Method trySendExceptionToClient

src/Server/HTTPHandler.cpp:854–922

}

void HTTPHandler::trySendExceptionToClient(
    const std::string & s, int exception_code, HTTPServerRequest & request, HTTPServerResponse & response, Output & used_output)
{
    try
    {
        response.set("X-ClickHouse-Exception-Code", toString<int>(exception_code));

        /// FIXME: make sure that no one else is reading from the same stream at the moment.

        /// If HTTP method is POST and Keep-Alive is turned on, we should read the whole request body
        /// to avoid reading part of the current request body in the next request.
        if (request.getMethod() == Poco::Net::HTTPRequest::HTTP_POST
            && response.getKeepAlive()
            && exception_code != ErrorCodes::HTTP_LENGTH_REQUIRED
            && !request.getStream().eof())
        {
            request.getStream().ignoreAll();
        }

        if (exception_code == ErrorCodes::REQUIRED_PASSWORD)
        {
            response.requireAuthentication("ClickHouse server HTTP API");
        }
        else
        {
            response.setStatusAndReason(exceptionCodeToHTTPStatus(exception_code));
        }

        if (!response.sent() && !used_output.out_maybe_compressed)
        {
            /// If nothing was sent yet and we don't even know if we must compress the response.
            *response.send() << s << std::endl;
        }
        else if (used_output.out_maybe_compressed)
        {
            /// Destroy CascadeBuffer to actualize buffers' positions and reset extra references
            if (used_output.hasDelayed())
                used_output.out_maybe_delayed_and_compressed.reset();

            /// Send the error message into already used (and possibly compressed) stream.
            /// Note that the error message will possibly be sent after some data.
            /// Also HTTP code 200 could have already been sent.

            /// If buffer has data, and that data wasn't sent yet, then no need to send that data
            bool data_sent = used_output.out->count() != used_output.out->offset();

            if (!data_sent)
            {
                used_output.out_maybe_compressed->position() = used_output.out_maybe_compressed->buffer().begin();
                used_output.out->position() = used_output.out->buffer().begin();
            }

            writeString(s, *used_output.out_maybe_compressed);
            writeChar('\n', *used_output.out_maybe_compressed);

            used_output.out_maybe_compressed->next();
            used_output.out->finalize();
        }