TCP Listen (G Dataflow)

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Last Modified: August 21, 2019

Creates a listener and waits for an accepted TCP network connection at the specified port.

Programming Patterns

Transferring Data over a Network Using TCP

net address

The network address of a network interface on the local device where this node listens for data.

If you do not specify a network address, the OS picks a default interface that is used to receive data. If the node is read/write and you do not specify a network address, this node sends and receives data on all interfaces.
If you have more than one network interface on your server, such as two Ethernet interfaces, you can specify an address so that this node listens for data only on the interface with that address.
If this input is on a node with write access, this is also the interface on which data will be transmitted.

Default: 0

service name

The name you want to associate with the port number that this node is listening for connections on.

If you specify a service name, this node registers the service name and the associated port number with the NI Service Locator. A client can then use this service name to query the NI Service Locator for the port number associated with that service name. By using registered service names, clients can establish connections with the server without specifying a port number.

What Is the NI Service Locator?

The NI Service Locator stores a list of registered service names and returns a corresponding port number to clients that query for a particular service name.

A client can use a service name to query the NI Service Locator and obtain the port number associated with that service name. Thus, a client does not need to know the port number of a registered service in order to request that service.

The NI Service Locator runs as a background service and requires no user interaction.

Registering Services with the NI Service Locator

Use this input to register a service name and associated port number with the NI Service Locator.

port

The port number where you want to listen for a connection.

By default, this node dynamically chooses an available TCP port to listen for connections on.

The following table lists valid port numbers as defined by the Internet Assigned Numbers Authority (IANA).

Type	Range
System/Well-Known Ports	0 through 1023
User/Registered Ports	1024 through 49151
Dynamic/Private Ports	49152 through 65535

timeout ms

Time, in milliseconds, that the node waits for a connection. If the node cannot establish a connection in the specified time, the node returns an error.

Default: -1 — This node waits indefinitely for a connection.

error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error	error in contains an error

If no error occurred before the node runs, the node begins execution normally. If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.	If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

resolve remote address

A Boolean that determines whether to return the remote address as an IP address or as a hostname.

True	This node returns the remote address as a hostname.
False	This node returns the remote address as an IP address.

Default: True

listener ID

A network connection refnum that uniquely identifies the listener.

connection ID

A network connection refnum that uniquely identifies the connection. Use this value to refer to this connection in subsequent node calls.

remote address

The network address of the client that establishes a connection with this server.

remote port

The port on the client that establishes a connection with the server.

error out

This node can return the following error codes.

54	The network address is invalid.
59	Network driver error.
60	The requested port is already in use.

Note

This is not a comprehensive list of errors this node can return.

Standard Error Behavior

error in does not contain an error	error in contains an error

If no error occurred before the node runs, the node begins execution normally. If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.	If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Why Should I Use TCP Create Listener and TCP Wait on Listener Instead of TCP Listen?

You can choose one of the following techniques to wait for an incoming connection:

Use TCP Listen to create a listener and wait for an accepted TCP connection at a specified port.
Use TCP Create Listener to create a listener and use TCP Wait on Listener to listen for and accept new connections. TCP Wait on Listener returns the same listener ID you wired to the node.

The advantage of using TCP Create Listener and TCP Wait on Listener is that you can listen for a connection without using a timeout. You can also explicitly close the listener, or you can cancel the listen when another condition becomes true.

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported

Web Server: Not supported in VIs that run in a web application

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