From 0e5b6af9b0843e8b0021b9c83fb33d7950fe2ac6 Mon Sep 17 00:00:00 2001
From: Kalle Olavi Niemitalo <kon@iki.fi>
Date: Sat, 24 Feb 2007 22:51:12 +0200
Subject: [PATCH] Various comments and tweaks in bzip2 decoding.

Do not assume that memset(ptr, 0, size) clears pointers to NULL.
The length of decoded data can be read in two ways; assert they match.
---
 src/encoding/bzip2.c | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/src/encoding/bzip2.c b/src/encoding/bzip2.c
index e3ddfe76d..9df4c658c 100644
--- a/src/encoding/bzip2.c
+++ b/src/encoding/bzip2.c
@@ -20,29 +20,52 @@
 #include "encoding/encoding.h"
 #include "util/memory.h"
 
+/* How many bytes of compressed data to read before decompressing.
+ * This is currently defined as BZ_MAX_UNUSED to make the behaviour
+ * similar to BZ2_bzRead; but other values would work too.  */
 #define ELINKS_BZ_BUFFER_LENGTH BZ_MAX_UNUSED
 
 struct bz2_enc_data {
 	bz_stream fbz_stream;
+
+	/* The file descriptor from which we read.  */
 	int fdread;
-	int last_read; /* If err after last bzDecompress was BZ_STREAM_END.. */
-	unsigned char buf[ELINKS_BZ_BUFFER_LENGTH]; /* must be the last */
+
+	/* Initially 0; set to 1 when BZ2_bzDecompress indicates
+	 * BZ_STREAM_END, which means it has found the bzip2-specific
+	 * end-of-stream marker and all data has been decompressed.
+	 * Then we neither read from the file nor call BZ2_bzDecompress
+	 * any more.  */
+	int last_read;
+
+	/* A buffer for data that has been read from the file but not
+	 * yet decompressed.  fbz_stream.next_in and fbz_stream.avail_in
+	 * refer to this buffer.  */
+	unsigned char buf[ELINKS_BZ_BUFFER_LENGTH];
 };
 
 static int
 bzip2_open(struct stream_encoded *stream, int fd)
 {
+	/* A zero-initialized bz_stream.  The compiler ensures that all
+	 * pointer members in it are null.  (Can't do this with memset
+	 * because C99 does not require all-bits-zero to be a null
+	 * pointer.)  */
+	static const bz_stream null_bz_stream = {0};
+
 	struct bz2_enc_data *data = mem_alloc(sizeof(*data));
 	int err;
 
-	stream->data = 0;
+	stream->data = NULL;
 	if (!data) {
 		return -1;
 	}
-	memset(data, 0, sizeof(struct bz2_enc_data) - ELINKS_BZ_BUFFER_LENGTH);
 
-	data->last_read = 0;
+	/* Initialize all members of *data, except data->buf[], which
+	 * will be initialized on demand by bzip2_read.  */
+	copy_struct(&data->fbz_stream, &null_bz_stream);
 	data->fdread = fd;
+	data->last_read = 0;
 	
 	err = BZ2_bzDecompressInit(&data->fbz_stream, 0, 0);
 	if (err != BZ_OK) {
@@ -97,7 +120,8 @@ bzip2_read(struct stream_encoded *stream, unsigned char *buf, int len)
 			return -1;
 		}
 	} while (data->fbz_stream.avail_out > 0);
-	
+
+	assert(len - data->fbz_stream.avail_out == data->fbz_stream.next_out - (char *) buf);
 	return len - data->fbz_stream.avail_out;
 }