IPV6 TCP server client program with Epoll system call ===================================================== .. tab-set:: .. tab-item:: IPv6 AF_INET6 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:`IPV6 AF_INET6 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 ` .. tab-set:: .. tab-item:: Enabling IPv6 on the Loopback Interface Before Program Execution .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Before executing the program that relies on IPv6, enable the loopback interface for IPv6 using the following command: .. code-block:: c sudo sysctl -w net.ipv6.conf.lo.disable_ipv6=0 * This command sets the disable_ipv6 parameter to 0 for the loopback interface (lo), allowing IPv6 functionality. * Ensure to use this command cautiously and consider the implications, especially on production systems. * After enabling IPv6, proceed to execute your program that relies on IPv6 functionality. .. _epoll_ipv6_af_inet6_tcp_socket: .. tab-set:: .. tab-item:: IPV6 AF_INET6 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 ``socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP)`` do? .. dropdown:: See Answer This call creates a TCP socket in the ``AF_INET6`` (IPv6) address family. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow When is it appropriate to use ``SOCK_STREAM`` with IPv6? .. dropdown:: See Answer For reliable, connection-oriented communication. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What privileges are required to create an IPv6 TCP socket? .. dropdown:: See Answer No special privileges. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can ``socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP)`` be used for regular UDP communication? .. dropdown:: See Answer No, it is designed only for TCP communication. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does an IPv6 TCP socket differ from an IPv4 TCP socket? .. dropdown:: See Answer IPv6 sockets handle communication using IPv6 addresses. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can I use IPv6 TCP sockets in a mixed IPv4/IPv6 environment? .. dropdown:: See Answer Yes, most modern systems support IPv6. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How do I specify a port number for an IPv6 TCP socket? .. dropdown:: See Answer Set the port number in the sin6_port field. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can I use IPv6 TCP sockets for non-blocking I/O? .. dropdown:: See Answer Yes, use setsockopt to enable non-blocking mode. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How do I handle connection establishment with IPv6 TCP sockets? .. dropdown:: See Answer Use the bind and listen functions. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Are there any compatibility issues with older systems when using IPv6 TCP sockets? .. dropdown:: See Answer Yes, older systems may lack IPv6 support. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How do I handle IPv6 DNS resolution in my application? .. dropdown:: See Answer Use functions like getaddrinfo to resolve hostnames. .. 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 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 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_tcp_socket_server_sequence_diagram: .. tab-set:: .. tab-item:: Step 1: Sequence Diagram for SERVER.c .. plantuml:: @startuml !theme spacelab start :socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP); :bind(tcp_server_fd, (struct sockaddr*)&tcp_addr, sizeof(tcp_addr)); :listen(tcp_server_fd, MAX_EVENTS); :tcp_client_fd = accept(tcp_server_fd, (struct sockaddr*) &tcp_addr, &tcp_addr_len); :epoll_fd = epoll_create1(0); :epoll_ctl(epoll_fd, EPOLL_CTL_ADD, tcp_client_fd, &event); while (while(1)) is (yes) :epoll_wait(epoll_fd, events, MAX_EVENTS, -1); if (events[0].data.fd == tcp_client_fd) then (yes) :recv(tcp_client_fd, buffer, sizeof(buffer) - 1, 0); :send(tcp_client_fd, buffer, strlen(buffer), 0); else (no) endif endwhile (CTRL+c) :(void)close(tcp_client_fd); stop @enduml .. _epoll_ipv6_af_inet6_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 tcp_server_fd = socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP); * ``bind()`` is used to associate the socket with a specific address and port. For example, .. code-block:: c ret = bind(tcp_server_fd, (struct sockaddr*)&tcp_addr, sizeof(tcp_addr)); * ``listen()`` is used to set up a socket to accept incoming connections. For example, .. code-block:: c ret = listen(tcp_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 tcp_client_fd = accept(tcp_server_fd, (struct sockaddr*) &tcp_addr, &tcp_addr_len); * ``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, tcp_server_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(tcp_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(tcp_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(tcp_client_fd); * See the full program below, .. literalinclude:: IPV6_AF_INET6_TCP/server/server.c :language: c :emphasize-lines: 95, 96, 111, 112, 160, 161, 162, 169, 170, 171, 179, 180, 190, 191, 192, 202, 214, 215, 223, 224, 225, 238, 239 .. _epoll_ipv6_af_inet6_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 8080 ::1 Port: 8080 IP Address: ::1 Server is 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_ipv6_af_inet6_tcp_socket_client_sequence_diagram: .. tab-set:: .. tab-item:: Step 4: Sequence Diagram for CLIENT.c .. plantuml:: @startuml !theme spacelab start :socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP); :connect(client_fd, (struct sockaddr*)&tcp_addr, tcp_addr_len); :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_ipv6_af_inet6_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_INET6, SOCK_STREAM, IPPROTO_TCP); * ``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*)&tcp_addr, tcp_addr_len); * ``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:: IPV6_AF_INET6_TCP/client/client.c :language: c :emphasize-lines: 81, 82, 106, 107, 161, 162, 163, 170, 171, 172, 181, 192, 193, 203, 204, 205, 218 .. _epoll_ipv6_af_inet6_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 8080 ::1 Port: 8080 IP Address: ::1 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 ^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_STREAM, IPPROTO_TCP)``. **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_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/ipv6_af_inet6_tcp/poll/poll` * Current topic * :doc:`../../../sockets/ipv6_af_inet6_tcp/epoll/epoll` * Next topic * :doc:`../../../sockets/ipv6_af_inet6_udp` * Other sockets * :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`