable for cgo. */
+#include <bzlib.h>
+
+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;
+}
+
+//!-

ch13/bzip-print/bzip2.go

@@ -0,0 +1,96 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 362.
+// This is the version that appears in print,
+// but it does not comply with the proposed
+// rules for passing pointers between Go and C.
+// (https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md)
+// See gopl.io/ch13/bzip for an updated version.
+//!+
+
+// 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 <bzlib.h>
+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

ch13/bzip-print/bzip2_test.go

@@ -0,0 +1,40 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+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")
+	}
+}

ch13/bzip/bzip2.c

@@ -17,6 +17,12 @@ int bz2compress(bz_stream *s, int action,
   int r = BZ2_bzCompress(s, action);
   *inlen -= s->avail_in;
   *outlen -= s->avail_out;
+
+  /* "C code may store a Go pointer in C memory subject to rule 2: 
+   * it must stop storing the pointer before it returns to Go." */
+  s->next_in = NULL;
+  s->next_out = NULL;
+  
   return r;
 }
 

ch13/bzip/bzip2.go

@@ -2,6 +2,20 @@
 // License: https://creativecommons.org/licenses/by-nc-sa/4.0/
 
 // See page 362.
+// The version of this file that appears in the book does not comply
+// with the proposed rules for passing pointers between Go and C.
+// (https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md)
+// The rules forbid a C function like bz2compress from storing 'in' and
+// 'out' (pointers to variables allocated by Go) into the Go variable 's',
+// even temporarily.
+//
+// To comply with the rules, the bz_stream variable must be allocated
+// by C code.  We have introduced two C functions, bz2alloc and
+// bz2free, to allocate and free instances of the bz_stream type.
+// Also, we have changed bz2compress so that before it returns, it
+// clears the fields of the bz_stream that contain point to Go
+// variables.
+
 //!+
 
 // Package bzip provides a writer that uses bzip2 compression (bzip.org).
@@ -11,8 +25,12 @@ package bzip
 #cgo CFLAGS: -I/usr/include
 #cgo LDFLAGS: -L/usr/lib -lbz2
 #include <bzlib.h>
+#include <stdlib.h>
+
+bz_stream* bz2alloc() { return calloc(1, sizeof(bz_stream)); }
 int bz2compress(bz_stream *s, int action,
                 char *in, unsigned *inlen, char *out, unsigned *outlen);
+void bz2free(bz_stream* s) { return free(s); }
 */
 import "C"
 
@@ -34,9 +52,7 @@ func NewWriter(out io.Writer) io.WriteCloser {
 		verbosity  = 0
 		workFactor = 30
 	)
-	// NOTE: This code may not work in future Go releases.
-	// See http://www.gopl.io/errata.html for explanation.
-	w := &writer{w: out, stream: new(C.bz_stream)}
+	w := &writer{w: out, stream: C.bz2alloc()}
 	C.BZ2_bzCompressInit(w.stream, blockSize, verbosity, workFactor)
 	return w
 }
@@ -75,6 +91,7 @@ func (w *writer) Close() error {
 	}
 	defer func() {
 		C.BZ2_bzCompressEnd(w.stream)
+		C.bz2free(w.stream)
 		w.stream = nil
 	}()
 	for {