commit: clear user-provided buffers

The functions `git_commit_header_field` and
`git_commit_extract_signature` both receive buffers used to hand back
the results to the user. While these functions called `git_buf_sanitize`
on these buffers, this is not the right thing to do, as it will simply
initialize or zero-terminate passed buffers. As we want to overwrite
contents, we instead have to call `git_buf_clear` to completely reset
them.

1 files changed, 6 insertions, 3 deletions

diff --git a/include/git2/commit.h b/include/git2/commit.h
index 4cc637466..692b3bdd9 100644
--- a/include/git2/commit.h
+++ b/include/git2/commit.h
@@ -255,7 +255,8 @@ GIT_EXTERN(int) git_commit_nth_gen_ancestor(
 /**
  * Get an arbitrary header field
  *
- * @param out the buffer to fill
+ * @param out the buffer to fill; existing content will be
+ * overwritten
  * @param commit the commit to look in
  * @param field the header field to return
  * @return 0 on succeess, GIT_ENOTFOUND if the field does not exist,
@@ -270,8 +271,10 @@ GIT_EXTERN(int) git_commit_header_field(git_buf *out, const git_commit *commit,
  * `GITERR_INVALID`. If the commit does not have a signature, the
  * error class will be `GITERR_OBJECT`.
  *
- * @param signature the signature block
- * @param signed_data signed data; this is the commit contents minus the signature block
+ * @param signature the signature block; existing content will be
+ * overwritten
+ * @param signed_data signed data; this is the commit contents minus the signature block;
+ * existing content will be overwritten
  * @param repo the repository in which the commit exists
  * @param commit_id the commit from which to extract the data
  * @param field the name of the header field containing the signature