Supported version field for version negotation packets

quic/packets.nim

@@ -88,9 +88,19 @@ proc `$`*(header: PacketHeader): string =
 
 proc `==`*(x: ConnectionId, y: ConnectionId): bool {.borrow.}
 
+proc supportedVersionSlice(header: PacketHeader): Slice[int] =
+  let start = header.sourceSlice().b + 1
+  result = start..<start+4
+
+proc supportedVersion*(header: PacketHeader): uint32 =
+  let versionBytes = header.bytes[header.supportedVersionSlice]
+  result.bytes[0] = versionBytes[0]
+  result.bytes[1] = versionBytes[1]
+  result.bytes[2] = versionBytes[2]
+  result.bytes[3] = versionBytes[3]
 proc packetLength*(header: PacketHeader): int =
   case header.kind:
   of packetVersionNegotiation:
-    return header.sourceSlice.b + 1 + 4
+    return header.supportedVersionSlice.b + 1
   else:
     return 0

tests/quic/testPackets.nim

@@ -121,6 +121,16 @@ suite "long headers":
         source.len + 1 +
         version1.len
 
+    test "has a supported version field":
+      let header = newPacketHeader(
+        type0 &
+        version0 &
+        destination.len.uint8 & destination &
+        source.len.uint8 & source &
+        version1
+      )
+      check header.supportedVersion == 1'u32
+
 suite "packet numbers":
 
   test "packet numbers are in the range 0 to 2^62-1":