socket-programming | 「Rustで始めるネットワークプログラミング」 4.5節(技術書典頒布版 :
kandi X-RAY | socket-programming Summary
kandi X-RAY | socket-programming Summary
「Rustで始めるネットワークプログラミング」 4.5節(技術書典頒布版: masterブランチ)、1章(web販売版: web-versionブランチ)のリポジトリです。
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QUESTION
I am trying to understand the following code. If I have 50 connections to this server and I send data through one of these sockets, the select
block with the inner loop will capture what I send and echo it back. But what happens if within a very short time-frame of the first message, I send another one? So fast that the inner loop (after select
- the loop iterating over all active client sockets) doesn't finish. Will that data be thrown away? Will it be what the next select
will be triggered with? What happens if I send two messages before the inner loop finishes ? Will I ever face the scenario where inside the loop iterating over all the active sockets I get more than 1 that has "activity" - i.e.: can two FD_ISSET(sd, &readfds)
be true within a single iteration of the loop ?
ANSWER
Answered 2020-Nov-22 at 17:45select()
is a level-triggered API, which means that it answers the question "are any of these file descriptors readable/writable now?", not "have these file descriptors become readable/writable?". That should answer most of your questions:
But what happens if within a very short time-frame of the first message, I send another one? [...] Will it be what the next
select
will be triggered with?
It will be what the next select()
will be triggered with.
What happens if I send two messages before the inner loop finishes ?
That depends on how long the messages are - TCP doesn't work in terms of messages, but in terms of a stream of bytes. The server might well read both messages in a single read()
. And if it doesn't, the socket will remain readable, and it will pick them up immediately on the next select()
.
Will I ever face the scenario where inside the loop iterating over all the active sockets I get more than 1 that has "activity" - i.e.: can two
FD_ISSET(sd, &readfds)
be true within a single iteration of the loop ?
Yes, if two clients send data at the same time (while you are out of select()
), select()
will report two readable file descriptors.
QUESTION
I'm new to socket programming. I have developed fundamental/simple client and server application where client successfully communicates with server. Currently, both the server is on my system (local host) and client is also my system.
Now I want to somehow allow clients outside the network ( network where my system belongs to) to communicate with the server but i have no idea what to do and how to proceed. Any help would be appreciated.
Here's a smaple code taken from here
server.py ...ANSWER
Answered 2020-Nov-20 at 18:21You don’t really need to change anything in your code, except for the IP that the client connects to. It needs to be the server PC’s public Internet IP instead of 127.0.0.1
.
If the server PC is connected directly to the Internet modem, then you are done.
Otherwise, if the server PC is behind a router or proxy, then you need to configure port forwarding on that router/proxy to forward traffic from its public WAN IP/port to the server PC’s LAN IP/port. Consult your router/proxy’s documentation for how to do that configuration.
If the router/proxy has uPNP enabled, your server code can dynamically forward the WAN IP/port to itself at runtime. See Python: Open a Listening Port Behind a Router (upnp?)
QUESTION
I am just trying to send some files from a socket and i am able to send those files without any interruption: also whether the size file is small or large that does not matter it sends like a charm.
But the problem in my case that is arising is the file that i sent is being corrupted, i.e. it is not playing like audio or video. I have already gone through this but it did not helped.
The code that I am using is below.
Server Side:
...ANSWER
Answered 2020-Aug-24 at 07:13So after the conversations in comments and as @MarquisofLorne told to delete the line that i have written in my server side code. i.e either delete this line from server side code:
QUESTION
I am trying to create a simple socket connection of a client and a server. I wrote something very basic, following this guide.
I am using the client.c:
...ANSWER
Answered 2020-Aug-20 at 06:52From the info you gave in the comments, linked with @Andreas Wenzel, @encs and @IS comments:
- You need to wait for the threads to finish. add a join function to block the main thread meanwhile the other threads are running
- use fflush() after every printf() to avoid issues related to buffering
- The server should be in Listen state before any client tries to connect. To ensure that, setup the server in the main thread, and create a pthread for everything below the accept() function.
QUESTION
I want to programmatically transfer a file from a Raspberry Pi with Wi-Fi access, running Linux (client), to an Android phone (host). I'm using this link as a guide for how to set up a P2P connection on Android, but I cannot find any references to handle the client side on non-Android devices. I understand I can use this link to provide documentation on connecting the client to the host, but I have no leads on how to actually send a file with it.
Essentially, what I'd like to know is: Is there anything I can do on Linux to get the same effect as this, from the Android documentation? Am I completely misguided?
...ANSWER
Answered 2020-Jun-06 at 20:54The solution for establishing a connection was in wpa_cli
Particularly, the commands p2p_find
to discover, p2p_peers
to see what found it, and p2p_connect pbc go_intent=0
to stop searching and connect to the Android host. You can see it show up as a local network with ip a
. However, now I seem to be having a problem on the Android side, and the adventure continues in this question, for anyone interested.
