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The argument is actually more like: don't use badly written middleman software that tries to parse messages it doesn't need to parse. I was at Google when the

The argument is actually more like: don't use badly written middleman software that tries to parse messages it doesn't need to parse. I was at Google when the "let's get rid of optional" crusade started. It didn't make sense to me then and over a decade later it still doesn't. If a program expects a field to be there then it has to be there, removing the protobuf level checking just meant that programs could now read garbage (some default value) instead of immediately crashing. But the whole reason we have types, assertions, bounds checking and so on is because, almost always, we'd like our software to NOT just blindly plough on into undefined territory when it doesn't understand something properly, so in reality it just means everyone ends up coding those very same required-ness assertions by hand. Now, Google's business model is remarkably robust to generating and processing corrupt data, so you can argue that in the specific case of this specific company, it is actually better to silently serve garbage than to crash. This argument was made explicitly in other forms, like when they deleted all the assertions from the HTTP load balancers. But in every case where I examined an anti-required argument carefully the actual problem would turn out to be elsewhere, and removing assertions was just covering things up. The fact that so much of Google's code is written in C++ that not only starts up slowly but also just immediately aborts the entire process when something goes wrong also contributes to the brittleness that encourages this kind of thing. If Google had been built on a language with usable exceptions right from the start it'd have been easier to limit the blast radius of data structure versioning errors to only the requests where that data structure turned up, instead of causing them to nuke the entire server (and then the RPC stack will helpfully retry because it doesn't know why the server died, promptly killing all of them). But this tolerance to undefined behavior is not true for almost any other business (except maybe video games?). In those businesses it's better to be stopped than wrong. If you don't then you can lose money, lose data, lose customers or in the worst cases even lose your life. I don't think people appreciate the extent to which the unique oddities of Google's business model and infrastructure choices have leaked out into the libraries their staffers/ex-staffers release.

kentonv 3y ago
> The argument is actually more like: don't use badly written middleman software that tries to parse messages it doesn't need to parse. The middleman software in question often needed to process some part of the message but not others. It wasn't realistic to define a boundary between what each middleman might need and what they wouldn't need, and somehow push the "not needed" part into nested encoded blobs. I'm not sure the rest of your comment is really addressing the issue here. The argument doesn't have anything to do with proceeding forward in the face of corrupt data or undefined behavior. The argument is that validation needs to happen at the consumer. There should still be validation.
- 3cats-in-a-coat 3y ago
  Honestly I wonder what is the big win in terms of performance by using static types here, because this sounds so terribly well fit for dynamic types (of which optionality by default is in fact a limited example). Such an odd choice to calcify a spec in a places where it changes all the time. "Static" optimizations should be local, not distributed.
- mike_hearn 3y ago
  I think you're defining consumer as the literal line of code where the field is read, whereas a more natural definition would be something like "the moment the data structure is deserialized". After all it's usually better to abort early than half way through an operation. It was quite realistic to improve protobufs to help dig web search out of their "everything+dog consumes an enormous monolithic datastructure" problem, assuming that's what you're thinking of (my memory of the details of this time is getting fuzzy). A simple brute-force fix for their situation would have been to make validation of required fields toggle-able on a per-parse level, so they could disable validation for their own parts of the stack without taking it away for everyone else (none of the projects I worked on had problems with required fields that I can recall). A better fix would have been for protobufs to support composition. They could then have started breaking down the mega-struct into overlapping protos, with the original being defined as a recursive merge of them. That'd have let them start narrowing down semantically meaningful views over what the programs really needed. The worst fix was to remove validation features from the language, thus forcing everyone to manually re-add them without the help of the compiler. Really, the protobuf type system was too simple for Google even in 2006. I recall during training wondering why it didn't have a URL type given that this was a web-centric company. Shortly after I discovered a very simple and obvious bug in web search in which some local business results were 404s even though the URL existed. It had been there for months, maybe years, and I found it by reading the user support forums (nobody else did this, my manager considered me way out of my lane for doing so). The bug was that nothing anywhere in the pipeline checked that the website address entered by the business owner started with https:// https://, so when the result was stuffed into an <a> tag it turned into <a href="www.business.com"> and so the user ended up at https://www.google.com/www.business.com https://www.google.com/www.business.com. Oops. These bad strings made it all the way from the business owner, through the LBC frontend, the data pipeline, the intermediate microservices and the web search frontends to the user's browser. The URL did pass crawl validation because when loaded into a URL type, the missing protocol was being added. SREs were trained to do post-mortems, so after it got fixed and the database was patched up, I naively asked whether there was a systematic fix for this, like maybe adding a URL type to protobufs so data would be validated right at the start. The answer was "it sounds like you're asking how to not write bugs" and nothing was done, sigh. It's entirely possible that similar bugs reoccurred dozens of times without being detected. Those are just a couple of cases where the simplicity (or primitivity) of the protobuf type system led to avoidable problems. Sure, there are complexity limits too, but the actual languages Googlers were using all had more sophisticated type systems than protobuf and bugs at the edges weren't uncommon.
3cats-in-a-coat 3y ago
That's valuable what you say, and it's kinda odd some people here discard practical experience in favor of their subjective flavor of theoretical correctness.
saghm 3y ago
> The argument is actually more like: don't use badly written middleman software that tries to parse messages it doesn't need to parse. > I was at Google when the "let's get rid of optional" crusade started. It didn't make sense to me then and over a decade later it still doesn't. If a program expects a field to be there then it has to be there, removing the protobuf level checking just meant that programs could now read garbage (some default value) instead of immediately crashing. But the whole reason we have types, assertions, bounds checking and so on is because, almost always, we'd like our software to NOT just blindly plough on into undefined territory when it doesn't understand something properly, so in reality it just means everyone ends up coding those very same required-ness assertions by hand. Yeah, that's what stuck out to me from the linked explanation as well; the issue wasn't that the field was required, it was that the message bus was not doing what was originally claimed. It sounds like either having the message bus _just_ process the header and not the entire message or having the header have a version number that indicated which fields are required (with versions numbers that are newer than the latest the bus was aware of being considered to have no required fields). I don't claim that it's never correct to design a protocol optimizing for robustness when consumed by poorly written clients, but I similarly struggle to see how making that the only possible way to implement a protocol is the only valid option. Maybe the goal of cap'n proto is to be prescriptive about this sort of thing, so it wouldn't be a good choice for uses where there's more rigor in the implementation of services using the protocol, but if its intended for more general usage, I don't understand this design decision at all.

