extend 03-connection with a proof object for chains that can't intros…

…pect their own consensus state. (#839)

* extend 03-connection with HostConsensusStateProof

* make hostConsensusStateProof optional

spec/core/ics-003-connection-semantics/README.md

@@ -376,13 +376,15 @@ function connOpenTry(
   proofClient: CommitmentProof,
   proofConsensus: CommitmentProof,
   proofHeight: Height,
-  consensusHeight: Height) {
+  consensusHeight: Height,
+  hostConsensusStateProof?: bytes,
+) {
     // generate a new identifier
     identifier = generateIdentifier()
 
     abortTransactionUnless(validateSelfClient(clientState))
     abortTransactionUnless(consensusHeight < getCurrentHeight())
-    expectedConsensusState = getConsensusState(consensusHeight)
+    expectedConsensusState = getConsensusState(consensusHeight, hostConsensusStateProof)
     expectedConnectionEnd = ConnectionEnd{INIT, "", getCommitmentPrefix(), counterpartyClientIdentifier,
                              clientIdentifier, counterpartyVersions, delayPeriodTime, delayPeriodBlocks}
 
@@ -413,12 +415,14 @@ function connOpenAck(
   proofClient: CommitmentProof,
   proofConsensus: CommitmentProof,
   proofHeight: Height,
-  consensusHeight: Height) {
+  consensusHeight: Height,
+  hostConsensusStateProof?: bytes,
+) {
     abortTransactionUnless(consensusHeight < getCurrentHeight())
     abortTransactionUnless(validateSelfClient(clientState))
     connection = provableStore.get(connectionPath(identifier))
     abortTransactionUnless((connection.state === INIT && connection.version.indexOf(version) !== -1)
-    expectedConsensusState = getConsensusState(consensusHeight)
+    expectedConsensusState = getConsensusState(consensusHeight, hostConsensusStateProof)
     expectedConnectionEnd = ConnectionEnd{TRYOPEN, identifier, getCommitmentPrefix(),
                              connection.counterpartyClientIdentifier, connection.clientIdentifier,
                              version, connection.delayPeriodTime, connection.delayPeriodBlocks}

spec/core/ics-024-host-requirements/README.md

@@ -8,7 +8,7 @@ requires: 23
 required-by: 2, 3, 4, 5, 18
 author: Christopher Goes <[email protected]>
 created: 2019-04-16
-modified: 2022-07-05
+modified: 2022-09-14
 ---
 
 ## Synopsis
@@ -170,11 +170,15 @@ Host state machines MUST define a unique `ConsensusState` type fulfilling the re
 Host state machines MUST provide the ability to introspect their own consensus state, with `getConsensusState`:
 
 ```typescript
-type getConsensusState = (height: Height) => ConsensusState
+type getConsensusState = (height: Height, proof?: bytes) => ConsensusState
 ```
 
 `getConsensusState` MUST return the consensus state for at least some number `n` of contiguous recent heights, where `n` is constant for the host state machine. Heights older than `n` MAY be safely pruned (causing future calls to fail for those heights).
 
+We provide an optional proof data which comes from the `MsgConnectionOpenAck` or `MsgConnectionOpenTry` for host state machines which are unable to introspect their own `ConsensusState` and must rely on off-chain data.
+<br />
+In this case host state machines MUST maintain a map of `n` block numbers to header hashes where the proof would contain full header which can be hashed and compared with the on-chain record.
+
 Host state machines MUST provide the ability to introspect this stored recent consensus state count `n`, with `getStoredRecentConsensusStateCount`:
 
 ```typescript