af unix tcp server client program with Select system call ========================================================== .. tab-set:: .. tab-item:: AF_UNIX 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:`AF_UNIX 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 ` .. _select_af_unix_tcp_socket: .. tab-set:: .. tab-item:: AF_UNIX 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 AF_UNIX represent in the socket call? .. dropdown:: See Answer ``AF_UNIX`` represents the Unix domain socket family. It is used for communication between processes on the same machine, using file system paths as addresses. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why use SOCK_STREAM as the socket type? .. dropdown:: See Answer ``SOCK_STREAM`` indicates a stream-oriented socket, providing a reliable, connection-oriented communication channel. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What does the third parameter (0) indicate in socket(AF_UNIX, SOCK_STREAM, 0)? .. dropdown:: See Answer Default protocol selected by the system. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How can I set up a server and client using AF_UNIX sockets? .. dropdown:: See Answer To set up a server and client, ``create a socket using socket(AF_UNIX, SOCK_STREAM, 0),`` ``bind the server to an address,`` ``isten for incoming connections, and establish connections from clients.`` ``Communication occurs through read and write operations on the established connections.`` .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow How should errors in the socket call be handled? .. dropdown:: See Answer Check the return value, handle errors using appropriate mechanisms. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What is the role of the file system path in AF_UNIX sockets? .. dropdown:: See Answer The file system path serves as the address for Unix domain sockets. It enables processes to locate and connect to the socket. he path is set in the ``sun_path`` field of the ``struct sockaddr_un`` structure. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow What is the role of the file system path in AF_UNIX sockets? .. dropdown:: See Answer Address. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Why might bind() or listen() fail in socket programming? .. dropdown:: See Answer bind() might fail if the specified address is already in use, or if the process lacks the necessary permissions. listen() might fail if the socket is not bound, or the operating system limit for pending connections is reached. .. 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 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_af_unix_tcp_socket_server_sequence_diagram: .. tab-set:: .. tab-item:: Step 1: Sequence Diagram for SERVER.c .. plantuml:: @startuml !theme spacelab start :socket(AF_UNIX, SOCK_STREAM, 0); :bind(server_fd, (struct sockaddr*)&server_addr, sizeof(server_addr)); :listen(server_fd, 5); :client_fd = accept(server_fd, NULL, NULL); while (while(1)) is (yes) :FD_ZERO(&read_fds); :FD_SET(client_fd, &read_fds); :select(fdmax + 1, &read_fds, NULL, NULL, NULL); if (FD_ISSET(client_fd, &read_fds)) then (yes) :recv(client_fd, buffer, sizeof(buffer) - 1, 0); :send(client_fd, buffer, strlen(buffer), 0); else (no) endif endwhile (CTRL+c) :(void)close(client_fd); stop @enduml .. _select_af_unix_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 * Accept Socket * Select * 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_UNIX, SOCK_STREAM, 0); * ``bind()`` is used to associate the socket with a specific address and port. For example, .. code-block:: c ret = bind(server_fd, (struct sockaddr*)&server_addr, sizeof(server_addr)); * ``listen()`` is used to set up a socket to accept incoming connections. For example, .. code-block:: c ret = listen(server_fd, 5); * ``accept()`` is used in network programming on the server side to accept a connection request from a client. For example, .. code-block:: c client_fd = accept(server_fd, NULL, NULL); * ``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(fdmax + 1, &read_fds, NULL, NULL, NULL); * ``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); * ``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); * ``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:: af_unix_tcp/server/server.c :language: c :emphasize-lines: 39, 40, 55, 56, 94, 95, 102, 103, 104, 112, 122, 123, 140, 141, 154, 155 .. _select_af_unix_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 Server listening connection accepted = 4 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 Sentbuffer = HELLO Received: HI ^CCaught sigINT! .. _select_af_unix_tcp_socket_client_sequence_diagram: .. tab-set:: .. tab-item:: Step 4: Sequence Diagram for CLIENT.c .. plantuml:: @startuml !theme spacelab start :socket(AF_UNIX, SOCK_STREAM, 0); :connect(client_fd, (struct sockaddr*)&server_addr, sizeof(struct sockaddr_un)); 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_af_unix_tcp_socket_client_code: .. tab-set:: .. tab-item:: Step 2: 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_UNIX, SOCK_STREAM, 0); * ``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*)&server_addr, sizeof(struct sockaddr_un)); * ``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:: af_unix_tcp/client/client.c :language: c :linenos: :emphasize-lines: 37, 38, 61, 62, 92, 93, 100, 101, 102, 116, 117, 130 .. _select_af_unix_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 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 Received: HELLO sentbuffer = HI ^CCaught sigINT! .. _select_af_unix_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/af_unix_tcp/Basic_example/Basic_example` * Current topic * :doc:`../../../sockets/af_unix_tcp/select/select` * Next topic * :doc:`../../../sockets/af_unix_tcp/poll/poll` * Other sockets * :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`