feat: F4.6g1 the echo server and the generic client windows

Oracle EchoWindowRun uses Java's echo server and client windows as a
person does; SaveAfterRunRun echo saves what Java keeps after the run.
The room takes setActive with a port, connect/disconnect/send, sends
both views and writes the server's port and the client's target back.
The editor's windows show Java's buttons, fields and lines; a port that
is no port is marked and not handed over (Java's button throws).
Core fix: an empty message (one empty segment with the push, as Java's
erstelleSegmente makes) counted as a repeat and never arrived.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/core/src/runtime/engine.ts

@@ -2799,11 +2799,21 @@ export class NetworkRuntimeEngine {
     }
   }
 
+  /**
+   * A data segment (TCPSocket's receive loop): new data goes into the
+   * message, a push ends it. An empty message is one empty segment with the
+   * push (TCPSocket.erstelleSegmente makes at least one; an empty segment
+   * comes here only with it). Java ends a message with every push, also with
+   * a repeated segment's (an ACK lost: an empty message more); here only
+   * with a new one's — but an empty segment repeated cannot be told from a
+   * new one by its number, which it does not count on, and is an empty
+   * message again (named).
+   */
   private receiveTcpPayload(socketId: Id, segment: TcpSegment): void {
     const session = this.stateValue.tcpSessionsById.get(socketId);
     if (session === undefined) return;
     const nextRemoteSequence = nextTcpSequenceNumber(segment);
-    if (nextRemoteSequence > session.remoteSequenceNumber) {
+    if (nextRemoteSequence > session.remoteSequenceNumber || segment.payload.length === 0) {
       session.remoteSequenceNumber = nextRemoteSequence;
       session.receiveAssembly = concatBytes(session.receiveAssembly, segment.payload);
       if ((segment.flags & TCP_FLAG.push) !== 0) {

packages/core/test/apps.test.ts

@@ -225,4 +225,20 @@ describe('the echo server and the generic client', () => {
     );
     expect(received).toEqual(['zuletzt', 'notConnected']);
   });
+
+  // Measured with EchoWindowRun (packages/sim/test/echoWindow.java.json): Java's echo answers an empty message.
+  it('echoes an empty message: one empty segment with the push, once, and the next message after it', () => {
+    const engine = startedEngine(network());
+    const client = engine.simpleClient(CLIENT)!;
+    client.connect('10.0.0.1', 55555);
+    advance(engine, 6_000);
+    client.send('');
+    advance(engine, 10_000);
+    client.send('danach');
+    advance(engine, 14_000);
+    const server = engine.echoServer(SERVER)!;
+    expect(server.log.all.filter((line) => line.kind === 'received' || line.kind === 'sent').map((line) => `${line.kind}:${'text' in line ? line.text : ''}`)).toEqual(['received:', 'sent:', 'received:danach', 'sent:danach']);
+    expect(client.log.all.filter((line) => line.kind === 'received').map((line) => ('text' in line ? line.text : ''))).toEqual(['', 'danach']);
   });
+});
+

packages/editor/browser/echo.spec.ts

@@ -0,0 +1,86 @@
+// The echo server and the generic client on two computers' desktops in
+// Chromium (F4.6g1), on browser/fixtures/web-pages.fls: installed while the
+// simulation runs; the server started on a port typed (one that is no port
+// marked and not handed over), the client connected, a message sent and
+// echoed, the fields locked while connected, the server's lines, "Trennen".
+
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { expect, test, type Page } from '@playwright/test';
+import { drawing, onDevice, serveEditor } from './editorPage.js';
+
+let server: { readonly base: string; readonly close: () => Promise<void> };
+
+test.beforeAll(async () => {
+  server = await serveEditor();
+});
+
+test.afterAll(async () => {
+  await server.close();
+});
+
+const FIXTURE = join(dirname(fileURLToPath(import.meta.url)), 'fixtures/web-pages.fls');
+
+async function openPages(page: Page): Promise<void> {
+  await page.goto(`${server.base}?example=new`);
+  await page.waitForSelector('svg.filius-canvas');
+  await page.locator('input[type="file"]').first().setInputFiles(FIXTURE);
+  await expect.poll(async () => (await drawing(page).catch(() => ({ nodes: [] }))).nodes.length).toBe(4);
+  await page.getByRole('button', { name: 'Wechselt in den Aktionsmodus' }).click();
+  await expect(page.locator('svg.filius-canvas')).toHaveAttribute('data-mode', 'simulation');
+}
+
+/** A computer's desktop opened with a tap, a program installed on it, and its window opened. */
+async function install(page: Page, name: string, program: string, label: string) {
+  const id = (await drawing(page)).nodes.find((node) => node.name === name)!.id;
+  const at = await onDevice(page, id);
+  await page.mouse.click(at.x, at.y);
+  const desktop = page.locator(`section[data-desktop="${id}"]`);
+  await desktop.locator('[data-program="installation"]').click();
+  const installation = desktop.locator('[data-program-window="installation"]');
+  await installation.locator('[data-list="available"] [role="option"]').filter({ hasText: label }).click();
+  await installation.getByRole('button', { name: 'Installieren' }).click();
+  await installation.getByRole('button', { name: 'Änderungen annehmen' }).click();
+  await desktop.locator(`[data-program="${program}"]`).click();
+  return { desktop, window: desktop.locator(`[data-program-window="${program}"]`) };
+}
+
+test('echoes a message from the generic client, as Java’s windows do', async ({ page }) => {
+  test.setTimeout(120_000);
+  await openPages(page);
+  const echo = await install(page, 'Server', 'echoServer', 'Echo-Server');
+  await expect(echo.window.locator('.program-titlebar h3')).toHaveText('Echo-Server');
+  const port = echo.window.getByRole('textbox', { name: 'Port:' });
+  await expect(port).toHaveValue('55555');
+  // A port that is no port: marked, the button does nothing.
+  await port.fill('abc');
+  await expect(port).toHaveAttribute('aria-invalid', 'true');
+  await echo.window.getByRole('button', { name: 'Starten' }).click();
+  await expect(echo.window.getByRole('button', { name: 'Starten' })).toBeVisible();
+  await port.fill('7777');
+  await echo.window.getByRole('button', { name: 'Starten' }).click();
+  await expect(echo.window.getByRole('button', { name: 'Anhalten' })).toBeVisible();
+  await expect(port).toHaveAttribute('readonly', '');
+  const serverLog = echo.window.getByLabel('Ausgabe');
+  await expect(serverLog).toHaveText('Annahme von Verbindungsanfragen gestartet\n');
+  await echo.desktop.locator('.desktop-close').click();
+
+  const client = await install(page, 'Browser', 'simpleClient', 'Einfacher Client');
+  const send = client.window.getByRole('button', { name: 'Senden' });
+  await expect(send).toBeDisabled();
+  await client.window.getByRole('textbox', { name: 'Server-Adresse:' }).fill('192.168.0.20');
+  await client.window.getByRole('textbox', { name: 'Server-Port:' }).fill('7777');
+  await client.window.getByRole('button', { name: 'Verbinden' }).click();
+  await expect(client.window.getByRole('button', { name: 'Trennen' })).toBeVisible({ timeout: 30_000 });
+  await expect(client.window.getByRole('textbox', { name: 'Server-Adresse:' })).toHaveAttribute('readonly', '');
+  const output = client.window.getByLabel('Ausgabe');
+  await expect(output).toHaveText('Verbindung hergestellt\n');
+  await client.window.getByRole('textbox', { name: 'Nachricht:' }).fill('Hallo Echo');
+  await send.click();
+  await expect(client.window.getByRole('textbox', { name: 'Nachricht:' })).toHaveValue('');
+  await expect(output).toHaveText('Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n', { timeout: 30_000 });
+  await client.window.getByRole('button', { name: 'Trennen' }).click();
+  await expect(client.window.getByRole('button', { name: 'Verbinden' })).toBeVisible({ timeout: 30_000 });
+  await expect(output).toContainText('Verbindung getrennt');
+  await expect(send).toBeDisabled();
+});

packages/editor/src/desktop/DesktopWindow.tsx

@@ -13,8 +13,8 @@
 // icon opens its window over the desktop (ProgramFrame), the home button
 // leaves it; so far the command line (F4.6b), the web browser and the web
 // server (F4.6d), the e-mail program and server (F4.6e), the text editor
-// (F4.6f2), the file explorer and the image viewer (F4.6f3) have one, the
+// (F4.6f2), the file explorer and the image viewer (F4.6f3), the echo
-// others follow. The browser's window takes its title from its page, the
+// server and the generic client (F4.6g1) have one, the others follow. The browser's window takes its title from its page, the
 // text editor's from its open file, the image viewer's from its picture, as
 // Java's do.
 
