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Post Mortem: A single whitespace character

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Re: Post Mortem: A single whitespace character

#121

Post by kstrauser »

shortstuffsushi wrote: post #105
kstrauser wrote: post #79

If this were my team, I would be unsettled by the fact that we never caught it in testing. Did no one write tests to exercise this part of the app - the one where we're handcrafting HTTP requests? Objectively, you need to write more tests. At the minimum, this bug should have a regression test so that it can never accidentally happen again (say when a dev merges an old branch in for whatever reason).

What test would you have written to catch this? One that checks the exact contents of headers passed along? It's possibly they even had tests around this, but were expecting the same output that they were inputting (copy+pasta). Perhaps they had a more "integration"-ee test that actually hit the web with that bad header. At the point they wrote it, that test would have been passing. It wasn't until the parsing server…

Yes, I would have written a test to confirm that input_a generates output_b. The first half of that function is nothing but a string builder and easily testable. If they were copy-and-pasting the actual output to get the expected output, then yes: they screwed that part up.

I'm far from a TDD purist, but it's clearly true that they're not sufficiently validating their code. If they had been, this would not have happened. I'm not saying this as an attack on their skills as programmers, but as caution to others reading the story: you have to - have to - test your stuff.

It's one thing to lean on third-party libraries and expect them to mostly Do The Right Thing, especially if they're popular and come from a culture of valuing test coverage. If you're writing a Rails app, for instance, you might be forgiven for not writing your own independent validations of the Ruby methods you call. But writing string-building code to implement RFC-defined network protocols? You should have some confidence that your program is generating the output that the other party will be expected. Especially with something as commonly proxied as unencrypted HTTP; you just have to assume that your data will be traversing and analyzed by systems 100% outside of your control.

Re: Post Mortem: A single whitespace character

#122

Post by ctz »

pjc50 wrote: post #82
ctz wrote: post #58

Earlier quoted context omitted.

This would require a vast, vast upgrade of client power to achieve the same communications performance. If you could achieve it all, SSL would also likely decrease reliability over a spotty GSM link.

Is client CPU actually a limiting factor? How does this affect reliability?

You cannot physically fit a whole SSL datagram (max size 16KB) into 8KB of RAM. SSL requires multiple passes over the data to (eg) decrypt and verify a datagram. At this point, you cannot use standard SSL at either the server side or client side.

On the subject of reliablity: a 8 bit uC running at 16MHz needs a long time to do the public key crypto required to set up the connection. This means you need a GSM data link to be continuously available for a longer period.

Re: Post Mortem: A single whitespace character

#123

Post by robomartin »

robomartin wrote: post #81
jrochkind1 wrote: post #7

This very example -- requests were technically illegal all the time without devs realizing, but something in the stack changed to start rejecting them -- demonstrates the fallacy of the "be liberal in what you accept, strict in what you issue" principal. If all the web servers involved had been strict in rejecting the illegal request from the start, they would have noticed the bug in development before deploying to f…

Not "principal", "principle". Not being critical, just pointing out a common mistake. http://blog.oxforddictionaries.com/2011/08/principle-or-prin... Principal: Main, most important Principle: A rule, a system of belief

It's really interesting to see something like this down-voted. There's nothing pedantic about this. It's offered with nothing but respect. Perhaps the comment writer isn't a native speaker and this was an honest point of confusion. What is wrong with trying to be helpful?

It is a common mistake I see all the time here on HN (along with "your" vs. "you're" vs. "you are"). Why is it that is offensive to the point of deserving a down-vote? Please help me understand.

Re: Post Mortem: A single whitespace character

#124

Post by DanBC »

robomartin wrote: post #123
robomartin wrote: post #81

Earlier quoted context omitted.

Not "principal", "principle". Not being critical, just pointing out a common mistake. http://blog.oxforddictionaries.com/2011/08/principle-or-prin... Principal: Main, most important Principle: A rule, a system of belief

It's really interesting to see something like this down-voted. There's nothing pedantic about this. It's offered with nothing but respect. Perhaps the comment writer isn't a native speaker and this was an honest point of confusion. What is wrong with trying to be helpful? It is a common mistake I see all the time here on HN (along with "your" vs. "you're" vs. "you are"). Why is it that is offensive to the point of de…

I didn't downvote.

People downvote corrections because they're usually noise. When someone makes a typo - and homophones are usually slips equivalent to typos - it's noise to point it out.

Re: Post Mortem: A single whitespace character

#125

Post by pjc50 »

ctz wrote: post #122
pjc50 wrote: post #82

Earlier quoted context omitted.

Is client CPU actually a limiting factor? How does this affect reliability?

You cannot physically fit a whole SSL datagram (max size 16KB) into 8KB of RAM. SSL requires multiple passes over the data to (eg) decrypt and verify a datagram. At this point, you cannot use standard SSL at either the server side or client side. On the subject of reliablity: a 8 bit uC running at 16MHz needs a long time to do the public key crypto required to set up the connection. This means you need a GSM data lin…

This is true, but if you're using GSM you have a much beefier processor handling the GSM side and there's no need to use a tiny microcontroller. Some of the GSM modules will offload the whole HTTP(S) request for you.

