Add message compression and versioning

[abdulmth]

Description of change

• Messages are compressed with brotli before saving them to the tangle, and decompressed before getting parsed.
• Introducing message version and encoding version.

The format of a message on the tangle is as follows:
$message_version $encoding_version $data

where

• $message_version is a one byte flag indicating the message version (1 for the current, not-modified message).
• $encoding_version is a one byte flag indicating the encoding version (1 for json + brotli).
• $data is the compressed data.

$message_version can be used in the future to indicate the format that follows the first byte.

Links to any relevant issues

implements issue #434

Type of change

Add an x to the boxes that are relevant to your changes.

• Bug fix (a non-breaking change which fixes an issue)
• Enhancement (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Fix

How the change has been tested

Unit tests, manual tests, wasm bindings tests.

Change checklist

Add an x to the boxes that are relevant to your changes.

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[abdulmth]

we might need to check if the license of Brotli is compatible with the library
https://github.com/dropbox/rust-brotli/blob/master/LICENSE

[olivereanderson]

we might need to check if the license of Brotli is compatible with the library https://github.com/dropbox/rust-brotli/blob/master/LICENSE

It looks like it is licensed under the BSD 3-Clause. According to the accepted answer here: https://softwareengineering.stackexchange.com/questions/40561/is-bsd-license-compatible-with-apache
it should be compatible with the Apache 2.0 License, but we might have to double check.

[olivereanderson]

Would it maybe make more sense to move compression_brotli.rs into the identity-core crate?

[cycraig]

Would it maybe make more sense to move compression_brotli.rs into the identity-core crate?

It's specific to IOTA messages.

[cycraig]

Looks good overall.

Mostly nits and questions from my side. We need to decide whether or not to support uncompressed messages at all, for instance. We might want to move around some of the files since the tangle folder is getting a bit crowded.

[cycraig]

Oh, forgot to add these comments: tests should be wrapped in a tests module to prevent compiling them by default.

[cycraig]

we might need to check if the license of Brotli is compatible with the library https://github.com/dropbox/rust-brotli/blob/master/LICENSE

It looks like it is licensed under the BSD 3-Clause. According to the accepted answer here: https://softwareengineering.stackexchange.com/questions/40561/is-bsd-license-compatible-with-apache
it should be compatible with the Apache 2.0 License, but we might have to double check.

crypto.rs allows dependencies with a BSD 3-Clause licence so I think we should be good: https://github.com/iotaledger/crypto.rs/blob/fe43116710074f8e3930823bb130c736e51f32c4/.github/workflows/about.toml

[olivereanderson]

I think it would be neater to change the module's constant to be an associated constant, apart from that this looks good to me.