Add client abridged protocol

mtproto/rpc/proxy_response.go

@@ -0,0 +1,51 @@
+package rpc
+
+import (
+	"bytes"
+	"fmt"
+
+	"github.com/9seconds/mtg/conntypes"
+)
+
+type ProxyResponseType uint8
+
+const (
+	ProxyResponseTypeAns ProxyResponseType = iota
+	ProxyResponseTypeSimpleAck
+	ProxyResponseTypeCloseExt
+)
+
+type ProxyResponse struct {
+	Type    ProxyResponseType
+	ConnID  conntypes.ConnID
+	Payload conntypes.Packet
+}
+
+func ParseProxyResponse(packet conntypes.Packet) (*ProxyResponse, error) {
+	var response ProxyResponse
+
+	if len(packet) < 4 {
+		return nil, fmt.Errorf("incorrect packet length: %d", len(packet))
+	}
+
+	tag := packet[:4]
+	switch {
+	case bytes.Equal(tag, TagProxyAns):
+		response.Type = ProxyResponseTypeAns
+		copy(response.ConnID[:], packet[8:16])
+		response.Payload = packet[16:]
+		return &response, nil
+
+	case bytes.Equal(tag, TagSimpleAck):
+		response.Type = ProxyResponseTypeSimpleAck
+		copy(response.ConnID[:], packet[4:12])
+		response.Payload = packet[12:]
+		return &response, nil
+
+	case bytes.Equal(tag, TagCloseExt):
+		response.Type = ProxyResponseTypeCloseExt
+		return &response, nil
+	}
+
+	return nil, fmt.Errorf("unknown response type %x", tag)
+}