I wrote an HTTP server in ARM64 Assembly to have fun with some low-level stuff.

You can check out the code at server.s.

I'm talking to macOS directly through syscalls, which you're not supposed to do since, being a private API, they can change at any point. However, I did so anyway since I just wanted to explore the lowest level.

To prevent hardcoding all the constants needed to talk to the OS, I'm generating a const.s file from the C headers of the system lib. I cannot distribute binaries, but at least I should have better luck building it in the future.

• Use fork to handle many connections at once
• Handle SIGINT to gracefully close the server
• Send Content-Length

On an Apple Silicon mac, run:

$ make

...and check out http://localhost:4520.

Some stuff that helped me get this working:

• AArch64 Instruction Set Architecture
• x86 and A64 common instructions comparison
• Assembly Preprocessor Directives
• Beej's Guide to Network Programming (for C)
• LLDB cheat sheet
• HTTP flow

Also just running man <SYSCALL> can be super helpful. I wish we had something like that for modern stuff :)