light: Fix absence proof verification by light client (backport #7639) (#7716)

- use the full key path to pass to the VerifyAbsence function

CHANGELOG_PENDING.md

@@ -25,3 +25,6 @@ Special thanks to external contributors on this release:
 ### IMPROVEMENTS
 
 ### BUG FIXES
+
+- [light] \#7640 Light Client: fix absence proof verification (@ashcherbakov)
+- [light] \#7641 Light Client: fix querying against the latest height (@ashcherbakov)

light/rpc/client.go

@@ -162,24 +162,25 @@ func (c *Client) ABCIQueryWithOptions(ctx context.Context, path string, data tmb
 	}
 
 	// Validate the value proof against the trusted header.
+
+	// build a Merkle key path from path and resp.Key
+	if c.keyPathFn == nil {
+		return nil, errors.New("please configure Client with KeyPathFn option")
+	}
+
+	kp, err := c.keyPathFn(path, resp.Key)
+	if err != nil {
+		return nil, fmt.Errorf("can't build merkle key path: %w", err)
+	}
+
+	// verify value
 	if resp.Value != nil {
-		// 1) build a Merkle key path from path and resp.Key
-		if c.keyPathFn == nil {
-			return nil, errors.New("please configure Client with KeyPathFn option")
-		}
-
-		kp, err := c.keyPathFn(path, resp.Key)
-		if err != nil {
-			return nil, fmt.Errorf("can't build merkle key path: %w", err)
-		}
-
-		// 2) verify value
 		err = c.prt.VerifyValue(resp.ProofOps, l.AppHash, kp.String(), resp.Value)
 		if err != nil {
 			return nil, fmt.Errorf("verify value proof: %w", err)
 		}
 	} else { // OR validate the absence proof against the trusted header.
-		err = c.prt.VerifyAbsence(resp.ProofOps, l.AppHash, string(resp.Key))
+		err = c.prt.VerifyAbsence(resp.ProofOps, l.AppHash, kp.String())
 		if err != nil {
 			return nil, fmt.Errorf("verify absence proof: %w", err)
 		}