IPV4 RAW AF INET TCP server client program with Poll system call
====================================================================
.. tab-set::
.. tab-item:: IPv4 RAW_AF_INET TCP
* In this program, you are going to learn
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* How to create a Socket ?
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* How to write a data ?
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* How to read a data ?
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* How to use socket APIs ?
* `socket <https://man7.org/linux/man-pages/man2/socket.2.html>`_
* `write <https://man7.org/linux/man-pages/man2/write.2.html>`_
* `read <https://man7.org/linux/man-pages/man2/read.2.html>`_
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Topics in this section,
* :ref:`IPV4 RAW_AF_INET TCP SOCKET FAQs <poll_ipv4_raw_af_inet_tcp_socket>`
* :ref:`Step 1: Sequence Diagram for SERVER.c <poll_ipv4_raw_af_inet_tcp_socket_server_sequence_diagram>`
* :ref:`Step 2: Program for Server.c <poll_ipv4_raw_af_inet_tcp_socket_server_code>`
* :ref:`Step 3: Compile and Execute Server.c <poll_ipv4_raw_af_inet_tcp_socket_server_side_compile_and_execute>`
* :ref:`Step 4: Sequence Diagram for CLIENT.c <poll_ipv4_raw_af_inet_tcp_socket_client_sequence_diagram>`
* :ref:`Step 5: Program for Client.c <poll_ipv4_raw_af_inet_tcp_socket_client_code>`
* :ref:`Step 6: Compile and Execute Client.c <poll_ipv4_raw_af_inet_tcp_socket_client_side_compile_and_execute>`
* :ref:`Summary <poll_ipv4_raw_af_inet_tcp_Summary>`
.. _poll_ipv4_raw_af_inet_tcp_socket:
.. tab-set::
.. tab-item:: IPV4 RAW_AF_INET TCP SOCKET : FAQs
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Let us answer few basic questions in this socket
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What does ``socket(AF_INET, SOCK_RAW, IPPROTO_TCP)`` do?
.. dropdown:: See Answer
This call creates a raw socket in the ``AF_INET`` address family for direct access to TCP packets.
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When is it appropriate to use ``SOCK_RAW`` sockets with TCP?
.. dropdown:: See Answer
It's suitable for tasks like packet capturing, network monitoring, or
implementing custom protocols where direct access to TCP packets is needed.
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Can this socket be used for regular TCP communication?
.. dropdown:: See Answer
While technically possible, it's not recommended for regular
communication due to increased complexity and potential security risks.
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How does a raw TCP socket differ from a regular TCP socket?
.. dropdown:: See Answer
A raw TCP socket provides direct access to the TCP layer, allowing for manual packet manipulation,
whereas regular TCP sockets handle packet details internally.
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What are some use cases for raw TCP sockets?
.. dropdown:: See Answer
Use cases include network sniffing, packet analysis, security auditing, and developing custom network protocols.
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How can I capture and analyze TCP packets using raw sockets?
.. dropdown:: See Answer
You can use the raw socket to capture TCP packets and analyze them using packet analysis tools like Wireshark.
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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.
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Why is it important to check the return value of read() and write() in socket programming?
.. dropdown:: See Answer
It detects issues such as network errors or closed connections.
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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_ipv4_raw_af_inet_tcp_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_TCP);
:bind(sock_fd, (struct sockaddr *)servaddr, sizeof(struct sockaddr_in));
:connect(sock_fd, (struct sockaddr*)client_addr, sizeof(struct sockaddr_in));
while (while(1)) is (yes)
:fds[0].fd = sock_fd;
:fds[0].events = POLLIN;
:poll(fds, 1, 1000);
if (fds[0].revents & POLLIN) then (yes)
:read(sock_fd, recvbuffer, sizeof(recvbuffer));
:write(sock_fd, buffer, sizeof(buffer));
else (no)
endif
endwhile (CTRL+c)
:(void)close(sock_fd);
stop
@enduml
.. _poll_ipv4_raw_af_inet_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
* Connect Socket
* Poll
* Write data_packet
* Read 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_TCP);
* ``bind()`` is used to associate the socket with a specific address and port. For example,
.. code-block:: c
ret = bind(sock_fd, (struct sockaddr*)servaddr, sizeof(struct sockaddr_in));
* ``connect()`` is used in network programming to establish a connection from a client to a server. For example,
.. code-block:: c
ret = connect(sock_fd, (struct sockaddr*)client_addr, sizeof(struct sockaddr_in));
* ``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);
* ``read`` system call in C is commonly used to read data from a file descriptor, such as a socket.
