Your Flying Car is Ready: Amazing Programming From the Future, Today!

What if simply writing tests was enough to produce a program which makes them pass? What if your compiler could guarantee that your “Heartbleed-free” OpenSSL replacement follows the TLS specification to the letter, and even finds inconsistencies in the specification itself? What if you could write a test which showed that your code had no unintentional behavior, ever? Microsoft Research is well known for its contributions to Kinect, F#, the Entity Framework, and more, but it's also the home of a number of programming tools which do things which many programmers would consider surprising, if not impossible. But they work, and in this session you'll see them in action.

Like the idea of code contracts, but concerned about runtime performance and errors? The Dafny language can check contracts at compile time. The Z3 theorem prover can solve problems from specifications alone, and is used to make Hyper-V and Windows Azure memory safe. The F7 specification language for F# was used by its authors used it to not only produce a TLS implementation which probably follows the spec, but also identified a dangerous hole in the TLS specification itself. You'll learn how Amazon uses the TLA+ specification language to prove that there are no edge cases in its internal protocols. Far from being research toys, these tools are in daily use in cases where stability, security, and reliability of code matters most. Can they help with your hardest problems? You might be surprised!

Transcript

1. CRAIG STUNTZ PROJECT DATE CLIENT 2014.09.29 YOUR FLYING CAR IS READY AMAZING PROGRAMMING TOOLS FROM THE FUTURE, TODAY! https://www.flickr.com/photos/ellenm1/7847402208
2. SLIDES https://speakerdeck.com/craigstuntz/your-flying-car-is-ready Slides are already online.
3. “THE FUTURE IS ALREADY HERE — IT’S JUST NOT VERY EVENLY DISTRIBUTED.” WILLIAM GIBSON Spoilers alert! Here’s the whole talk. 1. Software is broken; solves the wrong problem incorrectly. 2. Software is broken for a reason: Inessential complexity. 3. It’s possible to produce software which solves harder problems and isn’t broken. 4. The way to do better exists and is used to produce software you use every day.
4. “A LANGUAGE THAT DOESN'T AFFECT THE WAY YOU THINK ABOUT PROGRAMMING, IS NOT WORTH KNOWING.” ALAN PERLIS EPIGRAMS IN PROGRAMMING https://www.flickr.com/photos/randyread/2385812579 Will talk about tools most people don’t know exist, when it makes sense to use them. When not. “All languages are the same, just syntax.” <- Wrong!
5. “SOMETIMES WE DON’T PROGRAM TO SHIP; WE PROGRAM TO UNDERSTAND PROGRAMMING.” NADA AMIN PROGRAMMING SHOULD EAT ITSELF Do programming languages exist to produce programs? You can create a program without a PL, though it’s harder. We program not for its own sake (mostly) but to solve business problems. PLs and compilers produce exe code, yes, but find syntax errors, semantic errors, and are “tools of thought.” (And much more common!) My real goal here: To expand the set of problems you think you can solve with programming. To do that, you need new ways of approaching a language, not just tooling.
6. What Is the Upper Limit of Software Quality? function three() { return 1 + 2; } Want to show you a function I wrote. I’ll apologize in advance for this slide since it involves math. What’s interesting? It’s perfect! This is the only defect- free JS I’ll be showing you today. It also composes well. The notion of “perfect” code is controversial. But it’s clearly possible! How much quality are we willing to pay for? Does it depend on the application?
7. “LIFE WAS SIMPLE BEFORE WORLD WAR II. AFTER THAT, WE HAD SYSTEMS.” GRACE HOPPER Perfect code is trivial. Perfect programs, systems harder. Why is composition harder in some cases? This is essential! There are always external factors. That’s fine.
8. “BEWARE OF BUGS IN THE ABOVE CODE; I HAVE ONLY PROVED IT CORRECT, NOT TRIED IT.” DONALD KNUTH NOTES ON THE VAN EMDE BOAS CONSTRUCTION OF PRIORITY DEQUES: AN INSTRUCTIVE USE OF RECURSION https://www.flickr.com/photos/gem66/38298868 Dangerous ideas! I'll be showing a lot of languages which are “still in the lab.” You may find some of this useful in your work tomorrow, but not all experiments succeed.
