Update to gobook@27cf7b490526a0a0751ff12ed7cc4acd8afa2edc

ch1/dup3/main.go

@@ -3,9 +3,10 @@
 
 // See page 12.
 
-// Dup3 prints the count and text of lines that appear more than once
-// in the named input files.
 //!+
+
+// Dup3 prints the count and text of lines that
+// appear more than once in the named input files.
 package main
 
 import (

ch1/fetch/main.go

@@ -4,7 +4,7 @@
 // See page 16.
 //!+
 
-// Fetch prints the content found at a URL.
+// Fetch prints the content found at each specified URL.
 package main
 
 import (

ch13/bzip/bzip2.c

@@ -2,6 +2,14 @@
 // License: https://creativecommons.org/licenses/by-nc-sa/4.0/
 
 // See page 362.
+//
+// The version of this program that appeared in the first and second
+// printings did not comply with the proposed rules for passing
+// pointers between Go and C, described here:
+// https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md
+//
+// The version below, which appears in the third printing,
+// has been corrected.  See bzip2.go for explanation.
 
 //!+
 /* This file is gopl.io/ch13/bzip/bzip2.c,         */
@@ -17,12 +25,7 @@ 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;
-  
+  s->next_in = s->next_out = NULL;
   return r;
 }
 

ch13/bzip/bzip2.go

@@ -2,19 +2,23 @@
 // 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.
+// The version of this program that appeared in the first and second
+// printings did not comply with the proposed rules for passing
+// pointers between Go and C, described here:
+// 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.
+//
+// The version below, which appears in the third printing, has been
+// corrected.  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
+// pointers to Go variables.
 
 //!+
 
@@ -26,11 +30,10 @@ package bzip
 #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); }
+void bz2free(bz_stream* s) { free(s); }
 */
 import "C"
 
@@ -47,11 +50,9 @@ type writer struct {
 
 // NewWriter returns a writer for bzip2-compressed streams.
 func NewWriter(out io.Writer) io.WriteCloser {
-	const (
-		blockSize  = 9
-		verbosity  = 0
-		workFactor = 30
-	)
+	const blockSize = 9
+	const verbosity = 0
+	const workFactor = 30
 	w := &writer{w: out, stream: C.bz2alloc()}
 	C.BZ2_bzCompressInit(w.stream, blockSize, verbosity, workFactor)
 	return w