IPV4 RAW AF INET UDP server client program with Poll system call ================================================================== .. tab-set:: .. tab-item:: IPv4 RAW_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 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 `_ * `sendto `_ * `recvfrom `_ .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Topics in this section, * :ref:`IPV4 RAW_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_raw_af_inet_udp_socket: .. tab-set:: .. tab-item:: IPV4 RAW_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_RAW, IPPROTO_UDP)`` do? .. dropdown:: See Answer This call creates a raw socket in the ``AF_INET`` address family for direct access to UDP packets. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow When would I use ``SOCK_RAW`` sockets with ``IPPROTO_UDP``? .. dropdown:: See Answer This combination is used for tasks like packet sniffing, crafting custom protocols, or low-level UDP packet manipulation. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can ``SOCK_RAW`` sockets be used for regular UDP communication? .. dropdown:: See Answer While technically possible, it's not recommended. Higher-level APIs are more suitable for standard UDP communication. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What is the difference between ``IPPROTO_UDP`` and ``SOCK_RAW`` for UDP communication? .. dropdown:: See Answer ``IPPROTO_UDP`` specifies the transport protocol (UDP), while SOCK_RAW indicates a raw socket, providing more control over UDP packet content. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What are common issues when working with raw UDP sockets? .. dropdown:: See Answer Common issues include permission errors, endianness mismatches, and improper packet handling. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How do I handle errors when using raw UDP sockets? .. dropdown:: See Answer Use error codes returned by system calls like socket and sendto for error handling. Log and handle errors gracefully. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can raw UDP sockets be used for both sending and receiving data? .. dropdown:: See Answer Yes, raw UDP sockets can be used for both sending and receiving UDP packets. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why is it important to check the return value of sendto() and recvfrom() 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 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_raw_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_RAW, IPPROTO_UDP); :fds[0].fd = sock_fd; :fds[0].events = POLLIN; while (while(1)) is (yes) :poll(fds, 1, 1000); if (fds[0].revents & POLLIN) then (yes) :recvfrom(sock_fd, recvbuffer, (sizeof(struct iphdr) + sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, &length); :sendto(sock_fd, buffer, (sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, sizeof(struct sockaddr_in)); else (no) endif endwhile (CTRL+c) :(void)close(sock_fd); stop @enduml .. _poll_ipv4_raw_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 * Poll * Recvfrom data_packet * Sendto data_packet * Close socket * ``socket()`` is used to create a new socket. For example, .. code-block:: c sock_fd = socket(AF_INET, SOCK_RAW, 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, 1, 1000); * ``recvfrom`` is commonly used with 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 ret = recvfrom(sock_fd, recvbuffer, (sizeof(struct iphdr) + sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, &length); * ``sendto`` is used to send the encoded message to the specified server address and port using a socket. For example, .. code-block:: c ret = sendto(sock_fd, buffer, (sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, sizeof(struct sockaddr_in)); * ``close`` is used to close the socket To free up system resources associated with the socket. For example, .. code-block:: c (void)close(sock_fd); * See the full program below, .. literalinclude:: ipv4_raw_af_inet_udp/server/server.c :language: c :emphasize-lines: 111, 112, 113, 192, 203, 204, 205, 206, 207, 208, 229, 230, 231, 232, 233, 244 .. _poll_ipv4_raw_af_inet_udp_socket_server_side_compile_and_execute: .. tab-set:: .. tab-item:: Step 3: Compile and Execute server.c .. code-block:: c :emphasize-lines: 1, 3 $ gcc -o server server.c $ sudo ./server 127.0.0.1 IP Address: 127.0.0.1 checksum is 53fc Received :Hello server Received :Hello server Received :Hello server Received :Hello server Received :Hello server Received :Hello client Received :Hello server Received :Hello server Received :Hello client Received :Hello server Received :Hello server Received :Hello client ^C .. _poll_ipv4_raw_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_RAW, IPPROTO_UDP); :fds[0].fd = sockfd; :fds[0].events = POLLIN; while (while(1)) is (yes) :sendto(sockfd, buffer, (sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, sizeof(struct sockaddr_in)); :poll(fds, 1, 1000); if (fds[0].revents & POLLIN) then (yes) :recvfrom(sockfd, recvbuffer, (sizeof(struct iphdr) + sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, &length); else (no) endif endwhile (CTRL+c) :(void)close(sockfd); stop @enduml .. _poll_ipv4_raw_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 sockfd = socket(AF_INET, SOCK_RAW, 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, 1, 1000); * ``sendto`` is used to send the encoded message to the specified server address and port using a socket. For example, .. code-block:: c ret = sendto(sockfd, buffer, (sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, sizeof(struct sockaddr_in)); * ``recvfrom`` is commonly used with 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 ret = recvfrom(sockfd, recvbuffer, (sizeof(struct iphdr) + sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, &length); * ``close`` is used to close the socket To free up system resources associated with the socket. For example, .. code-block:: c (void)close(sockfd); * See the full program below, .. literalinclude:: ipv4_raw_af_inet_udp/client/client.c :language: c :emphasize-lines: 110, 111, 112, 191, 192, 193, 194, 195, 202, 213, 214, 215, 216, 217, 218, 245 .. _poll_ipv4_raw_af_inet_udp_socket_client_side_compile_and_execute: .. tab-set:: .. tab-item:: Step 6: Compile and Execute client.c .. code-block:: c :emphasize-lines: 1, 3 $ gcc -o client client.c $ sudo ./client 127.0.0.1 IP Address: 127.0.0.1 checksum is 4bec Received :Hello server Received :Hello server Received :Hello server Received :Hello server Received :Hello server Received :Hello client Received :Hello server Received :Hello server Received :Hello client Received :Hello server Received :Hello server Received :Hello client ^C .. 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_RAW, 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_raw_af_inet_udp_Summary: .. tab-set:: .. tab-item:: Summary ============== ================================================================================================================== Socket API Learning ============== ================================================================================================================== socket Create a new socket 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 socket. ============== ================================================================================================================== .. card:: See Also * previous topic * :doc:`../../../sockets/ipv4_raw_af_inet_udp/select/select` * current topic * :doc:`../../../sockets/ipv4_raw_af_inet_udp/poll/poll` * Next topic * :doc:`../../../sockets/ipv4_raw_af_inet_udp/epoll/epoll` * Other sockets * :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`