IPV6 UDP server client program with Select 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 `_ * `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 ` .. 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_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 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_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)); while (while(1)) is (yes) :FD_ZERO(&read_fds); :FD_SET(server_socket, &read_fds); :select(server_socket + 1, &read_fds, NULL, NULL, NULL); if (FD_ISSET(server_socket, &read_fds)) 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 .. _select_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 * Select * 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)); * ``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(server_socket + 1, &read_fds, NULL, NULL, NULL); * ``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: 88, 89, 90, 97, 98, 99, 113, 114, 123, 124, 125, 126, 139, 140, 141, 142, 158 .. _select_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 UDP listining Received: HI! Sent buffer= HELLO Received: HI! Sent buffer= HELLO Received: HI! Sent buffer= HELLO Received: HI! Sent buffer= HELLO Received: HI! Sent buffer= HELLO Received: HI! Sent buffer= HELLO Received: HI! ^CCaught sigINT! .. _select_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); while (while(1)) is (yes) :sendto(client_socket, buffer, strlen(buffer), 0, (struct sockaddr*)&server_addr, sizeof(server_addr)); :FD_ZERO(&read_fds); :FD_SET(client_socket, &read_fds); :select(client_socket + 1, &read_fds, NULL, NULL, NULL); if (FD_ISSET(client_socket, &read_fds)) then (yes) :recvfrom(client_socket, buffer, BUFFER_SIZE, 0, NULL, NULL); else (no) endif endwhile (CTRL+c) :(void)close(client_socket); stop @enduml .. _select_ipv6_af_inet6_udp_socket_client_code: .. tab-set:: .. tab-item:: Step 5: program for client.c * Create Socket * Select * 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); * ``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_socket + 1, &read_fds, NULL, NULL, NULL); * ``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); * ``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)); * ``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: 76, 77, 78, 128, 129, 130, 140, 141, 142, 143, 153, 154, 167 .. _select_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. .. _select_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 select Monitor multiple file descriptors (usually sockets) for read, write, or error conditions. 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/Basic_example/Basic_example` * Current topic * :doc:`../../../sockets/ipv6_af_inet6_udp/select/select` * Next topic * :doc:`../../../sockets/ipv6_af_inet6_udp/poll/poll` * 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`