implement the MAX_DATA and MAX_STREAM_DATA frames

For gQUIC WINDOW_UPDATEs are converted to MAX_DATA and MAX_STREAM_DATA,
respectively.

internal/wire/max_data_frame.go

@@ -0,0 +1,51 @@
+package wire
+
+import (
+	"bytes"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+	"github.com/lucas-clemente/quic-go/internal/utils"
+)
+
+// A MaxDataFrame carries flow control information for the connection
+type MaxDataFrame struct {
+	ByteOffset protocol.ByteCount
+}
+
+// ParseMaxDataFrame parses a MAX_DATA frame
+func ParseMaxDataFrame(r *bytes.Reader, version protocol.VersionNumber) (*MaxDataFrame, error) {
+	// read the TypeByte
+	if _, err := r.ReadByte(); err != nil {
+		return nil, err
+	}
+
+	frame := &MaxDataFrame{}
+	byteOffset, err := utils.GetByteOrder(version).ReadUint64(r)
+	if err != nil {
+		return nil, err
+	}
+	frame.ByteOffset = protocol.ByteCount(byteOffset)
+	return frame, nil
+}
+
+//Write writes a MAX_STREAM_DATA frame
+func (f *MaxDataFrame) Write(b *bytes.Buffer, version protocol.VersionNumber) error {
+	if !version.UsesMaxDataFrame() {
+		// write a gQUIC WINDOW_UPDATE frame (with stream ID 0, which means connection-level there)
+		return (&windowUpdateFrame{
+			StreamID:   0,
+			ByteOffset: f.ByteOffset,
+		}).Write(b, version)
+	}
+	b.WriteByte(0x4)
+	utils.GetByteOrder(version).WriteUint64(b, uint64(f.ByteOffset))
+	return nil
+}
+
+// MinLength of a written frame
+func (f *MaxDataFrame) MinLength(version protocol.VersionNumber) (protocol.ByteCount, error) {
+	if !version.UsesMaxDataFrame() { // writing this frame would result in a gQUIC WINDOW_UPDATE being written, which is longer
+		return 1 + 4 + 8, nil
+	}
+	return 1 + 8, nil
+}