IPV6 TCP server client program with Poll system call
=====================================================
.. tab-set::
.. tab-item:: IPv6 AF_INET6 TCP
* In this program, you are going to learn
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* How to create a Socket ?
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* How to bind a socket ?
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* How to listen a socket ?
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* How to connect a socket ?
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* How to accept a socket ?
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* How to send a data ?
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* How to recv a data ?
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* How to use socket APIs ?
* `socket <https://man7.org/linux/man-pages/man2/socket.2.html>`_
* `bind <https://man7.org/linux/man-pages/man2/bind.2.html>`_
* `listen <https://man7.org/linux/man-pages/man2/listen.2.html>`_
* `connect <https://man7.org/linux/man-pages/man2/connect.2.html>`_
* `accept <https://man7.org/linux/man-pages/man2/accept.2.html>`_
* `send <https://man7.org/linux/man-pages/man2/send.2.html>`_
* `recv <https://man7.org/linux/man-pages/man2/recv.2.html>`_
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Topics in this section,
* :ref:`IPV6 AF_INET6 TCP SOCKET FAQs <poll_ipv6_af_inet6_tcp_socket>`
* :ref:`Step 1: Sequence Diagram for SERVER.c <poll_ipv6_af_inet6_tcp_socket_server_sequence_diagram>`
* :ref:`Step 2: Program for Server.c <poll_ipv6_af_inet6_tcp_socket_server_code>`
* :ref:`Step 3: Compile and Execute Server.c <poll_ipv6_af_inet6_tcp_socket_server_side_compile_and_execute>`
* :ref:`Step 4:Sequence Diagram for CLIENT.c <poll_ipv6_af_inet6_tcp_socket_client_sequence_diagram>`
* :ref:`Step 5: Program for Client.c <poll_ipv6_af_inet6_tcp_socket_client_code>`
* :ref:`Step 6: Compile and Execute Client.c <poll_ipv6_af_inet6_tcp_socket_client_side_compile_and_execute>`
* :ref:`Summary <poll_ipv6_af_inet6_tcp_Summary>`
.. tab-set::
.. tab-item:: Enabling IPv6 on the Loopback Interface Before Program Execution
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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.
.. _poll_ipv6_af_inet6_tcp_socket:
.. tab-set::
.. tab-item:: IPV6 AF_INET6 TCP SOCKET : FAQs
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Let us answer few basic questions in this socket
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What does ``socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP)`` do?
.. dropdown:: See Answer
This call creates a TCP socket in the ``AF_INET6`` (IPv6) address family.
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When is it appropriate to use ``SOCK_STREAM`` with IPv6?
.. dropdown:: See Answer
For reliable, connection-oriented communication.
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What privileges are required to create an IPv6 TCP socket?
.. dropdown:: See Answer
No special privileges.
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Can ``socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP)`` be used for regular UDP communication?
.. dropdown:: See Answer
No, it is designed only for TCP communication.
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How does an IPv6 TCP socket differ from an IPv4 TCP socket?
.. dropdown:: See Answer
IPv6 sockets handle communication using IPv6 addresses.
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Can I use IPv6 TCP sockets in a mixed IPv4/IPv6 environment?
.. dropdown:: See Answer
Yes, most modern systems support IPv6.
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How do I specify a port number for an IPv6 TCP socket?
.. dropdown:: See Answer
Set the port number in the sin6_port field.
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Can I use IPv6 TCP sockets for non-blocking I/O?
.. dropdown:: See Answer
Yes, use setsockopt to enable non-blocking mode.
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How do I handle connection establishment with IPv6 TCP sockets?
.. dropdown:: See Answer
Use the bind and listen functions.
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Are there any compatibility issues with older systems when using IPv6 TCP sockets?
.. dropdown:: See Answer
Yes, older systems may lack IPv6 support.
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How do I handle IPv6 DNS resolution in my application?
.. dropdown:: See Answer
Use functions like getaddrinfo to resolve hostnames.
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How should you handle errors when using accept() in socket programming?
.. dropdown:: See Answer
Check the return value and handle errors appropriately
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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.
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Can you use a TCP socket (SOCK_STREAM) for sending and receiving data concurrently between a client and server?
.. dropdown:: See Answer
Yes, TCP sockets support bidirectional communication.
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What is the purpose of the poll system call?
.. dropdown:: See Answer
To block and wait for activity on one or more file descriptors.
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How does poll differ from poll in terms of usability?
.. dropdown:: See Answer
poll is more efficient than poll for monitoring multiple file descriptors.
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What types of file descriptors can be monitored using poll?
.. dropdown:: See Answer
sockets, files, timerfd, socketpair, message_queue, Namedpipes and shared_memory.
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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.
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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.
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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.
