Add base faketls processing

mtglib/internal/faketls/welcome.go

@@ -0,0 +1,88 @@
+package faketls
+
+import (
+	"crypto/hmac"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/binary"
+	"io"
+	mrand "math/rand"
+
+	"github.com/9seconds/mtg/v2/mtglib/internal/faketls/record"
+	"golang.org/x/crypto/curve25519"
+)
+
+func SendWelcomePacket(writer io.Writer, secret []byte, clientHello ClientHello) error {
+	buf := acquireBytesBuffer()
+	defer releaseBytesBuffer(buf)
+
+	rec := record.AcquireRecord()
+	defer record.ReleaseRecord(rec)
+
+	rec.Type = record.TypeHandshake
+	rec.Version = record.Version12
+
+	generateServerHello(&rec.Payload, clientHello)
+	rec.Dump(buf)
+	rec.Reset()
+
+	rec.Type = record.TypeChangeCipherSpec
+	rec.Version = record.Version12
+	rec.Payload.WriteByte(0x01)
+
+	rec.Dump(buf)
+	rec.Reset()
+
+	rec.Type = record.TypeApplicationData
+	rec.Version = record.Version12
+
+	if _, err := io.CopyN(&rec.Payload, rand.Reader, int64(1024+mrand.Intn(3092))); err != nil {
+		panic(err)
+	}
+
+	rec.Dump(buf)
+
+	packet := buf.Bytes()
+	mac := hmac.New(sha256.New, secret)
+
+	mac.Write(clientHello.Random[:])
+	mac.Write(packet)
+
+	copy(packet[WelcomePacketRandomOffset:], mac.Sum(nil))
+
+	if _, err := writer.Write(packet); err != nil {
+		return err // nolint: wrapcheck
+	}
+
+	return nil
+}
+
+func generateServerHello(writer io.Writer, clientHello ClientHello) {
+	bodyBuf := acquireBytesBuffer()
+	defer releaseBytesBuffer(bodyBuf)
+
+	sliceBuf := [2]byte{}
+	digest := [RandomLen]byte{}
+
+	binary.BigEndian.PutUint16(sliceBuf[:], uint16(record.Version12))
+	bodyBuf.Write(sliceBuf[:])
+	bodyBuf.Write(digest[:])
+	bodyBuf.WriteByte(byte(len(clientHello.SessionID)))
+	bodyBuf.Write(clientHello.SessionID)
+
+	binary.BigEndian.PutUint16(sliceBuf[:], clientHello.CipherSuite)
+	bodyBuf.Write(sliceBuf[:])
+	bodyBuf.Write(serverHelloSuffix)
+
+	scalar := [32]byte{}
+	rand.Read(scalar[:])
+	curve, _ := curve25519.X25519(scalar[:], curve25519.Basepoint)
+	bodyBuf.Write(curve)
+
+	header := [4]byte{0, 0, 0, 0}
+	binary.BigEndian.PutUint32(header[:], uint32(bodyBuf.Len()))
+	header[0] = HandshakeTypeServer
+
+	writer.Write(header[:])
+	bodyBuf.WriteTo(writer)
+}