Event lib support as it has been isn't scaling well, at the low level
libevent and libev headers have a namespace conflict so they can't
both be built into the same image, and at the distro level, binding
all the event libs to libwebsockets.so makes a bloaty situation for
packaging, lws will drag in all the event libs every time.
This patch implements the plan discussed here
https://github.com/warmcat/libwebsockets/issues/1980
and refactors the event lib support so they are built into isolated
plugins and bound at runtime according to what the application says
it wants to use. The event lib plugins can be packaged individually
so that only the needed sets of support are installed (perhaps none
of them if the user code is OK with the default poll() loop). And
dependent user code can mark the specific event loop plugin package
as required so pieces are added as needed.
The eventlib-foreign example is also refactored to build the selected
lib support isolated.
A readme is added detailing the changes and how to use them.
https://libwebsockets.org/git/libwebsockets/tree/READMEs/README.event-libs.md
Move the common plugin scanning dir stuff to be based on lws_dir, which
already builds for windows. Previously this was done via dirent for unix
and libuv for windows.
Reduce the dl plat stuff to just wrap instantiation and destruction of
dynlibs, establish common code in lib/misc/dir.c for plugin scanning
itself.
Migrate the libuv windows dl stuff to windows-plugins.c, so that he's
available even if later libuv loop support becomes and event lib plugin.
Remove the existing api exports scheme for plugins, just export a const struct
now which has a fixed header type but then whatever you want afterwards depending
on the class / purpose of the plugin. Place a "class" string in the header so
there can be different kinds of plugins implying different types exported.
Make the plugin apis public and add support for filter by class string, and
per instantation / destruction callbacks so the subclassed header type can
do its thing for the plugin class. The user provides a linked-list base
for his class of plugins, so he can manage them completely separately and
in user code / user export types.
Rip out some last hangers-on from generic sessions / tables.
This is all aimed at making the plugins support general enough so it can
provide event lib plugins later.
Currently we always reserve a fakewsi per pt so events that don't have a related actual
wsi, like vhost-protocol-init or vhost cert init via protocol callback can make callbacks
that look reasonable to user protocol handler code expecting a valid wsi every time.
This patch splits out stuff that user callbacks often unconditionally expect to be in
a wsi, like context pointer, vhost pointer etc into a substructure, which is composed
into struct lws at the top of it. Internal references (struct lws is opaque, so there
are only internal references) are all updated to go via the substructre, the compiler
should make that a NOP.
Helpers are added when fakewsi is used and referenced.
If not PLAT_FREERTOS, we continue to provide a full fakewsi in the pt as before,
although the helpers improve consistency by zeroing down the substructure. There is
a huge amount of user code out there over the last 10 years that did not always have
the minimal examples to follow, some of it does some unexpected things.
If it is PLAT_FREERTOS, that is a newer thing in lws and users have the benefit of
being able to follow the minimal examples' approach. For PLAT_FREERTOS we don't
reserve the fakewsi in the pt any more, saving around 800 bytes. The helpers then
create a struct lws_a (the substructure) on the stack, zero it down (but it is only
like 4 pointers) and prepare it with whatever we know like the context.
Then we cast it to a struct lws * and use it in the user protocol handler call.
In this case, the remainder of the struct lws is undefined. However the amount of
old protocol handlers that might touch things outside of the substructure in
PLAT_FREERTOS is very limited compared to legacy lws user code and the saving is
significant on constrained devices.
User handlers should not be touching everything in a wsi every time anyway, there
are several cases where there is no valid wsi to do the call with. Dereference of
things outside the substructure should only happen when the callback reason shows
there is a valid wsi bound to the activity (as in all the minimal examples).
This has no effect on user code or backward compatibility.
It moves the in-tree public api header libwebsockets.h from ./lib
to ./include, and introduces a dir ./include/libwebsockets/
The single public api header is split out into 31 sub-headers
in ./include/libwebsockets. ./include/libwebsockets.h contains
some core types and platform adaptation code, but the rest of it
is now 31 #include <libwebsockets/...>
At install time, /usr/[local/]include/libwebsockets.h is installed
as before, along now with the 31 sub-headers in ...include/libwebsockets/
There's no net effect on user code.
But the api header is now much easier to maintain and study, with 31
topic-based sub headers.
