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e4a3e8c4d4
This adds an lws cmake option that builds all the minimal examples as part of lws, it's useful for QA. It adds a macro to examples that depend on a particular lws configuration to understand they should just null out their project definition in builds where the lws configuration requirement is not met, and we are building as part of lws. It also adapts all the example library additions to select the just-built-but-not-yet-installed library in the case it is built as part of lws. If built standalone, it now uses the cmake platform-abstracted way to add the library requirement too.
85 lines
3.7 KiB
Markdown
85 lines
3.7 KiB
Markdown
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http-server|Minimal examples providing an http server
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ws-server|Minimal examples providing a ws server (and an http server)
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http-client|Minimal examples providing an http client
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ws-client|Minimal examples providing a ws client
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client-server|Minimal examples providing client and server connections simultaneously
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## FAQ
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### Getting started
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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)
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Then start with the simplest:
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`http-server/minimal-http-server`
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### Why are most of the sources split into a main C file file and a protocol file?
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Lws supports three ways to implement the protocol callback code:
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- you can just add it all in the same source file
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- you can separate it as these examples do, and #include it
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into the main sources
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- you can build it as a standalone plugin that is discovered
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and loaded at runtime.
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The way these examples are structured, you can easily also build
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the protocol callback as a plugin just with a different
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CMakeLists.txt... see https://github.com/warmcat/libwebsockets/tree/master/plugin-standalone
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for an example.
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### Why would we want the protocol as a plugin?
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You will notice a lot of the main C code is the same boilerplate
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repeated for each example. The actual interesting part is in
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the protocol callback only.
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Lws provides (-DLWS_WITH_LWSWS=1) a generic lightweight server app called 'lwsws' that
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can be configured by JSON. Combined with your protocol as a plugin,
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it means you don't actually have to make a special server "app"
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part, you can just use lwsws and pass per-vhost configuration
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from JSON into your protocol. (Of course in some cases you have
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an existing app you are bolting lws on to, then you don't care
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about this for that particular case).
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Because lwsws has no dependency on whatever your plugin does, it
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can mix and match different protocols randomly without needing any code
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changes. It reduces the size of the task to just writing the
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code you care about in your protocol handler, and nothing else to write
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or maintain.
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Lwsws supports advanced features like reload, where it starts a new server
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instance with changed config or different plugins, while keeping the old
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instance around until the last connection to it closes.
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### I get why there is a pss, but why is there a vhd?
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The pss is instantiated per-connection. But there are almost always
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other variables that have a lifetime longer than a single connection.
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You could make these variables "filescope" one-time globals, but that
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means your protocol cannot instantiate multiple times.
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Lws supports vhosts (virtual hosts), for example both https://warmcat.com
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and https://libwebsockets are running on the same lwsws instance on the
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same server and same IP... each of these is a separate vhost.
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Your protocol may be enabled on multiple vhosts, each of these vhosts
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provides a different vhd specific to the protocol instance on that
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vhost. For example many of the samples keep a linked-list head to
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a list of live pss in the vhd... that means it's cleanly a list of
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pss opened **on that vhost**. If another vhost has the protocol
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enabled, connections to that will point to a different vhd, and the
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linked-list head on that vhd will only list connections to his vhost.
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The example "ws-server/minimal-ws-server-threads" demonstrates how to deliver
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external configuration data to a specific vhost + protocol
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combination using code. In lwsws, this is simply a matter of setting
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the desired JSON config.
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