TCP HTTP Server written in Assembly

http://canonical.org/~kragen/sw/dev3/server.s

by thikonom • 13 years ago

154 70 13 years ago

tokenizer• 13 years ago

As a web developer who isn't familiar with assembly or any web server more barebones than nginx, what benefits does something like this provide? Speed? Could this be a solution for an extremely simple directory/static file web server?

hcarvalhoalves• 13 years ago

This is obviously a toy, or PoC.

ars_technician• 13 years ago

I don't know about calling it a piece of crap. Seems a little harsh. :-)

anonymouscowar16• 13 years ago

This is a simple, single-threaded single-process accept-read-respond-loop web server. It's vulnerable to trivial trickle DoS attacks and probably has other issues. There are no advantages, the author just did this for fun.

The TCP part comes from C code in the kernel, so this headline is a little misleading ;-).

kragen16• 13 years ago

Agreed. However, it should be safe from buffer overflows, path traversal attacks, XSS, and obviously CSRF. It should be fine other than DoS. Let me know if you find any exceptions.

knappador• 13 years ago

This is normally the kind of question I ask about anything involving HTML/CSS only or JS only =D PoC's based on low-level concepts are the ones that make you curious about everything from top to bottom. Even though assembly is the least abstract and most esoteric of programming (some would argue opposite) spaces, the program actually reveals itself quite quickly knowing just a few tid-bits. This is how you get to see that even the most low-level aspects of programming are quite accessible.

kragen16• 13 years ago

Thank you! I'm glad to hear that you found it so readable.

kragen16• 13 years ago

Nginx will almost certainly be faster, and is somewhat robust against DoS attacks. I didn't write this to provide benefits. There are situations where this would work better than nginx (where, say, you don't want to spend any time configuring anything) but there are better existing solutions for those cases.

mappu• 13 years ago

Cool!

My comments as an inexperienced assembly developer, assuming this is optimising for binary size:

- The pug/doN macros do an extra reg-reg copy if passed a register - and the recursive definition calls pop/pop/pop instead of just add %esp, -4*N, you could shave a few bytes

- AT&T syntax will always look weird to me, but the heavy use of macros and local labels is quite elegant

- A little bit of candid swearing in the comments? Fine by me, but is this officially associated with canonical?

aroman• 13 years ago

- A little bit of candid swearing in the comments? Fine by me, but is this officially associated with canonical?

Assuming you mean Canonical Ltd., the company behind Ubuntu, this has absolutely nothing with them — this is hosted on canonical.org, not canonical.com.

pbsd2• 13 years ago

Agree, AT&T syntax was just not designed for human reading. I doubt this is too optimized for size, since there are obvious tricks that it misses.

Another observation: the strlen code is incorrect, as it also counts the \0. We can fix this, and make the code 1 byte shorter (in glorious Intel syntax):

    lea esi, source        ; depends on source
    xor ecx, ecx           ; 2 bytes
    salc                   ; 1 byte
    cld                    ; 1 byte
    _back:
    scasb                  ; 1 byte 
    loopnz _back           ; 2 bytes
    not ecx                ; 2 bytes

kragen16• 13 years ago

Thank you! About the time you wrote this, I discovered that the strlen code was incorrect in a different way as well, and then I went to sleep. Sort of embarrassing.

kragen16• 13 years ago

BTW, I've fixed the strlen code (although differently). I didn't know about SALC! That's a very clever way of zeroing AL.

I think at this point I might be able to get away with CLD since I never STD any more :)

Some of the obvious tricks it misses are probably because they're not obvious to me, while others may be just because I haven't gotten to them yet.

derleth5• 13 years ago

you could shave a few bytes

This is practically axiomatic in assembly language programming.

It's just not worth it to turn you code into what you'd need to turn it into in order to make it as small (or as fast) as it can possibly be on that specific version of that specific microarchitecture from that specific manufacturer, such work being undone by the next version of the hardware.

AT&T syntax will always look weird to me

AT&T syntax is meant to be a generic assembly language syntax; it's supposed to look equally weird to everyone, regardless of what CPU they're writing code for. GAS will accept Intel syntax, or a somewhat heterodox variant thereof. NASM is the usual assembler of choice on modern x86 Unix-a-likes, I think.

http://www.nasm.us/

A little bit of candid swearing in the comments?

