Add /consensus_params RPC endpoint

[thanethomson]

Partial fulfillment of #832, and helps towards informalsystems/hermes#1336

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Added entry in .changelog/

[thanethomson]

@andynog a quick way of testing this would be to run the tendermint-rpc binary from this branch against a validator:

# Get the latest consensus parameters
cargo run --all-features --bin tendermint-rpc -- -u https://validator-address.com latest-consensus-params

# Get the consensus parameters at height 1234
cargo run --all-features --bin tendermint-rpc -- -u https://validator-address.com consensus-params 1234

[codecov-commenter]

Codecov Report

Merging #972 (1d5628b) into master (80559bd) will increase coverage by 0.0%.
The diff coverage is 79.3%.

@@          Coverage Diff           @@
##           master    #972   +/-   ##
======================================
  Coverage    72.1%   72.2%           
======================================
  Files         203     204    +1     
  Lines       16577   16591   +14     
======================================
+ Hits        11961   11985   +24     
+ Misses       4616    4606   -10     

Impacted Files	Coverage Δ
rpc/src/client.rs	16.9% <ø> (ø)
rpc/src/client/bin/main.rs	0.6% <0.0%> (-0.1%)	⬇️
rpc/src/method.rs	29.5% <50.0%> (+<0.1%)	⬆️
rpc/src/endpoint/consensus_params.rs	100.0% <100.0%> (ø)
rpc/tests/kvstore_fixtures.rs	95.4% <100.0%> (+<0.1%)	⬆️
rpc/src/paging.rs	0.0% <0.0%> (ø)
light-client/src/types.rs	29.5% <0.0%> (ø)
rpc/src/endpoint/unsubscribe.rs	0.0% <0.0%> (ø)
... and 5 more

---

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[adizere]

Also for testing, to complement Thane's instructions, we can patch in ibc-rs the main Cargo.toml to use this branch, and call into the latest_consensus_params from Andy's branch.

tendermint = { git = "https://github.com/informalsystems/tendermint-rs", branch = "thane/832-consensus-params" }
tendermint-rpc = { git = "https://github.com/informalsystems/tendermint-rs", branch = "thane/832-consensus-params" }
tendermint-proto = { git = "https://github.com/informalsystems/tendermint-rs", branch = "thane/832-consensus-params" }
tendermint-light-client = { git = "https://github.com/informalsystems/tendermint-rs", branch = "thane/832-consensus-params" }
tendermint-testgen = { git = "https://github.com/informalsystems/tendermint-rs", branch = "thane/832-consensus-params" }

@andynog is there a branch WIP for informalsystems/hermes#1336 already?

[andynog]

@andynog a quick way of testing this would be to run the tendermint-rpc binary from this branch against a validator:

# Get the latest consensus parameters
cargo run --all-features --bin tendermint-rpc -- -u https://validator-address.com latest-consensus-params

Tested this line:

{
  "block_height": "7673671",
  "consensus_params": {
    "block": {
      "max_bytes": "200000",
      "max_gas": "40000000",
      "time_iota_ms": "1000"
    },
    "evidence": {
      "max_age_num_blocks": "1000000",
      "max_age_duration": "172800000000000",
      "max_bytes": "50000"
    },
    "validator": {
      "pub_key_types": [
        "ed25519"
      ]
    }
  }
}

And this is the response from the server using the RPC endpoint

{
  "jsonrpc": "2.0",
  "id": -1,
  "result": {
    "block_height": "7673671",
    "consensus_params": {
      "block": {
        "max_bytes": "200000",
        "max_gas": "40000000",
        "time_iota_ms": "1000"
      },
      "evidence": {
        "max_age_num_blocks": "1000000",
        "max_age_duration": "172800000000000",
        "max_bytes": "50000"
      },
      "validator": {
        "pub_key_types": [
          "ed25519"
        ]
      },
      "version": {}
    }
  }
}

Most seems OK, the only difference I see is that the RPC outputs a version field. I don't need to use it as far as I know for now but just wanted to point that out.

Get the consensus parameters at height 1234

cargo run --all-features --bin tendermint-rpc -- -u https://validator-address.com consensus-params 1234

This line also seems to work fine:

{
  "block_height": "7673671",
  "consensus_params": {
    "block": {
      "max_bytes": "200000",
      "max_gas": "40000000",
      "time_iota_ms": "1000"
    },
    "evidence": {
      "max_age_num_blocks": "1000000",
      "max_age_duration": "172800000000000",
      "max_bytes": "50000"
    },
    "validator": {
      "pub_key_types": [
        "ed25519"
      ]
    }
  }
}

[andynog]

I think overall looks good to me. Had a minor comment about a version field

[romac]

Sorry, about be7c665 and its revert, I failed to notice the latest_consensus_params endpoint.

[romac]

All good from my side, we're now using the new endpoint succesfully in informalsystems/hermes#1361 :)

[thanethomson]

Awesome. Yeah if we eventually need the version field we can add it in a follow-up PR.