Fix bug related to requests in the same buffer (inhabitedtype#91)

When the remainder of one request body is the start of the buffer where
the subsequent request is stored, the first request needs to be taken
out of the request queue, otherwise the server could hang forever.

lib/server_connection.ml

@@ -260,10 +260,15 @@ and _final_read_operation_for t reqd =
        * non-empty `request_queue` has had the request handler called on its
        * head element. *)
        match Reader.next t.reader with
-       | `Error _ | `Read as operation ->
+       | `Error _ as op ->
          (* Keep reading when in a "partial" state (`Read).
           * Don't advance the request queue if in an error state. *)
-         operation
+         op
+       | `Read as op ->
+         (* we just don't advance the request queue in the case of a parser
+           error. *)
+         advance_request_queue t;
+         op
        | _ ->
          advance_request_queue t;
          _next_read_operation t

lib_test/test_server_connection.ml

@@ -1809,6 +1809,22 @@ let test_response_finished_before_body_read () =
   write_response t response ~body:"done";
 ;;
 
+let test_pipelined_requests_answer_before_reading_body () =
+  let response = Response.create `OK ~headers:(Headers.encoding_fixed 0) in
+  let request_handler reqd =
+    let response =
+      Response.create ~headers:(Headers.of_list ["content-length", "0"]) `OK
+    in
+    Reqd.respond_with_string reqd response ""
+  in
+  let t = create request_handler in
+  read_request t (Request.create `GET "/" ~headers:(Headers.encoding_fixed 5));
+  write_response t response;
+  (* Finish the request and send another *)
+  read_string t "helloGET / HTTP/1.1\r\nhost: localhost\r\ncontent-length: 5\r\n\r\n";
+  write_response t response;
+;;
+
 let tests =
   [ "initial reader state"  , `Quick, test_initial_reader_state
   ; "shutdown reader closed", `Quick, test_reader_is_closed_after_eof
@@ -1869,4 +1885,5 @@ let tests =
   ; "multiple requests with connection close", `Quick, test_multiple_requests_in_single_read_with_close
   ; "parse failure after checkpoint", `Quick, test_parse_failure_after_checkpoint
   ; "response finished before body read", `Quick, test_response_finished_before_body_read
+  ; "pipelined", `Quick, test_pipelined_requests_answer_before_reading_body
   ]