@@ -38,6 +38,7 @@ import { InstallationPanel } from './InstallationPanel.js';
 import { TerminalPanel } from './TerminalPanel.js';
 import { TextEditorPanel, useTextEditorWindow } from './TextEditorPanel.js';
 import { FileExplorerPanel } from './FileExplorerPanel.js';
+import { EchoServerPanel, SimpleClientPanel } from './EchoPanels.js';
 import { ImageViewerPanel, useImageViewer } from './ImageViewerPanel.js';
 import { WebServerPanel } from './WebServerPanel.js';
 import './desktop.css';
@@ -68,7 +69,7 @@ export interface DesktopWindowProps {
 export type DesktopWindowName = DesktopProgram | 'installation';
 
 /** The programs whose windows are built so far. */
-const WITH_WINDOW: ReadonlySet<DesktopProgram> = new Set(['commandPrompt', 'webBrowser', 'webServer', 'emailClient', 'emailServer', 'textEditor', 'fileExplorer', 'imageViewer']);
+const WITH_WINDOW: ReadonlySet<DesktopProgram> = new Set(['commandPrompt', 'webBrowser', 'webServer', 'emailClient', 'emailServer', 'textEditor', 'fileExplorer', 'imageViewer', 'echoServer', 'simpleClient']);
 
 /** The document's desktop of a computer, read anew after every change (a program installed, the label changed). */
 function useDesktopView(doc: Y.Doc, id: string) {
@@ -183,6 +184,8 @@ export function DesktopWindow({ doc, id, simulation, active, x, y, z, program: o
             {shown === 'textEditor' ? <TextEditorPanel doc={doc} node={id} /> : null}
             {shown === 'fileExplorer' ? <FileExplorerPanel doc={doc} node={id} /> : null}
             {shown === 'imageViewer' ? <ImageViewerPanel doc={doc} node={id} /> : null}
+            {shown === 'echoServer' ? <EchoServerPanel node={id} simulation={simulation} /> : null}
+            {shown === 'simpleClient' ? <SimpleClientPanel node={id} simulation={simulation} /> : null}
           </ProgramFrame>
         )}
         {info ? (

packages/editor/src/desktop/EchoPanels.tsx

@@ -0,0 +1,132 @@
+// A computer's echo server and generic client, after Java's
+// GUIApplicationServerBausteinWindow and GUIApplicationClientBausteinWindow
+// (measured with tools/java-oracle's EchoWindowRun). The server: its start
+// button ("Starten"/"Anhalten") with the port beside it, which can be typed
+// into only while it does not run, and its lines. The client: the server's
+// address and port (typed into only while it is not connected; they show the
+// program's again when it changes, as Java's window sets them from it),
+// "Verbinden"/"Trennen", the message and "Senden" (only while connected; the
+// message is emptied once it is sent) and the lines. The programs are the
+// room's: the panels show their views and lines and hand over what is done.
+//
+// Better than Java: a port that is no port (Java's Integer.parseInt throws,
+// and the button does nothing) is marked red, and the button hands it not
+// over.
+
+import { useEffect, useLayoutEffect, useRef, useState } from 'react';
+import type { LogLine, ServerLogEntry, SimpleClientLogEntry } from '@mdg-filius/core';
+import { portOfText, type EchoServerView, type SimpleClientView } from '@mdg-filius/protocol';
+import { useTranslate } from '../i18n/i18n.js';
+import type { Simulation } from '../simulation/useSimulation.js';
+import { serverLine, simpleClientLine } from './serverLines.js';
+
+const NO_LINES: readonly LogLine<never>[] = [];
+
+/** A program's lines as text, the newest in sight as Java's text area scrolls. */
+function useLines<Entry>(simulation: Simulation, topic: `app:${string}`, line: (entry: Entry) => string) {
+  const lines = (simulation.apps.get(topic as never)?.lines as readonly LogLine<Entry>[] | undefined) ?? NO_LINES;
+  const text = lines.map((each) => `${line(each)}\n`).join('');
+  const element = useRef<HTMLPreElement>(null);
+  useLayoutEffect(() => {
+    if (element.current !== null) element.current.scrollTop = element.current.scrollHeight;
+  }, [text]);
+  return { text, element };
+}
+
+export function EchoServerPanel({ node, simulation }: { readonly node: string; readonly simulation: Simulation }) {
+  const t = useTranslate();
+  const topic = `app:${node}/echoServer` as const;
+  const { watch, act } = simulation;
+  useEffect(() => watch([topic]), [watch, topic]);
+  const view = simulation.views.get(topic) as EchoServerView | null | undefined;
+  const [port, setPort] = useState(view === null || view === undefined ? '' : String(view.port));
+  useEffect(() => {
+    if (view !== null && view !== undefined) setPort(String(view.port));
+  }, [view]);
+  const { text, element } = useLines<ServerLogEntry>(simulation, topic, (entry) => serverLine(entry, t));
+  if (view === null || view === undefined) return <div className="web-server" />;
+  const typed = portOfText(port);
+  const press = () => {
+    if (view.active) act(node, 'echoServer', 'setActive', { active: false });
+    else if (typed !== undefined) act(node, 'echoServer', 'setActive', { active: true, port: typed });
+  };
+  return (
+    <div className="web-server echo-server">
+      <div className="web-server-bar">
+        <button type="button" onClick={press}>
+          {t(view.active ? 'echoServer.stop' : 'echoServer.start')}
+        </button>
+        <label>
+          {t('echoServer.port')}
+          <input
+            value={port}
+            inputMode="numeric"
+            readOnly={view.active}
+            aria-invalid={typed === undefined ? 'true' : undefined}
+            onChange={(event) => setPort(event.target.value)}
+            onKeyDown={(event) => event.key === 'Enter' && press()}
+          />
+        </label>
+      </div>
+      <pre className="web-server-log" ref={element} aria-label={t('echoServer.log')} tabIndex={0}>
+        {text}
+      </pre>
+    </div>
+  );
+}
+
+export function SimpleClientPanel({ node, simulation }: { readonly node: string; readonly simulation: Simulation }) {
+  const t = useTranslate();
+  const topic = `app:${node}/simpleClient` as const;
+  const { watch, act } = simulation;
+  useEffect(() => watch([topic]), [watch, topic]);
+  const view = simulation.views.get(topic) as SimpleClientView | null | undefined;
+  const [address, setAddress] = useState(view?.address ?? '');
+  const [port, setPort] = useState(view === null || view === undefined ? '' : String(view.port));
+  const [message, setMessage] = useState('');
+  useEffect(() => {
+    if (view === null || view === undefined) return;
+    setAddress(view.address);
+    setPort(String(view.port));
+  }, [view]);
+  const { text, element } = useLines<SimpleClientLogEntry>(simulation, topic, (entry) => simpleClientLine(entry, t));
+  if (view === null || view === undefined) return <div className="web-server" />;
+  const typed = portOfText(port);
+  const connect = () => {
+    if (view.connected) act(node, 'simpleClient', 'disconnect');
+    else if (typed !== undefined) act(node, 'simpleClient', 'connect', { address, port: typed });
+  };
+  const send = () => {
+    act(node, 'simpleClient', 'send', { text: message });
+    setMessage('');
+  };
+  return (
+    <div className="web-server simple-client">
+      <label className="simple-client-field">
+        <span>{t('simpleClient.address')}</span>
+        <input value={address} readOnly={view.connected} autoCapitalize="off" autoCorrect="off" spellCheck={false} onChange={(event) => setAddress(event.target.value)} />
+      </label>
+      <label className="simple-client-field">
+        <span>{t('simpleClient.port')}</span>
+        <input value={port} inputMode="numeric" readOnly={view.connected} aria-invalid={typed === undefined ? 'true' : undefined} onChange={(event) => setPort(event.target.value)} />
+      </label>
+      <div className="web-server-bar">
+        <button type="button" onClick={connect}>
+          {t(view.connected ? 'simpleClient.disconnect' : 'simpleClient.connect')}
+        </button>
+      </div>
+      <label className="simple-client-message">
+        <span>{t('simpleClient.message')}</span>
+        <textarea value={message} onChange={(event) => setMessage(event.target.value)} />
+      </label>
+      <div className="web-server-bar">
+        <button type="button" disabled={!view.connected} onClick={send}>
+          {t('simpleClient.send')}
+        </button>
+      </div>
+      <pre className="web-server-log" ref={element} aria-label={t('simpleClient.output')} tabIndex={0}>
+        {text}
+      </pre>
+    </div>
+  );
+}