9. In particular the lab is Microsoft Research. Many people know Kinect, WorldWide Telescope, F#, Entity Framework, Pex.
10. “IF YOU’RE GOING TO USE CUTTING EDGE TECHNOLOGY, DON’T EXPECT NICE BLOG POSTS THAT TELL YOU IT’S EASY.” JOE ARMSTRONG CHICAGO ERLANG PRESENTATION https://www.flickr.com/photos/vanchett/3180276972 I have a rule of thumb for application architecture. Consider the tech you want to be using in 5 years, because… Never specify tech the Hacker News Hipsters tell you that you should be using today. Try to see into the future. This is hard! However, every tool I discuss is real and is used in production software, including software you might use every day.
11. “YOUNG MAN, IN MATHEMATICS YOU DON'T UNDERSTAND THINGS. YOU JUST GET USED TO THEM.” JOHN VON NEUMANN LETTER TO FELIX T. SMITH https://www.flickr.com/photos/36621927@N00/8378574271 These languages operate very differently than those you probably use in your day to day work. Don't worry if you don't follow every bit of syntax. To be quite honest, I don't fully understand all of this stuff myself. The important thing is to know what is available, and to think about problems in new ways.
12. Some Specialized Languages Assembly SQL C F# C#? I’ll be talking about specialized tools. We’re biased towards general purpose languages. But we happily use SQL when needed. We grow domain-specific languages to GP when necessary.
13. “IF DEBUGGING IS THE PROCESS OF REMOVING SOFTWARE BUGS, THEN PROGRAMMING MUST BE THE PROCESS OF PUTTING THEM IN.” ATTRIBUTED TO EDSGER DIJKSTRA Sounds like Dijkstra! Let’s talk about bugs. Broken code should be obvious. Cognitive overhead from inessential complexity turns out to be surprisingly high. Let’s examine some buggy code. Been a hell of a week; the Internet keeps giving!
14. JavaScript function add(a, b) { return a + b; } In study of buggy code, makes sense to start with JavaScript. In contrast to earlier example, completely broken. No error. Anyone know what it returns? JS, so we never specified the return type. Type checker would find. A test might find the bug This is not a good part
15. http://blog.erratasec.com/2014/09/bash-bug-as-big-as-heartbleed.html#.VCN_7StdWwE PLs are usually specified in EBNF. Machine verifiable specs are easy (not always true!); bash doesn’t use them and has evolved to the point where can’t be specified. So there are edge cases…. Syntax which should not be allowed. Even when (maybe!) not wrong: Also Ruby. parser.y impenetrable. Half the size of all of Lua for parser alone. Other implementations are probably different than MRI. Formal PL grammars keep parsers maintainable.
16. Goto Fail static OSStatus SSLVerifySignedServerKeyExchange(SSLContext *ctx, bool isRsa, SSLBuffer signedParams, uint8_t *signature, UInt16 signatureLen) { OSStatus err; ... ! if ((err = SSLHashSHA1.update(&hashCtx, &serverRandom)) != 0) goto fail; if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0) goto fail; goto fail; if ((err = SSLHashSHA1.final(&hashCtx, &hashOut)) != 0) goto fail; ... ! fail: SSLFreeBuffer(&signedHashes); SSLFreeBuffer(&hashCtx); return err; } Besides the obvious… $AAPL lost $20B when iOS update couldn’t dial the phone. “fail” is not always fail, and “err” is not always err. Crappy code, maybe, but real production code, and not the worst I’ve ever seen.
17. "Quality software costs money — Heartbleed was free." Paul-Henning Kamp DOI:10.1145/2631095 Not a TLS spec bug (though those can happen). Possibly creeping featuritis in spec. Also, strings are kind of broken. That’s true for most languages, not just C.
