IPV6 UDP server client program with Epoll system call ====================================================== .. tab-set:: .. tab-item:: IPv6 AF_INET6 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:`IPV6 AF_INET6 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_ipv6_af_inet6_udp_socket: .. tab-set:: .. tab-item:: IPV6 AF_INET6 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_INET6, SOCK_DGRAM, IPPROTO_UDP)`` do? .. dropdown:: See Answer This call creates a UDP socket in the IPv6 address family. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow When is it appropriate to use ``SOCK_DGRAM`` with IPv6? .. dropdown:: See Answer ``SOCK_DGRAM`` is used for fast, connectionless communication, making it suitable for scenarios where reliability is less critical, such as real-time applications. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What privileges are required to create an IPv6 UDP socket? .. dropdown:: See Answer No special privileges are typically required to create an IPv6 UDP socket. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can this socket be used for TCP communication? .. dropdown:: See Answer No, this socket is specifically designed for UDP communication. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does an ``IPv6 UDP`` socket differ from an ``IPv4 UDP`` socket? .. dropdown:: See Answer ``IPv6 UDP`` sockets handle communication using IPv6 addresses, providing a larger address space compared to ``IPv4``. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can I use IPv6 UDP sockets in a mixed IPv4/IPv6 environment? .. dropdown:: See Answer Yes, most modern systems support IPv6, allowing communication with both IPv4 and IPv6 peers. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How do I specify a port number for an IPv6 UDP socket? .. dropdown:: See Answer Set the port number in the sin6_port field of the struct sockaddr_in6 structure. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can I use IPv6 UDP sockets for non-blocking I/O? .. dropdown:: See Answer Yes, you can set IPv6 UDP sockets to non-blocking mode using functions like fcntl or ioctl. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How do I handle connection establishment with IPv6 UDP sockets? .. dropdown:: See Answer UDP is connectionless, so there is no explicit connection establishment. Use the ``bind`` function to associate the socket with a local address. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Are there any compatibility issues with older systems when using IPv6 UDP sockets? .. dropdown:: See Answer Compatibility might be an issue on systems lacking IPv6 support. Ensure the target systems support IPv6. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How do I handle socket errors related to network communication? .. dropdown:: See Answer Functions like ``sendto`` and ``recvfrom`` return -1 on error. Check the return values and use perror or strerror to print detailed error messages. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow When handling socket errors, is it important to close the socket? .. dropdown:: See Answer Yes, it's generally a good practice to close the socket on error to release system resources. Always follow error-handling best practices. .. 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_ipv6_af_inet6_udp_socket_server_sequence_diagram: .. tab-set:: .. tab-item:: Step 1: Sequence Diagram for SERVER.c .. plantuml:: @startuml !theme spacelab start :socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP); :bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)); :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_addr, client_addr_len); else (no) endif endwhile (CTRL+c) :(void)close(server_socket); stop @enduml .. _epoll_ipv6_af_inet6_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_INET6, SOCK_DGRAM, IPPROTO_UDP); * ``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_addr, sizeof(server_addr)); * ``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_addr, client_addr_len); * ``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:: IPV6_AF_INET6_UDP/server/server.c :language: c :emphasize-lines: 94, 95, 96, 103, 104, 105, 113, 123, 124, 125, 135, 136, 147, 148, 149, 150, 163, 164, 165, 166, 167, 182, 183 .. _epoll_ipv6_af_inet6_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 8080 Port: 8080 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_ipv6_af_inet6_udp_socket_client_sequence_diagram: .. tab-set:: .. tab-item:: Step 4 : Sequence Diagram for CLIENT.c .. plantuml:: @startuml !theme spacelab start :socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP); :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_addr, sizeof(server_addr)); :epoll_wait(epoll_fd, events, MAX_EVENTS, -1); if (events[0].data.fd == client_socket) then (yes) :recvfrom(client_socket, buffer, BUFFER_SIZE, 0, NULL, NULL); else (no) endif endwhile (CTRL+c) :(void)close(client_socket); stop @enduml .. _epoll_ipv6_af_inet6_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 * 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_INET6, SOCK_DGRAM, IPPROTO_UDP); * ``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_addr, sizeof(server_addr)); * ``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, BUFFER_SIZE, 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:: IPV6_AF_INET6_UDP/client/client.c :language: c :emphasize-lines: 80, 81, 134, 135, 136, 143, 155, 156, 165, 166, 167, 168, 177, 178, 179, 192, 193 .. _epoll_ipv6_af_inet6_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 ::1 Port: 8080 IP Address: ::1 sendbuffer = HI Received: HELLO sendbuffer = HI Received: HELLO sendbuffer = HI Received: HELLO sendbuffer = HI Received: HELLO sendbuffer = HI Received: HELLO sendbuffer = HI Received: HELLO sendbuffer = HI Received: HELLO sendbuffer = HI ^CCaught sigINT! .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow $ sudo ./server 8080 ::1 $ sudo ./client 8080 ::1 program to run with elevated privileges, listen on port 8080, and bind to the loopback address ::1. decided by the user based on the connection. .. tab-set:: .. tab-item:: Enhanced Socket Flexibility with ``AF_INET6`` and ``PF_INET6`` Domains .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Default Domain:** By default, the socket is configured to work in the ``AF_INET6`` domain, handling all types of network data. **Additional Domain Support:** We expand the socket's capabilities to also function in the ``PF_INET6`` domain, allowing it to operate similarly to ``AF_INET6``. **Socket Creation:** We set up a network connection point known as a socket using ``socket(PF_INET6, SOCK_DGRAM, IPPROTO_UDP)``. **Working Scenario:** Despite the change in domain to ``PF_INET6``, the socket continues to operate the same way, handling general network data. .. _epoll_ipv6_af_inet6_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/ipv6_af_inet6_udp/poll/poll` * Current topic * :doc:`../../../sockets/ipv6_af_inet6_udp/epoll/epoll` * Next topic * :doc:`../../../sockets/ipv6_raw_af_inet6_icmp` * Other sockets * :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`