packages/editor/src/desktop/desktop.css

@@ -1026,3 +1026,60 @@
 .image-viewer-picture img {
   max-width: 100%;
 }
+
+/* The echo server and the generic client (GUIApplicationServerBausteinWindow,
+ * GUIApplicationClientBausteinWindow), on the web server's look. */
+.echo-server input,
+.simple-client input,
+.simple-client textarea {
+  min-height: 32px;
+  padding: 0 6px;
+  border: 1px solid #a0a0a0;
+  background: #ffffff;
+  color: #000000;
+  font: 16px Dialog, sans-serif;
+}
+
+.echo-server input {
+  width: 8em;
+}
+
+.echo-server [aria-invalid='true'],
+.simple-client [aria-invalid='true'] {
+  border-color: #ff0000;
+  color: #ff0000;
+}
+
+.echo-server input:read-only,
+.simple-client input:read-only {
+  background: #eeeeee;
+}
+
+.simple-client-field,
+.simple-client-message {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  flex: none;
+}
+
+.simple-client-field span {
+  flex: none;
+  width: 140px;
+}
+
+.simple-client-field input {
+  flex: 1;
+  min-width: 0;
+}
+
+.simple-client-message {
+  flex-direction: column;
+  align-items: stretch;
+}
+
+.simple-client-message textarea {
+  min-height: 3.5em;
+  padding: 4px 6px;
+  resize: vertical;
+}

packages/editor/src/desktop/serverLines.ts

@@ -1,8 +1,10 @@
 // A server's lines as Java's server windows write them (ServerAnwendung,
-// ServerMitarbeiter, TCPSocket's failures), in the person's language: one
+// ServerMitarbeiter, TCPSocket's failures), and the generic client's as its
-// line each, as Java appends them to its window's text area.
+// window writes them (ClientBaustein, Socket, TCPSocket), in the person's
+// language: one line each (a failed connection two), as Java appends them to
+// its window's text area.
 
-import type { ServerLogEntry } from '@mdg-filius/core';
+import type { ServerLogEntry, SimpleClientLogEntry } from '@mdg-filius/core';
 import type { Translate } from '../i18n/i18n.js';
 
 export function serverLine(entry: ServerLogEntry, t: Translate): string {
@@ -23,3 +25,23 @@ export function serverLine(entry: ServerLogEntry, t: Translate): string {
       return t(`server.sendFailed.${entry.failure}`);
   }
 }
+
+export function simpleClientLine(entry: SimpleClientLogEntry, t: Translate): string {
+  switch (entry.kind) {
+    case 'connected':
+    case 'disconnected':
+    case 'notConnected':
+    case 'receiveFailed':
+      return t(`simpleClient.${entry.kind}`);
+    case 'connectFailed':
+      return `${t('simpleClient.notConnected')}\n${t(`simpleClient.failure.${entry.failure}`)}`;
+    case 'connectionClosed':
+      return t('simpleClient.connectionClosed', { address: `${entry.address}:${entry.port}` });
+    case 'received':
+      return `>>${entry.text}`;
+    case 'sent':
+      return `<<${entry.text}`;
+    case 'sendFailed':
+      return t(`server.sendFailed.${entry.failure}`);
+  }
+}

packages/editor/src/i18n/de.json

@@ -59,6 +59,10 @@
   "dhcp.static": "Statische Adresszuweisung",
   "dhcp.subnetMask": "Netzmaske",
   "dhcp.upperBound": "Adress-Obergrenze",
+  "echoServer.log": "Ausgabe",
+  "echoServer.port": "Port:",
+  "echoServer.start": "Starten",
+  "echoServer.stop": "Anhalten",
   "emailClient.account": "Konto einrichten",
   "emailClient.accountHint": "E-Mail-Konto verwalten",
   "emailClient.accountInvalid": "Die Angaben sind entweder fehlerhaft oder unvollständig!",
@@ -293,6 +297,21 @@
   "sheet.title": "Einstellungen",
   "sheet.wireless": "Drahtlos (WLAN)",
   "sim.failed": "Die Simulation ist auf einen Fehler gestoßen und wurde beendet.",
+  "simpleClient.address": "Server-Adresse:",
+  "simpleClient.connect": "Verbinden",
+  "simpleClient.connected": "Verbindung hergestellt",
+  "simpleClient.connectionClosed": "Socket zu {address} getrennt",
+  "simpleClient.disconnect": "Trennen",
+  "simpleClient.disconnected": "Verbindung getrennt",
+  "simpleClient.failure.failed": "Aktives Öffnen des Sockets fehlgeschlagen",
+  "simpleClient.failure.timedOut": "Zeitüberschreitung beim Verbindungsaufbau",
+  "simpleClient.failure.unresolved": "Ziel konnte nicht bestimmt werden!",
+  "simpleClient.message": "Nachricht:",
+  "simpleClient.notConnected": "Fehler beim Verbindungsaufbau",
+  "simpleClient.output": "Ausgabe",
+  "simpleClient.port": "Server-Port:",
+  "simpleClient.receiveFailed": "Keine Verbindung hergestellt!",
+  "simpleClient.send": "Senden",
   "terminal.commands": "Befehle",
   "terminal.ctrlC": "Strg+C",
   "terminal.input": "Befehl eingeben",

packages/editor/src/i18n/en.json

@@ -59,6 +59,10 @@
   "dhcp.static": "Static Address Assignment",
   "dhcp.subnetMask": "Netmask",
   "dhcp.upperBound": "Upper bound of address",
+  "echoServer.log": "Output",
+  "echoServer.port": "Port:",
+  "echoServer.start": "Start",
+  "echoServer.stop": "Stop",
   "emailClient.account": "Account",
   "emailClient.accountHint": "Manage email account",
   "emailClient.accountInvalid": "Wrong or incomplete data!",
@@ -293,6 +297,21 @@
   "sheet.title": "Settings",
   "sheet.wireless": "Wireless (Wi-Fi)",
   "sim.failed": "The simulation ran into an error and was stopped.",
+  "simpleClient.address": "Server address:",
+  "simpleClient.connect": "Connect",
+  "simpleClient.connected": "Connection established",
+  "simpleClient.connectionClosed": "Socket to {address} disconnected",
+  "simpleClient.disconnect": "Disconnect",
+  "simpleClient.disconnected": "Disconnected",
+  "simpleClient.failure.failed": "Active opening of socket failed.",
+  "simpleClient.failure.timedOut": "Timeout while connecting",
+  "simpleClient.failure.unresolved": "Target does not exist!",
+  "simpleClient.message": "Message:",
+  "simpleClient.notConnected": "Error while connecting",
+  "simpleClient.output": "Output",
+  "simpleClient.port": "Server port:",
+  "simpleClient.receiveFailed": "No connection established!",
+  "simpleClient.send": "Send",
   "terminal.commands": "Commands",
   "terminal.ctrlC": "Ctrl+C",
   "terminal.input": "Enter a command",

packages/editor/test/i18n.test.ts

@@ -45,6 +45,22 @@ const FROM_JAVA: Readonly<Record<string, string>> = {
   'explorer.notImported': 'sw_fileexplorer_msg1',
   'explorer.tooLarge': 'sw_fileexplorer_msg3',
   'viewer.open': 'imageviewer_msg2',
+  'echoServer.port': 'serverbaustein_msg1',
+  'echoServer.stop': 'serverbaustein_msg2',
+  'echoServer.start': 'serverbaustein_msg3',
+  'simpleClient.address': 'clientbaustein_msg1',
+  'simpleClient.port': 'clientbaustein_msg2',
+  'simpleClient.connect': 'clientbaustein_msg3',
+  'simpleClient.message': 'clientbaustein_msg4',
+  'simpleClient.send': 'clientbaustein_msg5',
+  'simpleClient.disconnect': 'clientbaustein_msg6',
+  'simpleClient.connected': 'sw_clientbaustein_msg2',
+  'simpleClient.disconnected': 'sw_clientbaustein_msg3',
+  'simpleClient.notConnected': 'sw_clientbaustein_msg4',
+  'simpleClient.receiveFailed': 'sw_tcpsocket_msg9',
+  'simpleClient.failure.unresolved': 'sw_socket_msg1',
+  'simpleClient.failure.timedOut': 'sw_tcpsocket_msg2',
+  'simpleClient.failure.failed': 'sw_tcpsocket_msg3',
   'textEditor.new': 'texteditor_msg3',
   'textEditor.open': 'texteditor_msg4',
   'textEditor.save': 'texteditor_msg5',
@@ -269,6 +285,7 @@ const FROM_JAVA_MENDED: Readonly<Record<string, readonly [string, (java: string)
 /** Java's words around a value, as its programs join them („Verbindung zu“ + address + „hergestellt“). */
 const FROM_JAVA_JOINED: Readonly<Record<string, readonly [string, string, string]>> = {
   'server.connectionAccepted': ['sw_serveranwendung_msg4', '{address}', 'sw_serveranwendung_msg5'],
+  'simpleClient.connectionClosed': ['sw_clientbaustein_msg5', '{address}', 'sw_clientbaustein_msg6'],
   'server.connectionClosed': ['sw_servermitarbeiter_msg1', '{address}', 'sw_servermitarbeiter_msg2'],
   'emailServer.created': ['emailserver_msg22', '{name}', 'emailserver_msg23'],
   'mail.stored': ['sw_smtpmitarbeiter_msg12', '{name}', 'sw_smtpmitarbeiter_msg13'],