Hey, if the Linux kernel devs can do it, why not them?

pekk• 13 years ago

and I just got finished rewriting all my large webapps in some obscure Java framework for performance, because of some benchmarks I saw on HN. Guess now I have to rewrite it all in assembly, because more performance is always better right?

anonymouscowar16• 13 years ago

This is not a very fast webserver. Anything using sendfile() and threads/processes will beat it handily.

kragen16• 13 years ago

I haven't measured, but I'm pretty sure you're right.

yeukhon• 13 years ago

Well, the JVM might be doing something smarter than your assembler-from-scratch code.

pmiller2• 13 years ago

Neat little piece of performance art (pun intended).

jebblue• 13 years ago

Good way to put it, was trying to think of something similar.

kragen16• 13 years ago

Thank you :)

neverm0re• 13 years ago

Here's another simpler implementation of an HTTP server in Linux x86 assembly from last year, coincidentally by the one who did the Seiken Densetsu 3/Secret of Mana 3 translation hack and the old Starscream 68k emulator:

http://www.neillcorlett.com/etc/mohttpd.asm.txt

And a not so successful thread to go with it: https://news.ycombinator.com/item?id=4714971

kragen16• 13 years ago

That's very nice! Thanks! I spent a lot of last night figuring out how to use socketcall, and this should be helpful.

puppetmaster32• 13 years ago

Likely does not have any back door. Rumor is GCC opens back door for you know who.

StavrosK• 13 years ago

Voldemort?

puppetmaster32• 13 years ago

Shhh.

derefr• 13 years ago

Cool stuff. Really, though, this is still relying on a rather large runtime library: the physical, data-link, and network-layer drivers.

Now what'd be really awesome to see, would be one of those Operating System guides that shows you how to write an OS kernel, in assembler, that can speak HTTP. Even just limiting yourself to targeting the synthetic hardware of a VM program, it'd still be quite a feat.

Bonus points if the entire network stack has been flattened using the hand-rolled equivalent of stream-fusion. :)

proksoup• 13 years ago

omfg yes!

aortega2• 13 years ago

Here you go:

http://www.kyllikki.org/hardware/wwwpic2/src/wwwpic2.asm.htm...

Bonus: runs on 68 bytes of ram. Not a typo, it's bytes, and it's a "complete" http+tcp/ip server.

sillysaurus2• 13 years ago

Awesome. Can VirtualBox or VMWare run this?

mbell• 13 years ago

That is just running the TCP/IP layer speaking RS232 and relying on an external IC for lower layers. It's not at all what the GP is looking for.

It should probably also be noted that a minimum TCP header, with no data attached, is 20 bytes, so to implement a 'full stack' in 68 bytes is a pretty strong indication that you're relying on off SoC memory to handle the packet buffering.

csmuk• 13 years ago

Bet that handles TCP fragmentation well :)

Nice work though to whoever crammed that in a PIC.

kragen16• 13 years ago

Agreed, and also the filesystem. I think you may be looking for lwIP and Contiki.

gwu78• 13 years ago

Are you saying you'd like to see string procesing moved into the kernel?

meshko4• 13 years ago

OMG all these macros. It looks more like Python then Assembly. Come on, real men do not use macros.

UNIXgod2• 13 years ago

ahh yes, real programmers twiddle bits on their hard drive with a nothing more than a tiny magnet:

http://www.cs.utah.edu/~elb/folklore/mel.html

ckarmann• 13 years ago

real programmers use butterflies http://xkcd.com/378/

derleth5• 13 years ago

Come on, real men do not use macros.

The sexism and historical ignorance in this sentence are in a race to see which can be more breathtaking.

Regardless of which wins, meshko will look like a complete fool to anyone who knows what they're talking about.

derleth5• 13 years ago

Because downvoters don't win:

Come on, real men do not use macros.

The sexism and historical ignorance in this sentence are in a race to see which can be more breathtaking.

Regardless of which wins, meshko will look like a complete fool to anyone who knows what they're talking about.

meshko4• 13 years ago

Wait, are you serious?

meshko4• 13 years ago

Would the joking intent of the usage of men-centric idiom be more clear if I append "now get off my lawn" to the comment?

kragen16• 13 years ago

Thank you very much! This is the nicest comment in this entire thread!

asmman1• 13 years ago

You're right. Real men don't use Assembly, too, but do use binary instead of. :)

zw123456• 13 years ago

Very cool I think. But cooler, Web Server on a FPGA, without CPU, only VHDL http://www.youtube.com/watch?v=7syu5EC1OWg

Vektorweg• 13 years ago

I'm really happy that executable size doesn't matter for server software. Because Yesod produce really big execs.

mikkom• 13 years ago

Depends on the C libraries.

^ That tells everything you need to know.

radikalus• 13 years ago

No full tcp stack in assembly? =p

(Yes there's no point as it's better in hardware blah blah)

kragen16• 13 years ago

I hacked on httpdito some more, and it has been improved in several ways:

- it now forks so that it can handle multiple concurrent connections (up to a limit of 2048);

- it no longer uses libc at all, so it's down to 2088 bytes (I had it lower, but then I added forking);

- it's less complex now that it only has one way of invoking system calls instead of two;

- there are some performance results in the comments.

- it has a name, "httpdito";

- strlen works correctly.

Probably nobody will read this comment here, but I thought it was worth mentioning.

kragen16• 13 years ago

Down to 1928 bytes now, and has timeouts for robustness. You can still DoS it but it takes more work.

TCP HTTP Server written in Assembly

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