adr-018: abci validators

docs/architecture/adr-018-ABCI-Validators.md

@@ -0,0 +1,95 @@
+# ADR 018: ABCI Validator Improvements
+
+## Changelog
+
+05-08-2018: Initial draft
+
+## Context
+
+ADR 009 introduced major improvements to the ABCI around validators and the use
+of Amino. Here we follow up with some additional changes to improve the naming
+and expected use of Validator messages.
+
+We also fix how we communicate the commit round - there is no defined commit
+round, as validators can commit the same block in different rounds, so we
+should communicate the round each validator committed in.
+
+## Decision
+
+### Validator
+
+Currently a Validator contains address and `pub_key`, and one or the other is
+optional/not-sent depending on the use case. Instead, we should have a
+Validator (with just the address) and a ValidatorUpdate (with the pubkey):
+
+```
+message Validator {
+    bytes address
+    int64 power
+}
+
+message ValidatorUpdate {
+    PubKey pub_key
+    int64 power
+}
+```
+
+### RequestBeginBlock
+
+LastCommitInfo currently has an array of `SigningValidator` that contains
+information for each validator in the entire validator set.
+Instead, this should be called `VoteInfo`, since it is information about the
+validator votes.
+
+Additionally, we have a single CommitRound in the LastCommitInfo,
+but such a round does not exist. Instead, we
+should include the round associated with each commit vote:
+
+```
+message LastCommitInfo {
+  repeated VoteInfo commit_votes
+}
+
+message VoteInfo {
+    Validator validator
+    bool signed_last_block
+    int64 round
+}
+```
+
+### ResponseEndBlock
+
+Use ValidatorUpdates instead of Validators. Then it's clear we don't need an
+address, and we do need a pubkey.
+
+### InitChain
+
+Use ValidatorUpdates for both Request and Response. InitChain
+is about setting/updating the initial validator set, unlike BeginBlock
+which is just informational.
+
+## Status
+
+Proposal.
+
+## Consequences
+
+### Positive
+
+- Easier for developers to build on and understand the ABCI
+- Apps get more information about the votes (ie. the round they're from)
+
+### Negative
+
+- There are two validator types
+
+### Neutral
+
+-
+
+## References
+
+- [Latest ABCI Spec](https://github.com/tendermint/tendermint/blob/v0.22.8/docs/app-dev/abci-spec.md)
+- [ADR-009](https://github.com/tendermint/tendermint/blob/v0.22.8/docs/architecture/adr-009-ABCI-design.md)
+- [Issue #1712 - Don't send PubKey in
+  RequestBeginBlock](https://github.com/tendermint/tendermint/issues/1712)