packages/editor/test/serverLines.test.ts

@@ -6,8 +6,8 @@ import { readFileSync } from 'node:fs';
 import { dirname, join } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { describe, expect, it } from 'vitest';
-import type { ServerLogEntry } from '@mdg-filius/core';
+import type { ServerLogEntry, SimpleClientLogEntry } from '@mdg-filius/core';
-import { serverLine } from '../src/desktop/serverLines.js';
+import { serverLine, simpleClientLine } from '../src/desktop/serverLines.js';
 import { translate } from '../src/i18n/i18n.js';
 
 const java = JSON.parse(readFileSync(join(dirname(fileURLToPath(import.meta.url)), '../../sim/test/browserWindow.java.json'), 'utf8')) as { steps: { step: string; log?: string }[] };
@@ -39,3 +39,42 @@ describe("a server's lines", () => {
     expect(serverLine({ kind: 'connectionAccepted', address: '1.2.3.4', port: 5 }, (key, values) => translate('en', key, values))).toBe('Connection to 1.2.3.4:5 established');
   });
 });
+
+// The echo windows' lines against Java's (packages/sim/test/echoWindow.java.json, EchoWindowRun).
+const echo = JSON.parse(readFileSync(join(dirname(fileURLToPath(import.meta.url)), '../../sim/test/echoWindow.java.json'), 'utf8')) as {
+  steps: { step: string; server: { log: string }; client: { output: string } }[];
+};
+
+describe("the echo windows' lines", () => {
+  it("are Java's, line by line, the server's and the client's", () => {
+    const last = echo.steps.at(-1)!;
+    const [, port] = /Verbindung zu 192\.168\.0\.20:(\d+) hergestellt/.exec(last.server.log)!;
+    const server: ServerLogEntry[] = [
+      { kind: 'acceptingStarted' },
+      { kind: 'connectionAccepted', address: '192.168.0.20', port: Number(port) },
+      { kind: 'received', text: 'Zeile 1\nZeile 2' },
+      { kind: 'sent', text: 'Zeile 1\nZeile 2' },
+      { kind: 'acceptingStopped' },
+      { kind: 'connectionClosed', address: '192.168.0.20', port: Number(port) },
+      { kind: 'serverSocketClosed' },
+    ];
+    for (const entry of server) expect(last.server.log, entry.kind).toContain(`${serverLine(entry, t)}\n`);
+    const client: SimpleClientLogEntry[] = [
+      { kind: 'connected' },
+      { kind: 'sent', text: 'Hallo Echo' },
+      { kind: 'received', text: 'Hallo Echo' },
+      { kind: 'connectionClosed', address: '192.168.0.30', port: 55555 },
+      { kind: 'connectFailed', failure: 'timedOut' },
+      { kind: 'disconnected' },
+      { kind: 'connectFailed', failure: 'unresolved' },
+    ];
+    for (const entry of client) expect(last.client.output, entry.kind).toContain(`${simpleClientLine(entry, t)}\n`);
+    // Not in this story, in Java's words all the same (sw_clientbaustein_msg4, sw_tcpsocket_msg3, msg9, msg6).
+    expect([
+      simpleClientLine({ kind: 'notConnected' }, t),
+      simpleClientLine({ kind: 'connectFailed', failure: 'failed' }, t),
+      simpleClientLine({ kind: 'receiveFailed' }, t),
+      simpleClientLine({ kind: 'sendFailed', failure: 'notConnected' }, t),
+    ]).toEqual(['Fehler beim Verbindungsaufbau', 'Fehler beim Verbindungsaufbau\nAktives Öffnen des Sockets fehlgeschlagen', 'Keine Verbindung hergestellt!', 'Verbindung nicht aufgebaut!']);
+  });
+});

packages/protocol/src/echo.ts

@@ -0,0 +1,25 @@
+// What the echo server's and the generic client's windows show besides their
+// lines, as the room keeps them and every client shows them (plan §7.3),
+// after GUIApplicationServerBausteinWindow and
+// GUIApplicationClientBausteinWindow (measured with tools/java-oracle's
+// EchoWindowRun).
+
+/** The echo server: its button (running or not) and its port, which can be typed into only while it does not run. */
+export interface EchoServerView {
+  readonly active: boolean;
+  readonly port: number;
+}
+
+/** The generic client: "Verbinden" or "Trennen", and the server's address and port, which can be typed into only while it is not connected. */
+export interface SimpleClientView {
+  readonly connected: boolean;
+  readonly address: string;
+  readonly port: number;
+}
+
+/** A port as Java's windows take it (Integer.parseInt), and as a socket can have it: a whole number from 0 to 65535; undefined for any other text. */
+export function portOfText(text: string): number | undefined {
+  if (!/^\d+$/.test(text)) return undefined;
+  const port = Number(text);
+  return port <= 65_535 ? port : undefined;
+}

packages/protocol/src/index.ts

@@ -2,5 +2,6 @@
 export * from './host.js';
 export * from './sim.js';
 export * from './terminal.js';
+export * from './echo.js';
 export * from './mail.js';
 export * from './web.js';

packages/protocol/src/sim.ts

@@ -75,8 +75,10 @@ export type HostMessage =
   /**
    * What a program's window shows besides its lines (plan §7.3), whole: on
    * subscribing and when it changes; null while it has nothing (its program
-   * does not run, a browser that never ran). The browser's (BrowserView) and
+   * does not run, a browser that never ran): the browser's (BrowserView), the
-   * the web server's (WebServerView) so far.
+   * web server's (WebServerView), the e-mail program's and server's
+   * (EmailClientView, EmailServerView), the echo server's and the generic
+   * client's (EchoServerView, SimpleClientView).
    */
   | { readonly v: 1; readonly kind: 'view'; readonly node: string; readonly app: AppKind; readonly view: unknown }
   /**

packages/sim/src/room.ts

@@ -20,8 +20,9 @@
 //
 // A program's window may show more than its lines (plan §7.3): the browser's
 // page, the web server's button and table, the e-mail program's account and
-// folders, the e-mail server's domain and accounts go to the clients as a
+// folders, the e-mail server's domain and accounts, the echo server's button
-// view, whole, when they change.
+// and port, the generic client's connection go to the clients as a view,
+// whole, when they change.
 //
 // While the simulation runs, the document's programs are watched: a program
 // installed or removed on the desktop (Java's software installation) is
@@ -70,6 +71,8 @@ import {
   type Topic,
   type EmailClientView,
   type EmailServerView,
+  type EchoServerView,
+  type SimpleClientView,
   type TraceFrame,
   type WebServerView,
 } from '@mdg-filius/protocol';
@@ -237,7 +240,12 @@ export class SimulationRoom {
         settings.emailServer = emailServerAfterRun(configured as never, mailServerSettings);
       }
       const echo = this.engine.echoServer(id);
-      if (echo !== undefined) active.echoServer = echo.isActive;
+      if (echo !== undefined) {
+        active.echoServer = echo.isActive;
+        settings.echoServer = { port: echo.port };
+      }
+      const client = this.engine.simpleClient(id);
+      if (client !== undefined) settings.simpleClient = { targetAddress: client.targetAddress, targetPort: client.targetPort };
       settings.emailClient = snapshot.emailClientsByNodeId.get(id);
       settings.firewall = snapshot.firewallConfigurationsByNodeId.get(id);
       if (snapshot.dhcpClientConfigurationsByNodeId.get(id)?.isEnabled === true) settings.device = snapshot.deviceConfigurations.get(id);
@@ -442,6 +450,49 @@ export class SimulationRoom {
         return this.actInEmailClient(input);
       case 'emailServer':
         return this.actInEmailServer(input);
+      case 'echoServer':
+        return this.actInEchoServer(input);
+      case 'simpleClient':
+        return this.actInSimpleClient(input);
+      default:
+        return 'unknownAction';
+    }
+  }
+
+  /** The start button with the port typed (Java's window sets the port before and after it starts the server). */
+  private actInEchoServer(input: Extract<ClientMessage, { kind: 'input' }>): ErrorCode | undefined {
+    const server = this.engine.echoServer(input.node);
+    if (server === undefined) return 'unknownApp';
+    const { args } = input;
+    if (input.action !== 'setActive') return 'unknownAction';
+    if (typeof args.active !== 'boolean') return 'badArgs';
+    if (!args.active) {
+      server.setActive(false);
+      return undefined;
+    }
+    if (!isPort(args.port)) return 'badArgs';
+    server.setPort(args.port);
+    server.setActive(true);
+    return undefined;
+  }
+
+  /** "Verbinden" with the address and port typed, "Trennen", "Senden". */
+  private actInSimpleClient(input: Extract<ClientMessage, { kind: 'input' }>): ErrorCode | undefined {
+    const client = this.engine.simpleClient(input.node);
+    if (client === undefined) return 'unknownApp';
+    const { args } = input;
+    switch (input.action) {
+      case 'connect':
+        if (typeof args.address !== 'string' || !isPort(args.port)) return 'badArgs';
+        client.connect(args.address, args.port);
+        return undefined;
+      case 'disconnect':
+        client.disconnect();
+        return undefined;
+      case 'send':
+        if (typeof args.text !== 'string') return 'badArgs';
+        client.send(args.text);
+        return undefined;
       default:
         return 'unknownAction';
     }
@@ -583,6 +634,18 @@ export class SimulationRoom {
         const view: EmailClientView = { account: client.account, inbox: client.inbox.map((entry) => entry.mail), sent: client.sent.map((entry) => entry.mail) };
         return view;
       }
+      case 'echoServer': {
+        const server = this.engine.echoServer(node);
+        if (server === undefined) return null;
+        const view: EchoServerView = { active: server.isActive, port: server.port };
+        return view;
+      }
+      case 'simpleClient': {
+        const client = this.engine.simpleClient(node);
+        if (client === undefined) return null;
+        const view: SimpleClientView = { connected: client.isConnected, address: client.targetAddress, port: client.targetPort };
+        return view;
+      }
       case 'emailServer': {
         const server = this.engine.emailServer(node);
         if (server === undefined) return null;
@@ -732,6 +795,11 @@ export class SimulationRoom {
   }
 }
 
