IPV4 RAW AF INET ICMP server client program with Epoll system call ==================================================================== .. tab-set:: .. tab-item:: IPv4 RAW_AF_INET ICMP * 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 `_ * `epoll_create1 `_ * `epoll_ctl `_ * `epoll_wait `_ * `sendto `_ * `recvfrom `_ .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Topics in this section, * :ref:`IPV4 RAW_AF_INET ICMP 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 ` .. _epoll_ipv4_raw_af_inet_icmp_socket: .. tab-set:: .. tab-item:: IPV4 RAW_AF_INET ICMP 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_ICMP)`` do? .. dropdown:: See Answer This call creates a raw socket in the IPv4 address family ``(AF_INET)`` that can receive ``ICMP (Internet Control Message Protocol)`` packets directly. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why use ``AF_INET`` as the address family? .. dropdown:: See Answer ``AF_INET`` specifies that the socket will work with IPv4 addresses. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What is the purpose of ``SOCK_RAW`` in the socket type? .. dropdown:: See Answer ``SOCK_RAW`` allows the socket to operate at a lower level by providing direct access to the packet, including the IP and transport layer headers. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why specify ``IPPROTO_ICMP`` as the protocol? .. dropdown:: See Answer It filters the socket to receive only ICMP packets, allowing applications to handle ICMP messages directly. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can this socket send ICMP packets as well? .. dropdown:: See Answer Yes, the same socket can be used to send and receive ICMP packets. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How does this socket differ from a standard UDP or TCP socket? .. dropdown:: See Answer Unlike UDP or TCP sockets, a raw socket provides direct access to the IP and ICMP headers, making it suitable for low-level packet handling. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Is error checking needed after creating the socket? .. dropdown:: See Answer Yes, checking for errors ensures that the socket is created successfully before proceeding with further operations. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can this socket be used for other protocols besides ICMP? .. dropdown:: See Answer While created specifically for ICMP, the socket can be adapted for handling other IP protocols by changing the IPPROTO parameter. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why close the socket after processing? .. dropdown:: See Answer Closing the socket ensures proper resource cleanup and releases the associated system resources. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How is the source IP address extracted from the received packet? .. dropdown:: See Answer The source IP address can be extracted by parsing the IP header within the received packet. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Can this socket receive ICMP messages from any source? .. dropdown:: See Answer Yes, the socket can receive ICMP packets from any source as it operates at the network layer. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why cast to struct iphdr and struct icmphdr in packet processing? .. dropdown:: See Answer Casting allows the code to interpret the received buffer as IP and ICMP headers, facilitating packet analysis. .. 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_ipv4_raw_af_inet_icmp_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_ICMP); :epoll_fd = epoll_create1(0); :epoll_ctl(epoll_fd, EPOLL_CTL_ADD, server_socket, &event); while (while(1)) is (yes) :epoll_wait(epoll_fd, events, MAX_EVENTS, -1); if (events[0].data.fd == server_socket) then (yes) :recvfrom(server_socket, buffer, sizeof(buffer), 0, NULL, NULL); :sendto(server_socket, buffer, sizeof(struct icmphdr) + strlen(data), 0, (struct sockaddr*)&dest_addr, sizeof(dest_addr)); else (no) endif endwhile (CTRL+c) :(void)close(server_socket); stop @enduml .. _epoll_ipv4_raw_af_inet_icmp_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 * Epoll create1 * Epoll_ctl * Epoll_wait * 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_RAW, IPPROTO_ICMP); * ``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, server_socket, &event); * ``epoll_wait()`` The application then