Automatically de/serialize ABCI event attributes from/to base64

[thanethomson]

Closes #717

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Updated CHANGELOG.md

[codecov-io]

Codecov Report

Merging #718 (98ca62a) into master (25f7ba5) will increase coverage by 0.1%.
The diff coverage is 79.4%.

@@           Coverage Diff            @@
##           master    #718     +/-   ##
========================================
+ Coverage    40.0%   40.1%   +0.1%     
========================================
  Files         202     202             
  Lines       12805   12838     +33     
  Branches     3204    3214     +10     
========================================
+ Hits         5130    5160     +30     
+ Misses       7348    7331     -17     
- Partials      327     347     +20     

Impacted Files	Coverage Δ
rpc/src/endpoint/broadcast/tx_commit.rs	0.0% <0.0%> (ø)
tendermint/src/abci/tag.rs	46.8% <75.0%> (+23.7%)	⬆️
proto/src/serializers/bytes.rs	92.8% <100.0%> (-2.8%)	⬇️
rpc/tests/parse_response.rs	98.9% <100.0%> (+<0.1%)	⬆️
tendermint/src/abci/info.rs	27.2% <100.0%> (+27.2%)	⬆️
tendermint/src/abci/responses.rs	27.0% <100.0%> (+6.4%)	⬆️
rpc/src/order.rs	0.0% <0.0%> (ø)
rpc/src/query.rs	72.6% <0.0%> (ø)
rpc/src/client.rs	7.5% <0.0%> (ø)
... and 38 more

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[greg-szabo]

The code is technically correct and I like that the serialization is done using serde attributes (instead of custom derives) but I have some reservations about where the serialization module is located.

While trying to separate serialization from domain types, there were a few places where serialization code was gathered:

The tendermint_proto::serializers module contains most of the "raw" serializer/deserializer code in a reusable format. Things like serializing from a string that is supposed to be an integer, etc.
The tendermint::serializers module contains serializers that have specific validation requirements on the Tendermint domain-type level: for example a Hash is just a hexstring (serializer implemented in tendermint_proto) but it also has a length requirement that is validated in the domain type, hence the serializer needs to call that validation (in the form of a TryFrom trait in this case, which is implemented in tendermint).

Technically the base64string module would belong into tendermint_proto since it doesn't have any domain-type specific restrictions. I understand that this sounds a bit weird, since nothing in tendermint-proto is actually using the module.

So I leave it to you to decide if it's worth putting it there or keep it in tendermint, but I would really like to move it into one of the serializers modules, both for reusability and to keep the idea of a slow but constant separation of serialization from domain types.

[thanethomson]

So I leave it to you to decide if it's worth putting it there or keep it in tendermint, but I would really like to move it into one of the serializers modules, both for reusability and to keep the idea of a slow but constant separation of serialization from domain types.

Cool, I've moved just the deserializer into the tendermint-proto crate for now, since the serializer works for Strings. If we need a completely separate serialize/deserialize method then I can abstract it out into a separate module in the bytes.rs file, but it doesn't seem necessary right now.

[melekes]

👍