Improve performance of String and Vec<u8>

[evgenykuzyakov]

Optimizing strings/vec reads using custom implementation for Vec<u8> with a bit of unsafe code, but without UB.
Switching deserialization to use &mut &[u8] instead of BufRead. It allows us to switch to BorshError instead of std::io::Error in the future to go with no_std.

Test plan

• Added unit tests for String and Vec<T>
• Verified gas cost by linking borsh directly to gas fee meter. See Contract Examples and Metrics nearcore#1829
• Re-running benchmarks

[MaksymZavershynskyi]

Is it possible that https://doc.rust-lang.org/std/io/struct.BufReader.html implements this very functionality?

[evgenykuzyakov]

Is it possible that https://doc.rust-lang.org/std/io/struct.BufReader.html implements this very functionality?

I think we can use BufReader with raw fill_buf() functionality for a lot of what I did manually with read_exact

[evgenykuzyakov]

Input Highlights for gas fess:

Cost of Borsh input of (s: String) where s="" is 9,080,640,736
Average diff 131,604,521
Cost of Borsh input of (v: Vec) where v=[] is 8,455,908,634
Average diff 112,708,303
Cost of Borsh input of (v: Vec) where v=[] is 8,425,057,666
Average diff 651,364,504

Full results: near/nearcore#1829 (comment)

TODO: Add Vec<_> tests

[MaksymZavershynskyi]

Could you rerun https://github.com/nearprotocol/borsh/tree/master/borsh-rs/benchmarks and re-generate the graphs?

[MaksymZavershynskyi]

Could you also update the benchmarks so that http://borsh.io/ picks them up?

[MaksymZavershynskyi]

Could you also bump the versions?

[MaksymZavershynskyi]

P.S. My github UI is chocking on 8k files :) Could we please remvoe the docs temporarily until we are through the reviews and then add them later before the merge?

[evgenykuzyakov]

Trying switch to fn deserialize(buf: &mut [u8]) -> Result<Self, Error>;.
Will let you know

[evgenykuzyakov]

See #62 for slice reader version. Need to fix benchmarks, but overall looks clean.

Also once we switch serialize to &mut Vec<u8>, we can kill std:io::Error

[evgenykuzyakov]

Going to regenerate benchmarks with the slice run

[evgenykuzyakov]

Merged buf slice branch, so it's ready to go (once the new benchmarks are added)

[MaksymZavershynskyi]

How is it different from linguist-vendored and what does -diff do?

[evgenykuzyakov]

I don't know. It's used by nearcore

[evgenykuzyakov]

Also I'm not sure why you would request changes based on the question? Which changes do I need to make?

[evgenykuzyakov]

https://github.com/github/linguist#vendored-code
https://github.com/github/linguist#generated-code
https://git-scm.com/docs/gitattributes#_marking_files_as_binary

[MaksymZavershynskyi]

I somehow failed to duckduckgo this info. It should've been a comment instead of request for changes.