enters a loop where it waits for events using epoll_wait, For example, .. code-block:: c ready_fds = epoll_wait(epoll_fd, events, MAX_EVENTS, -1); * ``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(server_socket, buffer, sizeof(buffer), 0, NULL, NULL); * ``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(server_socket, buffer, sizeof(struct icmphdr) + strlen(data), 0, (struct sockaddr*)&dest_addr, sizeof(dest_addr)); * ``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_raw_af_inet_icmp/server/server.c :language: c :emphasize-lines: 64, 65, 66, 67, 68, 118, 119, 120, 131, 141, 142, 143, 153, 154, 161, 162, 163, 177 .. _epoll_ipv4_raw_af_inet_icmp_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 Received ICMP message: Source IP: 127.0.0.1 Type: 8 Code: 0 Original Data: Hello from client! Received ICMP message: Source IP: 127.0.0.1 Type: 8 Code: 0 Original Data: Hello from server! Received ICMP message: Source IP: 127.0.0.1 Type: 8 Code: 0 Original Data: Hello from client! Received ICMP message: Source IP: 127.0.0.1 Type: 8 Code: 0 Original Data: Hello from server! Received ICMP message: Source IP: 127.0.0.1 Type: 8 Code: 0 Original Data: Hello from server! Received ICMP message: Source IP: 127.0.0.1 Type: 8 Code: 0 Original Data: Hello from client! ^CCaught sigINT! .. _epoll_ipv4_raw_af_inet_icmp_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_ICMP); :epoll_fd = epoll_create1(0); :epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client_socket, &event); while (while(1)) is (yes) :sendto(client_socket, buffer, sizeof(struct icmphdr) + strlen(data), 0, (struct sockaddr*)&dest_addr, sizeof(dest_addr)); :epoll_wait(epoll_fd, events, MAX_EVENTS, -1); if (events[0].data.fd == client_socket) then (yes) :recvfrom(client_socket, buffer, sizeof(buffer), 0, NULL, NULL); else (no) endif endwhile (CTRL+c) :(void)close(client_socket); stop @enduml .. _epoll_ipv4_raw_af_inet_icmp_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 * Epoll create1 * Epoll_ctl * Epoll_wait * 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_RAW, IPPROTO_ICMP); * ``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_socket, &event); * ``epoll_wait()`` The application then enters a loop where it waits for events using epoll_wait, For example, .. code-block:: c ready_fds = epoll_wait(epoll_fd, events, MAX_EVENTS, -1); * ``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 len = recvfrom(client_socket, buffer, sizeof(buffer), 0, NULL, NULL); * ``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(client_socket, buffer, sizeof(struct icmphdr) + strlen(data), 0, (struct sockaddr*)&dest_addr, sizeof(dest_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:: ipv4_raw_af_inet_icmp/client/client.c :language: c :emphasize-lines: 83, 84, 85, 86, 87, 146, 147, 148, 158, 168, 169, 183, 184, 185, 192, 193, 194, 195, 206 .. _epoll_ipv4_raw_af_inet_icmp_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 Received ICMP message: Source IP: 127.0.0.1 Type: 8 Code: 0 Original Data: Hello from client! Received ICMP message: Source IP: 127.0.0.1 Type: 8 Code: 0 Original Data: Hello from server! Received ICMP message: Source IP: 127.0.0.1 Type: 8 Code: 0 Original Data: Hello from client! Received ICMP message: Source IP: 127.0.0.1 Type: 8 Code: 0 Original Data: Hello from server! Received ICMP message: Source IP: 127.0.0.1 Type: 8 Code: 0 Original Data: Hello from client! ^CCaught sigINT! .. 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_ICMP)``. **Working Scenario:** Despite the change in domain to ``PF_INET``, the socket continues to operate the same way, handling general network data. .. _epoll_ipv4_raw_af_inet_icmp_Summary: .. tab-set:: .. tab-item:: Summary ============== ================================================================================================================== Socket API Learning ============== ================================================================================================================== socket Create a new socket 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.. 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_icmp/poll/poll` * Current topic * :doc:`../../../sockets/ipv4_raw_af_inet_icmp/epoll/epoll` * Next topic * :doc:`../../../sockets/ipv4_raw_af_inet_raw` * Other sockets * :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`