18. C# static Type GetType<T>() where T : new() { T t = new T(); return t.GetType(); // * } ! static void Main(string[] args) { Console.WriteLine(GetType<int?>().ToSting()); } Appears contrived, but useful, because type system is broken and it fits on a slide. * line throws. Deeply weird that you can new up something and can’t ask for its type. Type systems help, but not 100% safe.
19. F# let average (someList: int list) = (List.sum someList) / (List.length someList) Type system is restricted. There is no type for a non-empty list. Could check in code, but requires code + test. Better type system could do it for us.
20. CAN WE DO BETTER? OR MUST WE DO BETTER? https://www.flickr.com/photos/jurvetson/5872448596 How?
21. “Attempting to prove any nontrivial theorem about your program will expose lots of bugs. “The particular choice of theorem makes little difference! “Typechecking is good because it proves lots and lots of little theorems about your program.” –Benjamin C. Pierce http://www.cis.upenn.edu/~bcpierce/papers/harmful-mfps.pdf Use strong types! There is a deep relationship between programs and mathematical proofs. Talk to me after, but types good! Strong types (especially for real strong types) are awesome for refactoring. Slash + burn. Don’t fix the bug. Change the data types to make the state which caused it impossible. C# types maybe not strong enough to succinctly only allow state which is correct by construction.
22. “PROGRAM TESTING CAN BE USED TO SHOW THE PRESENCE OF BUGS, BUT NEVER THEIR ABSENCE.” EDSGER DIJKSTRA STRUCTURED PROGRAMMING Tests are ∃, strong types are ∀. Testing is great; property-based testing (QuickCheck, etc.) even better Testing is evidence, not a proof But the 80/20 rule may hold
23. “WHAT’S TRUE OF EVERY BUG FOUND IN THE FIELD? IT HAS PASSED THE TYPE CHECKER… AND ALL OF THE TESTS.” RICH HICKEY SIMPLE MADE EASY https://www.flickr.com/photos/grouperkun/5351080866 Simplicity, conceptual clarity, is the silver bullet, not languages. "Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.” Brian Kernighan When you diverge from essential complexity, you’re creating a maintenance problem. Microkernels!
24. Hoare Verification {P} C {Q} Partial vs. total correctness Considered to be high-effort; 100/100 Tony Hoare, Algol (who has heard of Algol?) Anyone ever seen a null reference error? One can totally specify software. Precondition->Command->Postcondition
25. Z3 http://rise4fun.com/Z3 http://z3.codeplex.com/ https://www.flickr.com/photos/laughingsquid/102654032 So here’s your flying car! Z3 is a theorem prover. Sounds like math, but stay with me. When you hear “theorem prover,” think really strong types. Equivalent. Specification = always true about a system. “Formal specification” = verifiable by a machine. "Type errors are not just red flags: in a sufficiently well-specified theory, all errors are type errors." Evan Jenkins SMT solver. Take some specs, simplify them algebraically, and efficiently prove the spec satisfiable or not, with examples.
26. A Simple Problem Write a Ruby program that determines the smallest three digit number such that when said number is divided by the sum of its digits the answer is 20. Example: Number = 123. Sum of digits = 6 123/6 = 20.5, so not a solution. Hate it when speakers read slides out loud, but… Picked this because it’s a very simple problem. Z3 is ASM. Usually not used directly. Will see examples of systems which use it.
27. Ruby Most people would try something like… Seems reasonable, but it’s brute force solution. Have we fully understood the problem? Also, this is wrong. You probably have to be fairly good with Ruby to figure out why. Ruby is complicated; just try and parse it! Cognitive overhead for even a simple problem is very high!
28. Ruby Looks efficient! Is this right? Remember, I like to put buggy code on my slides! Bestowed? Is it the best solution? Do you want this in the code you maintain?
