af unix tcp server and client program with poll system call =========================================================== .. tab-set:: .. tab-item:: AF_UNIX TCP * In this program, you are going to learn .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to create a Socket ? .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to bind a socket ? .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to listen a socket ? .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to connect a socket ? .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to accept a socket ? .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to send a data ? .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to recv a data ? .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to use socket APIs ? * `socket `_ * `bind `_ * `listen `_ * `connect `_ * `accept `_ * `send `_ * `recv `_ .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Topics in this section, * :ref:`AF_UNIX TCP SOCKET FAQs ` * :ref:`Step 1: Sequence Diagram for SERVER.c ` * :ref:`Step 2: Program for Server.c ` * :ref:`Step 3: Compile and Execute Server.c ` * :ref:`Step 4: Sequence Diagram for CLIENT.c ` * :ref:`Step 5: Program for Client.c ` * :ref:`Step 6: Compile and Execute Client.c ` * :ref:`Summary ` .. _poll_af_unix_tcp_socket: .. tab-set:: .. tab-item:: AF_UNIX TCP SOCKET : FAQs .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Let us answer few basic questions in this socket .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What does AF_UNIX represent in the socket call? .. dropdown:: See Answer ``AF_UNIX`` represents the Unix domain socket family. It is used for communication between processes on the same machine, using file system paths as addresses. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why use SOCK_STREAM as the socket type? .. dropdown:: See Answer ``SOCK_STREAM`` indicates a stream-oriented socket, providing a reliable, connection-oriented communication channel. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What does the third parameter (0) indicate in socket(AF_UNIX, SOCK_STREAM, 0)? .. dropdown:: See Answer Default protocol selected by the system. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How can I set up a server and client using AF_UNIX sockets? .. dropdown:: See Answer To set up a server and client, ``create a socket using socket(AF_UNIX, SOCK_STREAM, 0),`` ``bind the server to an address,`` ``isten for incoming connections, and establish connections from clients.`` ``Communication occurs through read and write operations on the established connections.`` .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How should errors in the socket call be handled? .. dropdown:: See Answer Check the return value, handle errors using appropriate mechanisms. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What is the role of the file system path in AF_UNIX sockets? .. dropdown:: See Answer The file system path serves as the address for Unix domain sockets. It enables processes to locate and connect to the socket. he path is set in the ``sun_path`` field of the ``struct sockaddr_un`` structure. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What is the role of the file system path in AF_UNIX sockets? .. dropdown:: See Answer Address. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why might bind() or listen() fail in socket programming? .. dropdown:: See Answer bind() might fail if the specified address is already in use, or if the process lacks the necessary permissions. listen() might fail if the socket is not bound, or the operating system limit for pending connections is reached. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How should you handle errors when using accept() in socket programming? .. dropdown:: See Answer Check the return value and handle errors appropriately .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why is it important to check the return value of send() and recv() in socket programming? .. dropdown:: See Answer It detects issues such as network errors or closed connections. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What is a common practice for handling timeouts in socket programming? .. dropdown:: See Answer Use non-blocking sockets with functions like poll() or epoll(). .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can you use a TCP socket (SOCK_STREAM) for sending and receiving data concurrently between a client and server? .. dropdown:: See Answer Yes, TCP sockets support bidirectional communication. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What is the purpose of the poll system call? .. dropdown:: See Answer To block and wait for activity on one or more file descriptors. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does poll differ from poll in terms of usability? .. dropdown:: See Answer poll is more efficient than poll for monitoring multiple file descriptors. