From 2b735d8968eeb59bc3d5a5c7a9c71e7190fe288f Mon Sep 17 00:00:00 2001
From: Alexis Sellier <alexis@cloudhead.io>
Date: Tue, 8 Aug 2017 11:51:15 +0200
Subject: [PATCH] Support non-existence proof

---
 client/commands/query/get.go        | 53 ++++++++++++++++++++---------
 client/commands/query/query_test.go | 10 +++---
 2 files changed, 41 insertions(+), 22 deletions(-)

diff --git a/client/commands/query/get.go b/client/commands/query/get.go
index f608c71acc..46b6c64c5a 100644
--- a/client/commands/query/get.go
+++ b/client/commands/query/get.go
@@ -55,62 +55,81 @@ func Get(key []byte, prove bool) (data.Bytes, uint64, error) {
 		resp, err := node.ABCIQuery("/key", key, false)
 		return data.Bytes(resp.Value), resp.Height, err
 	}
-	val, h, _, err := GetWithProof(key)
+	val, h, _, _, err := GetWithProof(key)
 	return val, h, err
 }
 
 // GetWithProof returns the values stored under a given key at the named
 // height as in Get.  Additionally, it will return a validated merkle
 // proof for the key-value pair if it exists, and all checks pass.
-func GetWithProof(key []byte) (data.Bytes, uint64, *iavl.KeyExistsProof, error) {
+func GetWithProof(key []byte) (data.Bytes, uint64,
+	*iavl.KeyExistsProof, *iavl.KeyNotExistsProof, error) {
+
 	node := commands.GetNode()
 	cert, err := commands.GetCertifier()
 	if err != nil {
-		return nil, 0, nil, err
+		return nil, 0, nil, nil, err
 	}
 	return CustomGetWithProof(key, node, cert)
 }
 
 // TODO: fix this up alexis
-func CustomGetWithProof(key []byte, node client.Client,
-	cert Certifier) (data.Bytes, uint64, *iavl.KeyExistsProof, error) {
+func CustomGetWithProof(key []byte, node client.Client, cert Certifier) (data.Bytes, uint64,
+	*iavl.KeyExistsProof, *iavl.KeyNotExistsProof, error) {
 
 	resp, err := node.ABCIQuery("/key", key, true)
 	if err != nil {
-		return nil, 0, nil, err
+		return nil, 0, nil, nil, err
 	}
 	ph := int(resp.Height)
 
 	// make sure the proof is the proper height
 	if !resp.Code.IsOK() {
-		return nil, 0, nil, errors.Errorf("Query error %d: %s", resp.Code, resp.Code.String())
+		return nil, 0, nil, nil, errors.Errorf("Query error %d: %s", resp.Code, resp.Code.String())
 	}
-	// TODO: Handle null proofs
-	if len(resp.Key) == 0 || len(resp.Value) == 0 || len(resp.Proof) == 0 {
-		return nil, 0, nil, lc.ErrNoData()
+	if len(resp.Key) == 0 || len(resp.Proof) == 0 {
+		return nil, 0, nil, nil, lc.ErrNoData()
 	}
 	if ph != 0 && ph != int(resp.Height) {
-		return nil, 0, nil, lc.ErrHeightMismatch(ph, int(resp.Height))
+		return nil, 0, nil, nil, lc.ErrHeightMismatch(ph, int(resp.Height))
 	}
 
 	check, err := GetCertifiedCheckpoint(ph, node, cert)
 	if err != nil {
-		return nil, 0, nil, err
+		return nil, 0, nil, nil, err
 	}
 
-	proof := new(iavl.KeyExistsProof)
+	if len(resp.Value) > 0 {
+		// The key was found, construct a proof of existence.
+		proof := new(iavl.KeyExistsProof)
+		err = wire.ReadBinaryBytes(resp.Proof, &proof)
+		if err != nil {
+			return nil, 0, nil, nil, err
+		}
+
+		// validate the proof against the certified header to ensure data integrity
+		err = proof.Verify(resp.Key, resp.Value, check.Header.AppHash)
+		if err != nil {
+			return nil, 0, nil, nil, err
+		}
+
+		return data.Bytes(resp.Value), resp.Height, proof, nil, nil
+	}
+
+	// The key wasn't found, construct a proof of non-existence.
+	proof := new(iavl.KeyNotExistsProof)
 	err = wire.ReadBinaryBytes(resp.Proof, &proof)
 	if err != nil {
-		return nil, 0, nil, err
+		return nil, 0, nil, nil, err
 	}
 
 	// validate the proof against the certified header to ensure data integrity
-	err = proof.Verify(resp.Key, resp.Value, check.Header.AppHash)
+	err = proof.Verify(resp.Key, check.Header.AppHash)
 	if err != nil {
-		return nil, 0, nil, err
+		return nil, 0, nil, nil, err
 	}
 
-	return data.Bytes(resp.Value), resp.Height, proof, nil
+	return data.Bytes(resp.Value), resp.Height, nil, proof, nil
 }
 
 // GetCertifiedCheckpoint gets the signed header for a given height
diff --git a/client/commands/query/query_test.go b/client/commands/query/query_test.go
index 862b4ceb53..07c5716326 100644
--- a/client/commands/query/query_test.go
+++ b/client/commands/query/query_test.go
@@ -65,9 +65,9 @@ func TestAppProofs(t *testing.T) {
 
 	// Test existing key.
 
-	bs, _, proof, err := CustomGetWithProof(k, cl, cert)
+	bs, _, proofExists, _, err := CustomGetWithProof(k, cl, cert)
 	require.Nil(err, "%+v", err)
-	require.NotNil(proof)
+	require.NotNil(proofExists)
 
 	var data eyes.Data
 	err = wire.ReadBinaryBytes(bs, &data)
@@ -76,10 +76,10 @@ func TestAppProofs(t *testing.T) {
 
 	// Test non-existing key.
 
-	// TODO: This currently fails.
 	missing := []byte("my-missing-key")
-	bs, _, proof, err = CustomGetWithProof(missing, cl, cert)
+	bs, _, proofExists, proofNotExists, err := CustomGetWithProof(missing, cl, cert)
 	require.Nil(err, "%+v", err)
 	require.Nil(bs)
-	require.NotNil(proof)
+	require.Nil(proofExists)
+	require.NotNil(proofNotExists)
 }