I'm trying to upload videos to a server via TCP/IP using GCDAsyncSocket. Sometimes, the socket disconnects with an error that I haven't been able to eliminate:
2011-12-17 11:39:25.073 Hadza[433:707] socketDidDisconnect, error: Error Domain=NSPOSIXErrorDomain Code=12 "Cannot allocate memory" UserInfo=0x2aa260 {NSLocalizedFailureReason=Error in write() function, NSLocalizedDescription=Cannot allocate memory}
I've been looking everywhere but I can't really see what is the cause of this, how to fix it or workaround this issue.
The flow that the app follows to upload a file is the following:
Write to server (a media_id )
Read an ACK sign from server
Read number of bytes already sent
Write the video from bytes sent to the end
Read waiting for an ACK signal (meaning that the upload was ok)
If everything went OK , finish. If there was an error, restart from 1 or 3 depending on the error.
Related
I'm trying to create a server that sets up a Unix socket and listens for clients which send/receive data. I've made a small repository to recreate the problem.
The server runs and it can receive data from the clients that connect, but I can't get the server response to be read from the client without an error on the server.
I have commented out the offending code on the client and server. Uncomment both to recreate the problem.
When the code to respond to the client is uncommented, I get this error on the server:
thread '' panicked at 'called Result::unwrap() on an Err value: Os { code: 11, kind: WouldBlock, message: "Resource temporarily unavailable" }', src/main.rs:77:42
MRE Link
Your code calls set_read_timeout to set the timeout on the socket. Its documentation states that on Unix it results in a WouldBlock error in case of timeout, which is precisely what happens to you.
As to why your client times out, the likely reason is that the server calls stream.read_to_string(&mut response), which reads the stream until end-of-file. On the other hand, your client calls write_all() followed by flush(), and (after uncommenting the offending code) attempts to read the response. But the attempt to read the response means that the stream is not closed, so the server will wait for EOF, and you have a deadlock on your hands. Note that none of this is specific to Rust; you would have the exact same issue in C++ or Python.
To fix the issue, you need to use a protocol in your communication. A very simple protocol could consist of first sending the message size (in a fixed format, perhaps 4 bytes in length) and only then the actual message. The code that reads from the stream would do the same: first read the message size and then the message itself. Even better than inventing your own protocol would be to use an existing one, e.g. to exchange messages using serde.
For c send function(blocking way) it's specified what function returns with size of sent bytes when it's received on destinations. I'm not sure that I understand all nuances, also after writing "demo" app with WSAIoctl and WSARecv on server side.
When send returns with less bytes number than asked in buffer-length parameter?
What is considered as "received on destinations"? My first guess it's when it sit on server's OS buffer and server application is notified. My second one it's when server application recv call have read it fully?
Unless you are using a (somewhat exotic) library, a send on a socket will return the number of bytes passed to the TCP buffer successfully, not the number of bytes received by the peer (see Microsoft´s docs for example).
When you are streaming data via a socket, you need to check the bytes effectively accepted into the TCP send buffer. That´s why usually a send command is inside a loop that will issue several sends if needed.
Errors in send are local: for example if the socket is closed by the peer during a sending operation (making your socket invalid) or if the operation times out (TCP buffer not emptying, i. e. peer not receiving data fast enough or some other trouble).
After all send is completed you have no easy way of knowing if the peer received all the bytes you sent. You´ll usually just issue closesocket and make sure that your socket has a proper linger option set (i. e. only close after timeout or sucessfully finishing the send). Alternatively you wait for a confirmation by the peer (for example via a recv that returns zero bytes, indicating that the connection was gracefully closed).
Edit: typo
I've just started working with sockets.
I've connected to a socket (a bitcoin node), and when I send data with socket_send(), the socket will reply with data, but I don't know what the length of that data will be.
I would like to receive the full data response with socket_recv() and move on to issuing the next socket_send(), but I don't know what to put for the len or flags in this function to get the full message (and not wait for anything more).
How do you get a full message of unknown length with socket_recv()?
ASIDE: This combination seems to work, but it was just trial and error and I
don't know why:
socket_recv($socket, $buf, 10000000, MSG_WAITALL&MSG_DONTWAIT)
I am make a application base on lwip,the applcation just send data to the server;
When my app works for some times (about 5 hours),I found that the send thread hung in send() function,and after about 30min send() return 0,and my thread run agin;
In the server side ,have make a keepalive,its time is 5min,when my app hungs,5min later the server close the sockect,but my app have not get this,still hungs in send() until 30min get 0 return; why this happen?
1: the up speed is not enough to send data,it will hungs in send?
2: maybe the server have not read data on time,and it make send buff full and hungs?
how can i avoid these peoblems in my code ? I have try to set TCP_NODELAY,SO_SNDTIMEO and select before send,but also have this problem.
send() blocks when the receiver is too far behind the sender. recv() returns zero when the peer has closed the connection, which means you must close the socket and stop reading.
I am trying to set a timeout on write operations when using GCDAsyncSocket. The code is pretty simple and is the following.
[iAsyncSocket writeData:bytesToSend withTimeout:3.0 tag:0];
Then I disable the Internet connection on my Mac and wait for write timeout to occur, but nothing happens. I don't get a disconnection with a GCDAsyncSocketWriteTimeoutError error as I should.
I have also validated that my server stops, as expected, receiving the messages after I turn off the Internet connection.
I have looked inside the source code and I have found out that the writeTimer, that is responsible for firing a write timeout event, is always cancelled (function endCurrentWrite is called). Tracing back to where the timer is cancelled, I ended up at the following line of code.
ssize_t result = write(socketFD, buffer, (size_t)bytesToWrite);
The write system call always returns the total number of bytes that I am sending, as if the socket manages to send the data although there is no Internet connection. Is this logical?
Has anyone come up with the same problem or seen similar behaviour? Or has anyone managed to set a write timeout for a GCDAsyncSocket?
Thanks a lot.