perf(ext/fetch): Use the WebIDL conversion to DOMString rather than USVString for Response constructor

[lmalheiro]

Fixes performance issue #12090

• Replaces conversion to USVString by DOMString at the BodyInit WebIDL conversion.

• Adds benchmark response_string which produced the following results before and after the change:

  • using USVString:

  Benchmark #13: /home/luismalheiro/projects/deno_pr/target/release/deno run cli/tests/testdata/response_string_perf.js 
    Time (mean ± σ):     432.9 ms ±  26.8 ms    [User: 308.8 ms, System: 192.8 ms]
    Range (min … max):   409.5 ms … 485.4 ms    10 runs
  

  • using DOMString:

  Benchmark #13: /home/luismalheiro/projects/deno_pr/target/release/deno run cli/tests/testdata/response_string_perf.js 
    Time (mean ± σ):     175.8 ms ±  17.6 ms    [User: 168.6 ms, System: 73.9 ms]
    Range (min … max):   147.3 ms … 211.6 ms    18 runs
  

  Notice that the difference will increase non-linearly for larger strings.

This pull request replaces #12093

[lucacasonato]

This is not correct though. USVString normalization doesn't happen at all now.

[andreubotella]

This is not correct though. USVString normalization doesn't happen at all now.

The BodyInit type is only used in the Response constructor and in RequestInit, which itself is only used in the Request constructor (and in the fetch function, which defers to the Request constructor). In both of these cases, the BodyInit parameter is passed to extractBody before doing anything else with it – and extractBody will UTF-8 encode strings with replacement, effectively performing the USV normalization.

[andreubotella]

BodyInit is a WebIDL union type defined in the fetch specification. As I suggested in #12168 (comment), you should probably define a different WebIDL type (BodyInit_DOMString for example), to avoid confusion.

[lmalheiro]

@andreubotella, what would you suggest to do with the nullable converter BodyInit? ? Should I rename it too?

[andreubotella]

That's right

[lmalheiro]

Renamed.

[lucacasonato]

LGTM, thanks @lmalheiro and @andreubotella