TUN-4596: Add QUIC application protocol for QUIC stream handshake

- Vendored the capnproto library to cloudflared.
- Added capnproto schema defining application protocol.
- Added Pogs and application level read write of the protocol.

quic/quic_protocol.go

@@ -0,0 +1,115 @@
+package quic
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+
+	capnp "zombiezen.com/go/capnproto2"
+)
+
+// protocolSignature is a custom protocol signature to ensure that whoever performs a handshake does not write data
+// before writing the metadata.
+var protocolSignature = []byte{0x0A, 0x36, 0xCD, 0x12, 0xA1, 0x3E}
+
+// ReadConnectRequestData reads the handshake data from a QUIC stream.
+func ReadConnectRequestData(stream io.Reader) (*ConnectRequest, error) {
+	if err := verifySignature(stream); err != nil {
+		return nil, err
+	}
+
+	msg, err := capnp.NewDecoder(stream).Decode()
+	if err != nil {
+		return nil, err
+	}
+
+	r := &ConnectRequest{}
+	if err := r.fromPogs(msg); err != nil {
+		return nil, err
+	}
+	return r, nil
+}
+
+// WriteConnectRequestData writes requestMeta to a stream.
+func WriteConnectRequestData(stream io.Writer, dest string, connectionType ConnectionType, metadata ...Metadata) error {
+	connectRequest := &ConnectRequest{
+		Dest:     dest,
+		Type:     connectionType,
+		Metadata: metadata,
+	}
+
+	msg, err := connectRequest.toPogs()
+	if err != nil {
+		return err
+	}
+
+	if err := writePreamble(stream); err != nil {
+		return err
+	}
+	return capnp.NewEncoder(stream).Encode(msg)
+}
+
+// ReadConnectResponseData reads the response to a RequestMeta in a stream.
+func ReadConnectResponseData(stream io.Reader) (*ConnectResponse, error) {
+	if err := verifySignature(stream); err != nil {
+		return nil, err
+	}
+
+	msg, err := capnp.NewDecoder(stream).Decode()
+	if err != nil {
+		return nil, err
+	}
+
+	r := &ConnectResponse{}
+	if err := r.fromPogs(msg); err != nil {
+		return nil, err
+	}
+	return r, nil
+}
+
+// WriteConnectResponseData writes response to a QUIC stream.
+func WriteConnectResponseData(stream io.Writer, respErr error, metadata ...Metadata) error {
+	var connectResponse *ConnectResponse
+	if respErr != nil {
+		connectResponse = &ConnectResponse{
+			Error: respErr.Error(),
+		}
+	} else {
+		connectResponse = &ConnectResponse{
+			Metadata: metadata,
+		}
+	}
+
+	msg, err := connectResponse.toPogs()
+	if err != nil {
+		return err
+	}
+
+	if err := writePreamble(stream); err != nil {
+		return err
+	}
+	return capnp.NewEncoder(stream).Encode(msg)
+}
+
+func writePreamble(stream io.Writer) error {
+	return writeSignature(stream)
+	// TODO : TUN-4613 Write protocol version here
+}
+
+func writeSignature(stream io.Writer) error {
+	_, err := stream.Write(protocolSignature)
+	return err
+}
+
+func verifySignature(stream io.Reader) error {
+	signature := make([]byte, len(protocolSignature))
+	if _, err := io.ReadFull(stream, signature); err != nil {
+		return err
+	}
+
+	if !bytes.Equal(signature[0:], protocolSignature) {
+		return fmt.Errorf("Wrong signature: %v", signature)
+	}
+
+	return nil
+}