fix: eliminate bn.js and replace public key storage with JavaScript bigint

[steveluscher]

Problem

JavaScript bigint has been available in browsers since September 2020. Despite that we've implemented large value storage in PublicKey using the bn.js library. This library presently makes up ~13% of @solana/web3.js, or around 35K uncompressed.

Replacing this system with pure bigint storage would cut the size of this library down considerably.

Summary of Changes

• Patch borsh to serialize to and from bigint rather than BN instances. A pull request has been sent to the upstream project.
• Replace BN storage in PublicKey with bigint

Bundle size

Using package-build-stats:

const p = require('package-build-stats');
p.getPackageStats('~/solana/web3.js/').then(r => console.log(r))

Size before: 75299 gzipped bytes
Size after: 64191 gzipped bytes

Reduction of ~14%.

Notes

• Anyone who used to rely on accessing the private variable PublicKey::_bn will find that its type has changed from BN to bigint. Such is the risk when you reach into private variables.
• This change relies on patching borsh-js in a way that represents a breaking change. For this reason we modify the bundle script to bundle the modified version into the web3.js bundle. This has two implications:
  • An app that uses borsh outside of web3.js will end up bundling a second copy of it (presumably one that includes 'bn.js` which negates the benefits of this change)
  • Our patched version is accessible only within the confines of web3.js and will not cause a breaking change to the rest of the app.

Addresses #1103.

[codecov-commenter]

Codecov Report

Merging #1142 (2a08815) into master (34cf5d7) will decrease coverage by 0.29%.
The diff coverage is 70.83%.

@@            Coverage Diff             @@
##           master    #1142      +/-   ##
==========================================
- Coverage   76.35%   76.06%   -0.29%     
==========================================
  Files          56       56              
  Lines        3151     3159       +8     
  Branches      475      481       +6     
==========================================
- Hits         2406     2403       -3     
- Misses        578      585       +7     
- Partials      167      171       +4     

Impacted Files	Coverage Δ
src/publickey.ts	81.81% <70.83%> (-13.84%)	⬇️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[wireless-anon]

will this break the old PublicKey.equals when you pass in a new PublicKey object (i.e. a bigint-based one)?

concern is that calling a function from a library that uses an older version of @solana/web3.js and passing in a bigint-based PublicKey may fail

[steveluscher]

will this break the old PublicKey.equals when you pass in a new PublicKey object (i.e. a bigint-based one)?

Most certainly; good call-out.

Options:

1. Breaking version bump.
2. Add @solana/web3.js as a peerDependency of itself, meaning that when you install it, installing an older version of it somewhere else makes your project fail the peer dependency check.

I'm not sure if 2 would actually ‘work,’ but it does in my head. Thoughts, @joncinque, @jordansexton?

[github-actions]

Because there has been no activity on this PR for 14 days since it was merged, it has been automatically locked. Please open a new issue if it requires a follow up.