Java 27 and 26: runnable demos and captured output for every JEP, plus version lanes

Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01B38FGKKam5SCGgwgduVAh3
2026-09-21 15:08:50 +00:00
commit f59c1de96d
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+import java.io.DataInputStream;
+import java.net.InetAddress;
+import java.net.ServerSocket;
+import java.net.Socket;
+import javax.net.ssl.SSLSocket;
+import javax.net.ssl.SSLSocketFactory;
+
+/**
+ * How big is the TLS ClientHello this JDK sends?
+ *
+ * <p>A plain TCP server accepts the connection, reads the first TLS record header (5 bytes: type,
+ * version, 2-byte length) and then the record body, and reports the length. The client handshake
+ * never completes, and does not need to. Post-quantum key shares are large: this is the number that
+ * decides whether a hello still fits in one network packet. Explained in docs/04-post-quantum-tls.md.
+ */
+public class ClientHelloSize {
+
+    public static void main(String[] args) throws Exception {
+        try (ServerSocket listener = new ServerSocket(0, 1, InetAddress.getLoopbackAddress())) {
+            Thread client = new Thread(() -> {
+                try (SSLSocket s = (SSLSocket) SSLSocketFactory.getDefault()
+                        .createSocket(InetAddress.getLoopbackAddress(), listener.getLocalPort())) {
+                    s.setSoTimeout(1_000);
+                    s.startHandshake();        // will time out: nobody answers
+                } catch (Exception expected) {
+                    // the server side closes without replying
+                }
+            });
+            client.start();
+            try (Socket raw = listener.accept()) {
+                DataInputStream in = new DataInputStream(raw.getInputStream());
+                int type = in.readUnsignedByte();
+                int version = in.readUnsignedShort();
+                int length = in.readUnsignedShort();
+                byte[] body = new byte[length];
+                in.readFully(body);
+                System.out.printf("java.version           = %s%n", System.getProperty("java.version"));
+                System.out.printf("record type            = 0x%02x (0x16 = handshake)%n", type);
+                System.out.printf("ClientHello record     = %d bytes (+5 byte record header)%n", length);
+                System.out.printf("fits one TCP segment   = %s   (1460-byte MSS on a 1500-byte MTU)%n", length + 5 <= 1460 ? "yes" : "NO");
+            }
+            client.join();
+        }
+    }
+}