I am trying to send message with UDP protocol from client to server.
But
function send(sockfd, buf, strlen(buf), 0)
<socket.h>
which I use for send buffer returns -1, any time when I call it.
In description of func i read about results and i know if result = 0 or below - function finished with errors, and if result > 0 function successfully finised.
for example:
result of calling
send(socket, "1.2.3.4", 7, 0) will be -1.
What am I missing?
Related
I'm trying to make a serial communication between two ESP8266 Wifi chips.
To start, I tried sending a sample data 10 times in a for loop. Here is the code:
Transmiter:
for Packets = 1 : 10
SendData(client,Data(Packets));
end
Receiver:
Packets = 1
while(1)
Data(Packets) = ReceiveData(Server);
Packets = Packets + 1;
if (packets == 10)
break
end
end
it works good. The problem is when I want to send data with some delays, the transmitter should connect to receiver again and the server (receiver) receives some data indicating that connection is made again.
The received Buffer should be:
+IPD,0,1024:ùüþþþýýþþÿÿûûýþýûúþÿúóýÿþþþþþýúøûýþ...
but after reconnecting the received Buffer is:
0,CLOSED %Receiver Prompt, disconnected from Transmiter
0,CONNECT %Receiver Prompt,connected to Transmiter
+IPD,0,1024:ùüþþþýýþþÿÿûûýþýûúþÿúóýÿþþþþþýúøûýþ...
The remaining part of data will be read in next packet and same for next packets.
what should I do to receive just the data?
The send and receive functions:
function ReceivedBuffer = ReceiveData(SerialPort)
ReceivedBuffer = fread(server,1038); %Size data = 1038 Bytes
end
function SendData(SerialPort,Data)
fwrite(SerialPort,Data);
end
I have a recvfrom returning error 34, I have checked and it means "Numerical result out of range" but after it is receiving correctly the data and also the amount of data received is correct. I think it may crash after some time. Here i show the call to recvfrom:
int dataRCV = -55;
dataRCV = recvfrom ( sockfd2, data_CPV, sizeData_CPV, 0, (struct sockaddr*)&client_addr2,&client_addresslen2);
fprintf(%i %s, dataRCV,sterror(errno));
Thanks
recvfrom() returns the number of bytes read, not an error code. If recvfrom() fails, it will return -1 and errno will report the actual error code.
int dataRCV = recvfrom ( sockfd2, data_CPV, sizeData_CPV, 0, (struct sockaddr*)&client_addr2, &client_addresslen2);
if (dataRCV == -1)
fprintf(%i %s, errno, sterror(errno));
So if dataRCV is being set to 34 then recvfrom() has successfully read 34 bytes, not failed.
I have an application which listens to multiple connections and verifies whether the user is active or not
I use a 1 thread socket handling method with WSAASyncSelect.
The problem is that sometimes when a lot of users connecting at the same time some users get no reply
i think it is because the "send" hasn't been called yet and the program has received another connection so it goes again to handle the new connection ignoring the previous one. Like WSAASyncSelect has triggered and now it processing a new connection instead of completing the previous request.
So what to do to fix this issue? i tried to stop the events from WSAASyncSelect temporary by calling it with zero parameters when handling the connection until finish it then re enable network events but that didn't help either.
Here are the codes that handling the events (recieve then decrypt and then compare the bytes then send data according to what in listbox ie Active user or not)
This called upon receive of FD_READ
WSAAsyncSelect s, frmMain.hwnd, 0, 0 'Disabling Notifications event
Do Until bytesRecieved = SOCKET_ERROR
bytesRecieved = recv(wParam, buffer(Bytes), 500, 0)
If bytesRecieved > 0 Then
Bytes = Bytes + bytesRecieved
ElseIf bytesRecieved = 0 Then
Exit Sub
End If
Loop
Call MemCopy(ByVal decryptedArrival, buffer(0), Bytes)
WSAAsyncSelect s, frmMain.hwnd, WINSOCKMSG, FD_CONNECT + FD_READ + FD_CLOSE + FD_ACCEPT + FD_WRITE
If frmMain.chkSaveLog.value = vbChecked Then
frmMain.txtConnectionsLog.Text = frmMain.txtConnectionsLog.Text & Now & " Receiving a connection (" & wParam & ")" & vbNewLine
AutoScroll
If frmMain.chkAutoSave.value = vbChecked Then
strCurrentLogLine = Now & " Receiving a connection (" & wParam & ")"
AutoSaveLog (strCurrentLogLine)
frmMain.cmdClearLogs.Enabled = True
End If
End If
Below here is a decryption of bytes then comparing by ID as byte identifier like 1 = check for update
2 - send user info etc
in a Select Case statement following by a send Api.
