Lightweight C library for HTML5 websockets
Some notes for the windows jungle

This was how I compiled libwebsockets starting from a blank windows install in March - April 2020. Doing this on a linux distro is way simpler and quicker than all this!

Notes on vm installation

Disk size

For building you'll need 40GB+ available for the guest storage.

Required: Windows product key

Assuming like me the first thing you do with a new laptop is install Linux over the windows it came with, you can recover your 'windows tax' windows product key from your device typically using sudo strings /sys/firmware/acpi/tables/MSDM, and use that for your VM install.

Required: Spice guest

To have shared clipboard, and for windows video driver to match your vm window resolution, you must install spice guest tools inside the windows VM. It also installs some virtio pieces you will want.

Blood-pressure reduction: Firefox

When it's up, add-ons: ublock origin, privacy badger, noscript, disable search bar prediction

Blood-pressure reduction: Clink

This is a hack on cmd.exe that lets it understand Ctrl-R and fixup unix-style slashes automagically.

If you're usually using *nix, you definitely need this to keep your sanity.

Required: cmake

CMake have a windows installer thing downloadable from here


after that you can use cmake from the terminal OK.

Required: git

Visit the canonical git site to download their windows installer thing


Select the install option for "extra unix commands" so you can get ls -l, cp, mv and suchlike working in cmd.exe... that's awesome, thanks git!

Afterwards you can just use git as normal from cmd.exe as well.

Required: Install the "free" "community" visual studio

You can do this through "windows store" by searching for "visual studio"

I installed as little as possible, we just want the C "C++" tools... 7GB :-)

It still wouldn't link without the "mt" helper tool from the huge windows SDK, so you have to install GB of that as well.

They don't mention it during the install, but after 30 days this "free" "community" edition demands you open a microsoft account or it stops working. In the install they give you the option to add a microsoft account and the alternative is, "not now, maybe later". Compare and contrast to gcc or git or the other FOSS projects.

Required: OpenSSL

Ugh... I tried using prebuilts but it's unreliable and needs an unfeasible amount of trust. So I recommend bite the bullet and build your own... that's trivial on Linux but of course windows makes everything nasty.

At least hopefully all the "research" is done and listed out here.

OpenSSL build Prerequisite: install perl binary

Move the git version of perl out of the way, it won't work for OpenSSL build

mv /usr/bin/perl /usr/bin/perl-git

For windows, OpenSSL "recommends" ActiveState perl but it doesn't work for me, complaining about stuff needed from cpan and then dying when it was installed. "Strawberry Perl" is installed in C:\Strawberry and worked out the box.

The installer sets up PATH% if you open a new cmd window.

OpenSSL build Prerequisite: NASM

Go here and click on the latest stable, download the win32 .exe

Just install via the defaults. Then add it to the PATH temporarily...

$ set PATH=%PATH%;C:\Program Files (x86)\NASM

OpenSSL build setup: source VC env vars

These fix up the PATH and include dirs etc necessary for VC build in the cmd window.

$ call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat" x86_amd64

OpenSSL build:

Grab openssl from git... assuming the prerequisites above went well it will just sit there building for 30 minutes or whatever.

$ git clone
$ cd openssl
$ perl Configure VC-WIN64A
$ nmake

Afterwards, open an Administrator mode cmd.exe, redo the msvc path and then install the build.

$ cd openssl
$ call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat" x86_amd64
$ nmake install

Oh another grindingly slow windows build action. Finally it's in there in C:\Program Files\OpenSSL.

libraries are looking for a cert bundle at "C:\Program Files\Common Files\SSL\cert.pem"... it's not documented or included in the zip file from the above, so...

Installing a cert bundle

You can get a trusted cert bundle from here

drwetter/testssl cert bundle

Save it into C:\Program Files\Common Files\SSL\cert.pem where openssl will be able to see it.

Required: pthreads

It's amazing but after all these years windows doesn't offer pthreads compatibility itself. Just like the many other missing POSIX bits like fork().

I downloaded the latest (2012) zip release of pthreads-win32 from here

Then I created a dir "C:\Program Files (x86)\pthreads", and copied the dll, include and lib subdirs from the prebuilt folder in the zip there.

The cmake incantation to build against pthreads set up like that is

$ cmake .. -DLWS_HAVE_PTHREAD_H=1 -DLWS_EXT_PTHREAD_INCLUDE_DIR="C:\Program Files (x86)\pthreads\include" -DLWS_EXT_PTHREAD_LIBRARIES="C:\Program Files (x86)\pthreads\lib\x64\libpthreadGC2.a" -DLWS_WITH_MINIMAL_EXAMPLES=1

Building libwebsockets

We'll clone libwebsockets then use cmake to build via vs tools

> git clone
> cd libwebsockets
> mkdir build
> cd build
> cmake ..
> cmake --build . --config DEBUG

Installing requires admin privs, I opened a second cmd window as admin and did it there.

> cmake --install . --config DEBUG

Hack the libs into view

The libs we built against aren't visible in the system, I don't know what Real Windows Programmers are supposed to do about that, but I used an Admin cmd prompt to copy them into C:\windows\system32

$ cp "C:\Program Files (x86)\pthreads\dll\x64\pthreadGC2.dll" "C:\Program Files\OpenSSL\bin\libcrypto-3.dll" "C:\Program Files\OpenSSL\bin\libssl-3.dll" C:\Windows\system32

After that you can run the test apps OK, eg

$ libwebsockets-test-server.exe -s

Note about using paths with spaces in with cmake