Rename read_pipe() with read_fd() and make its buffer nul-terminated.

The new name is closer to the purpose of the function.

A NUL-terminated buffer makes things easier when callers need that.
Since the function returns only the memory written with data,
almost always allocating more space than needed because final
size is unknown, an extra NUL terminating the buffer is harmless.
It is not included in the returned size, so the function
remains working as before.

Also, now the function allows the buffer passed to be NULL at first,
and alloc_nr is now used for growing the buffer, instead size=*2.

Signed-off-by: Carlos Rica <jasampler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -2304,27 +2304,36 @@ int has_sha1_file(const unsigned char *sha1)
  *
  * returns 0 if anything went fine and -1 otherwise
  *
+ * The buffer is always NUL-terminated, not including it in returned size.
+ *
  * NOTE: both buf and size may change, but even when -1 is returned
  * you still have to free() it yourself.
  */
-int read_pipe(int fd, char** return_buf, unsigned long* return_size)
+int read_fd(int fd, char **return_buf, unsigned long *return_size)
 {
-	char* buf = *return_buf;
+	char *buf = *return_buf;
 	unsigned long size = *return_size;
 	ssize_t iret;
 	unsigned long off = 0;
 
+	if (!buf || size <= 1) {
+		size = 1024;
+		buf = xrealloc(buf, size);
+	}
+
 	do {
-		iret = xread(fd, buf + off, size - off);
+		iret = xread(fd, buf + off, (size - 1) - off);
 		if (iret > 0) {
 			off += iret;
-			if (off == size) {
-				size *= 2;
+			if (off == size - 1) {
+				size = alloc_nr(size);
 				buf = xrealloc(buf, size);
 			}
 		}
 	} while (iret > 0);
 
+	buf[off] = '\0';
+
 	*return_buf = buf;
 	*return_size = off;
 
@@ -2339,7 +2348,7 @@ int index_pipe(unsigned char *sha1, int fd, const char *type, int write_object)
 	char *buf = xmalloc(size);
 	int ret;
 
-	if (read_pipe(fd, &buf, &size)) {
+	if (read_fd(fd, &buf, &size)) {
 		free(buf);
 		return -1;
 	}