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What types of file descriptors can be monitored using poll? .. dropdown:: See Answer sockets, files, timerfd, socketpair, message_queue, Namedpipes and shared_memory. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does poll handle a set of file descriptors with different states (e.g., reading, writing, exception)? .. dropdown:: See Answer It uses different structures for each state in the pollfd array. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How do you handle errors when using the poll system call? .. dropdown:: See Answer Check the return value for -1 to detect errors, Use perror to print error messages. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does poll handle a set of file descriptors with different states (e.g., reading, writing, exception)? .. dropdown:: See Answer Array of pollfd Structures: Before calling poll, you need to create an array of pollfd structures, where each structure represents a file descriptor and its associated events. ``struct pollfd fds[NUM_FDS];`` NUM_FDS is the number of file descriptors you want to monitor. Initialize pollfd Structures: For each file descriptor you want to monitor, initialize the corresponding pollfd structure with the following information: `fd:` The file descriptor to monitor. `events:` The events of interest (e.g., POLLIN for readability, POLLOUT for writability). `revents:` Initially set to zero. After the poll call, this field is updated to indicate the events that occurred. ``fds[0].fd = fd1;`` ``fds[0].events = POLLIN;`` ``fds[0].revents = 0;`` ``fds[1].fd = fd2;`` ``fds[1].events = POLLIN;`` ``fds[1].revents = 0;`` Call poll: After initializing the pollfd array, call the poll function, providing the array, the number of file descriptors, and a timeout ``int ready_fds = poll(fds, NUM_FDS, timeout_ms);`` `ready_fds` will contain the number of file descriptors that are ready. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does poll Checking Ready File Descriptors? .. dropdown:: See Answer After the poll call, loop through the pollfd array and check the revents field for each file descriptor to determine which events occurred. .. code-block:: c for (int i = 0; i < NUM_FDS; ++i) { if (fds[i].revents & POLLIN) { // File descriptor i is ready for reading } if (fds[i].revents & POLLOUT) { // File descriptor i is ready for writing } // Check other events if needed (e.g., POLLERR, POLLHUP) } .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What does it mean if poll returns 0? .. dropdown:: See Answer No file descriptors are ready within the specified timeout. .. _poll_af_unix_tcp_socket_server_sequence_diagram: .. tab-set:: .. tab-item:: Step 1: Sequence Diagram for SERVER.c .. plantuml:: @startuml !theme spacelab start :socket(AF_UNIX, SOCK_STREAM, 0); :bind(server_fd, (struct sockaddr*)&server_addr, sizeof(struct sockaddr_un)); :listen(server_fd, MAX_CLIENTS); :client_fd = accept(server_fd, NULL, NULL); :fds[0].fd = client_fd; :fds[0].events = POLLIN; while (while(1)) is (yes) :poll(fds, MAX_CLIENTS + 1, -1); if (fds[0].revents & POLLIN) then (yes) :recv(client_fd, buffer, sizeof(buffer) - 1, 0); :send(client_fd, buffer, strlen(buffer), 0); else (no) endif endwhile (CTRL+c) :(void)close(client_fd); stop @enduml .. _poll_af_unix_tcp_socket_server_code: .. tab-set:: .. tab-item:: Step 2: Program for Server.c * There are many functions used in socket. We can classify those functions based on functionalities. * Create Socket * Bind Socket * Listen Socket * Accept Socket * Poll * Recv data_packet * Send data_packet * Close socket * ``socket()`` is used to create a new socket. For example, .. code-block:: c tcp_server_fd = socket(AF_UNIX, SOCK_STREAM, 0); * ``bind()`` is used to associate the socket with a specific address and port. For example, .. code-block:: c ret = bind(server_fd, (struct sockaddr*)&server_addr, sizeof(struct sockaddr_un)); * ``listen()`` is used to set up a socket to accept incoming connections. For example, .. code-block:: c ret = listen(server_fd, MAX_CLIENTS); * ``poll()`` is used for monitoring multiple file descriptors to see if I/O is possible on any of them. .. code-block:: c ret = poll(fds, MAX_CLIENTS + 1, -1); * ``accept()`` is used in network programming on the server side to accept a connection request from a client. For example, .. code-block:: c client_fd = accept(server_fd, NULL, NULL); * ``recv`` is used in network programming to receive data from a connected socket. For example, .. code-block:: c len = recv(client_fd, buffer, sizeof(buffer) - 1, 0); * ``send`` is used in network programming to send data over a connected socket. For example, .. code-block:: c ret = send(client_fd, buffer, strlen(buffer), 0); * ``close`` is used to close the socket To free up system resources associated with the socket. For example, .. code-block:: c (void)close(client_fd); * See the full program below, .. literalinclude:: af_unix_tcp/server/server.c :language: c :emphasize-lines: 43, 44, 59, 60, 99, 100, 107, 108, 109, 117, 118, 129, 130, 149, 160, 161 .. _poll_af_unix_tcp_socket_server_side_compile_and_execute: .. tab-set:: .. tab-item:: Step 3: Compile and Execute Server.c .. code-block:: c :linenos: :emphasize-lines: 1, 3 $ gcc -o server server.c $ sudo ./server Server listening connection accepted = 4 Received: HI Sentbuffer = HELLO Received: HI Sentbuffer = HELLO Received: HI Sentbuffer = HELLO Received: HI Sentbuffer = HELLO Received: HI Sentbuffer = HELLO Received: HI Sentbuffer = HELLO Received: HI Sentbuffer = HELLO Received: HI Sentbuffer = HELLO Received: HI ^CCaught sigINT! .. _poll_af_unix_tcp_socket_client_sequence_diagram: .. tab-set:: .. tab-item:: Step 4: Sequence Diagram for CLIENT.c .. plantuml:: @startuml !theme spacelab start :socket(AF_UNIX, SOCK_STREAM, 0); :connect(client_fd, (struct sockaddr*)&server_addr, sizeof(struct sockaddr_un)); while (while(1)) is (yes) :send(client_fd, buffer, strlen(buffer), 0); :fds[0].fd = client_fd; :fds[0].events = POLLIN; :poll(fds, 2, -1); if (fds[0].revents & POLLIN) then (yes) :recv(client_fd, buffer, sizeof(buffer) - 1, 0); else (no) endif endwhile (CTRL+c) :(void)close(client_fd); stop @enduml .. _poll_af_unix_tcp_socket_client_code: .. tab-set:: .. tab-item:: Step 5: Program for Client.c * There are many functions used in socket. We can classify those functions based on functionalities. * Create Socket * Connect Socket * Poll * Recv data_packet * Send data_packet * Close socket * ``socket`` is used to create a new socket. For example, .. code-block:: c client_fd = socket(AF_UNIX, SOCK_STREAM, 0); * ``connect`` is used in network programming to establish a connection from a client to a server. For example, .. code-block:: c cli_connect = connect(client_fd, (struct sockaddr*)&server_addr, sizeof(struct sockaddr_un)); * ``poll()`` is used for monitoring multiple file descriptors to see if I/O is possible on any of them. .. code-block:: c ret = poll(fds, 2, -1); * ``send`` is used in network programming to send data over a connected socket. For example, .. code-block:: c ret = send(client_fd, buffer, strlen(buffer), 0); * ``recv`` is used in network programming to receive data from a connected socket. For example, .. code-block:: c len = recv(client_fd, buffer, sizeof(buffer) - 1, 0); * ``close`` is used to close the socket To free up system resources associated with the socket. For example, .. code-block:: c (void)close(client_fd); * See the full program below, .. literalinclude: af_unix_tcp/client/client.c :language: c :emphasize-lines: 28, 29, 52, 53, 94, 95, 102, 103, 104, 120, 131 .. _poll_af_unix_tcp_socket_client_side_compile_and_execute: .. tab-set:: .. tab-item:: Step 6: Compile and Execute Client.c .. code-block:: c :linenos: :emphasize-lines: 1, 3 $ gcc -o client client.c $ sudo ./client sentbuffer = HI Received: HELLO sentbuffer = HI Received: HELLO sentbuffer = HI Received: HELLO sentbuffer = HI Received: HELLO sentbuffer = HI Received: HELLO sentbuffer = HI Received: HELLO sentbuffer = HI Received: HELLO sentbuffer = HI ^CCaught sigINT! .. _poll_af_unix_tcp_Summary: .. tab-set:: .. tab-item:: Summary ============== ========================================================================================= Socket API Learning ============== ========================================================================================= socket Create a new socket bind Associate the socket with a specific address and port listen Set up a socket to accept incoming connections. connect Establish a connection from a client to a server. accept Server side to accept a connection request from a client. poll Monitor multiple file descriptors (usually sockets) for read, write, or error conditions. recv Receive data from a connected socket. send Send data over a connected socket. ============== ========================================================================================= .. card:: See Also * previous topic * :doc:`../../../sockets/af_unix_tcp/select/select` * current topic * :doc:`../../../sockets/af_unix_tcp/poll/poll` * Next topic * :doc:`../../../sockets/af_unix_tcp/epoll/epoll` * Other sockets * :doc:`../../../sockets/af_unix_udp` * :doc:`../../../sockets/ipv4_raw_af_inet_icmp` * :doc:`../../../sockets/ipv4_raw_af_inet_raw` * :doc:`../../../sockets/ipv4_raw_af_inet_tcp` * :doc:`../../../sockets/ipv4_raw_af_inet_udp` * :doc:`../../../sockets/ipv6_af_inet6_tcp` * :doc:`../../../sockets/ipv6_af_inet6_udp` * :doc:`../../../sockets/ipv6_raw_af_inet6_icmp` * :doc:`../../../sockets/ipv6_raw_af_inet6_tcp` * :doc:`../../../sockets/ipv6_raw_af_inet6_udp` * :doc:`../../../sockets/ipv6_raw_af_inet6_raw` * :doc:`../../../sockets/raw_af_packet_raw_htons_ETH_P_ALL` * :doc:`../../../sockets/raw_af_packet_tcp_htons_ETH_P_ALL` * :doc:`../../../sockets/raw_af_packet_udp_htons_ETH_P_ALL` * Other IPCs * :doc:`../../../Message_queues/Message_queues` * :doc:`../../../NamedPipes/NamedPipes` * :doc:`../../../Netlink/Netlink` * :doc:`../../../Shared_Memory/Shared_Memory` * :doc:`../../../Shared_Memory_2_FDS/Shared_Memory_2_FDS` * :doc:`../../../SocketPair/SocketPair` * :doc:`../../../Timerfd/Timerfd`