Reference

Networking (`pkg10networking`)

Runnable demos: `pkg10networking`. Every demo runs fully offline (loopback / in-process server).

The stack

1Application : your code (HTTP, custom protocols)2Transport   : TCP (reliable, ordered)  |  UDP (fast, best-effort)3Network     : IP (addresses, routing)   <- InetAddress

TCP vs UDP

	TCP	UDP
Connection	yes (handshake)	none
Delivery	guaranteed, ordered	best-effort, unordered
Overhead	higher	low
Use for	HTTP, DB, files	DNS, video, games, metrics
Java	`Socket` / `ServerSocket`	`DatagramSocket` / `DatagramPacket`

Files in this package

#	File	Topic
1	`networking1InetAddress`	DNS, hostnames, local interfaces
2	`networking2TcpSocket`	TCP echo client+server (in-process)
3	`networking3UdpDatagram`	UDP send/receive over loopback
4	`networking4UrlAndConnection`	`URL` / `URLConnection` (legacy HTTP)
5	`networking5HttpClient`	`java.net.http.HttpClient` (Java 11+, modern)

HTTP clients: old vs new

Legacy: URL.openConnection() — verbose, blocking, no HTTP/2.
Modern (use this): HttpClient — fluent, HTTP/2, sync + async, timeouts, redirects.

java
1HttpClient client = HttpClient.newHttpClient();2HttpResponse<String> r = client.send(3    HttpRequest.newBuilder(URI.create("https://api.example.com")).GET().build(),4    HttpResponse.BodyHandlers.ofString());

Tips

Bind to port 0 to let the OS pick a free ephemeral port (great for tests).
accept(), receive(), and read() block — use threads or setSoTimeout.
Reuse one HttpClient; configure connectTimeout + per-request timeout.