af unix udp server client program with Epoll 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 `_ * `epoll_create1 `_ * `epoll_ctl `_ * `epoll_wait `_ * `sendto `_ * `recvfrom `_ .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Topics in this section, * :ref:`IPV4 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 ` .. _epoll_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 primary purpose of the epoll system call? .. dropdown:: See Answer To efficiently monitor multiple file descriptors for I/O events .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What types of file descriptors can be monitored using epoll? .. 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 What data structure is used by epoll to store events? .. dropdown:: See Answer Hash table .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How do you handle errors when using the epoll 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 epoll handle a set of file descriptors with different states (e.g., reading, writing, exception)? .. dropdown:: See Answer Create the epoll Instance: Before monitoring file descriptors, the application creates an epoll instance using the epoll_create system call. .. code-block:: c int epoll_fd = epoll_create1(0); Register File Discriptors: The application registers file descriptors with the epoll instance using the epoll_ctl system call. It specifies the file descriptor, the events it is interested in (EPOLLIN for readability, EPOLLOUT for writability, etc.), and a user-defined data associated with the file descriptor. .. code-block:: c struct epoll_event event; event.events = EPOLLIN | EPOLLOUT; // Interested in readability and writability event.data.fd = my_file_descriptor; // File descriptor to monitor epoll_ctl(epoll_fd, EPOLL_CTL_ADD, my_file_descriptor, &event); Wait for Events: The application enters a loop where it calls epoll_wait to wait for events. This call blocks until one or more registered file descriptors become ready or until a timeout occurs. .. code-block:: c #define MAX_EVENTS 10 struct epoll_event events[MAX_EVENTS]; int num_events = epoll_wait(epoll_fd, events, MAX_EVENTS, timeout_ms); Modify or Remove File Descriptors: The application can dynamically modify or remove file descriptors from the epoll set using the epoll_ctl system call. For example, to modify events for an existing file descriptor: .. code-block:: c struct epoll_event new_event; new_event.events = EPOLLOUT; // Modify to be interested in writability epoll_ctl(epoll_fd, EPOLL_CTL_MOD, my_file_descriptor, &new_event); To remove a file descriptor from the epoll set: .. code-block:: c epoll_ctl(epoll_fd, EPOLL_CTL_DEL, my_file_descriptor, NULL); .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does epoll Checking Ready File Descriptors? .. dropdown:: See Answer After epoll_wait returns, the application iterates through the returned events to identify which file descriptors are ready and for what types of events. .. code-block:: c for (int i = 0; i < num_events; ++i) { if (events[i].events & EPOLLIN) { // File descriptor i is ready for reading } if (events[i].events & EPOLLOUT) { // File descriptor i is ready for writing } // Check other events if needed (e.g., EPOLLERR, EPOLLHUP) } .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What does it mean if epoll returns 0? .. dropdown:: See Answer No file descriptors are ready within the specified timeout. .. _epoll_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)); :epoll_fd = epoll_create1(0); :epoll_ctl(epoll_fd, EPOLL_CTL_ADD, server_socket, &event); while (while(1)) is (yes) :epoll_wait(epoll_fd, events, MAX_EVENTS, -1); if (events[0].data.fd == server_socket) 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 .. _epoll_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 * Epoll create1 * Epoll_ctl * Epoll_wait * 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*)&server_address, sizeof(server_address)); * ``epoll_create1()`` creating an epoll instance using epoll_create1, The size parameter is an advisory hint for the kernel regarding the number of file descriptors expected to be monitored, For example, .. code-block:: c epoll_fd = epoll_create1(0); * ``epoll_ctl()`` After creating an epoll instance, file descriptors are added to it using epoll_ctl, For example, .. code-block:: c ret = epoll_ctl(epoll_fd, EPOLL_CTL_ADD, server_socket, &event); * ``epoll_wait()`` The application then enters a loop where it waits for events using epoll_wait, For example, .. code-block:: c ready_fds = epoll_wait(epoll_fd, events, MAX_EVENTS, -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: 48, 49, 50, 51, 94, 95, 102, 103, 104, 112, 122, 123, 124, 134, 135, 154, 155, 156, 157, 169 .. _epoll_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 ^CCaught sigINT! .. _epoll_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)); :epoll_fd = epoll_create1(0); :epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client_socket, &event); while (while(1)) is (yes) :sendto(client_socket, buffer, strlen(buffer), 0, (struct sockaddr*)&server_address, sizeof(server_address)); :epoll_wait(epoll_fd, events, MAX_EVENTS, -1); if (events[0].data.fd == client_socket) then (yes) :recvfrom(client_socket, buffer, sizeof(buffer), 0, NULL, NULL); else (no) endif endwhile (CTRL+c) :(void)close(client_socket); stop @enduml .. _epoll_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 * Epoll create1 * Epoll_ctl * Epoll_wait * 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_INET, SOCK_DGRAM, IPPROTO_UDP); * ``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)); * ``epoll_create1()`` creating an epoll instance using epoll_create1, The size parameter is an advisory hint for the kernel regarding the number of file descriptors expected to be monitored, For example, .. code-block:: c epoll_fd = epoll_create1(0); * ``epoll_ctl()`` After creating an epoll instance, file descriptors are added to it using epoll_ctl, For example, .. code-block:: c ret = epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client_socket, &event); * ``epoll_wait()`` The application then enters a loop where it waits for events using epoll_wait, For example, .. code-block:: c ready_fds = epoll_wait(epoll_fd, events, MAX_EVENTS, -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: 31, 32, 33, 90, 91, 98, 99, 100, 108, 119, 120, 130, 131, 132, 133, 143, 144, 145, 158 .. _epoll_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 8080 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! .. _epoll_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 epoll handles a set of file descriptors with different states, such as reading, writing, and exceptions, by using the struct epoll_event structure and the associated event flags.. 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/poll/poll` * Current topic * :doc:`../../../sockets/af_unix_udp/epoll/epoll` * Next topic * :doc:`../../../sockets/ipv4_raw_af_inet_icmp` * Other sockets * :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`