odb/source: make write_object_stream() function pluggable

Introduce a new callback function in `struct odb_source` to make the
function pluggable.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

odb.c

@@ -1013,7 +1013,7 @@ int odb_write_object_stream(struct object_database *odb,
 			    struct odb_write_stream *stream, size_t len,
 			    struct object_id *oid)
 {
-	return odb_source_loose_write_stream(odb->sources, stream, len, oid);
+	return odb_source_write_object_stream(odb->sources, stream, len, oid);
 }
 
 struct object_database *odb_new(struct repository *repo,

odb/source-files.c

@@ -109,6 +109,14 @@ static int odb_source_files_write_object(struct odb_source *source,
 					     oid, compat_oid, flags);
 }
 
+static int odb_source_files_write_object_stream(struct odb_source *source,
+						struct odb_write_stream *stream,
+						size_t len,
+						struct object_id *oid)
+{
+	return odb_source_loose_write_stream(source, stream, len, oid);
+}
+
 struct odb_source_files *odb_source_files_new(struct object_database *odb,
 					      const char *path,
 					      bool local)
@@ -128,6 +136,7 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
 	files->base.for_each_object = odb_source_files_for_each_object;
 	files->base.freshen_object = odb_source_files_freshen_object;
 	files->base.write_object = odb_source_files_write_object;
+	files->base.write_object_stream = odb_source_files_write_object_stream;
 
 	/*
 	 * Ideally, we would only ever store absolute paths in the source. This

odb/source.h

@@ -53,6 +53,7 @@ enum object_info_flags {
 struct object_id;
 struct object_info;
 struct odb_read_stream;
+struct odb_write_stream;
 
 /*
  * A callback function that can be used to iterate through objects. If given,
@@ -218,6 +219,18 @@ struct odb_source {
 			    struct object_id *oid,
 			    struct object_id *compat_oid,
 			    unsigned flags);
+
+	/*
+	 * This callback is expected to persist the given object stream into
+	 * the object source.
+	 *
+	 * The resulting object ID shall be written into the out pointer. The
+	 * callback is expected to return 0 on success, a negative error code
+	 * otherwise.
+	 */
+	int (*write_object_stream)(struct odb_source *source,
+				   struct odb_write_stream *stream, size_t len,
+				   struct object_id *oid);
 };
 
 /*
@@ -356,4 +369,19 @@ static inline int odb_source_write_object(struct odb_source *source,
 				    compat_oid, flags);
 }
 
+/*
+ * Write an object into the object database source via a stream. The overall
+ * length of the object must be known in advance.
+ *
+ * Return 0 on success, a negative error code otherwise. Populates the given
+ * out pointer for the object ID.
+ */
+static inline int odb_source_write_object_stream(struct odb_source *source,
+						 struct odb_write_stream *stream,
+						 size_t len,
+						 struct object_id *oid)
+{
+	return source->write_object_stream(source, stream, len, oid);
+}
+
 #endif