IPV6 TCP server client program with Select 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 `_ * `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. .. _select_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 purpose of the select system call in network programming? .. 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 select help in handling multiple sockets efficiently? .. dropdown:: See Answer It provides a way to wait for readiness on multiple sockets without blocking the entire program. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What types of file descriptors can be monitored using select? .. 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 is the significance of the timeout parameter in the select function? .. dropdown:: See Answer It specifies the maximum duration to wait for any file descriptor to become ready. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How do you handle errors when using the select 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 select handle a set of file descriptors with different states (e.g., reading, writing, exception)? .. dropdown:: See Answer Preparing File Descriptor Sets: ``select(readfds, writefds, exceptfds);`` Setting Up Readiness Conditions: If you are interested in monitoring file descriptors for readability, you add them to the readfds set. ``FD_ZERO(&readfds);`` ``FD_SET(fd1, &readfds);`` Setting Up Writability Conditions: If you are interested in monitoring file descriptors for writability, you add them to the writefds set. ``FD_ZERO(&writefds);`` ``FD_SET(fd2, &writefds);`` Setting Up Exceptional Conditions: If you are interested in monitoring file descriptors for exceptional conditions, you add them to the exceptfds set. ``FD_ZERO(&exceptfds);`` ``FD_SET(fd3, &exceptfds);`` .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does select Checking Ready File Descriptors? .. dropdown:: See Answer After select returns, you can check the sets to determine which file descriptors are ready for the specified conditions. .. code-block:: c if (FD_ISSET(fd1, &readfds)) { // fd1 is ready for reading } if (FD_ISSET(fd3, &writefds)) { // fd2 is ready for writing } if (FD_ISSET(fd4, &exceptfds)) { // fd3 has an exceptional condition } .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What does it mean if select returns 0? .. dropdown:: See Answer No file descriptors are ready within the specified timeout. .. _select_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, 5); :tcp_client_fd = accept(tcp_server_fd, (struct sockaddr*) &tcp_addr, &tcp_addr_len); :FD_ZERO(&read_fds); :FD_SET(tcp_client_fd, &read_fds); while (while(1)) is (yes) :select(fdmax + 1, &read_fds, NULL, NULL, NULL); if (FD_ISSET(tcp_client_fd, &read_fds)) 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 .. _select_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 * Select * Accept Socket * 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 bind_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 listen_ret = listen(tcp_server_fd, 5); * ``select()`` is used in network programming to monitor multiple file descriptors (usually sockets) for read, write, or error conditions. For example, .. code-block:: c select_ret = select(fdmax + 1, &read_fds, NULL, NULL, NULL); * ``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); * ``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 :linenos: :emphasize-lines: 91, 92, 107, 108, 154, 155, 156, 163, 164, 165, 174, 183, 184, 185, 201, 202, 215, 216 .. _select_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 IP Address: ::1 Server lsiten... 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! .. _select_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); while (while(1)) is (yes) :send(client_fd, buffer, strlen(buffer), 0); :FD_ZERO(&read_fds); :FD_SET(client_fd, &read_fds); :select(client_fd + 1, &read_fds, NULL, NULL, NULL); if (FD_ISSET(client_fd, &read_fds)) then (yes) :recv(client_fd, buffer, sizeof(buffer) - 1, 0); else (no) endif endwhile (CTRL+c) :(void)close(client_fd); stop @enduml .. _select_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 * Select * Recv data_packet * Send 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); * ``select`` is used in network programming to monitor multiple file descriptors (usually sockets) for read, write, or error conditions. For example, .. code-block:: c ret = select(client_fd + 1, &read_fds, NULL, NULL, NULL); * ``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: 78, 79, 102, 103, 154, 155, 156, 163, 164, 165, 180, 181, 194 .. _select_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 sentbuffer = 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_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. .. _select_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. select Monitor multiple file descriptors (usually sockets) for read, write, or error conditions. 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/Basic_example/Basic_example` * Current topic * :doc:`../../../sockets/ipv6_af_inet6_tcp/select/select` * Next topic * :doc:`../../../sockets/ipv6_af_inet6_tcp/poll/poll` * Other sockets * :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`