Listen on unused port TCP/IP

In this example, the port is displayed on the console, and the program will listen until a request is made. Ip4Address assigns a random port when setting port to 0.

//! Start an echo TCP server at an unused port. //! //! Test with //! echo "hello zig" | nc localhost <port> const std = @import("std"); const net = std.net; const print = std.debug.print; pub fn main() !void { const loopback = try net.Ip4Address.parse("127.0.0.1", 0); const localhost = net.Address{ .in = loopback }; var server = try localhost.listen(.{ .reuse_address = true, }); defer server.deinit(); const addr = server.listen_address; print("Listening on {}, access this port to end the program\n", .{addr.getPort()}); const client = try server.accept(); // In real world, you'd want to handle multiple clients, probably in separate threads. try handleClient(client); } fn handleClient(client: net.Server.Connection) !void { print("Accepted connection from {f}\n", .{client.address}); defer client.stream.close(); var stream_buf: [1024]u8 = undefined; var reader = client.stream.reader(&stream_buf); // Here we echo back what we read directly, so the writer buffer is empty var writer = client.stream.writer(&.{}); while (true) { print("Waiting for data from {f}...\n", .{client.address}); const msg = reader.interface().takeDelimiterInclusive('\n') catch |err| { if (err == error.EndOfStream) { print("{f} closed the connection\n", .{client.address}); return; } else { return err; } }; print("{f} says {s}", .{ client.address, msg }); try writer.interface.writeAll(msg); // No need to flush, as writer buffer is empty } } 

When start starts up, try test like this:

echo "hello zig" | nc localhost <port> 

By default, the program listens with IPv4. If you want IPv6, use ::1 instead of 127.0.0.1, replace net.Ip4Address.parse by net.Ip6Address.parse and the field .in in the creation of the net.Address with .in6.

(And connect to something like ip6-localhost, depending on the way your machine is set up.)

The next section will show how to connect to this server using Zig code.