lite2: correctly return the results of the "latest" block (#4931)

Closes #4837

- `/block_results`

  before:

  failed to update light client to 7: failed to obtain the header #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

cmd/tendermint/commands/lite.go

@@ -36,16 +36,16 @@ Example:
 
 start a fresh instance:
 
-lite cosmoshub-3 -p 52.57.29.196:26657 -w public-seed-node.cosmoshub.certus.one:26657
+lite cosmoshub-3 -p http://52.57.29.196:26657 -w http://public-seed-node.cosmoshub.certus.one:26657
 	--height 962118 --hash 28B97BE9F6DE51AC69F70E0B7BFD7E5C9CD1A595B7DC31AFF27C50D4948020CD
 
 continue from latest state:
 
-lite cosmoshub-3 -p 52.57.29.196:26657 -w public-seed-node.cosmoshub.certus.one:26657
+lite cosmoshub-3 -p http://52.57.29.196:26657 -w http://public-seed-node.cosmoshub.certus.one:26657
 `,
 	RunE: runProxy,
 	Args: cobra.ExactArgs(1),
-	Example: `lite cosmoshub-3 -p 52.57.29.196:26657 -w public-seed-node.cosmoshub.certus.one:26657
+	Example: `lite cosmoshub-3 -p http://52.57.29.196:26657 -w http://public-seed-node.cosmoshub.certus.one:26657
 	--height 962118 --hash 28B97BE9F6DE51AC69F70E0B7BFD7E5C9CD1A595B7DC31AFF27C50D4948020CD`,
 }
 
@@ -102,7 +102,7 @@ func runProxy(cmd *cobra.Command, args []string) error {
 
 	db, err := dbm.NewGoLevelDB("lite-client-db", home)
 	if err != nil {
-		return fmt.Errorf("new goleveldb: %w", err)
+		return fmt.Errorf("can't create a db: %w", err)
 	}
 
 	var c *lite.Client

lite2/rpc/client.go

@@ -302,8 +302,23 @@ func (c *Client) BlockByHash(hash []byte) (*ctypes.ResultBlock, error) {
 	return res, nil
 }
 
+// BlockResults returns the block results for the given height. If no height is
+// provided, the results of the block preceding the latest are returned.
 func (c *Client) BlockResults(height *int64) (*ctypes.ResultBlockResults, error) {
-	res, err := c.next.BlockResults(height)
+	var h int64
+	if height == nil {
+		res, err := c.next.Status()
+		if err != nil {
+			return nil, fmt.Errorf("can't get latest height: %w", err)
+		}
+		// Can't return the latest block results here because we won't be able to
+		// prove them. Return the results for the previous block instead.
+		h = res.SyncInfo.LatestBlockHeight - 1
+	} else {
+		h = *height
+	}
+
+	res, err := c.next.BlockResults(&h)
 	if err != nil {
 		return nil, err
 	}
@@ -314,14 +329,14 @@ func (c *Client) BlockResults(height *int64) (*ctypes.ResultBlockResults, error)
 	}
 
 	// Update the light client if we're behind.
-	h, err := c.updateLiteClientIfNeededTo(res.Height + 1)
+	trustedHeader, err := c.updateLiteClientIfNeededTo(h + 1)
 	if err != nil {
 		return nil, err
 	}
 
 	// Verify block results.
 	results := types.NewResults(res.TxsResults)
-	if rH, tH := results.Hash(), h.LastResultsHash; !bytes.Equal(rH, tH) {
+	if rH, tH := results.Hash(), trustedHeader.LastResultsHash; !bytes.Equal(rH, tH) {
 		return nil, fmt.Errorf("last results %X does not match with trusted last results %X",
 			rH, tH)
 	}