Node: Make llhttp default HTTP parser

[indutny]

Is your feature request related to a problem? Please describe.

Latest node.js can be compiled with --experimental-http-parser flag. Eventually, we'd want to swap things around and make it enable llhttp parser by default and hide http_parser under --legacy-http-parser flag.

Describe the solution you'd like

Hide http_parser under the flag when we're ready.

Describe alternatives you've considered

No alternatives.

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Let's discuss the earliest version of Node that we're going to try this in. http_parser is a major component and it would take a lot of testing to make sure that llhttp is on the par with it quality-wise.

cc @nodejs/release @nodejs/lts

[indutny]

cc @nodejs/http

[joyeecheung]

Is it possible to make it a runtime switch first? My impression is that it should be possible with some small C++ refactoring in the Parser class and make the decision when we get it from the binding based on the CLI option which should be available at that point

[rvagg]

related: I'm working on a sharedlibs builder in CI that'll test llhttp builds on all 11+ CI runs, so we'll soon be essentially mandating stability and quality for llhttp in parallel. Only covers one platform of course.

[addaleax]

@joyeecheung → https://github.com/nodejs/node/pull/24739

[ofrobots]

IMHO, we should make llhttp the default in Node 12. If we do not do so, we will have to maintain and fix security issues in _both_ http_parser and llhttp until 12 goes EOL in April 2022 at the earliest.

We will have 6 months of ecosystem testing available to us to harden llhttp before 12 goes LTS.