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libwebsockets/minimal-examples
Andy Green 2cfa260e62 sspc: refactor to allow different transports
This is a NOP for existing usecases.

At the moment the only implemented transport for serialized SS is wsi, it's
typically used with Unix Domain Sockets, but it also works over tcp the
same.

It generalizes the interface between serialized chunks and the
transport, separately for client and proxy.  The wsi transport is migrated
to use the new transport ops structs.

It will then be possible to "bring your own transport", so long as it is
reliable, and in-order, both for proxy and client / sspc.

We also adapt minimal-secure-streams-binance to build the -client variant
via SS proxy as well.

LWS_ONLY_SSPC is added so libwebsockets can be produced with just sspc
client support even for tiny targets.

A new embedded minimal example for rpi pico is also provided that
demonstrates using Serialized SS over a UART to an SS proxy, to implement
the SS Binance example on the pico, even though it has no networking itself.
2021-10-08 09:48:41 +01:00
..
abstract/protocols/smtp-client cmake: latest cmake shows dep warnings for scripts < 2.8.12 2020-12-06 19:44:54 +00:00
api-tests dsh: coalesce 2021-10-08 09:48:41 +01:00
client-server Wextra 2021-07-04 10:29:54 +01:00
crypto cose: keys and signing + validation 2021-08-31 05:45:35 +01:00
dbus-client sai: xenial 2021-02-28 19:05:25 +00:00
dbus-server Wextra 2021-07-04 10:29:54 +01:00
embedded sspc: refactor to allow different transports 2021-10-08 09:48:41 +01:00
gtk/minimal-gtk ss: mass update LE root to isrg part 2 2021-10-05 06:48:03 +01:00
http-client cmake: unbreak LWS_WITH_SYS_STATE disabled build 2021-10-05 07:40:17 +01:00
http-server minimal: eventlib-custom: handle fds removal in service 2021-08-19 05:31:15 +01:00
mqtt-client mqtt: allow indicating client_id is not on heap 2021-10-05 07:09:47 +01:00
raw Wextra 2021-07-04 10:29:54 +01:00
secure-streams sspc: refactor to allow different transports 2021-10-08 09:48:41 +01:00
ws-client sspc: refactor to allow different transports 2021-10-08 09:48:41 +01:00
ws-server cmake: unbreak LWS_WITH_SYS_STATE disabled build 2021-10-05 07:40:17 +01:00
CMakeLists.txt cmakelist: Augean Stables refactor 2020-05-27 08:40:12 +01:00
README.md client: secure streams 2020-03-04 12:17:49 +00:00

name demonstrates
client-server Minimal examples providing client and server connections simultaneously
crypto Minimal examples related to using lws crypto apis
dbus-server Minimal examples showing how to integrate DBUS into lws event loop
http-client Minimal examples providing an http client
http-server Minimal examples providing an http server
raw Minimal examples related to adopting raw file or socket descriptors into the event loop
secure-streams Minimal examples related to the Secure Streams client api
ws-client Minimal examples providing a ws client
ws-server Minimal examples providing a ws server (and an http server)

FAQ

Getting started

Build and install lws itself first (note that after installing lws on *nix, you need to run ldconfig one time so the OS can learn about the new library. Lws installs in /usr/local by default, Debian / Ubuntu ldconfig knows to look there already, but Fedora / CentOS need you to add the line /usr/local/lib to /etc/ld.so.conf and run ldconfig)

Then start with the simplest:

http-server/minimal-http-server

Why are most of the sources split into a main C file file and a protocol file?

Lws supports three ways to implement the protocol callback code:

  • you can just add it all in the same source file

  • you can separate it as these examples do, and #include it into the main sources

  • you can build it as a standalone plugin that is discovered and loaded at runtime.

The way these examples are structured, you can easily also build the protocol callback as a plugin just with a different CMakeLists.txt... see https://github.com/warmcat/libwebsockets/tree/master/plugin-standalone for an example.

Why would we want the protocol as a plugin?

You will notice a lot of the main C code is the same boilerplate repeated for each example. The actual interesting part is in the protocol callback only.

Lws provides (-DLWS_WITH_LWSWS=1) a generic lightweight server app called 'lwsws' that can be configured by JSON. Combined with your protocol as a plugin, it means you don't actually have to make a special server "app" part, you can just use lwsws and pass per-vhost configuration from JSON into your protocol. (Of course in some cases you have an existing app you are bolting lws on to, then you don't care about this for that particular case).

Because lwsws has no dependency on whatever your plugin does, it can mix and match different protocols randomly without needing any code changes. It reduces the size of the task to just writing the code you care about in your protocol handler, and nothing else to write or maintain.

Lwsws supports advanced features like reload, where it starts a new server instance with changed config or different plugins, while keeping the old instance around until the last connection to it closes.

I get why there is a pss, but why is there a vhd?

The pss is instantiated per-connection. But there are almost always other variables that have a lifetime longer than a single connection.

You could make these variables "filescope" one-time globals, but that means your protocol cannot instantiate multiple times.

Lws supports vhosts (virtual hosts), for example both https://warmcat.com and https://libwebsockets are running on the same lwsws instance on the same server and same IP... each of these is a separate vhost.

Your protocol may be enabled on multiple vhosts, each of these vhosts provides a different vhd specific to the protocol instance on that vhost. For example many of the samples keep a linked-list head to a list of live pss in the vhd... that means it's cleanly a list of pss opened on that vhost. If another vhost has the protocol enabled, connections to that will point to a different vhd, and the linked-list head on that vhd will only list connections to his vhost.

The example "ws-server/minimal-ws-server-threads" demonstrates how to deliver external configuration data to a specific vhost + protocol combination using code. In lwsws, this is simply a matter of setting the desired JSON config.