feat: require non-zero headers for Verify (#184)

* docs: document trusted header in Verify

* stricted verification

* Update verify.go

Co-authored-by: Hlib Kanunnikov <hlibwondertan@gmail.com>

---------

Co-authored-by: Hlib Kanunnikov <hlibwondertan@gmail.com>

headertest/verify_test.go

@@ -14,18 +14,21 @@ import (
 func TestVerify(t *testing.T) {
 	suite := NewTestSuite(t)
 	trusted := suite.GenDummyHeaders(1)[0]
+	var zero *DummyHeader
 
 	next := func() *DummyHeader {
 		next := *suite.NextHeader()
 		return &next
 	}
 
 	tests := []struct {
+		trusted *DummyHeader
 		prepare func() *DummyHeader
 		err     error
 		soft    bool
 	}{
 		{
+			trusted: trusted,
 			prepare: func() *DummyHeader {
 				untrusted := next()
 				untrusted.VerifyFailure = true
@@ -34,6 +37,7 @@ func TestVerify(t *testing.T) {
 			err: ErrDummyVerify,
 		},
 		{
+			trusted: trusted,
 			prepare: func() *DummyHeader {
 				untrusted := next()
 				untrusted.VerifyFailure = true
@@ -43,17 +47,20 @@ func TestVerify(t *testing.T) {
 			soft: true, // soft because non-adjacent
 		},
 		{
+			trusted: trusted,
 			prepare: func() *DummyHeader {
 				return next()
 			},
 		},
 		{
+			trusted: trusted,
 			prepare: func() *DummyHeader {
 				return nil
 			},
 			err: header.ErrZeroHeader,
 		},
 		{
+			trusted: trusted,
 			prepare: func() *DummyHeader {
 				untrusted := next()
 				untrusted.Chainid = "gtmb"
@@ -62,6 +69,7 @@ func TestVerify(t *testing.T) {
 			err: header.ErrWrongChainID,
 		},
 		{
+			trusted: trusted,
 			prepare: func() *DummyHeader {
 				untrusted := next()
 				untrusted.Timestamp = untrusted.Timestamp.Truncate(time.Minute * 10)
@@ -70,6 +78,7 @@ func TestVerify(t *testing.T) {
 			err: header.ErrUnorderedTime,
 		},
 		{
+			trusted: trusted,
 			prepare: func() *DummyHeader {
 				untrusted := next()
 				untrusted.Timestamp = untrusted.Timestamp.Add(time.Minute)
@@ -78,6 +87,7 @@ func TestVerify(t *testing.T) {
 			err: header.ErrFromFuture,
 		},
 		{
+			trusted: trusted,
 			prepare: func() *DummyHeader {
 				untrusted := next()
 				untrusted.HeightI = trusted.Height()
@@ -86,18 +96,33 @@ func TestVerify(t *testing.T) {
 			err: header.ErrKnownHeader,
 		},
 		{
+			trusted: trusted,
 			prepare: func() *DummyHeader {
 				untrusted := next()
 				untrusted.HeightI += 100000
 				return untrusted
 			},
 			err: header.ErrHeightFromFuture,
 		},
+		{
+			trusted: trusted,
+			prepare: func() *DummyHeader {
+				return zero
+			},
+			err: header.ErrZeroHeader,
+		},
+		{
+			trusted: zero,
+			prepare: func() *DummyHeader {
+				return next()
+			},
+			err: header.ErrZeroHeader,
+		},
 	}
 
 	for i, test := range tests {
 		t.Run(strconv.Itoa(i), func(t *testing.T) {
-			err := header.Verify(trusted, test.prepare(), 0)
+			err := header.Verify(test.trusted, test.prepare(), 0)
 			if test.err != nil {
 				var verErr *header.VerifyError
 				assert.ErrorAs(t, err, &verErr)

verify.go

@@ -11,8 +11,9 @@ import (
 const DefaultHeightThreshold uint64 = 80000 // ~ 14 days of 15 second headers
 
 // Verify verifies untrusted Header against trusted following general Header checks and
-// custom user-specific checks defined in Header.Verify
+// custom user-specific checks defined in Header.Verify.
 //
+// Given headers must be non-zero
 // If heightThreshold is zero, uses DefaultHeightThreshold.
 // Always returns VerifyError.
 func Verify[H Header[H]](trstd, untrstd H, heightThreshold uint64) error {
@@ -50,6 +51,9 @@ func verify[H Header[H]](trstd, untrstd H, heightThreshold uint64) error {
 		heightThreshold = DefaultHeightThreshold
 	}
 
+	if trstd.IsZero() {
+		return ErrZeroHeader
+	}
 	if untrstd.IsZero() {
 		return ErrZeroHeader
 	}