QUESTION
I am trying to do a simple communication between a server (running on Ubuntu from Qemu with Cortex-A53 cpu) and a client (running on CentOS from my pc), using sockets.
If I run the C++ code only from Centos (both client.c and server.c) it works fine. Same if I run both from Ubuntu. But if I start the server.c from Ubuntu and client.c from CentOS the communication doesn't work.
The C code I'm using is from this tutorial: https://www.geeksforgeeks.org/socket-programming-cc/
The Qemu command:
...ANSWER
Answered 2020-Aug-14 at 11:28The problem was that I was trying to connect to the socket from server part by using host address and port, but to access the Qemu data I had to connect to the socket using file descriptor /dev/vport3p1.
The server.c file should look something similar to this:
QUESTION
I have a requirement to send data asynchronously via TCP. It is a collection of strings ICollection
.
I searched and found a good starting example from Microsoft (see below). The sample seems to be under .NET Framework
, but I assume it applies to .NET Core
as well.
What I am doing:
I am re-purposing the code as a non-static class
I would like to send a collection of strings
ICollection
. I know I can rewrite it to send the collection of strings in the main method. Not a problem.I would like to receive a response for each message sent and do something with it. The current response is stored statically in
private static String response = String.Empty;
. I don't want it to be static. I want a local method variable.My challenge begins from item 3.. How do I return back that response message that seems only accessible from within
private static void ReceiveCallback( IAsyncResult ar )
I do not think changing it to
private static string ReceiveCallback( IAsyncResult ar )
would work. If so, how do I read it fromclient.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReceiveCallback), state);
?
I put out a 300point bounty on a very old post for a similar question I found: C# Asyn. Socket Programming. Happy to award anyone who answers here, then there.
An additional question is: Is it recommended practice to open a TCP connection, send the multiple messages, then close it? Or to open a TCP connection for each message being sent?
Microsoft Example
...ANSWER
Answered 2020-Jun-13 at 23:30You can create a class (non-static, I called it AsynchronousClient) that implements all the logic of the socket communication straight from the Microsoft example. The relevant additions are the 3 events (more on handling and raising events):
1) ConnectionComplete, fired when an asynchronous connection operation is completed;
2) SendComplete, fired when data (a string, in this example) is successfully sent;
3) DataReceived, fired when there is incoming data from the remote endpoint.
Basically, the class exposes 3 public methods: AsyncConnect, AsyncSend and AsyncReceive. On the 3 private callbacks the corresponding event in the list above is fired and the class using AsynchronousClient is notified of the termination of the operation.
QUESTION
I am trying to learn winsock2 by following a tutorial. The problem is that the last section where it tells you about handling multiple clients, has empty code. How would this be achieved with multi-threading in a nice-mannered way?
...ANSWER
Answered 2019-Aug-09 at 17:24To clarify: I would not use threads to handle multiple clients.
To your question:
- 1 thread should listen for new connections.
- When a connection is accepted a new socket is created.
- For each accepted socket: create a thread for reading/writing to that socket.
The reason I would not implement it this way, is because it will not scale well. After ~100 concurrent connections (maybe more, maybe less) the process will crash due to out of memory. (Threads are expensive).
Google "multi thread socket windows C++" you should find numerous examples including videos with explanations.
If you really want to create a scalable server review libraries such as libevent (which wrap asynchronous mechanisms such as epoll).
QUESTION
I am trying to make a client/server homework. I use Visual Studio 2017 and already changed the project settings that i can use sockets (Windows Socket Programming in C) but now my console always says "ERROR while creating Socket ... : No error"
This is my current code:
...ANSWER
Answered 2019-Jun-18 at 21:43Three problems:
First, you need to call
WSAStartup()
to initialize Winsock before you can then usesocket()
.Second, you need to compare the return value of
socket()
toINVALID_SOCKET
, as the documentation says.Third,
perror()
does not work with Winsock errors, as your example demonstrates.perror()
looks aterrno
, which Winsock does not set. UseWSAGetLastError()
instead to get the error code of a failed Winsock function, and then you can print it out as needed.
QUESTION
this maybe is a simple question but I'm trying to just read a server response using the sockets API adapting the code from Geeks for Geeks [site]1, when I try to read the data, it becomes blocked forever in the valread = read(server_fd, buffer, 2048);
line, and doesn't execute any of the prints. Am I doing something wrong?
ANSWER
Answered 2019-Jun-17 at 19:00You are connecting to an HTTP server. The HTTP protocol specifies that the client (that is, the side that makes the connection to the server) must send a request first. You aren't sending a request, so the server is not going to send you a reply.
Also, this is a bug:
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