af unix udp server client program with Poll system call ========================================================= .. tab-set:: .. tab-item:: AF_UNIX UDP * 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 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 `_ * `sendto `_ * `recvfrom `_ .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Topics in this section, * :ref:`AF_UNIX UDP 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_udp_socket: .. tab-set:: .. tab-item:: AF_UNIX UDP 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 socket(AF_UNIX, SOCK_DGRAM, 0) do? .. dropdown:: See Answer Creates a Unix domain socket for datagram communication. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does AF_UNIX differ from AF_INET in sockets? .. dropdown:: See Answer ``AF_UNIX`` is for local communication using file system paths, while ``AF_INET`` is for network communication using IP addresses. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why choose SOCK_DGRAM as the socket type? .. dropdown:: See Answer It enables connectionless, datagram-oriented communication. .. 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_DGRAM, 0)? .. dropdown:: See Answer The system chooses the default protocol for the specified domain and type. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What role does the file system path play in AF_UNIX datagram sockets? .. dropdown:: See Answer Serves as the address for Unix domain datagram sockets. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does error handling work with the socket call? .. dropdown:: See Answer Check the return value; if it's -1, an error occurred. Use appropriate error-handling mechanisms. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How is data flow managed in AF_UNIX datagram sockets? .. dropdown:: See Answer Data is sent and received in discrete, independent units known as datagrams. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can a Unix domain datagram socket connect to multiple servers? .. dropdown:: See Answer Yes, each datagram is independent, allowing communication with multiple servers. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What happens if the specified file system path in AF_UNIX datagram sockets doesn't exist? .. dropdown:: See Answer Typically results in an error; the path should exist or be creatable. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Are AF_UNIX datagram sockets suitable for bi-directional communication? .. dropdown:: See Answer Yes, they can handle both sending and receiving data independently. .. 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_udp_socket_server_sequence_diagram: .. tab-set:: .. tab-item:: Step 1: Sequence Diagram for SERVER.c .. plantuml:: @startuml !theme spacelab start :socket(AF_UNIX, SOCK_DGRAM, 0); :bind(server_socket, (struct sockaddr*)&unix_address, sizeof(unix_address)); :fds[0].fd = server_socket; :fds[0].events = POLLIN; while (while(1)) is (yes) :poll(fds, 1, -1); if (fds[0].revents & POLLIN) then (yes) :recvfrom(server_socket, buffer, BUFFER_SIZE, 0, (struct sockaddr*)&client_addr, &client_addr_len); :sendto(server_socket, buffer, strlen(buffer), 0, (struct sockaddr*)&client_address, sizeof(client_address)); else (no) endif endwhile (CTRL+c) :(void)close(server_socket); stop @enduml .. _poll_af_unix_udp_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 * Poll * Recvfrom data_packet * Sendto data_packet * Close socket * ``socket()`` is used to create a new socket. For example, .. code-block:: c server_socket = socket(AF_UNIX, SOCK_DGRAM, 0); * ``bind()`` is used to associate the socket with a specific address and port. For example, .. code-block:: c ret = bind(server_socket, (struct sockaddr*)&unix_address, sizeof(unix_address)); * ``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, 1, -1); * ``recvfrom`` is commonly used with UDP sockets, where communication is connectionless. it provides information about the source (sender) of the data, including the sender's IP address and port number. For example, .. code-block:: c len = recvfrom(server_socket, buffer, BUFFER_SIZE, 0, (struct sockaddr*)&client_addr, &client_addr_len); * ``sendto`` is used to send the encoded message to the specified server address and port using a UDP socket. For example, .. code-block:: c ret = sendto(server_socket, buffer, strlen(buffer), 0, (struct sockaddr*)&client_address, sizeof(client_address)); * ``close`` is used to close the socket To free up system resources associated