use xmallocz to avoid size arithmetic

We frequently allocate strings as xmalloc(len + 1), where
the extra 1 is for the NUL terminator. This can be done more
simply with xmallocz, which also checks for integer
overflow.

There's no case where switching xmalloc(n+1) to xmallocz(n)
is wrong; the result is the same length, and malloc made no
guarantees about what was in the buffer anyway. But in some
cases, we can stop manually placing NUL at the end of the
allocated buffer. But that's only safe if it's clear that
the contents will always fill the buffer.

In each case where this patch does so, I manually examined
the control flow, and I tried to err on the side of caution.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/check-ref-format.c

@@ -20,7 +20,7 @@ static const char builtin_check_ref_format_usage[] =
  */
 static char *collapse_slashes(const char *refname)
 {
-	char *ret = xmalloc(strlen(refname) + 1);
+	char *ret = xmallocz(strlen(refname));
 	char ch;
 	char prev = '/';
 	char *cp = ret;

builtin/merge-tree.c

@@ -174,7 +174,7 @@ static struct merge_list *create_entry(unsigned stage, unsigned mode, const unsi
 
 static char *traverse_path(const struct traverse_info *info, const struct name_entry *n)
 {
-	char *path = xmalloc(traverse_path_len(info, n) + 1);
+	char *path = xmallocz(traverse_path_len(info, n));
 	return make_traverse_path(path, info, n);
 }
 

builtin/worktree.c

@@ -52,7 +52,7 @@ static int prune_worktree(const char *id, struct strbuf *reason)
 		return 1;
 	}
 	len = st.st_size;
-	path = xmalloc(len + 1);
+	path = xmallocz(len);
 	read_in_full(fd, path, len);
 	close(fd);
 	while (len && (path[len - 1] == '\n' || path[len - 1] == '\r'))

column.c

@@ -173,9 +173,8 @@ static void display_table(const struct string_list *list,
 	if (colopts & COL_DENSE)
 		shrink_columns(&data);
 
-	empty_cell = xmalloc(initial_width + 1);
+	empty_cell = xmallocz(initial_width);
 	memset(empty_cell, ' ', initial_width);
-	empty_cell[initial_width] = '\0';
 	for (y = 0; y < data.rows; y++) {
 		for (x = 0; x < data.cols; x++)
 			if (display_cell(&data, initial_width, empty_cell, x, y))

combine-diff.c

@@ -1043,16 +1043,14 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
 				elem->mode = canon_mode(S_IFLNK);
 
 			result_size = len;
-			result = xmalloc(len + 1);
+			result = xmallocz(len);
 
 			done = read_in_full(fd, result, len);
 			if (done < 0)
 				die_errno("read error '%s'", elem->path);
 			else if (done < len)
 				die("early EOF '%s'", elem->path);
 
-			result[len] = 0;
-
 			/* If not a fake symlink, apply filters, e.g. autocrlf */
 			if (is_file) {
 				struct strbuf buf = STRBUF_INIT;

config.c

@@ -1878,7 +1878,7 @@ static int git_config_parse_key_1(const char *key, char **store_key, int *basele
 	 * Validate the key and while at it, lower case it for matching.
 	 */
 	if (store_key)
-		*store_key = xmalloc(strlen(key) + 1);
+		*store_key = xmallocz(strlen(key));
 
 	dot = 0;
 	for (i = 0; key[i]; i++) {
@@ -1902,8 +1902,6 @@ static int git_config_parse_key_1(const char *key, char **store_key, int *basele
 		if (store_key)
 			(*store_key)[i] = c;
 	}
-	if (store_key)
-		(*store_key)[i] = 0;
 
 	return 0;
 

dir.c

@@ -711,7 +711,7 @@ static int add_excludes(const char *fname, const char *base, int baselen,
 			close(fd);
 			return 0;
 		}
-		buf = xmalloc(size+1);
+		buf = xmallocz(size);
 		if (read_in_full(fd, buf, size) != size) {
 			free(buf);
 			close(fd);

entry.c

@@ -6,7 +6,7 @@
 static void create_directories(const char *path, int path_len,
 			       const struct checkout *state)
 {
-	char *buf = xmalloc(path_len + 1);
+	char *buf = xmallocz(path_len);
 	int len = 0;
 
