Update to gobook@0a3e8d997823052c6a8575feca6e515ac6f8299d

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 {