TcpListener

Struct · namespace System.Net · Since 0.30

struct TcpListener : IDisposable

A TCP server: listens on a port and accepts the connections of clients, each a TcpConnection.

using System;
using System.Net;

using var listener = try TcpListener.Start("127.0.0.1", 8080);
while (true)
{
    using var client = try listener.Accept();
    var request = new uint8[4096];
    int got = try client.Read(request, 0, request.Length);
    try client.WriteText("HTTP/1.1 200 OK\r\nContent-Length: 6\r\nConnection: close\r\n\r\nHello\n");
}

TcpListener.Pending and TcpConnection.WaitForData wait with a time limit: one thread can serve several connections and do other work in between. Like a FileStream, a listener is a struct around a handle of the operating system: copies of it share the handle, and TcpListener.Stop of one stops all of them; keep one owner. The zero value (TcpListener { }) is a stopped listener. Only IPv4.

Static methods

Name	Description
Start	Listens on port of address: "127.0.0.1" (or "localhost") accepts the connections from this computer only, "0.0.0.0" those from every network.

Start

static NetError<TcpListener> Start(StringSlice address, int port)

Listens on port of address: "127.0.0.1" (or "localhost") accepts the connections from this computer only, "0.0.0.0" those from every network. Port 0 takes a free port; TcpListener.Port says which one.

Errors

• NetError.CannotResolve: address is not an IPv4 address (or a name for one).
• NetError.CannotListen: the port is in use, or the program may not listen on it (ports below 1024 on Linux and macOS).
• NetError.NotSupported: WebAssembly and AmigaOS.

Panics when port is not in 0..65535.

Methods

Name	Description
IsListening	Whether it listens (it is not stopped).
Port	The port it listens on: the one given to TcpListener.Start, or the free one that the system chose for port 0.
Pending	Waits up to milliseconds for a client to connect (0: does not wait; -1: waits as long as it takes).
Accept	Takes the next connection of a client; waits for one if none is TcpListener.Pending.
Stop	Stops listening; the connections that it accepted stay open.
Dispose	Stops listening (TcpListener.Stop); using calls it.

IsListening

bool IsListening()

Whether it listens (it is not stopped).

Port

int Port()

The port it listens on: the one given to TcpListener.Start, or the free one that the system chose for port 0.

Pending

bool Pending(int milliseconds)

Waits up to milliseconds for a client to connect (0: does not wait; -1: waits as long as it takes).

Returns whether a connection is waiting: TcpListener.Accept then takes it without waiting.

Accept

NetError<TcpConnection> Accept()

Takes the next connection of a client; waits for one if none is TcpListener.Pending.

Errors

• NetError.ConnectionLost: the listener is stopped, or taking the connection failed.

Stop

void Stop()

Stops listening; the connections that it accepted stay open. Stopping again does nothing.

Dispose

void Dispose()

Stops listening (TcpListener.Stop); using calls it.