feat: async connect

[ronag]

Fixes: #885

[ronag]

@szmarczak

[codecov-commenter]

Codecov Report

Merging #887 (e618fb5) into main (104be9c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #887   +/-   ##
=======================================
  Coverage   99.81%   99.81%           
=======================================
  Files          26       26           
  Lines        2121     2132   +11     
=======================================
+ Hits         2117     2128   +11     
  Misses          4        4           

Impacted Files	Coverage Δ
lib/core/symbols.js	100.00% <ø> (ø)
lib/client.js	100.00% <100.00%> (ø)
lib/core/connect.js	100.00% <100.00%> (ø)
lib/pool.js	100.00% <100.00%> (ø)

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[mcollina]

the code looks good, could you also take a look at benchmarks?

[szmarczak]

@mcollina Seems like there's no performance regression. There is always some difference in various tests in other runs but they're heading for about the same value.

Node.js v16.5.0

async connect:

szm@solus ~/Desktop/undici $ node benchmarks/benchmark.js 
│ Tests               │ Samples │           Result │ Tolerance │ Difference with slowest │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ http - no keepalive │      10 │  6501.19 req/sec │  ± 2.71 % │                       - │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ http - keepalive    │      85 │  9121.99 req/sec │  ± 2.96 % │               + 40.31 % │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ undici - pipeline   │      70 │ 13159.92 req/sec │  ± 2.80 % │              + 102.42 % │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ undici - request    │      60 │ 15766.59 req/sec │  ± 2.97 % │              + 142.52 % │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ undici - stream     │      15 │ 20320.07 req/sec │  ± 2.56 % │              + 212.56 % │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ undici - dispatch   │      20 │ 23858.58 req/sec │  ± 2.85 % │              + 266.99 % │

main:

szm@solus ~/Desktop/undici $ node benchmarks/benchmark.js 
│ Tests               │ Samples │           Result │ Tolerance │ Difference with slowest │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ http - no keepalive │      15 │  5553.42 req/sec │  ± 2.52 % │                       - │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ http - keepalive    │      40 │  8982.60 req/sec │  ± 2.78 % │               + 61.75 % │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ undici - pipeline   │      70 │ 13000.28 req/sec │  ± 2.86 % │              + 134.10 % │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ undici - request    │      10 │ 18970.56 req/sec │  ± 2.80 % │              + 241.60 % │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ undici - stream     │      25 │ 21187.96 req/sec │  ± 2.64 % │              + 281.53 % │
|─────────────────────|─────────|──────────────────|───────────|─────────────────────────|
│ undici - dispatch   │      25 │ 22509.90 req/sec │  ± 2.90 % │              + 305.33 % │

[szmarczak]

This wrapper should provide support for native Node.js agents: https://gist.github.com/szmarczak/a4b23a3cd6f402b2de41e6eed0bcd011

Usage of ClientRequest by various proxy agents:

• https://github.com/koichik/node-tunnel/blob/5fb2fb424788597146b7be6729006cad1cf9e9a8/lib/tunnel.js#L157
• https://github.com/zjael/simple-proxy-agent/blob/7e15a0bf6a5d1cc9c8e3bf05d3198ec98ad8bb6a/src/http.js#L21-L39
• https://github.com/gajus/global-agent/blob/debc4e6379074a808ead584f6265d5f8605ff1ad/src/classes/Agent.js#L53-L209
• https://github.com/TooTallNate/node-http-proxy-agent/blob/ef184d6b7af42e02920b015ecea557a0ac201fdc/src/agent.ts#L108-L159
• https://github.com/TooTallNate/node-agent-base/blob/0288bc26f856dd0473a2923241dfbf1ab67b99b0/src/index.ts#L225-L329

The bad thing here is that some of the agents above try to mutate the request. undici doesn't allow this (IMO that's the right behavior), so it will throw.