fix a panic in stream with large window updates

fixes #143

stream.go

@@ -200,7 +200,7 @@ func (s *stream) Write(p []byte) (int, error) {
 			return 0, s.err
 		}
 
-		dataLen := utils.Min(len(p), int(remainingBytesInWindow))
+		dataLen := utils.MinByteCount(protocol.ByteCount(len(p)), remainingBytesInWindow)
 		data := make([]byte, dataLen)
 		copy(data, p)
 		err := s.session.queueStreamFrame(&frames.StreamFrame{
@@ -213,7 +213,7 @@ func (s *stream) Write(p []byte) (int, error) {
 			return 0, err
 		}
 
-		dataWritten += dataLen
+		dataWritten += int(dataLen) // We cannot have written more than the int range
 		s.flowController.AddBytesSent(protocol.ByteCount(dataLen))
 		if s.contributesToConnectionFlowControl {
 			s.connectionFlowController.AddBytesSent(protocol.ByteCount(dataLen))

stream_test.go

@@ -464,6 +464,16 @@ var _ = Describe("Stream", func() {
 				Expect(b).To(BeTrue())
 				Expect(err).To(MatchError(testErr))
 			})
+
+			It("works with large flow control windows", func() {
+				// This paniced before due to a wrong cast,
+				// see https://github.com/lucas-clemente/quic-go/issues/143
+				str.contributesToConnectionFlowControl = false
+				updated := str.UpdateSendFlowControlWindow(protocol.ByteCount(1) << 63)
+				Expect(updated).To(BeTrue())
+				_, err := str.Write([]byte("foobar"))
+				Expect(err).NotTo(HaveOccurred())
+			})
 		})
 	})