indexer: extract function reading stream objects

The loop inside of `git_indexer_append` iterates over every object that
is to be stored as part of the index. While the logic to retrieve every
object from the packfile stream is rather involved, it currently just
part of the loop, making it unnecessarily hard to follow.

Move the logic into its own function `read_stream_object`, which unpacks
a single object from the stream. Note that there is some subtletly here
involving the special error `GIT_EBUFS`, which indicates to the indexer
that no more data is currently available. So instead of returning an
error and aborting the whole loop in that case, we do have to catch that
value and return successfully to wait for more data to be read.

src/indexer.c

@@ -525,6 +525,93 @@ static int append_to_pack(git_indexer *idx, const void *data, size_t size)
 	return write_at(idx, data, idx->pack->mwf.size, size);
 }
 
+static int read_stream_object(git_indexer *idx, git_transfer_progress *stats)
+{
+	git_packfile_stream *stream = &idx->stream;
+	git_off_t entry_start = idx->off;
+	size_t entry_size;
+	git_otype type;
+	git_mwindow *w = NULL;
+	int error;
+
+	if (idx->pack->mwf.size <= idx->off + 20)
+		return GIT_EBUFS;
+
+	if (!idx->have_stream) {
+		error = git_packfile_unpack_header(&entry_size, &type, &idx->pack->mwf, &w, &idx->off);
+		if (error == GIT_EBUFS) {
+			idx->off = entry_start;
+			return error;
+		}
+		if (error < 0)
+			return error;
+
+		git_mwindow_close(&w);
+		idx->entry_start = entry_start;
+		git_hash_init(&idx->hash_ctx);
+
+		if (type == GIT_OBJ_REF_DELTA || type == GIT_OBJ_OFS_DELTA) {
+			error = advance_delta_offset(idx, type);
+			if (error == GIT_EBUFS) {
+				idx->off = entry_start;
+				return error;
+			}
+			if (error < 0)
+				return error;
+
+			idx->have_delta = 1;
+		} else {
+			idx->have_delta = 0;
+
+			error = hash_header(&idx->hash_ctx, entry_size, type);
+			if (error < 0)
+				return error;
+		}
+
+		idx->have_stream = 1;
+
+		error = git_packfile_stream_open(stream, idx->pack, idx->off);
+		if (error < 0)
+			return error;
+	}
+
+	if (idx->have_delta) {
+		error = read_object_stream(idx, stream);
+	} else {
+		error = hash_object_stream(idx, stream);
+	}
+
+	idx->off = stream->curpos;
+	if (error == GIT_EBUFS)
+		return error;
+
+	/* We want to free the stream reasorces no matter what here */
+	idx->have_stream = 0;
+	git_packfile_stream_dispose(stream);
+
+	if (error < 0)
+		return error;
+
+	if (idx->have_delta) {
+		error = store_delta(idx);
+	} else {
+		error = store_object(idx);
+	}
+
+	if (error < 0)
+		return error;
+
+	if (!idx->have_delta) {
+		stats->indexed_objects++;
+	}
+	stats->received_objects++;
+
+	if ((error = do_progress_callback(idx, stats)) != 0)
+		return error;
+
+	return 0;
+}
+
 int git_indexer_append(git_indexer *idx, const void *data, size_t size, git_transfer_progress *stats)
 {
 	int error = -1;
@@ -588,86 +675,12 @@ int git_indexer_append(git_indexer *idx, const void *data, size_t size, git_tran
 	git_mwindow_free_all(mwf);
 
 	while (stats->indexed_objects < idx->nr_objects) {
-		git_packfile_stream *stream = &idx->stream;
-		git_off_t entry_start = idx->off;
-		size_t entry_size;
-		git_otype type;
-		git_mwindow *w = NULL;
-
-		if (idx->pack->mwf.size <= idx->off + 20)
-			return 0;
-
-		if (!idx->have_stream) {
-			error = git_packfile_unpack_header(&entry_size, &type, mwf, &w, &idx->off);
-			if (error == GIT_EBUFS) {
-				idx->off = entry_start;
-				return 0;
-			}
-			if (error < 0)
+		if ((error = read_stream_object(idx, stats)) != 0) {
+			if (error == GIT_EBUFS)
+				break;
+			else
 				goto on_error;
-
-			git_mwindow_close(&w);
-			idx->entry_start = entry_start;
-			git_hash_init(&idx->hash_ctx);
-
-			if (type == GIT_OBJ_REF_DELTA || type == GIT_OBJ_OFS_DELTA) {
-				error = advance_delta_offset(idx, type);
-				if (error == GIT_EBUFS) {
-					idx->off = entry_start;
-					return 0;
-				}
-				if (error < 0)
-					goto on_error;
-
-				idx->have_delta = 1;
-			} else {
-				idx->have_delta = 0;
-
-				error = hash_header(&idx->hash_ctx, entry_size, type);
-				if (error < 0)
-					goto on_error;
-			}
-
-			idx->have_stream = 1;
-
-			error = git_packfile_stream_open(stream, idx->pack, idx->off);
-			if (error < 0)
-				goto on_error;
-		}
-
-		if (idx->have_delta) {
-			error = read_object_stream(idx, stream);
-		} else {
-			error = hash_object_stream(idx, stream);
 		}
-
-		idx->off = stream->curpos;
-		if (error == GIT_EBUFS)
-			return 0;
-
-		/* We want to free the stream reasorces no matter what here */
-		idx->have_stream = 0;
-		git_packfile_stream_dispose(stream);
-
-		if (error < 0)
-			goto on_error;
-
-		if (idx->have_delta) {
-			error = store_delta(idx);
-		} else {
-			error = store_object(idx);
-		}
-
-		if (error < 0)
-			goto on_error;
-
-		if (!idx->have_delta) {
-			stats->indexed_objects++;
-		}
-		stats->received_objects++;
-
-		if ((error = do_progress_callback(idx, stats)) != 0)
-			goto on_error;
 	}
 
 	return 0;