Add libIPC presentation.
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@ -5,6 +5,8 @@ libipc - Simple, easy-to-use IPC library
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See the introductory man page in `man/libipc.7`.
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See the presentation in [docs/presentation.md](docs/presentation.md).
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> This library is a work in progress, but is already used intensively in production.
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> It works, but we provide no warranty.
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docs/libipc.md
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docs/libipc.md
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## Before starting
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This file is a presentation.
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Better get the point tools here: https://git.baguette.netlib.re/Baguette/pointtools
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Have fun!
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## Why libIPC?
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Network code separation
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* networking: performed by dedicated services
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* other applications: think all communications are local
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Library code separation
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* make libraries language independent
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* micro-services are great, each of them does its part
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why not on base systems?
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Applications are better than libraries
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* implementations change
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* languages change
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* API… not so much (not as often at least)
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## Available libraries
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* libevent
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* DBUS
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* even more complicated stuff
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* RPC-style, like Corba
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#pause
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* ... or bare libc api
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* pipes
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* sockets (unix, inet, inet6)
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* shared memory
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## libevent
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* works with epoll and kqueue
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* great performances
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* works on Linux and *BSD
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* a bit complicated at first
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## DBUS
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* not well suited for our needs
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(a polite way to say: what a bloody mess)
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Is it designed *NOT* to be used?
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* over-engineered
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* complex
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* documentation isn't great
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* no code example
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And kinda obsolete: a big chunk of the documentation is
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about message format. Just use CBOR already!
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They even admit they did a poor job on the C part:
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> There is a low-level C binding, but that is probably too detailed
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> and cumbersome for anything but writing other bindings.
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Oh. And C++. YOU SHALL NOT PASS!
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This is a Linux requirement nowadays, wth?
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## Bare libc api
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All have great performances
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shared memory and semaphores
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* (kinda) complicated api
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* not about exchanging messages
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pipes, sockets
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* lack a conventional message format
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... but that's about it
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Great to start with!
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## LibIPC history
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1. based on pipes
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* because we gotta go fast!
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* ... but implementation was a bit of a mess
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#pause
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2. rewrite to work with unix sockets
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* performances are excellent, no need for absolute best
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* way nicer implementation
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* select(2) for listening on file descriptors
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#pause
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* ... wait, does select(2) support more than 1024 connections?
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#pause
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3. rewrite using poll(2)
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* many bugfixes later, way more tested than before
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* implementation now kinda production-ready
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* enough for altideal.com at least
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## Current implementation of libIPC
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implementation is simple: < 2000 lines of C code
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usage is simple
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1. init connection or server
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2. loop over events
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bindings are available in Crystal
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* as well as fancy mappings: JSON and CBOR class serialization
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#pause
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epoll (Linux) and kqueue (*BSD) were avoided
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* 'cause callbacks hell => harder to read and to write code
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#pause
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* but we need them for better performances with many connections
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though, API should stay the same for non threaded applications (simple implementation)
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#pause
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LibIPC doesn't handle parallelism, yet
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## How libIPC works
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LibIPC has a high level API for the user
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1. init a connection (client) or create an unix socket (service)
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example: ipc_server_init (context, "service")
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#pause
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2. loop, wait for events
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listening to file descriptors (libIPC ones or not)
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example:
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while(1) {
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wait_event (context, &event, &timer)
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switch (event.type) {
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case IPC_EVENT_TYPE_CONNECTION : ...
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case IPC_EVENT_TYPE_DISCONNECTION : ...
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case IPC_EVENT_TYPE_MESSAGE: {
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struct ipc_message *m = event.m;
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...
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}
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}
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}
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## How libIPC works
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3. send messages
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struct ipc_message m
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m.payload = ...
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m.length = strlen(m.payload)
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m.fd = event.fd
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m.type = ...
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m.user_type = ...
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ipc_write (context, &m)
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#pause
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4. add and remove fd from the context
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ipc_add_fd (context, fd)
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ipc_del_fd (context, fd)
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## How libIPC works
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LibIPC also helps to create "protocol daemons" like TCPd with
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automatic switching between file descriptors
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LibIPC takes callbacks to obtain libipc payloads inside arbitrary message structure
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Example: websocketd.
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Clients exchange data with a libipc service through websockets messages.
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websocketd binds both the client and its service file descriptors,
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then provides the libipc a callback to extract libipc messages from
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the websocket messages sent by the client.
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Same thing the other way.
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ipc_switching_callbacks (context, client_fd, cb_in, cb_out)
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## libIPC internal structures
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Main goal: simplest possible structures
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Examples:
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Message
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struct ipc_message {
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char type; => Internal message type, used by protocol daemons.
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char user_type; => User-defined message type (arbitrary).
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int fd; => File descriptor concerned about this message.
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uint32_t length; => Payload length.
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char *payload; => Actual payload.
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};
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Context of the whole networking state
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struct ipc_ctx {
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struct ipc_connection_info *cinfos; => Keeps track of connections.
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struct pollfd *pollfd; => List of "pollfd" structures within cinfos,
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so we can pass it to poll(2).
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size_t size; => Size of the connection list.
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struct ipc_messages tx; => Messages to send.
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struct ipc_switchings switchdb; => Relations between fd.
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};
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## Future of libIPC
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LibIPC will be rewritten in Zig
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* simpler to read and write
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* data structures are simpler to create with comptime
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* less code redundancy (more generic functions)
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* already existing error management as written in current libIPC
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* already existing loggin system
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* no more C's pitfalls
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* way better at exposing bugs
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* thanks to a better type system
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* way safer: cannot ignore errors
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* so I won't
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* simpler to cross-compile: same standard library for every OSs
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* simpler (and more secure) memory management
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Also: this won't change existing bindings! No excuses!
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## Why not use it?
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Current limitations
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* performances (libIPC is based on poll(2), not epoll nor kqueue)
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* it really isn't an issue until you have hundreds or thousands of clients
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* parallelism is not permitted
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nothing in libIPC is thread-safe
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The future Zig implementation will overcome these issues.
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## Questions?
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Ask! `karchnu at karchnu.fr`
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