Fix handling for spurious msgs and protocol errors

This fix prevents us from sending back a 400 error in response to
unexpected messages that may come in. The intent in the original
catch-all clause seems to be to match on TCP or SSL errors, but if we
get some other unexpected message coming in from the application layer,
then that will also trigger the catch-all. This can have especially bad
consequences if keepalives are enabled, as we may end up sending both a
valid response AND a 400 on the same connection for a single request.

At the same time, not all TCP/SSL errors necessarily warrant a 400
response, so most errors will now simply trigger us to close the socket.
The exception is emsgsize errors, since this typically comes from the
packet decoder, suggesting that there is indeed actually a problem with
the client request itself. This is also the only such case that is
explicitly tested in the eunit test code, so that behavior is maintained
with no need to fix any tests.

src/mochiweb_http.erl

@@ -72,8 +72,17 @@ request(Socket, Body) ->
         {ssl_closed, _} ->
             mochiweb_socket:close(Socket),
             exit(normal);
+        Msg = {ProtocolErr, _Socket, emsgsize} when
+              ProtocolErr =:= tcp_error ; ProtocolErr =:= ssl_error ->
+            handle_invalid_msg_request(Msg, Socket);
+        {ProtocolErr, _Socket, _Reason} when
+              ProtocolErr =:= tcp_error ; ProtocolErr =:= ssl_error ->
+            mochiweb_socket:close(Socket),
+            exit(normal);
         Other ->
-            handle_invalid_msg_request(Other, Socket)
+            error_logger:warning_msg("Got unexpected (leftover) message: ~w (to pid=~w)~n",
+                                     [Other, self()]),
+            request(Socket, Body)
     after ?REQUEST_RECV_TIMEOUT ->
         mochiweb_socket:close(Socket),
         exit(normal)
@@ -101,8 +110,19 @@ headers(Socket, Request, Headers, Body, HeaderCount) ->
         {tcp_closed, _} ->
             mochiweb_socket:close(Socket),
             exit(normal);
+        Msg = {ProtocolErr, _Socket, emsgsize} when
+              ProtocolErr =:= tcp_error ; ProtocolErr =:= ssl_error ->
+            handle_invalid_msg_request(Msg, Socket);
+        Msg = {ProtocolErr, _Socket, _Reason} when
+              ProtocolErr =:= tcp_error ; ProtocolErr =:= ssl_error ->
+            error_logger:warning_msg("Got unexpected TCP error message: ~w (to pid=~w)~n",
+                                     [Msg, self()]),
+            mochiweb_socket:close(Socket),
+            exit(normal);
         Other ->
-            handle_invalid_msg_request(Other, Socket, Request, Headers)
+            error_logger:warning_msg("Got unexpected (leftover) message: ~w (to pid=~w)~n",
+                                     [Other, self()]),
+            headers(Socket, Request, Headers, Body, HeaderCount)
     after ?HEADERS_RECV_TIMEOUT ->
         mochiweb_socket:close(Socket),
         exit(normal)