Slow _normalizeIPv6

[mcollina]

We are investigating slow startup time in Fastify, and we identified this library as our primary bottleneck (see also https://github.com/epoberezkin/ajv/issues/995).

This is a flamegraph of the startup time. Apparently, the bottleneck is normalizing IPv6 addresses in https://github.com/garycourt/uri-js/blob/4f6f600fade03398c08adf2755c3a2ad66d31b3c/src/uri.ts#L175.

Note that that RegExp is extremely long:

/^\[?((?:(?:(?:(?:[0-9A-Fa-f]{1,4})\:){6}(?:(?:(?:[0-9A-Fa-f]{1,4})\:(?:[0-9A-Fa-f]{1,4}))|(?:(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9]))))|(?:\:\:(?:(?:[0-9A-Fa-f]{1,4})\:){5}(?:(?:(?:[0-9A-Fa-f]{1,4})\:(?:[0-9A-Fa-f]{1,4}))|(?:(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9]))))|(?:(?:(?:[0-9A-Fa-f]{1,4}))?\:\:(?:(?:[0-9A-Fa-f]{1,4})\:){4}(?:(?:(?:[0-9A-Fa-f]{1,4})\:(?:[0-9A-Fa-f]{1,4}))|(?:(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9]))))|(?:(?:(?:(?:[0-9A-Fa-f]{1,4})\:){0,1}(?:[0-9A-Fa-f]{1,4}))?\:\:(?:(?:[0-9A-Fa-f]{1,4})\:){3}(?:(?:(?:[0-9A-Fa-f]{1,4})\:(?:[0-9A-Fa-f]{1,4}))|(?:(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9]))))|(?:(?:(?:(?:[0-9A-Fa-f]{1,4})\:){0,2}(?:[0-9A-Fa-f]{1,4}))?\:\:(?:(?:[0-9A-Fa-f]{1,4})\:){2}(?:(?:(?:[0-9A-Fa-f]{1,4})\:(?:[0-9A-Fa-f]{1,4}))|(?:(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9]))))|(?:(?:(?:(?:[0-9A-Fa-f]{1,4})\:){0,3}(?:[0-9A-Fa-f]{1,4}))?\:\:(?:[0-9A-Fa-f]{1,4})\:(?:(?:(?:[0-9A-Fa-f]{1,4})\:(?:[0-9A-Fa-f]{1,4}))|(?:(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9]))))|(?:(?:(?:(?:[0-9A-Fa-f]{1,4})\:){0,4}(?:[0-9A-Fa-f]{1,4}))?\:\:(?:(?:(?:[0-9A-Fa-f]{1,4})\:(?:[0-9A-Fa-f]{1,4}))|(?:(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9])\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9][0-9])|(?:0?[1-9][0-9])|0?0?[0-9]))))|(?:(?:(?:(?:[0-9A-Fa-f]{1,4})\:){0,5}(?:[0-9A-Fa-f]{1,4}))?\:\:(?:[0-9A-Fa-f]{1,4}))|(?:(?:(?:(?:[0-9A-Fa-f]{1,4})\:){0,6}(?:[0-9A-Fa-f]{1,4}))?\:\:)))(?:(?:\%25|\%(?![0-9A-Fa-f]{2}))((?:(?:[A-Za-z0-9\-\.\_\~\xA0-\u200D\u2010-\u2029\u202F-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]|(?:(?:%[EFef][0-9A-Fa-f]%[0-9A-Fa-f][0-9A-Fa-f]%[0-9A-Fa-f][0-9A-Fa-f])|(?:%[89A-Fa-f][0-9A-Fa-f]%[0-9A-Fa-f][0-9A-Fa-f])|(?:%[0-9A-Fa-f][0-9A-Fa-f])))+)))?\]?$/

This regexp is costly to evaluate at a 5-10ms each time on my machine (Node 10).

Do you think it's possible to simplify the above regexp so it's simpler and faster to execute?

[jsumners]

@mcollina I think that is the generally accepted way to validate a string as an IPv6 address. Other methods involve feeding the string into a library that validates by converting the string to bytes and determining if the bytes are a valid address -- https://guava.dev/releases/19.0/api/docs/src-html/com/google/common/net/InetAddresses.html#line.167

[garycourt]

Having looked into this, I am not able to reduce the complexity of this RegExp without sacrificing correctness, unfortunately.