Archived
3
0
This repository has been archived on 2024-06-18. You can view files and clone it, but cannot push or open issues or pull requests.
libipc-old/docs/libipc.md

330 lines
7.6 KiB
Markdown
Raw Normal View History

2020-12-09 15:33:54 +01:00
## Before starting
This file is a presentation.
Better get the point tools here: https://git.baguette.netlib.re/Baguette/pointtools
2023-01-20 22:35:19 +01:00
TODO: Explain the problem
TODO: Explain the solution
TODO: Explain why LibIPC
TODO: Explain how LibIPC
TODO: Explain other possible implementations
TODO: Explain future of LibIPC
TODO: Explain what can be done right now
TODO: Explain what I actually do with it
TODO: Explain LibIPC isn't a silver bullet but fine for what I want
2020-12-09 15:33:54 +01:00
Have fun!
2023-01-20 22:35:19 +01:00
## Programming problems
2020-12-09 15:33:54 +01:00
2023-01-20 22:35:19 +01:00
Libraries
* change often = hard to follow
* don't often provide a high-level interface
* each library is coded in its own way
* availability vary depending on the language
2020-12-09 15:33:54 +01:00
2023-01-20 22:35:19 +01:00
Example: libraries to access databases
* languages often have their own implementation
* functions may vary from a language to another
2020-12-09 15:33:54 +01:00
2023-01-20 22:35:19 +01:00
## Infrastructure problems
Infrastructure
* Always need to install all required libraries
* No clear way to sandbox part of an application
## What solution?
MAKE APPLICATIONS, NOT LIBRARIES
* apps talking to apps
Create an abstraction for
libraries
* languages, implementations, code modifications in general
network code
* networking: performed by dedicated services
- example: TCPd, UDPd, TLSd, HTTPd...
- LibIPC is independant from protocols and formats
* applications think communications are local
2020-12-09 15:33:54 +01:00
## In practice
usage must be simple
1. init connection or service
2. loop over events
#pause
events are simple and high level
1. connection and disconnection
2. message received and sent
2023-01-20 22:35:19 +01:00
#pause
message have a simple format: length + value
#pause
And that's it.
## When
LibIPC is useful when the app:
- cannot be a simple shell command
- needs a bidirectional communication
- is an abstraction over a library
2020-12-09 15:33:54 +01:00
## Available libraries
* DBUS
2023-01-20 22:35:19 +01:00
* libevent
2020-12-09 15:33:54 +01:00
* even more complicated stuff
* RPC-style, like Corba
#pause
* ... or bare libc api
2023-01-20 22:35:19 +01:00
* shared memory
2020-12-09 15:33:54 +01:00
* pipes
* sockets (unix, inet, inet6)
## DBUS
* not well suited for our needs
(a polite way to say: what a bloody mess)
Is it designed *NOT* to be used?
* over-engineered
* complex
* documentation isn't great
* no code example
## DBUS (bonus page!)
DBUS feels obsolete: a big chunk of the documentation is
2020-12-09 15:33:54 +01:00
about message format. Just use CBOR already!
#pause
2020-12-09 15:33:54 +01:00
They even admit they did a poor job on the C part:
> There is a low-level C binding, but that is probably too detailed
> and cumbersome for anything but writing other bindings.
#pause
2020-12-09 15:33:54 +01:00
Oh. And C++. YOU SHALL NOT PASS!
This is a Linux requirement nowadays, wth?
2023-01-20 22:35:19 +01:00
## libevent
* works with epoll and kqueue
* great performances
* works on Linux and *BSD
* a bit complicated
2020-12-09 15:33:54 +01:00
## Bare libc api
shared memory and semaphores
* (kinda) complicated api
* not about exchanging messages
pipes, sockets
* lack a conventional message format
... but that's about it
* Great to start with!
All have great performances to exchange data.
2020-12-09 15:33:54 +01:00
What is slow is the function to _wait_ for new events.
2020-12-09 15:33:54 +01:00
2023-01-20 22:35:19 +01:00
## LibIPC's choice
Unix sockets
- fast, simple, reliable, bidirectional
- remote connections will have their own service (ex: TCPd)
Dumbest possible message format
- length + value
- build your own format on top of it!
Wait on file descriptors with poll(2)
- slow, but available everywhere
- may upgrade to libevent
## LibIPC history (1/2)
2020-12-09 15:33:54 +01:00
1. based on pipes
* because we gotta go fast!