.. code-block:: c
ret = read(sock_fd, recvbuffer, sizeof(recvbuffer));
* ``write`` system call in C is used to write data to a file descriptor, such as a socket.
.. code-block:: c
ret = write(sock_fd, buffer, sizeof(buffer));
* ``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_tcp/server/server.c
:language: c
:emphasize-lines: 115, 116, 117, 137, 138, 139, 160, 161, 162, 226, 237, 238, 259, 260, 274
.. _poll_ipv4_raw_af_inet_tcp_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
IP Address: 127.0.0.1
checksum is c945
Received : Hello server
Received : Hello server
Received : Hello server
Received : Hello server
Received : Hello server
Received : Hello server
Received : Hello server
Received : Hello server
Received : Hello server
Received : Hello server
Received : Hello server
Received : Hello server
Received : Hello server
Received : Hello server
^C
.. _poll_ipv4_raw_af_inet_tcp_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_TCP);
:bind(sockfd, (struct sockaddr*)clientaddr, sizeof(struct sockaddr_in));
:connect(sockfd, (struct sockaddr*)serveraddr, sizeof(struct sockaddr_in));
:fds[0].fd = sockfd;
:fds[0].events = POLLIN;
while (while(1)) is (yes)
:write(sockfd, buffer, sizeof(buffer));
:poll(fds, 2, -1);
if (fds[0].revents & POLLIN) then (yes)
:read(sockfd, recvbuffer, sizeof(recvbuffer));
else (no)
endif
endwhile (CTRL+c)
:(void)close(sockfd);
stop
@enduml
.. _poll_ipv4_raw_af_inet_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
* Bind Socket
* Connect Socket
* Poll
* Write data_packet
* Read data_packet
* Close socket
* ``socket`` is used to create a new socket. For example,
.. code-block:: c
sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);
* ``bind()`` is used to associate the socket with a specific address and port. For example,
.. code-block:: c
ret = bind(sockfd, (struct sockaddr*)clientaddr, sizeof(struct sockaddr_in));
* ``connect()`` is used in network programming to establish a connection from a client to a server. For example,
.. code-block:: c
ret = connect(sockfd, (struct sockaddr*)serveraddr, sizeof(struct sockaddr_in));
* ``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);
* ``read`` system call in C is commonly used to read data from a file descriptor, such as a socket.
.. code-block:: c
ret = read(sockfd, recvbuffer, sizeof(recvbuffer));
* ``write`` system call in C is used to write data to a file descriptor, such as a socket.
.. code-block:: c
ret = write(sockfd, buffer, sizeof(buffer));
* ``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_tcp/client/client.c
:language: c
:emphasize-lines: 115, 116, 117, 137, 138, 139, 159, 160, 161, 228, 229, 236, 247, 248, 273
.. _poll_ipv4_raw_af_inet_tcp_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
IP Address: 127.0.0.1
checksum is c135
Received : Hello client
Received : Hello client
Received : Hello client
Received : Hello client
Received : Hello client
Received : Hello client
Received : Hello client
Received : Hello client
Received : Hello client
Received : Hello client
Received : Hello client
Received : Hello client
Received : Hello client
^C
.. tab-set::
.. tab-item:: Enhanced Socket Flexibility with ``AF_INET`` and ``PF_INET`` Domains
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**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_TCP)``.
**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_tcp_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.
write used to write data to a file descriptor, such as a socket.
read used to read data from a file descriptor, such as a socket.
============== ==================================================================================================================
.. card:: See Also
* previous topic
* :doc:`../../../sockets/ipv4_raw_af_inet_tcp/select/select`
* current topic
* :doc:`../../../sockets/ipv4_raw_af_inet_tcp/poll/poll`
* Next topic
* :doc:`../../../sockets/ipv4_raw_af_inet_tcp/epoll/epoll`
* Other sockets
* :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`