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Writing a fast HTTP parser
- 1. Lisp Meetup #22 Eitaro Fukamachi Writing a fast HTTP parser
- 2. Thank you for coming.
- 3. I’m Eitaro Fukamachi @nitro_idiot fukamachi
- 7. We’re hiring! Tell @Rudolph_Miller.
- 8. fast-http • HTTP request/response parser • Written in portable Common Lisp • Fast • Chunked body parser
- 9. fast-http Benchmarked with SBCL 1.2.5 / GCC v6.0.0
- 10. Let me tell why I had to write a fast HTTP parser.
- 12. Wookie is slower than Node.js • Wookie is 2 times slower than Node.js • Profiling result was saying “WOOKIE:READ-DATA” was pretty slow. • It was only calling “http-parse”. • “http-parse” which is an HTTP parser Wookie is using.
- 13. The bottleneck was HTTP parsing.
- 14. Wookie is slower than Node.js • Node.js’s HTTP parse is “http-parser”. • Written in C. • General version of Nginx’s HTTP parser. • Is it possible to beat it with Common Lisp?
- 15. Today, I’m talking what I did for writing a fast Common Lisp program.
- 16. 5 important things • Architecture • Reducing memory allocation • Choosing the right data types • Benchmark & Profile • Type declarations
- 17. 5 important things • Architecture • Reducing memory allocation • Choosing the right data types • Benchmark & Profile • Type declarations
- 18. A brief introduction of HTTP
- 19. HTTP request look like… GET /media HTTP/1.1↵ Host: somewrite.jp↵ Connection: keep-alive↵ Accept: */*↵ ↵
- 20. HTTP request look like… GET /media HTTP/1.1↵ Host: somewrite.jp↵ Connection: keep-alive↵ Accept: */*↵ ↵ First Line Headers Body (empty, in this case)
- 21. HTTP request look like… GET /media HTTP/1.1↵ Host: somewrite.jp↵ Connection: keep-alive↵ Accept: */*↵ ↵ CR + LF CRLF * 2 at the end of headers
- 22. HTTP response look like… HTTP/1.1 200 OK↵ Cache-Control: max-age=0↵ Content-Type: text/html↵ Date: Wed, 26 Nov 2014 04:52:55 GMT↵ ↵ <html> …
- 23. HTTP response look like… HTTP/1.1 200 OK↵ Status Line Cache-Control: max-age=0↵ Content-Type: text/html↵ Headers Date: Wed, 26 Nov 2014 04:52:55 GMT↵ ↵ <html> … Body
- 24. HTTP is… • Text-based protocol. (not binary) • Lines terminated with CRLF • Very lenient. • Ignore multiple spaces • Allow continuous header values
- 25. And, there’s another difficulty.
- 26. HTTP messages are sent over a network.
- 27. Which means, we need to think about long & incomplete HTTP messages.
- 28. There’s 2 ways to resolve this problem.
- 30. http-parser (used in Node.js) • https://github.com/joyent/http-parser • Written in C • Ported from Nginx’s HTTP parser • Written as Node.js’s HTTP parser • Stateful
- 31. http-parser (used in Node.js) for (p=data; p != data + len; p++) { … switch (parser->state) { case s_dead: … case s_start_req_or_res: … case s_res_or_resp_H: … } }
- 32. http-parser (used in Node.js) for (p=data; p != data + len; p++) { … switch (parser->state) { Process char by char case s_dead: … case s_start_req_or_res: … case s_res_or_resp_H: … } } Do something for each state
- 34. PicoHTTPParser (used in H2O) • https://github.com/h2o/picohttpparser • Written in C • Stateless • Reparse when the data is incomplete • Most HTTP request is small
- 36. fast-http is in the middle • Not track state for every character • Set state for every line • It makes the program simple • And easy to optimize
- 37. 5 important things • Architecture • Reducing memory allocation • Choosing the right data types • Benchmark & Profile • Type declarations
- 38. Memory allocation is slow • (in general) • Make sure not to allocate memory during processing • cons, make-instance, make-array… • subseq, append, copy-seq
- 39. 5 important things • Architecture • Reducing memory allocation • Choosing the right data types • Benchmark & Profile • Type declarations
- 40. Data types • Wrong data type makes your program slow. • List or Vector • Hash Table or Structure or Class
- 41. 5 important things • Architecture • Reducing memory allocation • Choosing the right data types • Benchmark & Profile • Type declarations
- 42. Benchmark is quite important • “Don’t guess, measure!” • Check if your changes improve the performance. • Benchmarking also keeps your motivation.
- 43. Profiling • SBCL has builtin profiler • (sb-profile:profile “FAST-HTTP” …) • (sb-profile:report)
- 44. 5 important things • Architecture • Reducing memory allocation • Choosing the right data types • Benchmark & Profile • Type declarations
- 45. Type declaration • Common Lisp has type declaration (optional) • (declare (type <type> <variable symbol>)) • It’s a hint for your Lisp compiler • (declare (optimize (speed 3) (safety 0))) • It’s your wish to your Lisp compiler See also: Cより高速なCommon Lispコードを書く
- 46. (safety 0) • (safety 0) means “don’t check the type & array index in run-time”. • Fast & unsafe (like C) • Is fixnum enough? • What do you do when someone passes a bignum to the function?
- 47. (safety 0) • fast-http has 2 layers • Low-level API • (speed 3) (safety 0) • High-level API (safer) • Check the variable type • (speed 3) (safety 2)
- 48. Attitude
- 49. Attitude • Write carefully. • It’s possible to beat C program • (if the program is complicated enough) • Don’t give up easily • Safety is more important than speed
- 50. Thanks.
- 51. EITARO FUKAMACHI 8arrow.org @nitro_idiot fukamachi