Make initial value of git_buf ptr always be a valid empty string.

Taking a page from core git's strbuf, this introduces git_buf_initbuf
which is an empty string that is used to initialize the git_buf ptr
value even for new buffers.  Now the git_buf ptr will always point to
a valid NUL-terminated string.

This change required jumping through a few hoops for git_buf_grow
and git_buf_free to distinguish between a actual allocated buffer
and the global initial value.  Also, this moves the allocation
related functions to be next to each other near the top of buffer.c.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/buffer.h b/src/buffer.h
index 9e8ebd058..fa0c7f0b8 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -14,8 +14,11 @@ typedef struct {
 	ssize_t asize, size;
 } git_buf;
 
-#define GIT_BUF_INIT {NULL, 0, 0}
+extern char git_buf_initbuf[];
 
+#define GIT_BUF_INIT { git_buf_initbuf, 0, 0 }
+
+void git_buf_init(git_buf *buf, size_t initial_size);
 int git_buf_grow(git_buf *buf, size_t target_size);
 void git_buf_free(git_buf *buf);
 void git_buf_swap(git_buf *buf_a, git_buf *buf_b);