fix: Include Content-Range header in 416 responses (#3)

Per RFC 7233 §4.4 and real GCS behavior, a 416 (Range Not Satisfiable)
response should include Content-Range: bytes */<length> so clients know
the actual object size and can adjust their requests.

The testbench was raising the error before reaching the header-setting
code, so the Content-Range header was never included. Fix by threading
the object length through range_not_satisfiable() and RestException.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: lcian

gcs/object.py

@@ -504,7 +504,7 @@ def rest_media(self, request, delay=time.sleep):
         )
         # Return 416 if the requested range cannot be satisfied.
         if range_header is not None and begin >= length:
-            testbench.error.range_not_satisfiable()
+            testbench.error.range_not_satisfiable(length=length)
 
         headers = {}
         content_range = "bytes %d-%d/%d" % (begin, end - 1, length)

testbench/error.py

@@ -23,20 +23,24 @@
 
 
 class RestException(Exception):
-    def __init__(self, msg, code):
+    def __init__(self, msg, code, headers=None):
         super().__init__()
         self.msg = msg
         self.code = code
+        self.headers = headers or {}
 
     def as_response(self):
         # Include both code and message so we follow the schema outlined in
         # https://cloud.google.com/apis/design/errors#error_model and some
         # clients depend on code being specified, otherwise behavior is
         # undefined.
-        return flask.make_response(
+        response = flask.make_response(
             flask.jsonify(error={"code": self.code, "message": self.msg}),
             self.code,
         )
+        for key, value in self.headers.items():
+            response.headers[key] = value
+        return response
 
     @staticmethod
     def handler(ex):
@@ -53,12 +57,12 @@ def _simple_json_error(msg):
     return json.dumps({"error": {"errors": [{"domain": "global", "message": msg}]}})
 
 
-def generic(msg, rest_code, grpc_code, context):
+def generic(msg, rest_code, grpc_code, context, headers=None):
     """Generate the appropriate error for REST or gRPC handlers."""
     if context is not None:
         context.abort(grpc_code, msg)
     else:
-        raise RestException(msg, rest_code)
+        raise RestException(msg, rest_code, headers=headers)
 
 
 def csek(context, rest_code=400, grpc_code=grpc.StatusCode.INVALID_ARGUMENT):
@@ -150,14 +154,20 @@ def already_exists(context=None):
 
 
 def range_not_satisfiable(
-    context=None, rest_code=416, grpc_code=grpc.StatusCode.OUT_OF_RANGE
+    length=None, context=None, rest_code=416, grpc_code=grpc.StatusCode.OUT_OF_RANGE
 ):
-    """Error returned when request range is not satisfiable."""
+    """Error returned when request range is not satisfiable.
+
+    Includes a Content-Range: bytes */<length> header when length is provided,
+    matching real GCS behavior per RFC 7233.
+    """
+    headers = {"Content-Range": "bytes */%d" % length} if length is not None else None
     generic(
         _simple_json_error("request range not satisfiable"),
         rest_code,
         grpc_code,
         context,
+        headers=headers,
     )
 
 

testbench/grpc_server.py

@@ -593,7 +593,9 @@ def ReadObject(self, request, context):
         start = request.read_offset
         read_end = len(blob.media)
         if start > read_end:
-            return testbench.error.range_not_satisfiable(context)
+            return testbench.error.range_not_satisfiable(
+                length=read_end, context=context
+            )
         if request.read_limit > 0:
             read_end = min(read_end, start + request.read_limit)
         content_range = None