odb: provide length and type with streaming read

The streaming read functionality should provide the length and the type
of the object, like the normal read functionality does.

include/git2/odb.h

@@ -357,11 +357,18 @@ GIT_EXTERN(void) git_odb_stream_free(git_odb_stream *stream);
  * @see git_odb_stream
  *
  * @param out pointer where to store the stream
+ * @param len pointer where to store the length of the object
+ * @param type pointer where to store the type of the object
  * @param db object database where the stream will read from
  * @param oid oid of the object the stream will read from
  * @return 0 if the stream was created; error code otherwise
  */
-GIT_EXTERN(int) git_odb_open_rstream(git_odb_stream **out, git_odb *db, const git_oid *oid);
+GIT_EXTERN(int) git_odb_open_rstream(
+	git_odb_stream **out,
+	size_t *len,
+	git_otype *type,
+	git_odb *db,
+	const git_oid *oid);
 
 /**
  * Open a stream for writing a pack file to the ODB.

include/git2/sys/odb_backend.h

@@ -56,7 +56,8 @@ struct git_odb_backend {
 		git_odb_stream **, git_odb_backend *, git_off_t, git_otype);
 
 	int (* readstream)(
-		git_odb_stream **, git_odb_backend *, const git_oid *);
+		git_odb_stream **, size_t *, git_otype *,
+		git_odb_backend *, const git_oid *);
 
 	int (* exists)(
 		git_odb_backend *, const git_oid *);

src/odb.c

@@ -1396,7 +1396,12 @@ void git_odb_stream_free(git_odb_stream *stream)
 	stream->free(stream);
 }
 
-int git_odb_open_rstream(git_odb_stream **stream, git_odb *db, const git_oid *oid)
+int git_odb_open_rstream(
+	git_odb_stream **stream,
+	size_t *len,
+	git_otype *type,
+	git_odb *db,
+	const git_oid *oid)
 {
 	size_t i, reads = 0;
 	int error = GIT_ERROR;
@@ -1409,7 +1414,7 @@ int git_odb_open_rstream(git_odb_stream **stream, git_odb *db, const git_oid *oi
 
 		if (b->readstream != NULL) {
 			++reads;
-			error = b->readstream(stream, b, oid);
+			error = b->readstream(stream, len, type, b, oid);
 		}
 	}