And the accepting procedure
This called upon receive of FD_ACCEPT
Function AcceptConnection(wParam As Long)
lpString = String(32, 0)
AcSock = accept(wParam, sockaddress, Len(sockaddress))
strTempIP = getascip(sockaddress.sin_addr)
frmMain.txtConnectionsLog.Text = frmMain.txtConnectionsLog.Text & Now & " Getting a connection from IP address: " & _
strTempIP & " (" & AcSock & ")" & vbNewLine
AutoScroll
If frmMain.chkAutoSave.value = vbChecked Then
strCurrentLogLine = Now & " Getting a connection from IP address: " & strTempIP & " (" & AcSock & ")" & vbNewLine
AutoSaveLog (strCurrentLogLine)
End If
End Function
Are there any suggestions for a better performance?
What you showed is NOT the correct way to use WSAAsyncSelect(). Try something more like this instead:
When creating a listening socket:
lSock = socket(...)
bind(lSock, ...)
listen(lSock, ...)
WSAAsyncSelect lSock, frmMain.hwnd, WINSOCKMSG, FD_ACCEPT
When a listening socket receives FD_ACCEPT:
Function AcceptConnection(wParam As Long)
AcSock = accept(wParam, sockaddress, Len(sockaddress))
If AcSock = INVALID_SOCKET Then
Exit Sub
End If
WSAAsyncSelect AcSock, frmMain.hwnd, WINSOCKMSG, FD_READ + FD_CLOSE + FD_WRITE
...
End Function
When an accepted client socket receives FD_READ:
Function ReadConnection(wParam As Long)
Do
bytesRecieved = recv(wParam, ReadBuffer(ReadBytes), 500, 0)
If bytesRecieved = SOCKET_ERROR Then
If WSAGetLastError() <> WSAEWOULDBLOCK Then
Exit Sub
End If
ElseIf bytesRecieved = 0 Then
Exit Sub
Else
ReadBytes = ReadBytes + bytesRecieved
End If
Loop Until bytesRecieved = SOCKET_ERROR
' process ReadBuffer up to ReadBytes number of bytes as needed...
' remove processed bytes from front of ReadBuffer and decrement ReadBytes accordingly
...
End Function
When an accepted client socket receives FD_WRITE:
Function WriteConnection(wParam As Long)
While SendBytes > 0
bytesSent = send(wParam, SendBuffer(0), SendBytes, 0)
If bytesSent = SOCKET_ERROR Then
Exit Sub
End If
' remove bytesSent number of bytes from front of SendBuffer ...
SendBytes = SendBytes - bytesSent;
End While
End Function
The trick is that you need to allocate separate ReadBuffer and SendBuffer buffers for each accepted client. Make sure that each time you receive FD_READ that you are appending bytes only to the ReadBuffer of the socket that triggered FD_READ, and each time you receive FD_WRITE that you are removing bytes only from the SendBuffer of the socket that triggered FD_WRITE.
When recv() has no more bytes to read, process that socket's ReadBuffer as needed, removing only complete messages from the front and leaving incomplete messages for later processing.
When send() fails with WSAEWOULDBLOCK, append any unsent bytes to the SendBuffer of the socket that caused send() to fail. When you receive an FD_WRITE event for a socket, check that socket's SenBuffer and resend any bytes that are in it, stopping when the buffer is exhausted or an WSAEWOULDBLOCK error occurs.
Very easy, and quite effective, way to do it is to fork out for every incoming connection. This will most likely require you to restructure your application, but the basic flow should be as follows:
1. New connection is opened to the server
2. Server accepts the connection and forks out
3. The fork closes the original socket for listening, so only the parent will be accepting new connections
4. And then your magic happens, separate from the original thread.
This way you do not have to worry about issues of concurrency, as long as your machine can handle all the traffic and load because each connections is independent.
I'm using Apple's "Simple Ping" example and it has almost all features that I need, but I don't know where I can set timeout of each packet. It seems that it isn't possible because function that is used to write data to socket doesn't have any timeout parameters. Does anybody have idea to change this app to get ability to set timeout like in windows ping command? By timeout I mean time for each packet sent to be discarded after waiting for response too long.
Windows ping command - timeout I need to have:
"-w Timeout : Specifies the amount of time, in milliseconds, to wait for the Echo Reply message that corresponds to a given Echo Request message to be received. If the Echo Reply message is not received within the time-out, the "Request timed out" error message is displayed. The default time-out is 4000 (4 seconds)."