Edit: or you could get a Cortex-M0 with 32K RAM for $2.

Re: Post Mortem: A single whitespace character

#126

Post by robomartin »

DanBC wrote: post #124
robomartin wrote: post #123

Earlier quoted context omitted.

It's really interesting to see something like this down-voted. There's nothing pedantic about this. It's offered with nothing but respect. Perhaps the comment writer isn't a native speaker and this was an honest point of confusion. What is wrong with trying to be helpful? It is a common mistake I see all the time here on HN (along with "your" vs. "you're" vs. "you are"). Why is it that is offensive to the point of de…

I didn't downvote. People downvote corrections because they're usually noise. When someone makes a typo - and homophones are usually slips equivalent to typos - it's noise to point it out.

It's only noise if it has no value. A post such as mine would not have to appear too frequently for HN readers who might be having difficulties with such words to understand the problem and correct their writing. Not going after perfect English, few of us could approach that. But I see a few common patterns on HN all the time and nobody takes a second to say "hey buddy, just in case this wasn't clear to you, here's a helpful tip". Some of these are confusing to non-native speakers. When trying to be helpful is frowned-upon what are you left with?

This comment needed to be left alone. No down vote, perhaps an up-vote by the comment writer if s/he found it helpful and that's it.

One of the things that continues to disturb me the most about HN is how thin skinned the community seems to be. It is impossible to consistently offer a contrasting point of view here without down-vote attacks that make your point of view virtually disappear. Mind you, this particular post isn't that. It just reminds me that HN is really weird.

I get down voted a lot despite the fact that I am a successful entrepreneur since age 15 who has built several companies and continues to do so. My perspective, however, seems seldom welcome here (based on how often I am down-voted) because I don't tow the line of the 20-somethings that are the bulk of this audience. Instead of learning they choose to pound what they don't like out of existence. Weird.

Re: Post Mortem: A single whitespace character

#127

Post by drblast »

ams6110 wrote: post #111
asveikau wrote: post #97

strcpy( ( char * ) commsOrderBuffer, "GET /v1/printer/"); strcat( ( char * ) commsOrderBuffer, ( char * ) settings.getIMEI()); strcat( ( char * ) commsOrderBuffer, "/orders.txt HTTP/1.1\r\n"); strcat( ( char * ) commsOrderBuffer, "HOST: "); strcat( ( char * ) commsOrderBuffer, SERVER_NAME); strcat( ( char * ) commsOrderBuffer, "\r\n"); strcat( ( char * ) commsOrderBuffer, "Authorization: Basic "); What the.... O(n) s…

Those would be "safe" (assuming that settings.getIMEI() is completely under your control, everything else is string literals) but yeah snprintf seems way better here (though it's been well over 20 years since I wrote any significant C code.

Since these are all string literals you really don't need any concatenation function at all except to concatenate with the output of getIMEI().

  char *a = "Hello " "world!";
Works just fine.

Edit to add: You can really see the difference in code between someone coming to C/C++ from a high level language and someone who learned assembly first, where a list of literals is a common idiom. The original style is not functionally wrong, but it does look like Java :-)

Also: DON'T post your potentially insecure string handling code on the Internet; are you crazy?

Re: Post Mortem: A single whitespace character

#128

Post by angersock »

goleksiak wrote: post #100
angersock wrote: post #94

Earlier quoted context omitted.

I'm just curious why the default response is still to reach for an Arduino--much more powerful SoC chips are cheap these days.

For us, the reason is that my co-founder and I (both are not hardware guys) were able to build a proof of concept in my garage and Arduino seemed like the best (easiest) choice. Since then, we hired a hardware guy who designed a custom PCB etc. HTTPS would be great but we don't transmit any personal data so it's not a high priority right now.

Hey, no worries. Real artists ship. :)

Re: Post Mortem: A single whitespace character

#130

Post by mischanix »

3ds wrote: post #102
mischanix wrote: post #13

Earlier quoted context omitted.

It's simple enough to single out Heroku: $ cat

Your example fails with or without the whitespace. These work though: Request printf 'GET / HTTP/1.1\r\nHost: example.herokuapp.com\r\n\r\n' | nc example.herokuapp.com 80 Response HTTP/1.1 200 OK Connection: keep-alive Server: SimpleHTTP/0.6 Python/2.7.6 Request printf 'GET / HTTP/1.1\r\nHost: example.herokuapp.com\r\n\r\n' | nc example.herokuapp.com 80 Response HTTP/1.1 505 HTTP Version Not Supported Connection: clo…

Ah right, forgot about the newline specification. I guess, for reference, the smallest string I can come up with to get Cowboy to spit that error message is '\x20\x20\n'. Parsers are fun.
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