CLIENT SERVER CLIENT - SERVER UDP & TCP APPLICATION

Drinciu Cristina 324CA

This program implements a client-server TCP and UDP for message management. TCP clients can subscribe or unsubcribe to topics and the UDP clients send messages to the sub- scribers through the server. The topics are many and the subscribtion can use wildcards. The UDP clients send the message to the subscribers that match the topic, handling the wildcards.

Subscriber.cpp

• for this part I have used most of the code from lab07
• the program receives parametres such as client ID, IP and PORT from the command line.

Connection Setup

• The client initializes a TCP connection to the server using the provided IP address and port number.
• Nagle's algorithm is disabled to ensure that messages are sent immediately without delay.

Run Client

• Affter connect() to the server, the client sends a message to the server with its ID
• Create the vector of pollfd structures, that will contain 2 elements:
  • a file descriptor for the socket that makes possible the communication from the server
  • a file descriptor for the STDIN, where the client can receive commands from
• When an event occures on one of the file descriptors, execute the necessary opperation
  • if it receives a message from the server, it means that it receives an udp_message from the subscriber topic and the message is printed to the STDOUT
  • if it receives something from the STDIN it is a command which can be:
    • SUBSCRIBE: it sents a message to the server with the topic it wants to receive messages from now on
    • UNSUBSCRIBE: sents a message to the serber with the topic it wants to unsubscribe
    • EXIT: stops the connection to the server and stops the client
• It uses a structure for the tcp_messages for an easier job:

  • struct tcp_message {
    command cmd;
    char id[MAX_ID_LEN];
    char ip[MAX_IP_LEN];
    uint16_t port;
    char topic[MAX_TOPIC_LEN];
    } __attribute__((packed));
    

Server.cpp

• also for this part is used most of the code (in main function) from lab07

Initialization

• initialize the server, create the sockets for listening other connections and for the udp_clipents
• bind the sockets
• listen for incoming connections

Flow

• the server needs to stock some information about the subscribers and the topics they subscribed to, so we have 2 global variables:
  • subscribers: a set that stores the unique clients (structure tcp_client)
  • topics: a map that stores for each existent topic a vector of tcp_clients(subscribers)
• it is created the vector of pollfd structures with the existent file descriptors
  • the listen fd
  • the udp fd
  • the STDIN fd
  • the file descriptors for the future tcp clients
• depending on which file descriptor is triggered after the poll, it does the necessary operations:
  • listenfd: it mean that a new tcp client/subscriber wants to connect to the server, so accept the connection, add the new file descriptor to the vector and the new client to the set
  • STDIN: it only receives the exit command that closes the server and all the connections, freeing the resources
  • udp_fd: it receives a message (a buffer) from an udp_client, so:
    • it first builds the message in an udp_message structure for easier work
    • it check if the topic is in the map (if not, that means that there are no subscribers so the message is not forwarded)
    • check if the topic matches any of the keys in the map (cause the key topics may be wth wildcards)
    • forwards the message to the tcp_clients, also keeping evidence of the subscribers that already received the message, so that in case the topic matches multimple entries in the map and a subscriber may appear more than once, it won't receive the message twice
  • tcp_fds: it receives either the connect message(the id from the client) or a command:
    • CONNECT: it receives the id, so now check if the id already exists
    • if the client exists, check if it is offline, so make sure to reconnect it
    • if the client exists and it is online, refuse the connection
    • is the client does not exist, complete the id field from the structure in the set
    • SUBSCRIBE: add the client to the vector of the specified topic in the map, or if the topic is not there, add it as a key
    • UNSUBSCRIBE: remove the client from the specified topic from the map
    • EXIT: close the connection with the client and remove it from the fd vector, but from the set of clients, just mark it offline

Common.cpp and Common.h

• it containts the DIE macro for deffensive programming
• the structures that are used in the program:
  • tcp_message
  • udp_message
  • tcp_client
• the useful functions that are used both in server.cpp and subscriber.cpp,recv_all and send_all that receives/sends the exact number of bits as given.
• the build_udp_message that extracts the topic, type and content of the message
• the print_udp_message that will print the mesage based on the existent types:
  • int
  • float
  • short_real
  • string
• the get_command_argumens that will build a vector with the argumens of a command
• is_commnd_valid will check is the command is valid
• match_topic works with two strings, the topic and the patter to see if the topic matches a pattern with or without wildcards (both * and +)