blob: introduce creating a blob by writing into a stream

The pair of `git_blob_create_frombuffer()` and
`git_blob_create_frombuffer_commit()` is meant to replace
`git_blob_create_fromchunks()` by providing a way for a user to write a
new blob when they want filtering or they do not know the size.

This approach allows the caller to retain control over when to add data
to this buffer and a more natural fit into higher-level language's own
stream abstractions instead of having to handle IO wait in the callback.

The in-memory buffer size of 2MB is chosen somewhat arbitrarily to be a
round multiple of usual page sizes and a value where most blobs seem
likely to be either going to be way below or way over that size. It's
also a round number of pages.

This implementation re-uses the helper we have from `_fromchunks()` so
we end up writing everything to disk, but hopefully more efficiently
than with a default filebuf. A later optimisation can be to avoid
writing the in-memory contents to disk, with some extra complexity.

1 files changed, 92 insertions, 0 deletions

diff --git a/src/blob.c b/src/blob.c
index ad0f4ac62..a1ef2479e 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -334,6 +334,98 @@ cleanup:
 	return error;
 }
 
+typedef struct {
+	git_writestream parent;
+	git_filebuf fbuf;
+	git_repository *repo;
+	char *hintpath;
+} blob_writestream;
+
+static int blob_writestream_close(git_writestream *_stream)
+{
+	blob_writestream *stream = (blob_writestream *) _stream;
+
+	git_filebuf_cleanup(&stream->fbuf);
+	return 0;
+}
+
+static void blob_writestream_free(git_writestream *_stream)
+{
+	blob_writestream *stream = (blob_writestream *) _stream;
+
+	git_filebuf_cleanup(&stream->fbuf);
+	git__free(stream->hintpath);
+	git__free(stream);
+}
+
+static int blob_writestream_write(git_writestream *_stream, const char *buffer, size_t len)
+{
+	blob_writestream *stream = (blob_writestream *) _stream;
+
+	return git_filebuf_write(&stream->fbuf, buffer, len);
+}
+
+int git_blob_create_fromstream(git_writestream **out, git_repository *repo, const char *hintpath)
+{
+	int error;
+	git_buf path = GIT_BUF_INIT;
+	blob_writestream *stream;
+
+	assert(out && repo);
+
+	stream = git__calloc(1, sizeof(blob_writestream));
+	GITERR_CHECK_ALLOC(stream);
+
+	if (hintpath) {
+		stream->hintpath = git__strdup(hintpath);
+		GITERR_CHECK_ALLOC(stream->hintpath);
+	}
+
+	stream->repo = repo;
+	stream->parent.write = blob_writestream_write;
+	stream->parent.close = blob_writestream_close;
+	stream->parent.free  = blob_writestream_free;
+
+	if ((error = git_buf_joinpath(&path,
+				      git_repository_path(repo), GIT_OBJECTS_DIR "streamed")) < 0)
+		goto cleanup;
+
+	if ((error = git_filebuf_open_withsize(&stream->fbuf, git_buf_cstr(&path), GIT_FILEBUF_TEMPORARY,
+					       0666, 2 * 1024 * 1024)) < 0)
+		goto cleanup;
+
+	*out = (git_writestream *) stream;
+
+cleanup:
+	if (error < 0)
+		blob_writestream_free((git_writestream *) stream);
+
+	git_buf_free(&path);
+	return error;
+}
+
+int git_blob_create_fromstream_commit(git_oid *out, git_writestream *_stream)
+{
+	int error;
+	blob_writestream *stream = (blob_writestream *) _stream;
+
+	/*
+	 * We can make this more officient by avoiding writing to
+	 * disk, but for now let's re-use the helper functions we
+	 * have.
+	 */
+	if ((error = git_filebuf_flush(&stream->fbuf)) < 0)
+		goto cleanup;
+
+	error = git_blob__create_from_paths(out, NULL, stream->repo, stream->fbuf.path_lock,
+					    stream->hintpath, 0, !!stream->hintpath);
+
+cleanup:
+	blob_writestream_free(_stream);
+	return error;
+
+}
+
 int git_blob_is_binary(const git_blob *blob)
 {
 	git_buf content = GIT_BUF_INIT;