* ... but implementation was a bit of a mess
#pause
2. rewrite to work with unix sockets
2023-01-20 22:35:19 +01:00
* performances are excellent, no need for _absolute best_
2020-12-09 15:33:54 +01:00
* way nicer implementation
* select(2) for listening on file descriptors
#pause
* ... wait, does select(2) support more than 1024 connections?
2023-01-20 22:35:19 +01:00
## LibIPC history (2/2)
2020-12-09 15:33:54 +01:00
3. rewrite using poll(2)
* many bugfixes later, way more tested than before
2023-01-20 22:35:19 +01:00
* implementation was (kinda) production-ready
* implementation was simple: < 2000 lines of C code
2020-12-09 15:33:54 +01:00
2023-01-20 22:35:19 +01:00
Still wasn't as simple as I wanted
2020-12-09 15:33:54 +01:00
## Current implementation of libIPC
2023-01-20 22:35:19 +01:00
Written in Zig
bindings available in Crystal
2020-12-09 15:33:54 +01:00
* as well as fancy mappings: JSON and CBOR class serialization
#pause
epoll (Linux) and kqueue (*BSD) were avoided
* 'cause callbacks hell => harder to read and to write code
#pause
* but we need them for better performances with many connections
though, API should stay the same for non threaded applications (simple implementation)
#pause
LibIPC doesn't handle parallelism, yet
## How libIPC works
LibIPC has a high level API for the user
1. init a connection (client) or create an unix socket (service)
2023-01-20 22:35:19 +01:00
example: ipc_service_init (context, "service")
2020-12-09 15:33:54 +01:00
#pause
2. loop, wait for events
listening to file descriptors (libIPC ones or not)
example:
2020-12-09 15:33:54 +01:00
while(1) {
wait_event (context, &event, &timer)
switch (event.type) {
2023-01-20 22:35:19 +01:00
case IPC_CONNECTION : ...
case IPC_DISCONNECTION : ...
case IPC_MESSAGE: {
2020-12-09 15:33:54 +01:00
struct ipc_message *m = event.m;
...
}
}
}
## How libIPC works
3. send messages
```c
2020-12-09 15:33:54 +01:00
struct ipc_message m
m.payload = ...
m.length = strlen(m.payload)
m.fd = event.fd
m.type = ...
m.user_type = ...
ipc_write (context, &m)
```
2020-12-09 15:33:54 +01:00
#pause
4. add and remove fd from the context
ipc_add_fd (context, fd)
ipc_del_fd (context, fd)
## How libIPC works
LibIPC also helps to create "protocol daemons" like TCPd with
automatic switching between file descriptors
LibIPC takes callbacks to obtain libipc payloads inside arbitrary message structure
Example: websocketd.
Clients exchange data with a libipc service through websockets messages.
websocketd binds both the client and its service file descriptors,
then provides the libipc a callback to extract libipc messages from
the websocket messages sent by the client.
Same thing the other way.
ipc_switching_callbacks (context, client_fd, cb_in, cb_out)
## libIPC internal structures
Main goal: simplest possible structures
Examples:
Message
2020-12-09 15:33:54 +01:00
struct ipc_message {
char type; => Internal message type, used by protocol daemons.
char user_type; => User-defined message type (arbitrary).
int fd; => File descriptor concerned about this message.
uint32_t length; => Payload length.
char *payload; => Actual payload.
};
Context of the whole networking state
2020-12-09 15:33:54 +01:00
struct ipc_ctx {
struct ipc_connection_info *cinfos; => Keeps track of connections.
struct pollfd *pollfd; => List of "pollfd" structures within cinfos,
so we can pass it to poll(2).
size_t size; => Size of the connection list.
struct ipc_messages tx; => Messages to send.
struct ipc_switchings switchdb; => Relations between fd.
};
## Future of libIPC
LibIPC will be rewritten in Zig
* simpler to read and write
* data structures are simpler to create with comptime
* less code redundancy (more generic functions)
* already existing error management as written in current libIPC
* already existing loggin system
* no more C's pitfalls
* way better at exposing bugs
* thanks to a better type system
* way safer: cannot ignore errors
* so I won't
* simpler to cross-compile: same standard library for every OSs
* simpler (and more secure) memory management
Also: this won't change existing bindings! No excuses!
## Why not use it?
Current limitations
* performances (libIPC is based on poll(2), not epoll nor kqueue)
* it really isn't an issue until you have hundreds or thousands of clients
* parallelism is not permitted
nothing in libIPC is thread-safe
The future Zig implementation will overcome these issues.
## Questions?
Ask! `karchnu at karchnu.fr`