From eecd71abeb5d8318f61944d4e3ef274685b5cd5b Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Sat, 6 Feb 2021 00:06:01 +0300
Subject: [PATCH] payload: treat zero-length headers as error

See neo-project/neo#2259.
---
 pkg/network/payload/headers.go      |  9 +++++++++
 pkg/network/payload/headers_test.go | 19 ++++++++++---------
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/pkg/network/payload/headers.go b/pkg/network/payload/headers.go
index 61b27053e..7c8c53d30 100644
--- a/pkg/network/payload/headers.go
+++ b/pkg/network/payload/headers.go
@@ -1,6 +1,7 @@
 package payload
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/nspcc-dev/neo-go/pkg/config/netmode"
@@ -24,10 +25,18 @@ const (
 // ErrTooManyHeaders is an error returned when too many headers were received.
 var ErrTooManyHeaders = fmt.Errorf("too many headers were received (max: %d)", MaxHeadersAllowed)
 
+// ErrNoHeaders is returned for zero-elements Headers payload which is considered to be invalid.
+var ErrNoHeaders = errors.New("no headers (zero length array)")
+
 // DecodeBinary implements Serializable interface.
 func (p *Headers) DecodeBinary(br *io.BinReader) {
 	lenHeaders := br.ReadVarUint()
 
+	if br.Err == nil && lenHeaders == 0 {
+		br.Err = ErrNoHeaders
+		return
+	}
+
 	var limitExceeded bool
 
 	// C# node does it silently
diff --git a/pkg/network/payload/headers_test.go b/pkg/network/payload/headers_test.go
index 38ef5183b..a8ea27e8b 100644
--- a/pkg/network/payload/headers_test.go
+++ b/pkg/network/payload/headers_test.go
@@ -13,14 +13,20 @@ func TestHeadersEncodeDecode(t *testing.T) {
 	t.Run("normal case", func(t *testing.T) {
 		headers := newTestHeaders(3)
 
-		testHeadersEncodeDecode(t, headers, 3, false)
+		testHeadersEncodeDecode(t, headers, 3, nil)
 	})
 
 	t.Run("more than max", func(t *testing.T) {
 		const sent = MaxHeadersAllowed + 1
 		headers := newTestHeaders(sent)
 
-		testHeadersEncodeDecode(t, headers, MaxHeadersAllowed, true)
+		testHeadersEncodeDecode(t, headers, MaxHeadersAllowed, ErrTooManyHeaders)
+	})
+
+	t.Run("zero", func(t *testing.T) {
+		headers := newTestHeaders(0)
+
+		testHeadersEncodeDecode(t, headers, 0, ErrNoHeaders)
 	})
 }
 
@@ -42,19 +48,14 @@ func newTestHeaders(n int) *Headers {
 	return headers
 }
 
-func testHeadersEncodeDecode(t *testing.T, headers *Headers, expected int, limit bool) {
+func testHeadersEncodeDecode(t *testing.T, headers *Headers, expected int, retErr error) {
 	data, err := testserdes.EncodeBinary(headers)
 	assert.Nil(t, err)
 
 	headersDecode := &Headers{}
 	rErr := testserdes.DecodeBinary(data, headersDecode)
 
-	err = nil
-	if limit {
-		err = ErrTooManyHeaders
-	}
-
-	assert.Equal(t, err, rErr)
+	assert.Equal(t, retErr, rErr)
 	assert.Equal(t, expected, len(headersDecode.Hdrs))
 
 	for i := 0; i < len(headersDecode.Hdrs); i++ {