TUN-4597: Add a QUIC server skeleton

- Added a QUIC server to accept streams
- Unit test for this server also tests ALPN
- Temporary echo capability for HTTP ConnectionType

vendor/github.com/lucas-clemente/quic-go/internal/wire/crypto_frame.go

@@ -0,0 +1,102 @@
+package wire
+
+import (
+	"bytes"
+	"io"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+	"github.com/lucas-clemente/quic-go/quicvarint"
+)
+
+// A CryptoFrame is a CRYPTO frame
+type CryptoFrame struct {
+	Offset protocol.ByteCount
+	Data   []byte
+}
+
+func parseCryptoFrame(r *bytes.Reader, _ protocol.VersionNumber) (*CryptoFrame, error) {
+	if _, err := r.ReadByte(); err != nil {
+		return nil, err
+	}
+
+	frame := &CryptoFrame{}
+	offset, err := quicvarint.Read(r)
+	if err != nil {
+		return nil, err
+	}
+	frame.Offset = protocol.ByteCount(offset)
+	dataLen, err := quicvarint.Read(r)
+	if err != nil {
+		return nil, err
+	}
+	if dataLen > uint64(r.Len()) {
+		return nil, io.EOF
+	}
+	if dataLen != 0 {
+		frame.Data = make([]byte, dataLen)
+		if _, err := io.ReadFull(r, frame.Data); err != nil {
+			// this should never happen, since we already checked the dataLen earlier
+			return nil, err
+		}
+	}
+	return frame, nil
+}
+
+func (f *CryptoFrame) Write(b *bytes.Buffer, _ protocol.VersionNumber) error {
+	b.WriteByte(0x6)
+	quicvarint.Write(b, uint64(f.Offset))
+	quicvarint.Write(b, uint64(len(f.Data)))
+	b.Write(f.Data)
+	return nil
+}
+
+// Length of a written frame
+func (f *CryptoFrame) Length(_ protocol.VersionNumber) protocol.ByteCount {
+	return 1 + quicvarint.Len(uint64(f.Offset)) + quicvarint.Len(uint64(len(f.Data))) + protocol.ByteCount(len(f.Data))
+}
+
+// MaxDataLen returns the maximum data length
+func (f *CryptoFrame) MaxDataLen(maxSize protocol.ByteCount) protocol.ByteCount {
+	// pretend that the data size will be 1 bytes
+	// if it turns out that varint encoding the length will consume 2 bytes, we need to adjust the data length afterwards
+	headerLen := 1 + quicvarint.Len(uint64(f.Offset)) + 1
+	if headerLen > maxSize {
+		return 0
+	}
+	maxDataLen := maxSize - headerLen
+	if quicvarint.Len(uint64(maxDataLen)) != 1 {
+		maxDataLen--
+	}
+	return maxDataLen
+}
+
+// MaybeSplitOffFrame splits a frame such that it is not bigger than n bytes.
+// It returns if the frame was actually split.
+// The frame might not be split if:
+// * the size is large enough to fit the whole frame
+// * the size is too small to fit even a 1-byte frame. In that case, the frame returned is nil.
+func (f *CryptoFrame) MaybeSplitOffFrame(maxSize protocol.ByteCount, version protocol.VersionNumber) (*CryptoFrame, bool /* was splitting required */) {
+	if f.Length(version) <= maxSize {
+		return nil, false
+	}
+
+	n := f.MaxDataLen(maxSize)
+	if n == 0 {
+		return nil, true
+	}
+
+	newLen := protocol.ByteCount(len(f.Data)) - n
+
+	new := &CryptoFrame{}
+	new.Offset = f.Offset
+	new.Data = make([]byte, newLen)
+
+	// swap the data slices
+	new.Data, f.Data = f.Data, new.Data
+
+	copy(f.Data, new.Data[n:])
+	new.Data = new.Data[:n]
+	f.Offset += n
+
+	return new, true
+}