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Introduction to CMake

CMake is a multi-platform build tool that can generate build files for many different target platforms. See more info at http://www.cmake.org

CMake also allows/recommends you to do "out of source"-builds, that is, the build files are separated from your sources, so there is no need to create elaborate clean scripts to get a clean source tree, instead you simply remove your build directory.

Libwebsockets has been tested to build successfully on the following platforms with SSL support (both OpenSSL/CyaSSL):

  • Windows
  • Linux (x86 and ARM)
  • OSX
  • NetBSD

Building the library and test apps

The project settings used by CMake to generate the platform specific build files is called CMakeLists.txt. CMake then uses one of its "Generators" to output a Visual Studio project or Make file for instance. To see a list of the available generators for your platform, simply run the "cmake" command.

Note that by default OpenSSL will be linked, if you don't want SSL support see below on how to toggle compile options.

Building on Unix:

  1. Install CMake 2.8 or greater: http://cmake.org/cmake/resources/software.html (Most Unix distributions comes with a packaged version also)

  2. Install OpenSSL.

  3. Generate the build files (default is Make files):

    $ cd /path/to/src
$ mkdir build
$ cd build
$ cmake ..

    (NOTE: The build/`` directory can have any name and be located anywhere on your filesystem, and that the argument ..` given to cmake is simply the source directory of libwebsockets containing the CMakeLists.txt project file. All examples in this file assumes you use "..")

    NOTE2: A common option you may want to give is to set the install path, same as --prefix= with autotools. It defaults to /usr/local. You can do this by, eg

    $ cmake -DCMAKE_INSTALL_PREFIX:PATH=/usr ..

    NOTE3: On machines that want libraries in lib64, you can also add the following to the cmake line

    -DLIB_SUFFIX=64

    NOTE4: If you are building against a non-distro OpenSSL (eg, in order to get access to ALPN support only in newer OpenSSL versions) the nice way to express that in one cmake command is eg,

    $ cmake .. -DOPENSSL_ROOT_DIR=/usr/local/ssl \
	 -DCMAKE_INCLUDE_DIRECTORIES_PROJECT_BEFORE=/usr/local/ssl \
	 -DLWS_WITH_HTTP2=1

    When you run the test apps using non-distro SSL, you have to force them to use your libs, not the distro ones

    $ LD_LIBRARY_PATH=/usr/local/ssl/lib libwebsockets-test-server --ssl

  4. Finally you can build using the generated Makefile:

    $ make

Quirk of cmake

When changing cmake options, for some reason the only way to get it to see the changes sometimes is delete the contents of your build directory and do the cmake from scratch.

Building on Windows (Visual Studio)

  1. Install CMake 2.6 or greater: http://cmake.org/cmake/resources/software.html

  2. Install OpenSSL binaries. http://www.openssl.org/related/binaries.html (Preferably in the default location to make it easier for CMake to find them)

  3. Generate the Visual studio project by opening the Visual Studio cmd prompt:

    cd <path to src>
md build
cd build
cmake -G "Visual Studio 10" ..

    (NOTE: There is also a cmake-gui available on Windows if you prefer that)

  4. Now you should have a generated Visual Studio Solution in your <path to src>/build directory, which can be used to build.

Setting compile options

To set compile time flags you can either use one of the CMake gui applications or do it via command line.

Command line

To list avaialable options (ommit the H if you don't want the help text):

cmake -LH ..

Then to set an option and build (for example turn off SSL support):

cmake -DLWS_WITH_SSL=0 ..

or cmake -DLWS_WITH_SSL:BOOL=OFF ..

Unix GUI

If you have a curses enabled build you simply type: (not all packages include this, my debian install does not for example).

ccmake

Windows GUI

On windows CMake comes with a gui application: Start -> Programs -> CMake -> CMake (cmake-gui)

CyaSSL replacement for OpenSSL

CyaSSL is a lightweight SSL library targeted at embedded system: http://www.yassl.com/yaSSL/Products-cyassl.html

It contains a OpenSSL compatability layer which makes it possible to pretty much link to it instead of OpenSSL, giving a much smaller footprint.

NOTE: cyassl needs to be compiled using the --enable-opensslextra flag for this to work.

Compiling libwebsockets with CyaSSL

cmake .. -DLWS_USE_CYASSL=1 \
	 -DLWS_CYASSL_INCLUDE_DIRS=/path/to/cyassl \
	 -DLWS_CYASSL_LIB=/path/to/cyassl/cyassl.a ..

NOTE: On windows use the .lib file extension for LWS_CYASSL_LIB instead.

Reproducing HTTP2.0 tests

You must have built and be running lws against a version of openssl that has ALPN / NPN. Most distros still have older versions. You'll know it's right by seeing

lwsts[4752]:  Compiled with OpenSSL support
lwsts[4752]:  Using SSL mode
lwsts[4752]:  HTTP2 / ALPN enabled

at lws startup.

For non-SSL HTTP2.0 upgrade

$ nghttp -nvasu http://localhost:7681/test.htm

For SSL / ALPN HTTP2.0 upgrade

$ nghttp -nvas https://localhost:7681/test.html

Cross compiling

To enable cross compiling libwebsockets using CMake you need to create a "Toolchain file" that you supply to CMake when generating your build files. CMake will then use the cross compilers and build paths specified in this file to look for dependencies and such.

Libwebsockets includes an example toolchain file cross-arm-linux-gnueabihf.cmake you can use as a starting point.

The commandline to configure for cross with this would look like

$ cmake .. -DCMAKE_INSTALL_PREFIX:PATH=/usr \
	 -DCMAKE_TOOLCHAIN_FILE=../cross-arm-linux-gnueabihf.cmake \
	 -DWITHOUT_EXTENSIONS=1 -DWITH_SSL=0

The example shows how to build with no external cross lib dependencies, you need to provide the cross libraries otherwise.

NOTE: start from an EMPTY build directory if you had a non-cross build in there before the settings will be cached and your changes ignored.

Additional information on cross compilation with CMake: http://www.vtk.org/Wiki/CMake_Cross_Compiling

Memory efficiency

Embedded server-only configuration without extensions (ie, no compression on websocket connections), but with full v13 websocket features and http server, built on ARM Cortex-A9:

Update at 8dac94d (2013-02-18)

$ ./configure --without-client --without-extensions --disable-debug --without-daemonize

Context Creation, 1024 fd limit[2]:   16720 (includes 12 bytes per fd)
Per-connection [3]:                      72 bytes, +1328 during headers

.text	.rodata	.data	.bss
11512	2784	288	4

This shows the impact of the major configuration with/without options at 13ba5bbc633ea962d46d using Ubuntu ARM on a PandaBoard ES.

These are accounting for static allocations from the library elf, there are additional dynamic allocations via malloc. These are a bit old now but give the right idea for relative "expense" of features.

Static allocations, ARM9

.text .rodata .data .bss
All (no without) 35024 9940 336 4104
without client 25684 7144 336 4104
without client, exts 21652 6288 288 4104
without client, exts, debug[1] 19756 3768 288 4104
without server 30304 8160 336 4104
without server, exts 25382 7204 288 4104
without server, exts, debug[1] 23712 4256 288 4104

[1] --disable-debug only removes messages below lwsl_notice. Since that is the default logging level the impact is not noticeable, error, warn and notice logs are all still there.

[2] 1024 fd per process is the default limit (set by ulimit) in at least Fedora and Ubuntu. You can make significant savings tailoring this to actual expected peak fds, ie, at a limit of 20, context creation allocation reduces to 4432 + 240 = 4672)

[3] known header content is freed after connection establishment