with the socket. For example, .. code-block:: c (void)close(server_socket); * See the full program below, .. literalinclude:: af_unix_udp/server/server.c :language: c :emphasize-lines: 35, 36, 37, 38, 75, 76, 98, 99, 100, 113, 129, 130, 131, 132, 144 .. _poll_af_unix_udp_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 Received: Hello, Server! sentbufffer = HELLO Received: Hello, Server! sentbufffer = HELLO Received: Hello, Server! sentbufffer = HELLO Received: Hello, Server! sentbufffer = HELLO Received: Hello, Server! sentbufffer = HELLO Received: Hello, Server! sentbufffer = HELLO Received: Hello, Server! sentbufffer = HELLO Received: Hello, Server! sentbufffer = HELLO Received: Hello, Server! sentbufffer = HELLO ^Caught sigINT! .. _poll_af_unix_udp_socket_client_sequence_diagram: .. tab-set:: .. tab-item:: Step 4 : Sequence Diagram for CLIENT.c .. plantuml:: @startuml !theme spacelab start :socket(AF_UNIX, SOCK_DGRAM, 0); :bind(client_socket, (struct sockaddr *)&client_address, sizeof(client_address)); :fds[0].fd = client_socket; :fds[0].events = POLLIN; while (while(1)) is (yes) :sendto(client_socket, buffer, strlen(buffer), 0, (struct sockaddr*)&server_address, sizeof(server_address)); :poll(fds, 1, -1); if (fds[0].revents & POLLIN) then (yes) :recvfrom(client_socket, buffer, sizeof(buffer), 0, NULL, NULL); else (no) endif endwhile (CTRL+c) :(void)close(client_socket); stop @enduml .. _poll_af_unix_udp_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 * Bind * Select * Sendto data_packet * Recvfrom data_packet * Close socket * ``socket`` is used to create a new socket. For example, .. code-block:: c client_socket = socket(AF_UNIX, SOCK_DGRAM, 0); * ``bind()`` is used to associate the socket with a specific address and port. For example, .. code-block:: c ret = bind(client_socket, (struct sockaddr*)&client_address, sizeof(client_address)); * ``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, 1, -1); * ``sendto`` is used to send the encoded message to the specified server address and port using a UDP socket. For example, .. code-block:: c ret = sendto(client_socket, buffer, strlen(buffer), 0, (struct sockaddr*)&server_address, sizeof(server_address)); * ``recvfrom`` is commonly used with UDP sockets, where communication is connectionless. it provides information about the source (sender) of the data, including the sender's IP address and port number. For example, .. code-block:: c len = recvfrom(client_socket, buffer, sizeof(buffer), 0, NULL, NULL); * ``close`` is used to close the socket To free up system resources associated with the socket. For example, .. code-block:: c (void)close(client_socket); * See the full program below, .. literalinclude:: af_unix_udp/client/client.c :language: c :emphasize-lines: 30, 31, 32, 70, 71, 92, 93, 94, 106, 107, 108, 109, 119, 131 .. _poll_af_unix_udp_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 = Hello, Server! Received: HELLO sentbuffer = Hello, Server! Received: HELLO sentbuffer = Hello, Server! Received: HELLO sentbuffer = Hello, Server! Received: HELLO sentbuffer = Hello, Server! Received: HELLO sentbuffer = Hello, Server! Received: HELLO sentbuffer = Hello, Server! Received: HELLO sentbuffer = Hello, Server! Received: HELLO sentbuffer = Hello, Server! Received: HELLO sentbuffer = Hello, Server! Received: HELLO ^CCaught sigINT! .. _poll_af_unix_udp_Summary: .. tab-set:: .. tab-item:: Summary ============== ================================================================================================================== Socket API Learning ============== ================================================================================================================== socket Create a new socket bind Associate the socket with a specific address and port poll Monitor multiple file descriptors (usually sockets) for read, write, or error conditions. recvfrom It provides information about the source (sender) of the data, including the sender's IP address and port number. sendto Send the encoded message to the specified server address and port using a UDP socket. ============== ================================================================================================================== .. card:: See Also * previous topic * :doc:`../../../sockets/af_unix_udp/select/select` * current topic * :doc:`../../../sockets/af_unix_udp/poll/poll` * Next topic * :doc:`../../../sockets/af_unix_udp/epoll/epoll` * Other sockets * :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`