+/** A port a socket can have. */
+function isPort(value: unknown): value is number {
+  return Number.isInteger(value) && (value as number) >= 0 && (value as number) <= 65_535;
+}
+
 /** A card's frames as the capture window shows them, both views. */
 export function traceFramesOf(frames: readonly CapturedFrame[]): TraceFrame[] {
   const byNumber = (rows: readonly CaptureRow[]) => {

packages/sim/test/echoWindow.java.json

@@ -0,0 +1,424 @@
+{
+  "steps": [
+    {
+      "step": "open",
+      "server": {
+        "button": "Starten",
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "log": ""
+      },
+      "client": {
+        "connect": "Verbinden",
+        "sendEnabled": false,
+        "address": {
+          "text": "",
+          "editable": true
+        },
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "message": "",
+        "output": ""
+      },
+      "thrown": []
+    },
+    {
+      "step": "server: start with port abc",
+      "server": {
+        "button": "Starten",
+        "port": {
+          "text": "abc",
+          "editable": true
+        },
+        "log": ""
+      },
+      "client": {
+        "connect": "Verbinden",
+        "sendEnabled": false,
+        "address": {
+          "text": "",
+          "editable": true
+        },
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "message": "",
+        "output": ""
+      },
+      "thrown": [
+        "NumberFormatException: For input string: \"abc\""
+      ]
+    },
+    {
+      "step": "server: start with port 55555",
+      "server": {
+        "button": "Anhalten",
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\n"
+      },
+      "client": {
+        "connect": "Verbinden",
+        "sendEnabled": false,
+        "address": {
+          "text": "",
+          "editable": true
+        },
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "message": "",
+        "output": ""
+      },
+      "thrown": []
+    },
+    {
+      "step": "client: connect with port x",
+      "server": {
+        "button": "Anhalten",
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\n"
+      },
+      "client": {
+        "connect": "Verbinden",
+        "sendEnabled": false,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": true
+        },
+        "port": {
+          "text": "x",
+          "editable": true
+        },
+        "message": "",
+        "output": ""
+      },
+      "thrown": [
+        "NumberFormatException: For input string: \"x\""
+      ]
+    },
+    {
+      "step": "client: connect to 192.168.0.30:55555",
+      "server": {
+        "button": "Anhalten",
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n"
+      },
+      "client": {
+        "connect": "Trennen",
+        "sendEnabled": true,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": false
+        },
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "message": "",
+        "output": "Verbindung hergestellt\n"
+      },
+      "thrown": []
+    },
+    {
+      "step": "client: send Hallo Echo",
+      "server": {
+        "button": "Anhalten",
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n>>Hallo Echo\n<<Hallo Echo\n"
+      },
+      "client": {
+        "connect": "Trennen",
+        "sendEnabled": true,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": false
+        },
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "message": "",
+        "output": "Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n"
+      },
+      "thrown": []
+    },
+    {
+      "step": "client: send nothing",
+      "server": {
+        "button": "Anhalten",
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n>>Hallo Echo\n<<Hallo Echo\n>>\n<<\n"
+      },
+      "client": {
+        "connect": "Trennen",
+        "sendEnabled": true,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": false
+        },
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "message": "",
+        "output": "Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n<<\n>>\n"
+      },
+      "thrown": []
+    },
+    {
+      "step": "client: send two lines",
+      "server": {
+        "button": "Anhalten",
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n>>Hallo Echo\n<<Hallo Echo\n>>\n<<\n>>Zeile 1\nZeile 2\n<<Zeile 1\nZeile 2\n"
+      },
+      "client": {
+        "connect": "Trennen",
+        "sendEnabled": true,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": false
+        },
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "message": "",
+        "output": "Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n<<\n>>\n<<Zeile 1\nZeile 2\n>>Zeile 1\nZeile 2\n"
+      },
+      "thrown": []
+    },
+    {
+      "step": "server: stop while connected",
+      "server": {
+        "button": "Starten",
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n>>Hallo Echo\n<<Hallo Echo\n>>\n<<\n>>Zeile 1\nZeile 2\n<<Zeile 1\nZeile 2\nAnnahme von Verbindungsanfragen beendet\nSocket zu 192.168.0.20:57292 geschlossen\nServer-Socket geschlossen\n"
+      },
+      "client": {
+        "connect": "Verbinden",
+        "sendEnabled": false,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": true
+        },
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "message": "",
+        "output": "Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n<<\n>>\n<<Zeile 1\nZeile 2\n>>Zeile 1\nZeile 2\nSocket zu 192.168.0.30:55555 getrennt\n"
+      },
+      "thrown": []
+    },
+    {
+      "step": "client: send after the server stopped",
+      "server": {
+        "button": "Starten",
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n>>Hallo Echo\n<<Hallo Echo\n>>\n<<\n>>Zeile 1\nZeile 2\n<<Zeile 1\nZeile 2\nAnnahme von Verbindungsanfragen beendet\nSocket zu 192.168.0.20:57292 geschlossen\nServer-Socket geschlossen\n"
+      },
+      "client": {
+        "connect": "Verbinden",
+        "sendEnabled": false,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": true
+        },
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "message": "noch da?",
+        "output": "Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n<<\n>>\n<<Zeile 1\nZeile 2\n>>Zeile 1\nZeile 2\nSocket zu 192.168.0.30:55555 getrennt\n"
+      },
+      "thrown": []
+    },
+    {
+      "step": "client: Trennen",
+      "server": {
+        "button": "Starten",
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n>>Hallo Echo\n<<Hallo Echo\n>>\n<<\n>>Zeile 1\nZeile 2\n<<Zeile 1\nZeile 2\nAnnahme von Verbindungsanfragen beendet\nSocket zu 192.168.0.20:57292 geschlossen\nServer-Socket geschlossen\n"
+      },
+      "client": {
+        "connect": "Verbinden",
+        "sendEnabled": false,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": true
+        },
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "message": "noch da?",
+        "output": "Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n<<\n>>\n<<Zeile 1\nZeile 2\n>>Zeile 1\nZeile 2\nSocket zu 192.168.0.30:55555 getrennt\n"
+      },
+      "thrown": []
+    },
+    {
+      "step": "server: start again",
+      "server": {
+        "button": "Anhalten",
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n>>Hallo Echo\n<<Hallo Echo\n>>\n<<\n>>Zeile 1\nZeile 2\n<<Zeile 1\nZeile 2\nAnnahme von Verbindungsanfragen beendet\nSocket zu 192.168.0.20:57292 geschlossen\nServer-Socket geschlossen\nAnnahme von Verbindungsanfragen gestartet\n"
+      },
+      "client": {
+        "connect": "Verbinden",
+        "sendEnabled": false,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": true
+        },
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "message": "noch da?",
+        "output": "Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n<<\n>>\n<<Zeile 1\nZeile 2\n>>Zeile 1\nZeile 2\nSocket zu 192.168.0.30:55555 getrennt\n"
+      },
+      "thrown": []
+    },
+    {
+      "step": "client: connect again",
+      "server": {
+        "button": "Anhalten",
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n>>Hallo Echo\n<<Hallo Echo\n>>\n<<\n>>Zeile 1\nZeile 2\n<<Zeile 1\nZeile 2\nAnnahme von Verbindungsanfragen beendet\nSocket zu 192.168.0.20:57292 geschlossen\nServer-Socket geschlossen\nAnnahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:55719 hergestellt\n"
+      },
+      "client": {
+        "connect": "Trennen",
+        "sendEnabled": true,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": false
+        },
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "message": "noch da?",
+        "output": "Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n<<\n>>\n<<Zeile 1\nZeile 2\n>>Zeile 1\nZeile 2\nSocket zu 192.168.0.30:55555 getrennt\nFehler beim Verbindungsaufbau\nZeitüberschreitung beim Verbindungsaufbau\nVerbindung hergestellt\n"
+      },
+      "thrown": []
+    },
+    {
+      "step": "client: Trennen again",
+      "server": {
+        "button": "Anhalten",
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n>>Hallo Echo\n<<Hallo Echo\n>>\n<<\n>>Zeile 1\nZeile 2\n<<Zeile 1\nZeile 2\nAnnahme von Verbindungsanfragen beendet\nSocket zu 192.168.0.20:57292 geschlossen\nServer-Socket geschlossen\nAnnahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:55719 hergestellt\nSocket zu 192.168.0.20:55719 geschlossen\n"
+      },
+      "client": {
+        "connect": "Verbinden",
+        "sendEnabled": false,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": true
+        },
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "message": "noch da?",
+        "output": "Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n<<\n>>\n<<Zeile 1\nZeile 2\n>>Zeile 1\nZeile 2\nSocket zu 192.168.0.30:55555 getrennt\nFehler beim Verbindungsaufbau\nZeitüberschreitung beim Verbindungsaufbau\nVerbindung hergestellt\nVerbindung getrennt\nSocket zu 192.168.0.30:55555 getrennt\n"
+      },
+      "thrown": []
+    },
+    {
+      "step": "client: connect to a port nobody listens on",
+      "server": {
+        "button": "Anhalten",
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n>>Hallo Echo\n<<Hallo Echo\n>>\n<<\n>>Zeile 1\nZeile 2\n<<Zeile 1\nZeile 2\nAnnahme von Verbindungsanfragen beendet\nSocket zu 192.168.0.20:57292 geschlossen\nServer-Socket geschlossen\nAnnahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:55719 hergestellt\nSocket zu 192.168.0.20:55719 geschlossen\n"
+      },
+      "client": {
+        "connect": "Verbinden",
+        "sendEnabled": false,
+        "address": {
+          "text": "192.168.0.30",
+          "editable": true
+        },
+        "port": {
+          "text": "4711",
+          "editable": true
+        },
+        "message": "noch da?",
+        "output": "Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n<<\n>>\n<<Zeile 1\nZeile 2\n>>Zeile 1\nZeile 2\nSocket zu 192.168.0.30:55555 getrennt\nFehler beim Verbindungsaufbau\nZeitüberschreitung beim Verbindungsaufbau\nVerbindung hergestellt\nVerbindung getrennt\nSocket zu 192.168.0.30:55555 getrennt\nFehler beim Verbindungsaufbau\nZeitüberschreitung beim Verbindungsaufbau\n"
+      },
+      "thrown": []
+    },
+    {
+      "step": "client: connect to a name nobody knows",
+      "server": {
+        "button": "Anhalten",
+        "port": {
+          "text": "55555",
+          "editable": false
+        },
+        "log": "Annahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:57292 hergestellt\n>>Hallo Echo\n<<Hallo Echo\n>>\n<<\n>>Zeile 1\nZeile 2\n<<Zeile 1\nZeile 2\nAnnahme von Verbindungsanfragen beendet\nSocket zu 192.168.0.20:57292 geschlossen\nServer-Socket geschlossen\nAnnahme von Verbindungsanfragen gestartet\nVerbindung zu 192.168.0.20:55719 hergestellt\nSocket zu 192.168.0.20:55719 geschlossen\n"
+      },
+      "client": {
+        "connect": "Verbinden",
+        "sendEnabled": false,
+        "address": {
+          "text": "gibtsnicht",
+          "editable": true
+        },
+        "port": {
+          "text": "55555",
+          "editable": true
+        },
+        "message": "noch da?",
+        "output": "Verbindung hergestellt\n<<Hallo Echo\n>>Hallo Echo\n<<\n>>\n<<Zeile 1\nZeile 2\n>>Zeile 1\nZeile 2\nSocket zu 192.168.0.30:55555 getrennt\nFehler beim Verbindungsaufbau\nZeitüberschreitung beim Verbindungsaufbau\nVerbindung hergestellt\nVerbindung getrennt\nSocket zu 192.168.0.30:55555 getrennt\nFehler beim Verbindungsaufbau\nZeitüberschreitung beim Verbindungsaufbau\nFehler beim Verbindungsaufbau\nZiel konnte nicht bestimmt werden!\n"
+      },
+      "thrown": []
+    }
+  ]
+}

