ETCM-254: Optionally allow decoding packets bigger than the maximum.

input-output-hk · Oct 20, 2020 · 30693b4 · 30693b4
1 parent ec459dc
commit 30693b4
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Showing 2 changed files with 15 additions and 4 deletions.
diff --git a/scalanet/discovery/src/io/iohk/scalanet/discovery/ethereum/v4/Packet.scala b/scalanet/discovery/src/io/iohk/scalanet/discovery/ethereum/v4/Packet.scala
@@ -34,12 +34,12 @@ object Packet {
       Attempt.successful(DecodeResult(bits, BitVector.empty))
     }
 
-  private val packetDecoder: Decoder[Packet] =
+  private def packetDecoder(allowDecodeOverMaxPacketSize: Boolean): Decoder[Packet] =
     for {
       _ <- Decoder { bits =>
         Attempt
           .guard(
-            bits.size <= MaxPacketBitsSize,
+            allowDecodeOverMaxPacketSize || bits.size <= MaxPacketBitsSize,
             "Packet to decode exceeds maximum size."
           )
           .map(_ => DecodeResult((), bits))
@@ -61,8 +61,11 @@ object Packet {
       } yield bits
     }
 
-  implicit val packetCodec: Codec[Packet] =
-    Codec[Packet](packetEncoder, packetDecoder)
+  /** Create a codec for packets. Some Ethereum clients don't respect the size limits;
+    * for compatibility with them the check during decode can be turned off.
+    */
+  def packetCodec(allowDecodeOverMaxPacketSize: Boolean): Codec[Packet] =
+    Codec[Packet](packetEncoder, packetDecoder(allowDecodeOverMaxPacketSize))
 
   /** Serialize the payload, sign the data and compute the hash. */
   def pack(

diff --git a/scalanet/discovery/test/src/io/iohk/scalanet/discovery/ethereum/v4/PacketSpec.scala b/scalanet/discovery/test/src/io/iohk/scalanet/discovery/ethereum/v4/PacketSpec.scala
@@ -14,6 +14,8 @@ class PacketSpec extends FlatSpec with Matchers {
   import DefaultCodecs._
   implicit val sigalg = new MockSigAlg()
 
+  implicit val packetCodec = Packet.packetCodec(allowDecodeOverMaxPacketSize = false)
+
   val MaxPacketBytesSize = Packet.MaxPacketBitsSize / 8
   val MacBytesSize = Packet.MacBitsSize / 8
   val SigBytesSize = Packet.SigBitsSize / 8
@@ -78,6 +80,12 @@ class PacketSpec extends FlatSpec with Matchers {
       Codec.decode[Packet](nBytesAsBits(MaxPacketBytesSize + 1))
     }
   }
+
+  it should "optionally allow the data to exceed the maximum size" in {
+    val permissiblePacketCodec: Codec[Packet] = Packet.packetCodec(allowDecodeOverMaxPacketSize = true)
+    Codec.decode[Packet](nBytesAsBits(MaxPacketBytesSize * 2))(permissiblePacketCodec).isSuccessful shouldBe true
+  }
+
   it should "fail if there's less data than the hash size" in {
     expectFailure(
       s"Hash: cannot acquire ${Packet.MacBitsSize} bits from a vector that contains ${Packet.MacBitsSize - 8} bits"