add gramjs support (#110)

* Add gramjs.go

* Update sessionConstructor.go

support gramjs

* Create main.go

Create gramjs examples

* Update gramjs.go

Author: qingmeng1

examples/auth-using-string-session/gramjs-string/main.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/celestix/gotgproto"
+	"github.com/celestix/gotgproto/sessionMaker"
+)
+
+func main() {
+	client, err := gotgproto.NewClient(
+		// Get AppID from https://my.telegram.org/apps
+		123456,
+		// Get ApiHash from https://my.telegram.org/apps
+		"API_HASH_HERE",
+		// ClientType, as we defined above
+		gotgproto.ClientTypePhone("PHONE_NUMBER_HERE"),
+		// Optional parameters of client
+		&gotgproto.ClientOpts{
+			Session: sessionMaker.GramjsSession("enter session string here").
+        // Sqlite session name (if you're not using memory session)
+				// i.e. InMemory in ClientOpts is set to false
+				// It will be saved as my_session.session as per this example.
+				Name("my_session"),
+		},
+	)
+	if err != nil {
+		log.Fatalln("failed to start client:", err)
+	}
+
+	fmt.Printf("client (@%s) has been started...\n", client.Self.Username)
+
+	client.Idle()
+}

sessionMaker/gramjs.go

@@ -0,0 +1,84 @@
+package sessionMaker
+
+import (
+	"encoding/base64"
+	"encoding/binary"
+	"net"
+	"strconv"
+	"bytes"
+	"github.com/go-faster/errors"
+	"github.com/gotd/td/session"
+	"github.com/gotd/td/crypto"
+)
+
+func DecodeGramjsSession(hx string) (*session.Data, error) {
+	return decodeGramjsSession(hx)
+}
+
+func decodeGramjsSession(sessionStr string) (*session.Data, error) {
+	data := struct {
+		Version       string
+		DCID          uint8
+		ServerAddress string
+		Port          int16
+		Key           []byte
+		AuthKey       string
+		KeyId         string
+	}{}
+
+	if len(sessionStr) == 0 || sessionStr[0] != '1' {
+		return nil, errors.New("invalid session string")
+	}
+	strsession := sessionStr[1:]
+	decodedBytes, err := base64.StdEncoding.DecodeString(strsession)
+	if err != nil {
+		return nil, err
+	}
+
+	reader := bytes.NewReader(decodedBytes)
+
+	data.Version = "1"
+
+	err = binary.Read(reader, binary.BigEndian, &data.DCID)
+	if err != nil {
+		return nil, err
+	}
+
+	addressLength := make([]byte, 2)
+	_, err = reader.Read(addressLength)
+	if err != nil {
+		return nil, err
+	}
+
+	addressLen := int(binary.BigEndian.Uint16(addressLength))
+	addressBuffer := make([]byte, addressLen)
+	_, err = reader.Read(addressBuffer)
+	if err != nil {
+		return nil, err
+	}
+	data.ServerAddress = string(bytes.TrimRight(addressBuffer, "\x00"))
+
+	portBuffer := make([]byte, 2)
+	_, err = reader.Read(portBuffer)
+	if err != nil {
+		return nil, err
+	}
+	data.Port = int16(binary.BigEndian.Uint16(portBuffer))
+
+	keyLength := len(decodedBytes) - (5 + addressLen) // DCID(1 byte), Address Length(2 bytes), Address, Port(2 bytes)
+	data.Key = make([]byte, keyLength)
+	_, err = reader.Read(data.Key)
+	if err != nil {
+		return nil, err
+	}
+
+	data.AuthKey = base64.StdEncoding.EncodeToString(data.Key)
+	keyid := crypto.Key(data.Key).WithID().ID
+	data.KeyId = base64.StdEncoding.EncodeToString(keyid[:])
+	return &session.Data{
+		DC:        int(data.DCID),
+		Addr:      net.JoinHostPort(data.ServerAddress, strconv.Itoa(int(data.Port))),
+		AuthKey:   data.Key,
+		AuthKeyID: keyid[:],
+	}, nil
+}

sessionMaker/sessionConstructor.go

@@ -157,3 +157,28 @@ func (s *TdataSessionConstructor) loadSession() (sessionName, []byte, error) {
 	})
 	return sessionNameString(s.name), data, err
 }
+
+type GramjsSessionConstructor struct {
+	name, value string
+}
+
+func GramjsSession(value string) *GramjsSessionConstructor {
+	return &GramjsSessionConstructor{value: value}
+}
+
+func (s *GramjsSessionConstructor) Name(name string) *GramjsSessionConstructor {
+	s.name = name
+	return s
+}
+
+func (s *GramjsSessionConstructor) loadSession() (sessionName, []byte, error) {
+	sd, err := DecodeGramjsSession(s.value)
+		if err != nil {
+		return sessionNameString(s.name), nil, err
+	}
+	data, err := json.Marshal(jsonData{
+		Version: storage.LatestVersion,
+		Data:    *sd,
+	})
+	return sessionNameString(s.name), data, err
+}