Add a test for non-zero content-length header in a 304 response (inha…

…bitedtype#88)

similar to what we tested for in inhabitedtype#87

lib/response.ml

@@ -56,7 +56,15 @@ let proxy_error  = `Error `Bad_gateway
 let server_error = `Error `Internal_server_error
 let body_length ?(proxy=false) ~request_method { status; headers; _ } =
   match status, request_method with
-  | (`No_content | `Not_modified), _           -> `Fixed 0L
+  | (`No_content | `Not_modified), _           ->
+    (* From RFC7230§3.3.2:
+         A server MAY send a Content-Length header field in a 304 (Not
+         Modified) response to a conditional GET request (Section 4.1 of
+         [RFC7232]); a server MUST NOT send Content-Length in such a response
+         unless its field-value equals the decimal number of octets that would
+         have been sent in the payload body of a 200 (OK) response to the same
+         request. *)
+    `Fixed 0L
   | _, `HEAD                                   ->
     (* From RFC7230§3.3.2:
          A server MAY send a Content-Length header field in a response to a

lib_test/test_client_connection.ml

@@ -1377,6 +1377,31 @@ let test_chunked_error () =
   connection_is_shutdown t;
 ;;
 
+let test_304_not_modified () =
+  let error_handler_called = ref false in
+  let request' = Request.create `GET "/" in
+  let response = Response.create
+      ~headers:(Headers.of_list ["content-length", "5"])
+      `Not_modified
+  in
+
+  let t = create ?config:None in
+  let body =
+    request
+      t
+      request'
+      ~response_handler:(default_response_handler response)
+      ~error_handler:(fun _ -> error_handler_called := true)
+  in
+  Body.close_writer body;
+  write_request t request';
+  read_response t response;
+  let c = read_eof t Bigstringaf.empty ~off:0 ~len:0 in
+  Alcotest.(check int) "read_eof with no input returns 0" 0 c;
+  connection_is_shutdown t;
+  Alcotest.(check bool) "error handler not called" false !error_handler_called;
+;;
+
 let tests =
   [ "commit parse after every header line", `Quick, test_commit_parse_after_every_header
   ; "GET"         , `Quick, test_get
@@ -1412,4 +1437,5 @@ let tests =
   ; "reader EOF race condition causes state machine to issue writer yield", `Quick, test_race_condition_writer_issues_yield_after_reader_eof
   ; "multiple responses in single read", `Quick, test_multiple_responses_in_single_read
   ; "test chunked error", `Quick, test_chunked_error
+  ; "304 Not Modified with Content-Length", `Quick, test_304_not_modified
   ]

nix/sources.nix

@@ -3,7 +3,7 @@
 let
   overlays =
     builtins.fetchTarball
-      https://github.com/anmonteiro/nix-overlays/archive/ce6fc101.tar.gz;
+      https://github.com/anmonteiro/nix-overlays/archive/7fc23e0.tar.gz;
 
 in