Writing a Minecraft server from scratch in Bash (2022)

For Minecraft, very much so. Minecraft, especially the Java version, is in a comparatively odd place in that it receives significant free content updates AND officially supports running any historical version AND has an extremely vibrant modding community.

Minecraft (Java) is as much of a game engine for others to build on as it is a game itself.

Not just servers but for some games clients too https://runelite.net/

I think it will always be a thing for those who play games & like to dabble with tech, either to fix a bug, learn a language, or just see how the sausage is made.

AFAIK yes, the RE scene is still active.

would love to see how poll() and select() etc work this way

woah that's cool :) also hello tavis

Lol, holy shit what did I just read?

Amazing, installing now. I want to be part of the problem.

I mean if it's good enough for python...

I‘m not sure you should have done that, but it is impressive for the sheer chuzpa of it. Like reanimating Frankenstein.

Awesome, but beside the point of writing something in bash that never needed to be in bash for any technical reason.

Meaning if it requires bash plus some specially installed compiled c code, then it might as well require c or python or anything else and there is no point in calling it "written in bash", or writing it in mostly-bash-plus-special-plugin.

I do know who I'm speaking to so please assume I say this respectfully. :) I have no problem with a "pointless" project like that as I'll show in a second.

That said, this minecraft project itself relies on externals like xxd when it doesn't need to, so using ctypes.sh would be no worse in this case, so you are right, in this case they might as well have.

But for the record it is possible to read, store, manipulate, do math on, and output binary in pure bash without anything like dd or xxd.

The only byte that is a problem is null, and there is a way to deal with that. You can't directly store a null, but you can detect that you read one and store that info, and reconstruct it on output later, or do math on it, use it's numerical value as an array index or byte offset or whatever the byte is for.

For a minimal example, just copying a binary file: while LANG=C IFS= read -d '' -r -n 1 x ;do printf '%c' "$x" ;done <bin1 >bin2

That's a bit too minimal since it doesn't show what other kinds of things you can do that are more useful than cat-without-cat.

A bit more generic and useful: https://gist.github.com/bkw777/c1413d0e3de6c54524ddae890fe8d...

The LANG=C, IFS= , and -d'' all combine to render all bytes accessible except 0x00, and then the return value from read() tells you the difference between "we read a 0x00" and "we didn't read anything" and "input ended"

And it doesn't have to use < and > on the overall while() comand either. You can exec 3<>file_or_fifo_or_tty and read -u3 / printf >&3 etc inside the loop instead.

An example reading from a serial port: https://gist.github.com/bkw777/ddde771cc85fdd888c7ec74953193...

Used in anger: https://github.com/bkw777/pdd.sh see tpdd_read, tpdd_write, file_to_fhex, str_to_shex reading and writing both a serial port and local files and doing all kinds of processing on the data.

And these loops are not even subshells let alone externals. You can manipulate variables inside the loop and you are still in the same original context. I'd say parent shell but there are no childern.

Those all read a single byte at a time with read -n 1, but they don't have to.

You can read without the -n1 and each iteration of the loop will collect as much as it can between nulls instead of always one byte. That would consume less ram and less loop iterations.

But the things I'm using them for want to slice & dice the individual bytes and byte-ranges at numerical offsets anyway and the data is always small (by todays standards) so the array-of-hex-pairs is just too convenient where a[n] == byte n, and all bytes are treated the same whether printable, non-printable, or null, and aside from merely storing and regenerating the bytes with printf you can also use the numerical values directly as well by simply prepending 0x, so 0x$n or 0x${a[n]} almost anywhere you would normally have a simple integer. So you can do math on them and use them as array indexes and byte offsets etc.

Read the 2nd byte of h[] as a length of the payload to follow, and clip out that payload: ${h[@]:2:0x${h[1]}}

I dislike bash because I'm not good with it. It sucks but is still often the best solution available. Actually, one of my regret was not to invest more time on it when I was a student (a while ago) because it's one of these rare tools that accompanied me my whole career.

with shellcheck and good habits, bash can be readable and safe as well.

My favorite thing to do with shellcheck: add it to CI. Developers hate this one trick!

A lot of times CI and Dockerfiles have inline bash scripts. My next favorite thing to do is to move all of that inlined bash to their own script files. Now that CI has shellcheck: all that stuff gets checked too! Developers seem to hate this though because it's "less readable". Less readable my ass, it's way more safe.

Next problem: the same bash scripts are now in the same files in multiple repositories (a distributed build). I'm open to ideas for improvements here.

I don't understand how this would help the author. Since the bash doesn't support floating point numbers anyway

Thanks! Macroexpanded:

My thoughts on writing a Minecraft server from scratch in Bash - https://news.ycombinator.com/item?id=30347501 - Feb 2022 (90 comments)