feat(xml/unstable): add XML parsing and serialization module

[tomas-zijdemans]

New XML parsing and serialization module

What @std/xml has:

• Streaming parser, DOM-style parser, serialization
• Browser compatible, position tracking, spec-compliant

What @std/xml doesn't Have:

• Namespace resolution, DTD/Schema validation, HTML entities
• Custom entities, XPath/selectors, object-to-XML builder

My use case is a 600MB file of product data in a Google Shopping/Merchant Center XML format. I use Sax for this, as it can stream.

Benchmark Results

I picked Sax (for streaming) and fast-xml-parser (for non-streaming) as the reference cases. These seem like the most widely used packages, but please leave a comment if you would like to see a comparison to another package.

I ran these benchmarks a few hundred times (except the big streaming test that I ran about 15-20 times). All on a MacBook M1 Max. The test files are located in testdata (not the 600MB one naturally)

Small Files (<10KB)

Parser	Time	vs Baseline
Deno std xml	0.015ms	baseline
SAX	0.027ms	1.8x slower
fast-xml-parser	0.042ms	2.8x slower

Large Files (large.xml - 300KB)

Parser	Time	vs Baseline
Deno std xml	3.03ms	baseline
SAX	7.40ms	2.4x slower
fast-xml-parser	11.05ms	3.6x slower

Streaming (597MB file)

Parser	Time	Throughput	vs Baseline
Deno std xml	11.59s	65.4K products/s	baseline
SAX	17.04s	44.5K products/s	1.5x slower

[crowlKats]

could we get some benchmarks comparing to other parsers?

[tomas-zijdemans]

could we get some benchmarks comparing to other parsers?

Yes, that's a good idea. I'll look into it.

[codecov]

Codecov Report

❌ Patch coverage is 98.65526% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.49%. Comparing base (6b93b78) to head (9b1fe20).

Files with missing lines	Patch %	Lines
xml/_parse_sync.ts	96.08%	13 Missing ⚠️
xml/_tokenizer.ts	98.90%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6942      +/-   ##
==========================================
+ Coverage   94.28%   94.49%   +0.20%     
==========================================
  Files         584      593       +9     
  Lines       43186    44822    +1636     
  Branches     6933     7357     +424     
==========================================
+ Hits        40720    42353    +1633     
- Misses       2413     2417       +4     
+ Partials       53       52       -1     

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[tomas-zijdemans]

could we get some benchmarks comparing to other parsers?

Updated the description now. Let me know if you would like to benchmark against a specific package

[tomas-zijdemans]

Sorry, I have no idea why this formatting is happening 😅

[timreichen]

Ref: denoland/deno#24995
There was no reply if DOMParser or something similar was to be implemented in deno, so I like this PR in general.
However, it might be worth to check with the deno core team what their current stance is on this before merging anything.