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0 pointsbsder4y ago0 comments

> Or maybe those people know what they are talking about and the truth is that many people who are big fans of automated testing tend to overrate its value when it comes to many areas of software development.

I would normally agree with you, but a TCP Stack is one of those things where I vehemently disagree.

Communication stacks, in general, are giant piles of implicit state unless you go out of your way to manage the state explicitly. As such, they have obscure bugs which are difficult to find when some of the cases are hit rarely.

A communication stack really needs to be written such that the inputs (including TIME), the outputs, the current state, and the next state are all quite explicit. This enables you to test the stack because it is now deterministic with respect to inputs and outputs.

Yes, it's not easy. And it requires that you really mean it and architect it that way. You may not be able to evolve your current stack and may have to throw it away--that's never going to be popular.

However, every single time I have done this for a communication stack (USB, CANopen, BLE, etc.), the result was that the new stack quickly overtook the old stack on basically every metric worth monitoring (throughput, latency, reliability, bug rate, etc.).

Now, to be fair, I was obviously replacing a communication stack that was some level of "pile of crap" or I wouldn't have done it. However, I'm just one person, and those stacks generally came from a company who had a vested interest in it not sucking. I'm not some amazing programmer, and I certainly didn't spend more time on it than the original stack, so it really comes down to the fact that the "underlying architecture" was simply a better idea.

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yurish4y ago

> A communication stack really needs to be written such that the inputs (including TIME), the outputs, the current state, and the next state are all quite explicit. This enables you to test the stack because it is now deterministic with respect to inputs and outputs.

Do you have something open source to look at that uses this approach? The idea is great but I wonder how complicated becomes code when using it.

bsderOP4y ago

Sadly, no. I don't rewrite communication stacks for fun. And someone who pays me to do so generally sees it as a competitive advantage.

The complication is that the "event loop" is atomized. This means that initialization, teardown, and iteration are now in your hands. You're responsible for making sure that the "iteration" function is called often enough (ie. both because of timers and incoming packets), not the stack. Of course, because time is an input, you can clearly identify "Oops. I didn't call this often enough."

The advantage is that your "event loops" can now compose. Quite often, it's very hard to get different communication stacks to cooperate because they all want to be the "primary event loop". (A good example of this failure is "async" frameworks--"How do I wait on a screen refresh, a tcp socket, and a character device descriptor simultaneously?"--if your async executor doesn't take all of those into account you're gonna have a bad time) Since the event loops are atomized, you can interleave the "iteration" calls and wait/sleep however you like.

As for open source, to be honest, I probably wouldn't release anything open source these days unless I got a very significant personal benefit somehow. It's not enough to simply create something and put it out there--everybody expects you to be a maintainer and have some infinite well of tactfulness in the face of idiots who deserve to be slapped silly.

For me, the grief from the whiny, entitled contingent is far too high to make producing open source worthwhile nowadays. I respect the people who do it but have no desire to join them.

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