packages/sim/test/echoWindow.test.ts

@@ -0,0 +1,251 @@
+// The echo server's and the generic client's windows in the room, against
+// Java's (echoWindow.java.json, EchoWindowRun): Java's steps played as the
+// editor's panels play them — the start button with the port typed,
+// "Verbinden" with the address and port typed (or "Trennen" while
+// connected), "Senden" only while connected —, the buttons, fields and lines
+// both windows show after each; and what Java's project keeps of them after
+// a run (fixtures/after-run-echo.fls, SaveAfterRunRun).
+//
+// Named: a port that is no number is not handed to the room (Java's window
+// throws and does nothing; the panel marks the field); a connection attempt
+// lasts three SYNs (F2.3c), so the one to the stopped server is awaited
+// before it starts again. The client's own port is the threads' draw, in
+// Java as here: written as PORT.
+
+import { readFileSync } from 'node:fs';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { describe, expect, it } from 'vitest';
+import * as Y from 'yjs';
+import type { EchoServerLogEntry, SimpleClientLogEntry } from '@mdg-filius/core';
+import { addDevice, connect, emptyProject, readProject, setHostAddress, setSoftware, writeProject } from '@mdg-filius/doc';
+import { openProjectArchive } from '@mdg-filius/fls';
+import { portOfText, type EchoServerView, type HostMessage, type SimpleClientView } from '@mdg-filius/protocol';
+import { clientText, serverText } from '../../core/test/programLines.js';
+import { SimulationRoom, TICK_MILLISECONDS } from '../src/index.js';
+
+interface WindowField {
+  readonly text: string;
+  readonly editable: boolean;
+}
+
+interface JavaStep {
+  readonly step: string;
+  readonly server: { readonly button: string; readonly port: WindowField; readonly log: string };
+  readonly client: { readonly connect: string; readonly sendEnabled: boolean; readonly address: WindowField; readonly port: WindowField; readonly message: string; readonly output: string };
+  readonly thrown: readonly string[];
+}
+
+const here = dirname(fileURLToPath(import.meta.url));
+const java = JSON.parse(readFileSync(join(here, 'echoWindow.java.json'), 'utf8')) as { readonly steps: readonly JavaStep[] };
+const corpus = join(here, '../../../corpus/java-examples');
+
+/** The client's own port, drawn by the threads. */
+const ownPort = (text: string) => text.replace(/192\.168\.0\.20:\d+/g, '192.168.0.20:PORT');
+
+function setUp() {
+  const doc = new Y.Doc();
+  writeProject(doc, emptyProject());
+  let counter = 0;
+  const newId = () => `port-${++counter}`;
+  addDevice(doc, { kind: 'pc', id: 'client', name: 'Client', x: 0, y: 0, newId }, 'me');
+  addDevice(doc, { kind: 'pc', id: 'server', name: 'Server', x: 200, y: 0, newId }, 'me');
+  addDevice(doc, { kind: 'networkSwitch', id: 'switch', name: 'Switch', x: 100, y: 100, newId }, 'me');
+  connect(doc, { node: 'client' }, { node: 'switch' }, 'cable-1', 'me');
+  connect(doc, { node: 'server' }, { node: 'switch' }, 'cable-2', 'me');
+  setHostAddress(doc, 'client', 'ipAddress', '192.168.0.20', 'me');
+  setHostAddress(doc, 'server', 'ipAddress', '192.168.0.30', 'me');
+  setSoftware(doc, 'server', { install: ['echoServer'], remove: [] }, 'de', 'me');
+  setSoftware(doc, 'client', { install: ['simpleClient'], remove: [] }, 'de', 'me');
+  let now = 0;
+  const room = new SimulationRoom(doc, { now: () => now, seed: () => 3 });
+  const views = new Map<string, unknown>();
+  const lines = new Map<string, unknown[]>();
+  const errors: string[] = [];
+  const id = room.connect((message: HostMessage) => {
+    if (message.kind === 'view') views.set(message.app, message.view);
+    if (message.kind === 'app') lines.set(message.app, [...(lines.get(message.app) ?? []).slice(0, message.from), ...message.lines]);
+    if (message.kind === 'error') errors.push(message.code);
+  });
+  const send = (fields: object) => room.receive(id, { v: 1, ...fields });
+  send({ kind: 'sub', topics: ['app:server/echoServer', 'app:client/simpleClient'] });
+  send({ kind: 'start' });
+  const run = (milliseconds: number) => {
+    for (let elapsed = 0; elapsed < milliseconds; elapsed += TICK_MILLISECONDS) {
+      now += TICK_MILLISECONDS;
+      room.tick();
+    }
+  };
+  const act = (node: string, app: string, action: string, args: object = {}) => send({ kind: 'input', node, app, action, args, reqId: action });
+  return { doc, room, views, lines, errors, run, act, send };
+}
+
+describe("the echo server's and the generic client's windows, against Java's", () => {
+  it("play Java's steps as the panels play them", () => {
+    const { views, lines, run, act, errors } = setUp();
+    run(TICK_MILLISECONDS);
+    // What the panels hold: the fields as typed, the message.
+    let serverPortText = '';
+    let clientAddressText = '';
+    let clientPortText = '';
+    let message = '';
+    const server = () => views.get('echoServer') as EchoServerView;
+    const client = () => views.get('simpleClient') as SimpleClientView;
+    const serverLog = () => ((lines.get('echoServer') ?? []) as EchoServerLogEntry[]).map((line) => `${serverText(line)}\n`).join('');
+    const clientOutput = () => ((lines.get('simpleClient') ?? []) as SimpleClientLogEntry[]).map((line) => `${clientText(line)}\n`).join('');
+    // The fields follow the program when it changes (Java's aktualisieren sets them from it).
+    let seenServer = server();
+    let seenClient = client();
+    const follow = () => {
+      if (server() !== seenServer) serverPortText = String(server().port);
+      if (client() !== seenClient) {
+        clientAddressText = client().address;
+        clientPortText = String(client().port);
+      }
+      seenServer = server();
+      seenClient = client();
+    };
+    serverPortText = String(server().port);
+    clientAddressText = client().address;
+    clientPortText = String(client().port);
+    const shown = () => {
+      follow();
+      return {
+        server: { button: server().active ? 'Anhalten' : 'Starten', port: { text: serverPortText, editable: !server().active }, log: ownPort(serverLog()) },
+        client: {
+          connect: client().connected ? 'Trennen' : 'Verbinden',
+          sendEnabled: client().connected,
+          address: { text: clientAddressText, editable: !client().connected },
+          port: { text: clientPortText, editable: !client().connected },
+          message,
+          output: clientOutput(),
+        },
+      };
+    };
+    // The failed attempt, awaited (see below), is in the window one step before Java's shows it.
+    const timedOut = `${clientText({ kind: 'connectFailed', failure: 'timedOut' })}\n`;
+    const expected = (step: JavaStep) => ({
+      server: { ...step.server, log: ownPort(step.server.log) },
+      client: step.step === 'server: start again' ? { ...step.client, output: step.client.output + timedOut } : step.client,
+    });
+    // The panels' buttons.
+    const startStop = () => {
+      if (server().active) act('server', 'echoServer', 'setActive', { active: false });