kentonv 3y ago

> The argument is actually more like: don't use badly written middleman software that tries to parse messages it doesn't need to parse. The middleman software in question often needed to process some part of the message but not others. It wasn't realistic to define a boundary between what each middleman might need and what they wouldn't need, and somehow push the "not needed" part into nested encoded blobs. I'm not sure the rest of your comment is really addressing the issue here. The argument doesn't have anything to do with proceeding forward in the face of corrupt data or undefined behavior. The argument is that validation needs to happen at the consumer. There should still be validation.

3cats-in-a-coat 3y ago
Honestly I wonder what is the big win in terms of performance by using static types here, because this sounds so terribly well fit for dynamic types (of which optionality by default is in fact a limited example). Such an odd choice to calcify a spec in a places where it changes all the time. "Static" optimizations should be local, not distributed.
mike_hearn 3y ago
I think you're defining consumer as the literal line of code where the field is read, whereas a more natural definition would be something like "the moment the data structure is deserialized". After all it's usually better to abort early than half way through an operation. It was quite realistic to improve protobufs to help dig web search out of their "everything+dog consumes an enormous monolithic datastructure" problem, assuming that's what you're thinking of (my memory of the details of this time is getting fuzzy). A simple brute-force fix for their situation would have been to make validation of required fields toggle-able on a per-parse level, so they could disable validation for their own parts of the stack without taking it away for everyone else (none of the projects I worked on had problems with required fields that I can recall). A better fix would have been for protobufs to support composition. They could then have started breaking down the mega-struct into overlapping protos, with the original being defined as a recursive merge of them. That'd have let them start narrowing down semantically meaningful views over what the programs really needed. The worst fix was to remove validation features from the language, thus forcing everyone to manually re-add them without the help of the compiler. Really, the protobuf type system was too simple for Google even in 2006. I recall during training wondering why it didn't have a URL type given that this was a web-centric company. Shortly after I discovered a very simple and obvious bug in web search in which some local business results were 404s even though the URL existed. It had been there for months, maybe years, and I found it by reading the user support forums (nobody else did this, my manager considered me way out of my lane for doing so). The bug was that nothing anywhere in the pipeline checked that the website address entered by the business owner started with https:// https://, so when the result was stuffed into an <a> tag it turned into <a href="www.business.com"> and so the user ended up at https://www.google.com/www.business.com https://www.google.com/www.business.com. Oops. These bad strings made it all the way from the business owner, through the LBC frontend, the data pipeline, the intermediate microservices and the web search frontends to the user's browser. The URL did pass crawl validation because when loaded into a URL type, the missing protocol was being added. SREs were trained to do post-mortems, so after it got fixed and the database was patched up, I naively asked whether there was a systematic fix for this, like maybe adding a URL type to protobufs so data would be validated right at the start. The answer was "it sounds like you're asking how to not write bugs" and nothing was done, sigh. It's entirely possible that similar bugs reoccurred dozens of times without being detected. Those are just a couple of cases where the simplicity (or primitivity) of the protobuf type system led to avoidable problems. Sure, there are complexity limits too, but the actual languages Googlers were using all had more sophisticated type systems than protobuf and bugs at the edges weren't uncommon.

3cats-in-a-coat 3y ago

That's valuable what you say, and it's kinda odd some people here discard practical experience in favor of their subjective flavor of theoretical correctness.

saghm 3y ago

> The argument is actually more like: don't use badly written middleman software that tries to parse messages it doesn't need to parse. > I was at Google when the "let's get rid of optional" crusade started. It didn't make sense to me then and over a decade later it still doesn't. If a program expects a field to be there then it has to be there, removing the protobuf level checking just meant that programs could now read garbage (some default value) instead of immediately crashing. But the whole reason we have types, assertions, bounds checking and so on is because, almost always, we'd like our software to NOT just blindly plough on into undefined territory when it doesn't understand something properly, so in reality it just means everyone ends up coding those very same required-ness assertions by hand. Yeah, that's what stuck out to me from the linked explanation as well; the issue wasn't that the field was required, it was that the message bus was not doing what was originally claimed. It sounds like either having the message bus _just_ process the header and not the entire message or having the header have a version number that indicated which fields are required (with versions numbers that are newer than the latest the bus was aware of being considered to have no required fields). I don't claim that it's never correct to design a protocol optimizing for robustness when consumed by poorly written clients, but I similarly struggle to see how making that the only possible way to implement a protocol is the only valid option. Maybe the goal of cap'n proto is to be prescriptive about this sort of thing, so it wouldn't be a good choice for uses where there's more rigor in the implementation of services using the protocol, but if its intended for more general usage, I don't understand this design decision at all.