Simple Ping code I'm using:
http://developer.apple.com/library/mac/#samplecode/SimplePing/Introduction/Intro.html
Apple sample code:
bytesSent = sendto(
CFSocketGetNative(self->_socket),
sock,
[packet bytes],
[packet length],
0,
(struct sockaddr *) [self.hostAddress bytes],
(socklen_t) [self.hostAddress length]
);
to change the timeout:
CFSocketNativeHandle sock = CFSocketGetNative(self->_socket);
struct timeval tv;
tv.tv_sec = 0;
tv.tv_usec = 100000; // 0.1 sec
setsockopt(sock, SOL_SOCKET, SO_SNDTIMEO, (void *)&tv, sizeof(tv));
bytesSent = sendto(
sock,
[packet bytes],
[packet length],
0,
(struct sockaddr *) [self.hostAddress bytes],
(socklen_t) [self.hostAddress length]
);
See Apple's docs: setsockopt
From the above referenced doc:
SO_SNDTIMEO is an option to set a timeout value for output operations. It accepts a struct timbal parameter with the number of seconds and microseconds used to limit waits for output operations to complete. If a send operation has blocked for this much time, it returns with a partial count or with the error EWOULDBLOCK if no data were sent. In the current implementation, this timer is restarted each time additional data are delivered to the protocol, implying that the limit applies to output portions ranging in size from the low-water mark to the high-water mark for output.
for example:
tv.tv_sec = 0;
tv.tv_usec = 1000;
setsockopt(recv_sock, SOL_SOCKET, SO_RCVTIMEO, (char *)&tv,sizeof(struct timeval));
setsockopt(send_sock, SOL_SOCKET, SO_SNDTIMEO, (char *)&tv,sizeof(struct timeval));
for additional options:
http://developer.apple.com/library/ios/#documentation/system/conceptual/manpages_iphoneos/man2/setsockopt.2.html
I am writing an application which is continuously sending and receiving data. My initial send/receive is running successfully but when I am expecting data of size 512 bytes in the recvfrom I get its return value as -1 which is "Resource temporarily unavailable." and errno is set to EAGAIN. If I use a blocking call i.e. without Timeout the application just hangs in recvfrom. Is there any max limit on recvfrom on iPhone? Below is the function which receives data from the server. I am unable to figure out what can be going wrong.
{ struct timeval tv;
tv.tv_sec = 3;
tv.tv_usec = 100000;
setsockopt (mSock, SOL_SOCKET, SO_RCVTIMEO, (char *)&tv, sizeof tv);
NSLog(#"Receiving.. sock:%d",mSock);
recvBuff = (unsigned char *)malloc(1024);
if(recvBuff == NULL)
NSLog(#"Cannot allocate memory to recvBuff");
fromlen = sizeof(struct sockaddr_in);
n = recvfrom(mSock,recvBuff,1024,0,(struct sockaddr *)&from, &fromlen);
if (n == -1) {
[self error:#"Recv From"];
return;
}
else
{
NSLog(#"Recv Addr: %s Recv Port: %d",inet_ntoa(from.sin_addr), ntohs(from.sin_port));
strIPAddr = [[NSString alloc] initWithFormat:#"%s",inet_ntoa(from.sin_addr)];
portNumber = ntohs(from.sin_port);
lIPAddr = [KDefine StrIpToLong:strIPAddr];
write(1,recvBuff,n);
bcopy(recvBuff, data, n);
actualRecvBytes = n;
free(recvBuff);
}
}
Read the manpage:
If no messages are available at the socket, the receive call waits for a message to arrive, unless the socket is nonblocking (see fcntl(2)) in which case the value -1 is returned and the external variable errno set to EAGAIN.
I was writing a UDP application and think I came across a similar issue. Peter Hosey is correct in stating that the given result of recvfrom means that there is no data to be read; but you were wondering, how can there be no data?
If you are sending several UDP datagrams at a time from some host to your iphone, some of those datagrams may be discarded because the receive buffer size (on the iphone) is not large enough to accommodate that much data at once.
The robust way to fix the problem is to implement a feature that allows your application to request a retransmission of missing datagrams. A not as robust solution (that doesn't solve all the issues that the robust solution does) is to simply increase the receive buffer size using setsockopt(2).
The buffer size adjustment can be done as follows:
int rcvbuf_size = 128 * 1024; // That's 128Kb of buffer space.
if (setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF,
&rcvbuf_size, sizeof(rcvbuf_size)) == -1) {
// put your error handling here...
}
You may have to play around with buffer size to find what's optimal for your application.
For me it was a casting issue. Essentially a was assigning the returned value to an int instead of size_t
int rtn = recvfrom(sockfd,... // wrong
instead of:
size_t rtn = recvfrom(sockfd,...// correct