The server constantly runs in an infinite loop and listens for client requests to accept a connection from a client. Once a client request is found, The server accepts the request using the accept method. The accept method returns a tuple client, address. Here, client represents a new socket object that we use to send and receive messages.
The address is where the client socket is bound. We use the send method to send a message to the client. The send method is invoked on the client object returned by the accept method. We use the recv method to receive the messages. The recv method, when invoked on the client object, accepts a number representing the maximum number of bytes it can read from the connection.
After execution, it returns the data read from the connection. After all the operations are completed, we need to close the connection. For this, we invoke the close method on the client object returned by the accept method.
Now that we have created a server let us create a client process that will communicate to the server. To create a client, we first need to create a socket with the socket method as we did while creating the server. Remember that the protocols defined for the client socket should be the same as the server socket. Otherwise, the program will not work as desired. After creating the socket, we need to connect it to the server. For this, we will use the connect method.
Here, the parameter host denotes the address of the server. The parameter port denotes the port number the server socket is created. You should give the same values as input to the host and port parameter you provided to the bind method while creating the server. After connecting to the server, you can communicate with the server using the send and recv methods. Finally, it would help close the connection from the client-side using the close method. Having created the server and the client, let us now run the programs.
Remember that you should run both the client program and the server program simultaneously so that both the processes can be alive simultaneously and communicate with each other.
In the previous sections, we have created sockets that follow the TCP protocol in the connection. In TCP protocol, the connection between the client and the server is maintained throughout the communication. However, there are many situations where we cannot maintain a stable connection between the client and the server due to resource constraints. For this, we use the UDP protocol. To create a connection with the UDP protocol, we need to follow the following steps while implementing the server.
Using the following Python program, you can implement a server process that communicates with UDP protocol. After creating the socket, we can directly start communicating with the server using the sendto and recvfrom methods. Using the following Python program, you can implement a client process that communicates with UDP protocol. Again, to observe the output, you should run both the client program and the server program simultaneously so that both the processes can be alive at the same time and can communicate with each other.
The client then uses an ifstream to open and extract the lines of the file into a vector of strings. The lineCount was incremented for each line added to the vector. The strings in the vector were then copied iteratively into a character array buffer and sent to edge. The client then waits for a response from edge. At startup, edge. This code is a slightly modifued version of Beej's Network Tutorial.
The majority of the code was kept the same. The while loop that keeps the edge server running on Beej's tutorial, as well as the fork distinction, was removed as our program is a one-to-one connection with only one client. Thus, every time a TCP connection with the client is finished, we must reboot the server again from the start.
Intuitively, this defeats the purpose of having an always-on server, but for the case of this project and a one-to-one client-server connection this is the way it works. When the edge server receives and accepts a connection from the client, it runs the UDPcircuit while loop.
From there, it sends the line to the sendToBackEnd method, which opens a UDP client to send the line to the designated back-end server for computation. THe UDP circuit while loop then runs the receiveFromBackEnd method to open a UDP server to take back the result of the client and stuff it into a vector of strings containing the results.
Similarly to client. The edge server shuts down. Both of the back-end servers work in a similar fashion, with minor differences in the computational step. The UDP server boots at startup and enters a while loop. At this point, the server is ready to receive the character array buffer from the edge server for computation.
When the back-end finally receives the buffer, it makes an initial scan to determine the character count of the two binary numbers from the line. The back-end server then creates two temporary character arrays to extract the two binary numbers from the line, basing the size of the array on the larger of the two binary numbers.
The temporary character array pads the array with 0's for the binary number with the smaller character count. Computation is performed by comparing each individual character of the two temporary character arrays and outputting a resulting value into a paddedResult character array. After that, it sends all incoming data back using a convenient method sendall which inside repeatedly calls send. And after that it simply closes the client's connection.
This example can serve only one incoming connection because it does not call accept in a cycle. Here instead of bind and listen it calls only connect and immediately sends data to the server. Then it receives bytes back, closes the socket, and prints the received data. All socket methods are blocking. For example, when it reads from a socket or writes to it the program can't do anything else. One possible solution is to delegate working with clients to separate threads.
However, creating threads and switching contexts between them is not really a cheap operation. To address this problem, there is a so-called asynchronous way of working with sockets. The main idea is to delegate maintaining the socket's state to an operating system and letting it notify the program when there is something to read from the socket or when it is ready for writing.
As you can see, there is much more code than in the blocking Echo server. That is primarily because we have to maintain a set of queues for different lists of sockets, i. Creating server socket looks the same except for one line: server. This is done to make the socket nonblocking.
This server is more advanced since it can serve more than one client.
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