nobel861017 / Client-Server_chat

Packet forwarding between client and server

Computer Network Final Project

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• b05902121 黃冠博
• b04902131 黃郁凱

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Protocol Specification

• These are the flags for operators
  • line_protocol_magic specifies whether the header is a request or a response
  • line_protocol_op specifies the operator which implies what the request wants to do
  • line_protocol_status specifies the status of the sender of the response

typedef enum {
    LINE_PROTOCOL_MAGIC_REQ = 0x90,
    LINE_PROTOCOL_MAGIC_RES = 0x91,
} line_protocol_magic;

typedef enum {
    LINE_PROTOCOL_OP_LOGIN = 0x00,
    LINE_PROTOCOL_OP_SYNC_META = 0x01,
    LINE_PROTOCOL_OP_SYNC_LOG = 0x02,
    LINE_PROTOCOL_OP_REGISTER = 0x03,
    LINE_PROTOCOL_OP_END = 0x04,
    LINE_PROTOCOL_OP_MATCH = 0x05,
    LINE_PROTOCOL_OP_UNMATCH = 0x06,
    LINE_PROTOCOL_OP_ADD_FRIEND = 0x07,
} line_protocol_op;

typedef enum {
    LINE_PROTOCOL_STATUS_OK = 0x00,
    LINE_PROTOCOL_STATUS_FAIL = 0x01,
    LINE_PROTOCOL_STATUS_MORE = 0x02,
} line_protocol_status;

• This is the structure for the header

typedef union {
    struct {
        uint8_t magic;
        uint8_t op;
        uint8_t status;
        uint16_t client_id;
        uint32_t datalen;
    } req;
    struct {
        uint8_t magic;
        uint8_t op;
        uint8_t status;
        uint16_t client_id;
        uint32_t datalen;
    } res;
    uint8_t bytes[9];
} line_protocol_header;

• This is the structure for login
  • It records the user name, password and the md5 hash of the password

typedef union {
    struct {
        line_protocol_header header;
        struct {
            uint8_t user[USER_LEN_MAX];
            char passwd[PASSWD_LEN_MAX];
            uint8_t passwd_hash[MD5_DIGEST_LENGTH];
        } body;
    } message;
    uint8_t bytes[sizeof(line_protocol_header) + MD5_DIGEST_LENGTH * 2];
} line_protocol_login;

• This is the structure for match request
  • It records the username that the sender of the request wants to match

typedef union {
    struct {
        line_protocol_header header;
        struct {
            char match_username[USER_LEN_MAX];
        } body;
    } message;
    uint8_t bytes[sizeof(line_protocol_header) + sizeof(char) * USER_LEN_MAX];
} line_protocol_match;

• This is the structure for message files
  • it is for sending messages and files
  • is_msg specifies whether it header is for message sending or not
  • first specifies whether this is the first fragment of the file
  • finish specifies whether this is the last fragment of the file
  • data_len specifies the length of the message or file(fragment size, not the whole size of the file)
  • filename specifies the name of the sending file
  • sender specifies the name of the sender
  • recv_user specifies the name of the reciever

typedef union {
    struct {
        line_protocol_header header;
        struct {
            int is_msg;
            int first;
            int finished;
            int data_len;
            char data[DATA_LEN_MAX];
            char sender[FILE_LEN_MAX];
            char filename[FILE_LEN_MAX];
            char recv_user[USER_LEN_MAX];
        } body;
    } message;
    uint8_t bytes[sizeof(line_protocol_header) +
                    sizeof(int) * 4 +
                    sizeof(char) * (DATA_LEN_MAX + FILE_LEN_MAX*2 + USER_LEN_MAX)];
} line_protocol_msg_file

User and Operator Guide

Instructions on how to run server & clients

• In src:

  • make
  • make clean

• In bin (need three terminals):

  • ./port_register
  • ./server ../config/server.cfg
  • ./client ../config/client.cfg

User Interface(terminal) Guide

• Once you run client
  • Login: 0, Signup: 1
  • It will ask you to enter user name and password
• Once login success
  • Chat: c / Quit: q
  • If quit:
    • logout from server
    • Close chating window
  • If chat:
    • Insert name who you want to chat with
    • Please enter what you want to say
    • command ":q" go back to Chat: c / Quit: q stage
    • command ":f" send file to current matching client
      • enter [num of files] [file1] [file2] ...
    • command ":a" add friend with current matching client
      • add friend to friend file list
    • command ":l" list out the historical sent and received messages of the current matching client

System and Program Design

Message Sending

• message format:

  • is_msg specifies whether this message is a chatting message or a file-sending message

  ex : 1,0,1546498631,hi

  is_msg	is_read	time	message content
  1	0	1546498631	hi

• When user A sends a chatting message "hi" to user B, the message is written to a file sdir/A/talk_B.csv in the format above

• When user B is online, the server automatically sends the messages with is_read == 0 to user B, and sets the flag is_read to 1.

• Only the messages with is_msg == 1 are printed to stdout.

• If is_msg == 0, this message is a file-sending message, the output of the receiver is:

  • Client B receive file as follow: ../cdir/[receiver name]/file1.txt

• The file sdir/A/talk_B.csv and sdir/B/talk_A.csv is the log kept on the server for user A to query.

  • When user A types command ":l", the server reads the two files sdir/A/talk_B.csv and sdir/B/talk_A.csv, reorders the messages according to the time and forwards the reordered messages to user A.

Sending File

• Read the file with read() with buffer size 40960 bytes

• Send the data to server, and the server will forward it to the current matched user.

• The sending record we be saved at sdir/A/talk_B.csv in the format below, where A is the sender and B is the receiver.

  is_msg	is_read	time	message content
  0	0	1546500884	file1.txt

• The client that receives the file actually receives fragments of the file.

  • When first == 1, the client opens or creates the file with the specified file name and appends the received data to the file.
  • When finished == 1, this means that the receiver has received the last fragment of the file, and will write it to the corresponding file and closes the file after finish writing.
    • Notice that we do not need to reopen the file when we receive a new file fragment, since continuously openning and closing files wastes lots of time.

• In order to send multiple files at once, we use multi-thread to send every file(One thread for each file).

Bonus

• Password md5 hash.
  • server checks the md5 of the correct password with the md5 of the password the user enters
    • If they are the same: login success
    • Else: login fail
• Add friends
  • Already matched users can type the command ":a" to add the currently matched friend to its friend list. By the way, the currently matched friend also adds the user that sent the add-friend request to its friend list.
• Logout
  • Server records the client to be offline
  • During Chat: c / Quit: q stage, the user can logout by typing the command "q". The server then erases the clients conn_fd from the table.
  • The client proccess terminates.
• Message Sending Encryption
  • Caesar Cypher Algorithm Encryption
  • The chatting messages are encrypted before sending to the server. Hence, the server can not see the original text.
• Send stickers
  • One can send stickers to the other by typing :s [sticker number]
  • There are 5 stickers numbered with 1 to 5. Users can add tailor made stickers for themselves.
• Message send time
  • When client receives a message, the send time of the message is shown aside.
  • ex: (5 seconds ago)
• Can send file and chat with other users simultaneously.