IPV4 UDP server client program with Poll system call ==================================================== .. tab-set:: .. tab-item:: IPv4 AF_INET 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:`IPV4 AF_INET 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 ` .. _poll_ipv4_af_inet_udp_socket: .. tab-set:: .. tab-item:: IPV4 AF_INET 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_INET SOCK_DGRAM,IPPROTO_UDP) create? .. dropdown:: See Answer A UDP socket .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What does AF_INET signify in socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)? .. dropdown:: See Answer IPv4 address family .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why might you choose SOCK_DGRAM when creating a socket? .. dropdown:: See Answer For connectionless communication .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What is the purpose of IPPROTO_UDP in socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)? .. dropdown:: See Answer It is optional and can be omitted. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does a UDP socket differ from a TCP socket created using socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)? .. dropdown:: See Answer UDP is connectionless, while TCP is connection-oriented, .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What is the typical use case for a UDP socket created with socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)? .. dropdown:: See Answer DNS resolution .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How would you bind a specific IP address and port to a UDP socket created using socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)? .. dropdown:: See Answer Use the bind() function after creating the socket. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What is the purpose of the poll system call? .. 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 poll differ from poll in terms of usability? .. dropdown:: See Answer poll is more efficient than poll for monitoring multiple file descriptors. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What types of file descriptors can be monitored using poll? .. 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 How does poll handle a set of file descriptors with different states (e.g., reading, writing, exception)? .. dropdown:: See Answer It uses different structures for each state in the pollfd array. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How do you handle errors when using the poll 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 poll handle a set of file descriptors with different states (e.g., reading, writing, exception)? .. dropdown:: See Answer Array of pollfd Structures: Before calling poll, you need to create an array of pollfd structures, where each structure represents a file descriptor and its associated events. ``struct pollfd fds[NUM_FDS];`` NUM_FDS is the number of file descriptors you want to monitor. Initialize pollfd Structures: For each file descriptor you want to monitor, initialize the corresponding pollfd structure with the following information: `fd:` The file descriptor to monitor. `events:` The events of interest (e.g., POLLIN for readability, POLLOUT for writability). `revents:` Initially set to zero. After the poll call, this field is updated to indicate the events that occurred. ``fds[0].fd = fd1;`` ``fds[0].events = POLLIN;`` ``fds[0].revents = 0;`` ``fds[1].fd = fd2;`` ``fds[1].events = POLLIN;`` ``fds[1].revents = 0;`` Call poll: After initializing the pollfd array, call the poll function, providing the array, the number of file descriptors, and a timeout ``int ready_fds = poll(fds, NUM_FDS, timeout_ms);`` `ready_fds` will contain the number of file descriptors that are ready. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does poll Checking Ready File Descriptors? .. dropdown:: See Answer After the poll call, loop through the pollfd array and check the revents field for each file descriptor to determine which events occurred. .. code-block:: c for (int i = 0; i < NUM_FDS; ++i) { if (fds[i].revents & POLLIN) { // File descriptor i is ready for reading } if (fds[i].revents & POLLOUT) { // File descriptor i is ready for writing } // Check other events if needed (e.g., POLLERR, POLLHUP) } .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What does it mean if poll returns 0? .. dropdown:: See Answer No file descriptors are ready within the specified timeout. .. _poll_ipv4_af_inet_udp_socket_server_sequence_diagram: .. tab-set:: .. tab-item:: Step 1: Sequence Diagram for SERVER.c .. plantuml:: @startuml !theme spacelab start :socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); :bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)); :fds[0].fd = server_socket; :fds[0].events = POLLIN; while (while(1)) is (yes) :poll(fds, 1, 1000); if (fds[0].revents & POLLIN) 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 .. _poll_ipv4_af_inet_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 * Poll * 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_INET, 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)); * ``poll()`` is used for monitoring multiple file descriptors to see if I/O is possible on any of them. .. code-block:: c ret = poll(fds, 1, 1000); * ``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:: IPV4_AF_INET_UDP/server/server.c :language: c :emphasize-lines: 69, 70, 71, 72, 85, 86, 87, 88, 89, 129, 130, 131, 138, 139, 140, 156, 169 .. _poll_ipv4_af_inet_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 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! .. _poll_ipv4_af_inet_udp_socket_client_sequence_diagram: .. tab-set:: .. tab-item:: Step 4 : Sequence Diagram for CLIENT.c .. plantuml:: @startuml !theme spacelab start :socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); while (while(1)) is (yes) :sendto(client_socket, buffer, strlen(buffer), 0, (struct sockaddr*)&server_addr, sizeof(server_addr)); :fds[0].fd = client_socket; :fds[0].events = POLLIN; :poll(fds, 2, 1000); if (fds[0].revents & POLLIN) then (yes) :recvfrom(client_socket, buffer, BUFFER_SIZE, 0, NULL, NULL); else (no) endif endwhile (CTRL+c) :(void)close(client_socket); stop @enduml .. _poll_ipv4_af_inet_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 * Poll * 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_INET, SOCK_DGRAM, IPPROTO_UDP); * ``poll()`` is used for monitoring multiple file descriptors to see if I/O is possible on any of them. .. code-block:: c ret = poll(fds, 2, 1000); * ``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:: IPV4_AF_INET_UDP/client/client.c :language: c :emphasize-lines: 77, 78, 129, 130, 131, 139, 140, 141, 142, 154, 167 .. _poll_ipv4_af_inet_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 127.0.0.1 Port: 8080 IP Address: 127.0.0.1 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 Received: HELLO sendbuffer = HI ^CCaught sigINT! .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow $ sudo ./server 8080 127.0.0.1 $ sudo ./client 8080 127.0.0.1 program to run with elevated privileges, listen on port 8080, and bind to the loopback address 127.0.0.1. decided by the user based on the connection. .. tab-set:: .. tab-item:: Enhanced Socket Flexibility with ``AF_INET`` and ``PF_INET`` 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_INET`` domain, handling all types of network data. **Additional Domain Support:** We expand the socket's capabilities to also function in the ``PF_INET`` domain, allowing it to operate similarly to ``AF_INET``. **Socket Creation:** We set up a network connection point known as a socket using ``socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)``. **Working Scenario:** Despite the change in domain to ``PF_INET``, the socket continues to operate the same way, handling general network data. .. _poll_ipv4_af_inet_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 poll 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/ipv4_af_inet_udp/select/select` * current topic * :doc:`../../../sockets/ipv4_af_inet_udp/poll/poll` * Next topic * :doc:`../../../sockets/ipv4_af_inet_udp/epoll/epoll` * Other sockets * :doc:`../../../sockets/af_unix_tcp` * :doc:`../../../sockets/af_unix_udp` * :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`