feat(NODE-5861): optimize parsing basic latin strings

[nbbeeken]

Description

What is changing?

• BSON's UTF8 parsing logic will attempt to use String.fromCharCode if bytes are under 128
• Move UTF8 validation after attempting the above, if bytes are below 128 there is nothing to validate

Is there new documentation needed for these changes?

• No

What is the motivation for this change?

This has shown to have much better performance for strings that fit in the basic latin range. Quite often this is BSON keys.

Release Highlight

BSON short basic latin string parsing performance improved!

The BSON library's string decoding logic now attempts to optimize for basic latin (ASCII) characters. This will apply to both BSON keys and BSON values that are or contain strings. If strings are less than 6 bytes we observed approximately ~100% increase in speed while around 15 bytes the performance was about ~30% better. For any non-basic latin bytes or at 20 bytes or greater the BSON library will continue to use Node.js' Buffer.toString API.

The intent is to generally target the deserialization of BSON keys which are often short and only use basic latin, Et tu, _id?

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket

[addaleax]

🚀

[baileympearson]

just one small suggestion, otherwise looks good