+      else if (portOfText(serverPortText) !== undefined) act('server', 'echoServer', 'setActive', { active: true, port: portOfText(serverPortText) });
+    };
+    const connectButton = () => {
+      if (client().connected) act('client', 'simpleClient', 'disconnect');
+      else if (portOfText(clientPortText) !== undefined) act('client', 'simpleClient', 'connect', { address: clientAddressText, port: portOfText(clientPortText) });
+    };
+    const sendButton = () => {
+      if (!client().connected) return;
+      act('client', 'simpleClient', 'send', { text: message });
+      message = '';
+    };
+    const plays: Record<string, () => void> = {
+      'server: start with port abc': () => ((serverPortText = 'abc'), startStop(), run(500)),
+      'server: start with port 55555': () => ((serverPortText = '55555'), startStop(), run(1000)),
+      'client: connect with port x': () => ((clientAddressText = '192.168.0.30'), (clientPortText = 'x'), connectButton(), run(500)),
+      'client: connect to 192.168.0.30:55555': () => ((clientAddressText = '192.168.0.30'), (clientPortText = '55555'), connectButton(), run(6000)),
+      'client: send Hallo Echo': () => ((message = 'Hallo Echo'), sendButton(), run(4000)),
+      'client: send nothing': () => ((message = ''), sendButton(), run(4000)),
+      'client: send two lines': () => ((message = 'Zeile 1\nZeile 2'), sendButton(), run(4000)),
+      'server: stop while connected': () => (startStop(), run(4000)),
+      'client: send after the server stopped': () => ((message = 'noch da?'), sendButton(), run(8000)),
+      'client: Trennen': () => (connectButton(), run(3000)),
+      'server: start again': () => (startStop(), run(1000)),
+      'client: connect again': () => (connectButton(), run(6000)),
+      'client: Trennen again': () => (connectButton(), run(3000)),
+      // Three SYNs (F2.3c) last longer than Java's one: until the attempt failed.
+      'client: connect to a port nobody listens on': () => {
+        clientPortText = '4711';
+        connectButton();
+        for (let waited = 0; !clientOutput().endsWith(timedOut) && waited < 60_000; waited += 1000) run(1000);
+      },
+      'client: connect to a name nobody knows': () => ((clientAddressText = 'gibtsnicht'), (clientPortText = '55555'), connectButton(), run(12000)),
+    };
+    for (const step of java.steps) {
+      if (step.step !== 'open') plays[step.step]!();
+      expect(shown(), step.step).toEqual(expected(step));
+      // The press on "Verbinden" with the server stopped: Java's one SYN times out before the server starts again,
+      // the core's three (named in F2.3c) only later — awaited here, so that the server starts after it as in Java.
+      if (step.step === 'client: Trennen') {
+        for (let waited = 0; !clientOutput().endsWith(timedOut) && waited < 60_000; waited += 1000) run(1000);
+      }
+      // Java's window threw for a port that is no number; the panel hands nothing over.
+      expect(step.thrown.length > 0, step.step).toBe(step.step.includes('port abc') || step.step.includes('port x'));
+    }
+    expect(errors).toEqual([]);
+  });
+
+  it("leave in the project what Java's leaves after a run: the server's port and that it runs, the client's server", () => {
+    let ids = 0;
+    const project = openProjectArchive(new Uint8Array(readFileSync(join(corpus, 'email_komplett.fls'))), () => `00000000-0000-0000-0000-${(++ids).toString(16).padStart(12, '0')}`);
+    const doc = new Y.Doc();
+    writeProject(doc, project);
+    const id = (name: string) => readProject(doc).graph.nodes.find((node) => node.displayName === name)!.id;
+    setSoftware(doc, id('Rechner 2'), { install: ['echoServer'], remove: [] }, 'de', 'me');
+    setSoftware(doc, id('Rechner 1'), { install: ['simpleClient'], remove: [] }, 'de', 'me');
+    let now = 0;
+    const room = new SimulationRoom(doc, { now: () => now, seed: () => 5 });
+    const client = room.connect(() => {});
+    const act = (node: string, app: string, action: string, args: object = {}) => room.receive(client, { v: 1, kind: 'input', node: id(node), app, action, args, reqId: action });
+    const run = (milliseconds: number) => {
+      for (let elapsed = 0; elapsed < milliseconds; elapsed += TICK_MILLISECONDS) {
+        now += TICK_MILLISECONDS;
+        room.tick();
+      }
+    };
+    room.receive(client, { v: 1, kind: 'start' });
+    run(1000);
+    act('Rechner 2', 'echoServer', 'setActive', { active: true, port: 7777 });
+    run(1000);
+    const address = readProject(doc).deviceConfigurations.get(id('Rechner 2'))!.ipAddress;
+    act('Rechner 1', 'simpleClient', 'connect', { address, port: 7777 });
+    run(6000);
+    act('Rechner 1', 'simpleClient', 'send', { text: 'Hallo' });
+    run(4000);
+    room.receive(client, { v: 1, kind: 'stop' });
+
+    let javaIds = 0;
+    const saved = openProjectArchive(new Uint8Array(readFileSync(join(here, 'fixtures/after-run-echo.fls'))), () => `00000000-0000-0000-0000-${(++javaIds).toString(16).padStart(12, '0')}`);
+    const ours = readProject(doc);
+    for (const name of ['Rechner 1', 'Rechner 2']) {
+      const of = (each: typeof ours) => {
+        const node = each.graph.nodes.find((candidate) => candidate.displayName === name)!.id;
+        return { echoServer: each.echoServerConfigurations.get(node), simpleClient: each.simpleClientConfigurations.get(node), active: [...(each.activePrograms.get(node) ?? [])].sort() };
+      };
+      expect(of(ours), name).toEqual(of(saved));
+    }
+  });
+
+  it('refuses what the panels never hand over: a port that is no port, an action the program has not', () => {
+    const { run, act, errors, views } = setUp();
+    run(TICK_MILLISECONDS);
+    act('server', 'echoServer', 'setActive', { active: true, port: 70_000 });
+    act('server', 'echoServer', 'setActive', { active: true, port: 1.5 });
+    act('server', 'echoServer', 'setActive', { active: 'yes' });
+    act('server', 'echoServer', 'setActive', { active: 0 });
+    act('server', 'echoServer', 'restart');
+    act('client', 'simpleClient', 'connect', { address: '192.168.0.30', port: -1 });
+    act('client', 'simpleClient', 'connect', { address: 5, port: 80 });
+    act('client', 'simpleClient', 'send', {});
+    act('client', 'simpleClient', 'reset');
+    act('client', 'echoServer', 'setActive', { active: false });
+    act('server', 'simpleClient', 'disconnect');
+    expect(errors).toEqual(['badArgs', 'badArgs', 'badArgs', 'badArgs', 'unknownAction', 'badArgs', 'badArgs', 'badArgs', 'unknownAction', 'unknownApp', 'unknownApp']);
+    expect([portOfText('0'), portOfText('65535'), portOfText('000080'), portOfText('65536'), portOfText('+5'), portOfText(' 5'), portOfText('123456')]).toEqual([
+      0,
+      65_535,
+      80,
+      undefined,
+      undefined,
+      undefined,
+      undefined,
+    ]);
+    // What is handed over is in the view: the port.
+    act('server', 'echoServer', 'setActive', { active: true, port: 7777 });
+    run(TICK_MILLISECONDS);
+    expect(views.get('echoServer')).toEqual({ active: true, port: 7777 });
+  });
+});