 	while (len < path_len) {

grep.c

@@ -1741,15 +1741,14 @@ static int grep_source_load_file(struct grep_source *gs)
 	i = open(filename, O_RDONLY);
 	if (i < 0)
 		goto err_ret;
-	data = xmalloc(size + 1);
+	data = xmallocz(size);
 	if (st.st_size != read_in_full(i, data, size)) {
 		error(_("'%s': short read %s"), filename, strerror(errno));
 		close(i);
 		free(data);
 		return -1;
 	}
 	close(i);
-	data[size] = 0;
 
 	gs->buf = data;
 	gs->size = size;

imap-send.c

@@ -892,12 +892,11 @@ static char *cram(const char *challenge_64, const char *user, const char *pass)
 	response = xstrfmt("%s %s", user, hex);
 	resp_len = strlen(response) + 1;
 
-	response_64 = xmalloc(ENCODED_SIZE(resp_len) + 1);
+	response_64 = xmallocz(ENCODED_SIZE(resp_len));
 	encoded_len = EVP_EncodeBlock((unsigned char *)response_64,
 				      (unsigned char *)response, resp_len);
 	if (encoded_len < 0)
 		die("EVP_EncodeBlock error");
-	response_64[encoded_len] = '\0';
 	return (char *)response_64;
 }
 
@@ -1188,7 +1187,7 @@ static void lf_to_crlf(struct strbuf *msg)
 		j++;
 	}
 
-	new = xmalloc(j + 1);
+	new = xmallocz(j);
 
 	/*
 	 * Second pass: write the new string.  Note that this loop is

ll-merge.c

@@ -205,7 +205,7 @@ static int ll_ext_merge(const struct ll_merge_driver *fn,
 	if (fstat(fd, &st))
 		goto close_bad;
 	result->size = st.st_size;
-	result->ptr = xmalloc(result->size + 1);
+	result->ptr = xmallocz(result->size);
 	if (read_in_full(fd, result->ptr, result->size) != result->size) {
 		free(result->ptr);
 		result->ptr = NULL;

progress.c

@@ -247,7 +247,7 @@ void stop_progress_msg(struct progress **p_progress, const char *msg)
 		size_t len = strlen(msg) + 5;
 		struct throughput *tp = progress->throughput;
 
-		bufp = (len < sizeof(buf)) ? buf : xmalloc(len + 1);
+		bufp = (len < sizeof(buf)) ? buf : xmallocz(len);
 		if (tp) {
 			unsigned int rate = !tp->avg_misecs ? 0 :
 					tp->avg_bytes / tp->avg_misecs;

refs.c

@@ -124,7 +124,7 @@ int refname_is_safe(const char *refname)
 		char *buf;
 		int result;
 
-		buf = xmalloc(strlen(refname) + 1);
+		buf = xmallocz(strlen(refname));
 		/*
 		 * Does the refname try to escape refs/?
 		 * For example: refs/foo/../bar is safe but refs/foo/../../bar

setup.c

@@ -88,7 +88,7 @@ char *prefix_path_gently(const char *prefix, int len,
 	const char *orig = path;
 	char *sanitized;
 	if (is_absolute_path(orig)) {
-		sanitized = xmalloc(strlen(path) + 1);
+		sanitized = xmallocz(strlen(path));
 		if (remaining_prefix)
 			*remaining_prefix = 0;
 		if (normalize_path_copy_len(sanitized, path, remaining_prefix)) {
@@ -499,14 +499,13 @@ const char *read_gitfile_gently(const char *path, int *return_error_code)
 		error_code = READ_GITFILE_ERR_OPEN_FAILED;
 		goto cleanup_return;
 	}
-	buf = xmalloc(st.st_size + 1);
+	buf = xmallocz(st.st_size);
 	len = read_in_full(fd, buf, st.st_size);
 	close(fd);
 	if (len != st.st_size) {
 		error_code = READ_GITFILE_ERR_READ_FAILED;
 		goto cleanup_return;
 	}
-	buf[len] = '\0';
 	if (!starts_with(buf, "gitdir: ")) {
 		error_code = READ_GITFILE_ERR_INVALID_FORMAT;
 		goto cleanup_return;

strbuf.c

@@ -685,7 +685,7 @@ char *xstrdup_tolower(const char *string)
 	size_t len, i;
 
 	len = strlen(string);
-	result = xmalloc(len + 1);
+	result = xmallocz(len);
 	for (i = 0; i < len; i++)
 		result[i] = tolower(string[i]);
 	result[i] = '\0';