af unix tcp server client program with Epoll 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 `_ * `epoll_create1 `_ * `epoll_ctl `_ * `epoll_wait `_ * `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 ` .. _epoll_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 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_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); :ret = bind(server_fd, (struct sockaddr*)&server_addr, sizeof(struct sockaddr_un)); :listen(server_fd, MAX_EVENTS); :client_fd = accept(server_fd, NULL, NULL); :epoll_fd = epoll_create1(0); :epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client_fd, &event); while (while(1)) is (yes) :epoll_wait(epoll_fd, events, MAX_EVENTS, -1); if (events[0].data.fd == client_fd) 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 .. _epoll_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 * Epoll create1 * Epoll_ctl * Epoll_wait * Recv data_packet * Send data_packet * Close socket * ``socket()`` is used to create a new socket. For example, .. code-block:: c 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); * ``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); * ``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_fd, &event); * ``epoll_wait()`` The application then enters a loop where it waits for events using epoll_wait, For example, .. code-block:: c ret = epoll_wait(epoll_fd, events, MAX_EVENTS, -1); * ``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: 45, 46, 61, 62, 102, 103, 110, 111, 112, 120, 121, 132, 133, 143, 153, 154, 155, 163, 164, 165, 178, 179 .. _epoll_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 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! .. _epoll_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)); :epoll_fd = epoll_create1(0); :epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client_fd, &event); while (while(1)) is (yes) :send(client_fd, buffer, strlen(buffer), 0); :epoll_wait(epoll_fd, events, MAX_EVENTS, -1); if (events[0].data.fd == client_fd) then (yes) :recv(client_fd, buffer, sizeof(buffer) - 1, 0); else (no) endif endwhile (CTRL+c) :(void)close(client_fd); stop @enduml .. _epoll_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 * Epoll create1 * Epoll_ctl * Epoll_wait * Send data_packet * Recv 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)); * ``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_fd, &event); * ``epoll_wait()`` The application then enters a loop where it waits for events using epoll_wait, For example, .. code-block:: c ret = epoll_wait(epoll_fd, events, MAX_EVENTS, -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: 31, 32, 56, 57, 100, 101, 108, 109, 110, 120, 131, 132, 142, 143, 144, 157 .. _epoll_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 connected 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 Received: HELLO sentbuffer = HI ^CCaught sigINT! .. _epoll_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. 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.. recv Receive data from a connected socket. send Send data over a connected socket. ============== ============================================================================================ .. card:: See Also * Previous topic * :doc:`../../../sockets/af_unix_tcp/poll/poll` * Current topic * :doc:`../../../sockets/af_unix_tcp/epoll/epoll` * Next topic * :doc:`../../../sockets/af_unix_udp` * 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`