29. SMT-LIB I know, (). SMT-LIB language used to compare/benchmark solvers. You don’t typically use this for production. Minimal interface to Z3. Did live in rehearsal. Awkward! See me in person for demos. “Formal” spec for most of problem. Machine checkable. Omitted one part.
30. SMT-LIB Variable?
31. SMT-LIB Test-only programming. Does forall make sense?
32. SMT-LIB
33. http://rise4fun.com/Z3/7VZh Had to write digit-sum
34. Note that the model is valid SMT-LIB code. Optimized! Really important. Complex definitions tend to be wrong when first written out. They can also be complete nonsense! !
35. Add one clause
36. Not “can’t find.” Doesn’t exist.
37. Who uses this? Hyper-V hypervisor. If this is wrong the world ends. 100000 lines C, 5000 lines x64 ASM Complex implementation, fairly simple spec. Around 1.5 person years, incl learn VCC. 18 hours execution. Xen flaw to be disclosed Wednesday. Also Dafny, F*, etc.
38. DAFNY http://rise4fun.com/Dafny http://research.microsoft.com/dafny https://www.flickr.com/photos/marcusjb/440973101/
39. Dafny Useful for education. Correctness more important than executability. Looks like code contracts but proven at compile time! Imperative code. What must go right? Solver proves that mathematical and imperative definitions equivalent. Important, especially for optimization. Similar to 180 example.
40. Who uses Dafny? Rice University “Reasoning about algorithms”
41. https://www.flickr.com/photos/ayman/21226117 F* based on F#. Subsumes F7 and other MSR projects.
42. Append function for length-indexed list. Heavy effort, heavy return. Remember C# variance annotations: Useful, even if you don’t write them!
44. F7 source for miTLS
45. Compiles to…
46. Funny thing about formally verifying specs. Sounds awesome that the code meets spec.
47. TLA+ http://research.microsoft.com/en-us/um/people/lamport/tla/tla.html "Writing is nature’s way of letting you know how sloppy your thinking is." Richard Guindon "Mathematics is nature’s way of letting you know how sloppy your writing is.... Formal mathematics is nature’s way of letting you know how sloppy your mathematics is." Leslie Lamport "Specification is not an end in itself; it is just a tool that an engineer should be able to use when appropriate." p. 76 "TLA+ is particularly effective at revealing concurrency errors—ones that arise through the interaction of asynchronous components." TLA book, p. 76.
48. http://lorinhochstein.wordpress.com/2014/06/04/crossing-the-river-with-tla/
50. http://somethingofthatilk.com/index.php?id=135
54. Who Uses TLA+? http://research.microsoft.com/en-us/um/people/lamport/tla/formal-methods-amazon.pdf Anything on AWS: Netflix, Heroku
55. WHAT HAVE WE LEARNED? Thinking about specification, and formal specs keep you honest! Force you to consider whole problem. Make a spec which is internally consistent. Double entry check vs. code. Useful when problem domain too large (AWS) or too complex (Ruby) to test. Proves optimized code equivalent to readable code.
56. ARE FLYING CARS A BAD IDEA? https://www.flickr.com/photos/bobjagendorf/4934950194/ Tooling is an issue. Proving production code matches spec can be challenging. __agl verify ECC C code Impractical for complex systems. Good when it makes you simplify! Exhaustive testing, when possible, can give you similar return for less effort. Not always possible.
57. Gratitude The people of Microsoft Research Others I’ve learned from SMT-LIB: Laurentiu Nicola (blog comment) Dafny: Swarat Chaudhuri’s articles TLA+: Chris Newcombe, Tim Rath, Fan Zhang, Bogdan Munteanu, Marc Brooker, and Michael Deardeuff and Lorin Hochstein’s blog Photographers (credited on each slide where used) My family, employer, and coworkers, for putting up with me spending time on this stuff
58. CRAIG STUNTZ @CraigStuntz Craig.Stuntz@ImprovingEnterprises.com http://blogs.teamb.com/craigstuntz http://www.meetup.com/Papers-We-Love-Columbus/ Least interesting part, but…. Questions?