R4R: LCD proof verification

PENDING.md

@@ -24,6 +24,7 @@ FEATURES
 * Gaia CLI  (`gaiacli`)
   * [\#3429](https://github.com/cosmos/cosmos-sdk/issues/3429) Support querying
   for all delegator distribution rewards.
+  * \#3449 Proof verification now works with absence proofs
 
 * Gaia
   - [\#3397](https://github.com/cosmos/cosmos-sdk/pull/3397) Implement genesis file sanitization to avoid failures at chain init.

client/context/context.go

@@ -24,7 +24,10 @@ import (
 	sdk "github.com/cosmos/cosmos-sdk/types"
 )
 
-var verifier tmlite.Verifier
+var (
+	verifier     tmlite.Verifier
+	verifierHome string
+)
 
 // CLIContext implements a typical CLI context created in SDK modules for
 // transaction handling and queries.
@@ -43,6 +46,7 @@ type CLIContext struct {
 	Async         bool
 	PrintResponse bool
 	Verifier      tmlite.Verifier
+	VerifierHome  string
 	Simulate      bool
 	GenerateOnly  bool
 	FromAddress   sdk.AccAddress
@@ -68,8 +72,9 @@ func NewCLIContext() CLIContext {
 	}
 
 	// We need to use a single verifier for all contexts
-	if verifier == nil {
+	if verifier == nil || verifierHome != viper.GetString(cli.HomeFlag) {
 		verifier = createVerifier()
+		verifierHome = viper.GetString(cli.HomeFlag)
 	}
 
 	return CLIContext{

client/context/query.go

@@ -219,6 +219,13 @@ func (ctx CLIContext) verifyProof(queryPath string, resp abci.ResponseQuery) err
 	kp = kp.AppendKey([]byte(storeName), merkle.KeyEncodingURL)
 	kp = kp.AppendKey(resp.Key, merkle.KeyEncodingURL)
 
+	if resp.Value == nil {
+		err = prt.VerifyAbsence(resp.Proof, commit.Header.AppHash, kp.String())
+		if err != nil {
+			return errors.Wrap(err, "failed to prove merkle proof")
+		}
+		return nil
+	}
 	err = prt.VerifyValue(resp.Proof, commit.Header.AppHash, kp.String(), resp.Value)
 	if err != nil {
 		return errors.Wrap(err, "failed to prove merkle proof")