Archive for the ‘libwebsockets’ Category

libwebsockets new features

Sunday, March 6th, 2011

More platforms

In addition to Linux, there are now users of libwebsockets on win32, OSX and iOS that have contributed patches now in git at http://git.warmcat.com/cgi-bin/cgit/libwebsockets OSX wasn’t too hard thanks to some patches from Darin Willits, win32 was a bit tougher despite a big patch from Peter Hinz, I was really surprised to find the the Microsoft compiler doesn’t support simple C99 features like named member initialization of structs. Anyway after dumbing down the few structs that used it, and adapting a few other things it’s now possible to use libwebsockets on win32 thanks to Peter’s work.

v05 and v06 protocol support

Both v05 and v06 support was added within 12 hours of the spec being released, at the time of writing v06 is the current version.

I also added v00 client support by request from a developer using the socket.io server library which doesn’t support anything except 76 / 00. That means that in libwebsockets, both server and client support now covers all combinations of v00. v04, v05 and v06.

Extensions and deflate-stream

There’s a new extension support infrastructure added, including an implementation of zlib compression to provide the standardized “deflate-stream” extension.

The benefit of running with compression depends a lot on the payload size and content; in order to reduce latency the compression buffers are partially flushed every frame. But it is an important part of the websockets standard that libwebsockets now supports.

Integration with external poll arrays

Libwebsockets is being integrated into a fork of ircd, the daemon which runs the IRC network. The challenge there is to interoperate will the existing single poll() loop in a way that maximizes blocking and maintains serialization of poll service in a single thread to avoid the need for locking.

In addition to its default private poll array management libwebsockets now provides poll array callbacks into the user code which enables integration of websocket event loop functionality into an existing, master poll() array.

Callbacks occur into user code when file descriptors must be added, removed or have their event masks changed. There are hash tables implemented in libwebsockets to allow everything to remain opaque to the host code using just the file descriptor as an index.

With this technique, it has been possible to integrate websocket functionality into an existing irc server while keeping all details about websocket functionality and protocol versioning in the library.

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libwebsockets now with SSL / WSS

Monday, November 8th, 2010

happy phoneSSL encrypted websockets

The websocket protocol allows for two kinds of transport, unencrypted ws:// sockets and encrypted wss:// ones.  The server on a given port is either listening unencrypted initially for http:// connections, or encrypted for https:// ones using SSL.

Today I added optional SSL support for libwebsockets using OpenSSL, so it now supports encrypted or unencrypted types.  When you connect by encrypted, you simply use a https:// URL to the server.  The server returns the script over the encrypted link, and the script on the client side opens a wss:// websocket on the server.  Otherwise the encryption is completely transparent.  In particular, the callback the library makes back into the user code for the server is totally unaware if it is being used over SSL or not.

I adapted the javascript that the test server sends to open ws:// or wss:// according to whether its own URL was http:// or https://.

The test server builds its own test https:// certificate, browsers correctly warn that the CA is not recognized but otherwise the certs work correctly in Firefox 4.0b6 and Chrome 8.0.552.28 beta, both current on Fedora F15 rawhide.

Changed license to lgpl2.1

I realized that GPL2 isn’t the best idea for this as a library so I changed the terms to LGPL-2.1 making it easier to integrate with systems using other licenses.

Autotools

The build system has also been moved to autotools / libtool so it has a traditional ./configure structure that should survive crossplatform builds better.  It now has an –enable-openssl switch to control if openssl is needed.

You can get libwebsocket via git by:

git clone git://git.warmcat.com/libwebsockets

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libwebsockets – HTML5 Websocket server library in C

Monday, November 1st, 2010

Browser vs Apps

It’s been clear since browsers first started becoming popular in the 90s that they were going to be the answer to standardized cross-platform support, but somehow there were never quite enough pieces of the puzzle to replace applications outright. Java or Flash or me-toos like Sliverlight were needed and despite Flash solving the problem of video delivery, there hasn’t really been a shift away from old-style apps to the browser. (When I wrote Penumbra in 2007, I was able to use an exclusively https browser interface, but that’s only because it was fundamentally a filesharing app that didn’t challenge simple HTML).

The issue has never been more urgent because the number of incompatible platforms in wide use has been increasing, with iPhone. Android, Macs and Linux boxes alongside Windows. Making native apps for each platform is still possible, but it’s now a very large effort to cover and support all the platforms well natively.

HTML5 vs flash

HTML5 looks like it might have enough firepower to eliminate flash, it has already proven with web-m that it will be able to replace flash for the most critical job it does for the internet as a whole, video delivery, without having to worry too much about patents. Because of that, it has increasing mindshare and there’s already a lot of support in place in recent browsers, eg, Chrome and Firefox 4.0b6 at the time of writing, and considering Chrome is webkit, that covers many embedded scenarios too; Apple have committed themselves to HTML5 support in order to screw over Adobe… uh… I mean as part of their love of open standards.

Adobe did make actionscript a standard, but they have never been able to get away from being denounced as the main cause of browser crashes.  HTML5 moves all the hard work Adobe tried to do by themselves in terms of cross-platform media support to the people writing the browser and eliminates the need for Flash.

Websockets

Websockets are a new part of HTML5 that allow the client to get away from the ancient bias of browsers that any network connection is ultimately there to serve some kind of …ML, HTML or XML or whatever.  Websockets start off life as an HTTP connection, but the client immediately sends a request to the HTTP server to “upgrade” the protocol to websocket protocol.

After a complex handshake confirming both sides really speak websocket, websocket protocol is MUCH simpler than HTTP.  In the case of UTF-8 text packets, it’s as simple as sending 0×00 <vari-size payload> 0xff to terminate.  Binary payload packets have a slightly more complex length descriptor and then the payload with no terminator.

The value of it over http is the javascript on the client side can just get the raw binary or UTF-8 payload, and the socket stays open for async traffic in either direction.  There is no HTTP header overhead on each packet, as mentioned for UTF-8 the protocol overhead is 2 bytes per packet only.  There’s no huge XML encode / decode overhead either, so this is a great transport for low-latency data like speech, and it’s no-messing async nature lets it carry event information too ajax-style.

Because (once the connection is established) the protocol overhead is so low, it’s very suitable for weak embedded devices that have some kind of network connectivity but no real UI capability or CPU cycles for bloating data into formats browsers otherwise prefer.

Websocket servers

Sounds good right?  Well, to use it practically you need server-side support, because you are literally using a new socket-level protocol other than http.  There are Java and Python implementations suitable for Apache… but… unlike http there are no C library implementations suitable for embedded devices.  So, I wrote libwebsockets to allow embedded devices to participate in the new UIs possible with HTML5 and websockets.

Introducing libwebsockets

libwebsockets (in git at http://git.warmcat.com/cgi-bin/cgit/libwebsockets/ ) is a lightweight GPL2 http and websocket server that hides all the protocol handshakes and detail from the user code driving the server.

Because it supports file serving on http, it is able to provide a single listening socket that can serve your html script page normally and then when the browser starts running your script, come back and make websocket connections to the same port.

A test server is provided

http://git.warmcat.com/cgi-bin/cgit/libwebsockets/tree/test-server/test-server.c

because everything to do with the protocols is handled by the library, it’s very simply able to serve http and websockets using a single callback.

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