use different source and destination connection IDs

internal/protocol/connection_id.go

@@ -12,7 +12,7 @@ type ConnectionID []byte
 
 // GenerateConnectionID generates a connection ID using cryptographic random
 func GenerateConnectionID() (ConnectionID, error) {
-	b := make([]byte, 8)
+	b := make([]byte, ConnectionIDLen)
 	if _, err := rand.Read(b); err != nil {
 		return nil, err
 	}

internal/protocol/server_parameters.go

@@ -137,3 +137,9 @@ const MinStreamFrameSize ByteCount = 128
 // If the packet packing frequency is higher, multiple packets might be sent at once.
 // Example: For a packet pacing delay of 20 microseconds, we would send 5 packets at once, wait for 100 microseconds, and so forth.
 const MinPacingDelay time.Duration = 100 * time.Microsecond
+
+// ConnectionIDLen is the length of the source Connection ID used on IETF QUIC packets.
+// The Short Header contains the connection ID, but not the length,
+// so we need to know this value in advance (or encode it into the connection ID).
+// TODO: make this configurable
+const ConnectionIDLen = 8