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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)
}
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What does it mean if poll returns 0?
.. dropdown:: See Answer
No file descriptors are ready within the specified timeout.
.. _poll_ipv6_af_inet6_tcp_socket_server_sequence_diagram:
.. tab-set::
.. tab-item:: Step 1: Sequence Diagram for SERVER.c
.. plantuml::
@startuml
!theme spacelab
start
:socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP);
:bind(tcp_server_fd, (struct sockaddr*)&tcp_addr, sizeof(tcp_addr));
:listen(tcp_server_fd, MAX_CLIENTS);
:tcp_client_fd = accept(tcp_server_fd, (struct sockaddr*) &tcp_addr, &tcp_addr_len);
:fds[0].fd = tcp_client_fd;
:fds[0].events = POLLIN;
while (while(1)) is (yes)
:poll(fds, MAX_CLIENTS + 1, -1);
if (fds[0].revents & POLLIN) then (yes)
:recv(tcp_client_fd, buffer, sizeof(buffer) - 1, 0);
:send(tcp_client_fd, buffer, strlen(buffer), 0);
else (no)
endif
endwhile (CTRL+c)
:(void)close(tcp_client_fd);
stop
@enduml
.. _poll_ipv6_af_inet6_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
* Poll
* Accept Socket
* 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_INET6, SOCK_STREAM, IPPROTO_TCP);
* ``bind()`` is used to associate the socket with a specific address and port. For example,
.. code-block:: c
ret = bind(tcp_server_fd, (struct sockaddr*)&tcp_addr, sizeof(tcp_addr));
* ``listen()`` is used to set up a socket to accept incoming connections. For example,
.. code-block:: c
ret = listen(tcp_server_fd, MAX_CLIENTS);
* ``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, MAX_CLIENTS + 1, -1);
* ``accept()`` is used in network programming on the server side to accept a connection request from a client. For example,
.. code-block:: c
tcp_client_fd = accept(tcp_server_fd, (struct sockaddr*) &tcp_addr, &tcp_addr_len);
* ``recv`` is used in network programming to receive data from a connected socket. For example,
.. code-block:: c
len = recv(tcp_client_id, 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(tcp_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(tcp_client_fd);
* See the full program below,
.. literalinclude:: IPV6_AF_INET6_TCP/server/server.c
:language: c
:emphasize-lines: 95, 96, 111, 112, 159, 160, 161, 168, 169, 170, 178, 179, 189, 190, 191, 208, 220, 221
.. _poll_ipv6_af_inet6_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 8080 ::1
Port: 8080
IP Address: ::1
Serverlistening...
Connection Accept
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_ipv6_af_inet6_tcp_socket_client_sequence_diagram:
.. tab-set::
.. tab-item:: Step 4: Sequence Diagram for CLIENT.c
.. plantuml::
@startuml
!theme spacelab
start
:socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP);
:connect(client_fd, (struct sockaddr*)&tcp_addr, tcp_addr_len);
while (while(1)) is (yes)
:send(client_fd, buffer, strlen(buffer), 0);
:fds[0].fd = client_fd;
:fds[0].events = POLLIN;
:poll(fds, 2, -1);
if (fds[0].revents & POLLIN) then (yes)
:recv(client_fd, buffer, sizeof(buffer) - 1, 0);
else (no)
endif
endwhile (CTRL+c)
:(void)close(client_fd);
stop
@enduml
.. _poll_ipv6_af_inet6_tcp_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
* Connect Socket
* Poll
* 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_INET6, SOCK_STREAM, IPPROTO_TCP);
* ``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*)&tcp_addr, tcp_addr_len);
* ``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, -1);
* ``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:: IPV6_AF_INET6_TCP/client/client.c
:language: c
:emphasize-lines: 79, 80, 103, 104, 155, 156, 157, 164, 165, 166, 181, 193
.. _poll_ipv6_af_inet6_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 8080 ::1
Port: 8080
IP Address: 127.0.0.1
connected
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
^CCaught sigINT!
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$ 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.
<port_number> <ip_address> decided by the user based on the connection.
.. tab-set::
.. tab-item:: Enhanced Socket Flexibility with ``AF_INET6`` and ``PF_INET6`` Domains
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**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_STREAM, IPPROTO_TCP)``.
**Working Scenario:**
Despite the change in domain to ``PF_INET6``, the socket continues to operate the same way, handling general network data.
.. _poll_ipv6_af_inet6_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.
poll 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/ipv6_af_inet6_tcp/select/select`
* current topic
* :doc:`../../../sockets/ipv6_af_inet6_tcp/poll/poll`
* Next topic
* :doc:`../../../sockets/ipv6_af_inet6_tcp/epoll/epoll`
* Other sockets
* :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`