lite2: correctly return the results of the "latest" block

[melekes]

Closes #4837

• /block_results

  before:

  failed to update light client to 7: failed to obtain the header Fix p2p/switch.Broadcast impl #7: signed header not found

  after:

  We can't return the latest block results because we won't be able to
  prove them. Return the results for the previous block instead.

• /block_results?height=X`

  no changes

[auto-comment]

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[codecov-commenter]

Codecov Report

Merging #4931 into master will decrease coverage by 0.08%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #4931      +/-   ##
==========================================
- Coverage   62.84%   62.75%   -0.09%     
==========================================
  Files         198      198              
  Lines       20047    20055       +8     
==========================================
- Hits        12598    12585      -13     
- Misses       6427     6443      +16     
- Partials     1022     1027       +5     

Impacted Files	Coverage Δ
cmd/tendermint/commands/lite.go	24.65% <0.00%> (ø)
lite2/rpc/client.go	0.00% <0.00%> (ø)
consensus/reactor.go	72.64% <0.00%> (-2.33%)	⬇️
blockchain/v0/pool.go	78.02% <0.00%> (-0.64%)	⬇️
p2p/pex/pex_reactor.go	82.12% <0.00%> (ø)
consensus/state.go	74.23% <0.00%> (+0.67%)	⬆️
statesync/snapshots.go	94.07% <0.00%> (+1.48%)	⬆️

[cmwaters]

I spun it up and it seemed to work as expected 👍

[egonspace]

I met following error when I tested it.

curl -s "localhost:8888/block_results"
{
  "jsonrpc": "2.0",
  "id": -1,
  "error": {
    "code": -32603,
    "message": "Internal error",
    "data": "last results  does not match with trusted last results 4837665DFE640A370E7496C691987562D02462142C5F34F59E185911A12370EA"
  }
}

I wonder if this code is right.

// in /light/rpc/client.go: BlockResults()
results := types.NewResults(res.TxsResults)
if rH, tH := results.Hash(), trustedHeader.LastResultsHash; !bytes.Equal(rH, tH)

// LastResultsHash is defined as following
LastResultsHash = ABCIResponsesResultsHash(abciResponses) // merkle.HashFromByteSlices([][]byte{bbeBytes, results.Hash(), ebeBytes})

If TxsResults is nil, then rH is byte[0] but tH is an array having 32 bytes length.

And there's another problem, Validators rpc seems to have not fixed it.

curl -s "localhost:8888/validators"
{
  "jsonrpc": "2.0",
  "id": -1,
  "error": {
    "code": -32603,
    "message": "Internal error",
    "data": "failed to update light client to 1756: failed to obtain the header #1756: signed header not found"
  }
}