From da813e4e36748430700ea02b5b11f0628db9df4e Mon Sep 17 00:00:00 2001
From: Callum Waters <cmwaters19@gmail.com>
Date: Tue, 11 Feb 2020 10:41:58 +0100
Subject: [PATCH] lite2: manage witness dropout (#4380)

* witnesses are dropped after no response

* test witness dropout

* corrected import structure

* moved non responsiveness check to compare function

* removed dropout test as witnesses are never dropped

* created test to compare witnesses
---
 lite2/client.go      | 45 ++++++++++++++++++++++++-------------
 lite2/client_test.go | 53 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+), 15 deletions(-)

diff --git a/lite2/client.go b/lite2/client.go
index 5dc1878eb..668a46203 100644
--- a/lite2/client.go
+++ b/lite2/client.go
@@ -915,27 +915,42 @@ func (c *Client) compareNewHeaderWithWitnesses(h *types.SignedHeader) error {
 		return errors.New("could not find any witnesses")
 	}
 
-	// 1. Loop through all witnesses.
-	for _, witness := range c.witnesses {
+	matchedHeader := false
+
+	for attempt := uint16(1); attempt <= c.maxRetryAttempts; attempt++ {
+		// 1. Loop through all witnesses.
+		for _, witness := range c.witnesses {
+
+			// 2. Fetch the header.
+			altH, err := witness.SignedHeader(h.Height)
+			if err != nil {
+				c.logger.Info("No Response from witness ", "witness", witness)
+				continue
+			}
+
+			// 3. Compare hashes.
+			if !bytes.Equal(h.Hash(), altH.Hash()) {
+				// TODO: One of the providers is lying. Send the evidence to fork
+				// accountability server.
+				return errors.Errorf(
+					"header hash %X does not match one %X from the witness %v",
+					h.Hash(), altH.Hash(), witness)
+			}
+
+			matchedHeader = true
 
-		// 2. Fetch the header.
-		altH, err := witness.SignedHeader(h.Height)
-		if err != nil {
-			return errors.Wrapf(err,
-				"failed to obtain header #%d from the witness %v", h.Height, witness)
 		}
 
-		// 3. Compare hashes.
-		if !bytes.Equal(h.Hash(), altH.Hash()) {
-			// TODO: One of the providers is lying. Send the evidence to fork
-			// accountability server.
-			return errors.Errorf(
-				"header hash %X does not match one %X from the witness %v",
-				h.Hash(), altH.Hash(), witness)
+		// 4. Check that one responding witness has returned a matching header
+		if matchedHeader {
+			return nil
 		}
+
+		time.Sleep(backoffTimeout(attempt))
+
 	}
 
-	return nil
+	return errors.New("awaiting response from all witnesses exceeded dropout time")
 }
 
 func (c *Client) removeNoLongerTrustedHeadersRoutine() {
diff --git a/lite2/client_test.go b/lite2/client_test.go
index 3f7038e89..4f0e9c600 100644
--- a/lite2/client_test.go
+++ b/lite2/client_test.go
@@ -1033,3 +1033,56 @@ func Test_NewClientFromTrustedStore(t *testing.T) {
 	assert.NoError(t, err)
 	assert.EqualValues(t, 1, h.Height)
 }
+
+func TestCompareWithWitnesses(t *testing.T) {
+	const (
+		chainID = "TestCompareWithWitnesses"
+	)
+
+	var (
+		keys = genPrivKeys(4)
+		// 20, 30, 40, 50 - the first 3 don't have 2/3, the last 3 do!
+		vals     = keys.ToValidators(20, 10)
+		bTime, _ = time.Parse(time.RFC3339, "2006-01-02T15:04:05Z")
+		h1       = keys.GenSignedHeader(chainID, 1, bTime, nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+		h2 = keys.GenSignedHeaderLastBlockID(chainID, 2, bTime.Add(30*time.Minute), nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys), types.BlockID{Hash: h1.Hash()})
+		h3 = keys.GenSignedHeaderLastBlockID(chainID, 3, bTime.Add(1*time.Hour), nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys), types.BlockID{Hash: h2.Hash()})
+		liveProvider = mockp.New(
+			chainID,
+			map[int64]*types.SignedHeader{
+				1: h1,
+				2: h2,
+				3: h3,
+			},
+			map[int64]*types.ValidatorSet{
+				1: vals,
+				2: vals,
+				3: vals,
+				4: vals,
+			},
+		)
+		deadProvider = mockp.NewDeadMock(chainID)
+	)
+
+	c, err := NewClient(
+		chainID,
+		TrustOptions{
+			Period: 1 * time.Hour,
+			Height: 2,
+			Hash:   h2.Hash(),
+		},
+		liveProvider,
+		[]provider.Provider{deadProvider, deadProvider, deadProvider},
+		dbs.New(dbm.NewMemDB(), chainID),
+		UpdatePeriod(0),
+		Logger(log.TestingLogger()),
+		MaxRetryAttempts(1),
+	)
+	require.NoError(t, err)
+	err = c.Update(time.Now())
+	assert.Error(t, err)
+
+}