Week 2

This week was all about MHD code analysis and design of the new API.

MHD code

• function MHD_start_daemon_va: starts the web server

  • Parses options parse_options_va()
  • (if https) Initializes HTTPS certificates
  • bind()s and listen()s
  • Creates the thread that runs the epoll/poll/select loop (until the daemon is explicitly shut down)

• In the event processing function, the following functions are called:

  • MHD_accept_connection: accept()s an incoming connection.
  • internal_add_connection: creates an MHD_Connection object, set the receive and send callbacks (see next item), and inserts the connection in the connections list.
  • MHD_set_http_callbacks_ / MHD_set_https_callbacks: set recv_cls and send_cls callbacks, functions for reading requests and writing responses:
    • http: recv_param_adapter, send_param_adapter
    • https: recv_tls_adapter, send_tls_adapter

• Connection handlers (both HTTP and HTTPS):

  • MHD_connection_handle_read: reads data from socket to read_buffer by calling recv_cls.
  • MHD_connection_handle_idle: parses data from read_buffer. Expects HTTP/1 syntax.
  • MHD_connection_handle_write: writes data to socket by calling send_cls

Connection states

These are the different states that a connection can be in:

Connection state: Request

Connection state: Response

Design

List inspired by The practice of programming:

• Interfaces: what services and access are provided?
  • connection_http2.c: handles a single HTTP/2 connection (session), with its own streams, frames, flow control, prioritization and server push services. Defines its own MHD_connection_handle_read, MHD_connection_handle_idle and MHD_connection_handle_write HTTP2 functions.
• Information hiding: what is visible? what is private?
  • Visible: same API as in connection.h:
    • MHD_set_http_callbacks_
    • MHD_connection_handle_read
    • MHD_connection_handle_write
    • MHD_connection_handle_idle
    • MHD_connection_mark_closed_
    • MHD_connection_close_
    • MHD_connection_finish_forward_
    • MHD_connection_epoll_update_
    • MHD_update_last_activity_
  • Private:
    • Session (connection) data
    • Streams: add, remove from session (stored in a DLL)
    • Set nghttp2_session_callbacks
    • Send and receive data from nghttp2 library
• Resource management: memory, shared information, sockets.
  • As in connection.c
• Error handling: detect, report, how? Recovery.
  • As in connection.c