str: introduce `git_str` for internal, `git_buf` is externalethomson/gitstr

libgit2 has two distinct requirements that were previously solved by
`git_buf`.  We require:

1. A general purpose string class that provides a number of utility APIs
   for manipulating data (eg, concatenating, truncating, etc).
2. A structure that we can use to return strings to callers that they
   can take ownership of.

By using a single class (`git_buf`) for both of these purposes, we have
confused the API to the point that refactorings are difficult and
reasoning about correctness is also difficult.

Move the utility class `git_buf` to be called `git_str`: this represents
its general purpose, as an internal string buffer class.  The name also
is an homage to Junio Hamano ("gitstr").

The public API remains `git_buf`, and has a much smaller footprint.  It
is generally only used as an "out" param with strict requirements that
follow the documentation.  (Exceptions exist for some legacy APIs to
avoid breaking callers unnecessarily.)

Utility functions exist to convert a user-specified `git_buf` to a
`git_str` so that we can call internal functions, then converting it
back again.

1 files changed, 23 insertions, 0 deletions

diff --git a/src/commit.h b/src/commit.h
index 318ce5cba..9378eab2d 100644
--- a/src/commit.h
+++ b/src/commit.h
@@ -33,6 +33,29 @@ struct git_commit {
 	char *body;
 };
 
+int git_commit__header_field(
+	git_str *out,
+	const git_commit *commit,
+	const char *field);
+
+int git_commit__extract_signature(
+	git_str *signature,
+	git_str *signed_data,
+	git_repository *repo,
+	git_oid *commit_id,
+	const char *field);
+
+int git_commit__create_buffer(
+	git_str *out,
+	git_repository *repo,
+	const git_signature *author,
+	const git_signature *committer,
+	const char *message_encoding,
+	const char *message,
+	const git_tree *tree,
+	size_t parent_count,
+	const git_commit *parents[]);
+
 void git_commit__free(void *commit);
 int git_commit__parse(void *commit, git_odb_object *obj);
 int git_commit__parse_raw(void *commit, const char *data, size_t size);