TPC/IP write failed

Hello,

I want to make a connection between Matlab and Labview using TPC/IP protocol.

I tried to create a server TCP/IP using tcpserver matlab command.

I send via LabVIEW a "TEST_COMM;" message and I correctly read the data with matlab by using read command.

The issue is on the write. I want to send a message to labview (client) via matlab (server) with write command but matlab returns an error: "Failed to write from the server. A TCP/IP client must be connected to the server"

Code below:

clear

[~,hostname] = system('hostname');

hostname = string(strtrim(hostname));

address = resolvehost(hostname,"address");

server = tcpserver("0.0.0.0",4000);

datatoread = server.NumBytesAvailable;

while (datatoread==0)

datatoread = server.NumBytesAvailable;

end

data = server.read(2,"char");

data2 = server.read(base2dec(data,10), "char");

disp(data)

disp(data2)

disp(server)

if (data2=="TEST_COMM;")

%server.write("TEST_COMM_ACK;")

write(server,"TEST_COMM_ACK;","string");

end

Thanks in advance for your help

Answer 1

[Anavi Somani]

Try this with a couple of changes in the code, where the client accepts, waits and closes the connection.

[~,hostname] = system('hostname');
hostname = string(strtrim(hostname));
address = resolvehost(hostname,"address");
server = tcpserver("0.0.0.0", 4000);

% Wait for a client to connect
client = server.accept();
datatoread = server.NumBytesAvailable;
while (datatoread == 0)
    datatoread = server.NumBytesAvailable;
end

data = server.read(2, "char");
data2 = server.read(base2dec(data, 10), "char");
disp(data)
disp(data2)
disp(server)

if (data2 == "TEST_COMM;")
    % Write data to the client
    write(client, "TEST_COMM_ACK;", "string");
end

% Close the connection
client.close();
server.close();

In this updated code, the accept() method is used to wait for a client to connect to the server.

Once the client is connected, you can use the write() method on the client object to send data back to the LabVIEW client.

Remember to close the connection using client.close() and server.close() after you have finished communicating with the client. Make sure to update your LabVIEW code to establish a connection with the Matlab server before sending the "TEST_COMM;" message.

[Jeremy]

thanks for your answer.

It dosen't seems to work. The command server.accept() is not recognized.

I have tried another simple code:

clear

server = tcpserver("0.0.0.0",4000);

client = server.Connected;

nb = server.NumBytesAvailable;

while nb == 0

nb = server.NumBytesAvailable;

end

disp(server)

I arrive to open the connection with labview et send a command. The nb value in matlab pass from 0 to 2 but I when the server status is displayed "Connected" is 0:

TCPServer with properties:

ServerAddress: "0.0.0.0"

ServerPort: 4000

Connected: 0

ClientAddress: ""

ClientPort: []

NumBytesAvailable: 2

So I can't use the write command while "connected" is 0

[Anavi Somani]

The tcpserver object does not have a direct accept() method to accept incoming connections.

Try this if it helps.

server = tcpserver("0.0.0.0", 4000);

% Wait for a client to connect
while ~server.Connected
    pause(0.1);
end

% Retrieve the client information
clientInfo = server.Message;

% Display the client information
disp(clientInfo);

% Read data from the client
data = server.read();
disp(data);

% Send data to the client
message = "TEST_COMM_ACK;";
server.write(message);

% Close the connection
server.close();

Please ensure that your LabVIEW code establishes a connection with the Matlab server using the correct IP address and port number (in this case, "0.0.0.0" and 4000).

And go through the document link suggested by Ram Sreekar.

[Jeremy]

ok thanks, it helps to debug,

now I have more information on the behavior, I tried this code:

clear server

server = tcpserver("localhost",5000,"ConnectionChangedFcn",@connectionFcn);

client = server.Connected;

while ~client

client = server.Connected;

pause(0.1);

end

disp(server)

data = server.read(12,"char");

disp(data);

function connectionFcn(src,~)

if src.Connected

disp("This message is sent by the server after accepting the client connection request.")

disp(src)

src.write("TEST_COMM_ACK;");

else

disp("Client has disconnected.")

disp(src)

end

end

I detect a connection to the server (connected pass to 1) but just after I receive a disconnection. On the Labview I receive well the TEST_COMM_ACK; data but I don't understand the deconnection:

>>tcp2

This message is sent by the server after accepting the client connection request.

TCPServer with properties:

ServerAddress: "127.0.0.1"

ServerPort: 5000

Connected: 1

ClientAddress: "127.0.0.1"

ClientPort: 58301

NumBytesAvailable: 12

Show all properties, functions

Client has disconnected.

TCPServer with properties:

ServerAddress: "127.0.0.1"

ServerPort: 5000

Connected: 0

ClientAddress: ""

ClientPort: []

NumBytesAvailable: 12

Show all properties, functions

TCPServer with properties:

ServerAddress: "127.0.0.1"

ServerPort: 5000

Connected: 0

ClientAddress: ""

ClientPort: []

NumBytesAvailable: 12

Show all properties, functions

10TEST_COMM;

Answer 2

[Ram Sreekar]

Hi Jeremy,

I see that you are trying to send data from MATLAB to LabView and vice-versa.

After reviewing your code, it appears that you have successfully utilized the ‘ tcpserver’ object in MATLAB to receive data from the LabVIEW client. However, the problem arises when you attempt to send data back to the LabVIEW client using the write function.

To resolve this issue, you can rectify the problem by substituting the 'write' function with the ‘ fwrite’ function. You can rectify this problem by substituting the write function with the ‘ fwrite’ function. This adjustment will enable you to effectively transmit data from the MATLAB server to the LabVIEW client.

You can refer to the sample code given below.

if (data2=="TEST_COMM;")
    ack = "TEST_COMM_ACK;";
    fwrite(client, ack 'char');
end

For more information about MATLAB and LabView data exchange over TCP/IP you can refer to the link given below.

https://www.mathworks.com/matlabcentral/fileexchange/42567-matlab-and-labview-data-exchange-over-tcp-ip?s_tid=answers_rc2-2_p5_MLT

Hope this helps you resolve your query.

[Jeremy]

Hello, I have the same issue with fwrite. Matlab detects no connection to tcpserver.

Here the display:

>> untitled2

10

TEST_COMM;

TCPServer with properties:

ServerAddress: "0.0.0.0"

ServerPort: 4000

Connected: 0

ClientAddress: ""

ClientPort: []

NumBytesAvailable: 0

Show all properties, functions

Error using matlabshared.transportlib.internal.compatibility.LegacyBinaryMixin/writeHook

Failed to write from the server. A TCP/IP client must be connected to the server.

Error in matlabshared.transportlib.internal.compatibility.LegacyBinaryMixin/fwrite (line 100)

writeHook(obj, data, precision);

Error in untitled2 (line 21)

server.fwrite("TEST_COMM_ACK;");