packages/sim/test/room.test.ts

@@ -458,7 +458,7 @@ describe("a simulation room's browser and web server windows", () => {
       [server, 'webServer', 'setVirtualHost', { row: 0, column: 1, value: 2 }, 'badArgs'],
       [server, 'webServer', 'restart', {}, 'unknownAction'],
       [notebook, 'webServer', 'setActive', { active: true }, 'unknownApp'],
-      [server, 'echoServer', 'setActive', { active: true }, 'unknownAction'],
+      [server, 'gnutella', 'join', {}, 'unknownAction'],
     ];
     for (const [target, app, action, args, code] of cases) {
       send({ kind: 'input', node: target, app, action, args, reqId: `${app}.${action}.${JSON.stringify(args)}` });

tools/java-oracle/README.md

@@ -1460,3 +1460,36 @@ Gemessen (03.10.2026):
 * Der Bildbetrachter heißt nach dem Öffnen wie die Datei; jedes geöffnete
   Bild legt Java über das vorige, eine Textdatei zeigt es als leeres Bild,
   ohne Fund bleibt alles.
+
+### Echo-Server und Einfacher Client (F4.6g1)
+
+`EchoWindowRun` öffnet Javas `GUIApplicationServerBausteinWindow` und
+`GUIApplicationClientBausteinWindow` auf je einem `GUIDesktopPanel` im Netz
+von mail-lan (Server 192.168.0.30, Client 192.168.0.20) und benutzt sie wie
+eine Person: Port tippen und starten (auch „abc“), Adresse und Port tippen
+und „Verbinden“ (auch Port „x“), Nachrichten senden (auch eine leere und
+eine mit zwei Zeilen), den Server anhalten, während der Client verbunden
+ist, „Trennen“, ein Port ohne Server, ein unbekannter Name. Je Schritt:
+Knöpfe, Felder (und ob sie beschreibbar sind), Zeilen beider Fenster und die
+Ausnahmen, die Javas Knöpfe warfen (`packages/sim/test/echoWindow.java.json`).
+`SaveAfterRunRun echo` speichert danach, was Java vom Echo im Projekt
+behält (`packages/sim/test/fixtures/after-run-echo.fls`).
+
+Gemessen (03.10.2026):
+
+* Server: „Starten“/„Anhalten“, Port 55555, das Feld nur angehalten
+  beschreibbar; ein Port, der keine Zahl ist, wirft
+  (`NumberFormatException`) und nichts geschieht.
+* Client: Adresse leer, Port 55555; „Verbinden“/„Trennen“; „Senden“ nur
+  verbunden, danach ist das Nachrichtenfeld leer; die Felder sind verbunden
+  gesperrt und zeigen nach jeder Zeile wieder die Werte des Programms.
+* Eine leere Nachricht geht als ein leeres Segment mit PSH hinaus
+  (`erstelleSegmente` macht mindestens eines) und kommt als „>>“, „<<“
+  zurück; Java beendet eine Nachricht mit jedem PSH, auch dem eines
+  wiederholten Segments.
+* Der angehaltene Server schließt die Verbindung („Socket zu … geschlossen“,
+  beim Client „Socket zu … getrennt“). Ein Port ohne Server endet in
+  „Zeitüberschreitung beim Verbindungsaufbau“, ein unbekannter Name in „Ziel
+  konnte nicht bestimmt werden!“.
+* Nach dem Lauf speichert Java den Port des Servers, dass er läuft, und
+  Adresse und Port, die der Client zuletzt nahm.

tools/java-oracle/run.sh

@@ -21,7 +21,7 @@ if [ ! -f "$upstream/target/filius.jar" ]; then
 fi
 classpath="$upstream/target/filius.jar:$upstream/target/lib/*"
 mkdir -p "$here/.build"
-javac -encoding UTF-8 -d "$here/.build" -cp "$classpath" "$here/src/FlsOracle.java" "$here/src/GetterDefaults.java" "$here/src/IpCheckCases.java" "$here/src/DnsHostsCases.java" "$here/src/EmailFileCases.java" "$here/src/BeansDump.java" "$here/src/Base64Cases.java" "$here/src/ScenarioNetwork.java" "$here/src/DhcpRun.java" "$here/src/TcpRun.java" "$here/src/DnsRun.java" "$here/src/ArpRun.java" "$here/src/RipRun.java" "$here/src/NatRun.java" "$here/src/WlanRun.java" "$here/src/ExampleRun.java" "$here/src/EchoRun.java" "$here/src/WebRun.java" "$here/src/RouterWebRun.java" "$here/src/KonfigCases.java" "$here/src/EmailRun.java" "$here/src/MailCases.java" "$here/src/EmailClientRun.java" "$here/src/TerminalCases.java" "$here/src/TerminalRun.java" "$here/src/FileCases.java" "$here/src/GnutellaRun.java" "$here/src/NewDeviceRun.java" "$here/src/SheetRun.java" "$here/src/TerminalWindowRun.java" "$here/src/InstallRun.java" "$here/src/BrowserWindowRun.java" "$here/src/MailWindowRun.java" "$here/src/SaveAfterRunRun.java" "$here/src/TextEditorWindowRun.java" "$here/src/FileExplorerWindowRun.java"
+javac -encoding UTF-8 -d "$here/.build" -cp "$classpath" "$here/src/FlsOracle.java" "$here/src/GetterDefaults.java" "$here/src/IpCheckCases.java" "$here/src/DnsHostsCases.java" "$here/src/EmailFileCases.java" "$here/src/BeansDump.java" "$here/src/Base64Cases.java" "$here/src/ScenarioNetwork.java" "$here/src/DhcpRun.java" "$here/src/TcpRun.java" "$here/src/DnsRun.java" "$here/src/ArpRun.java" "$here/src/RipRun.java" "$here/src/NatRun.java" "$here/src/WlanRun.java" "$here/src/ExampleRun.java" "$here/src/EchoRun.java" "$here/src/WebRun.java" "$here/src/RouterWebRun.java" "$here/src/KonfigCases.java" "$here/src/EmailRun.java" "$here/src/MailCases.java" "$here/src/EmailClientRun.java" "$here/src/TerminalCases.java" "$here/src/TerminalRun.java" "$here/src/FileCases.java" "$here/src/GnutellaRun.java" "$here/src/NewDeviceRun.java" "$here/src/SheetRun.java" "$here/src/TerminalWindowRun.java" "$here/src/InstallRun.java" "$here/src/BrowserWindowRun.java" "$here/src/MailWindowRun.java" "$here/src/SaveAfterRunRun.java" "$here/src/TextEditorWindowRun.java" "$here/src/FileExplorerWindowRun.java" "$here/src/EchoWindowRun.java"
 # FILIUS writes its settings below $HOME; keep them out of the real one.
 mkdir -p "$here/.build/home"
 # Removed first: a crashed run must not leave the previous result standing.
@@ -391,8 +391,9 @@ test -s "$output"
 
 # What a run leaves in FILIUS' project: an example started, a story played,
 # stopped as the design mode stops it and saved (SaveAfterRunRun): the room's
-# write-back into the document (packages/sim/test/writeBack.test.ts).
+# write-back into the document (packages/sim/test/writeBack.test.ts; echo:
-for run in email:email_komplett dhcp:einfaches_rechnernetz_komplett; do
+# packages/sim/test/echoWindow.test.ts).
+for run in email:email_komplett dhcp:einfaches_rechnernetz_komplett echo:email_komplett; do
     story="${run%%:*}"
     output="$root/packages/sim/test/fixtures/after-run-$story.fls"
     rm -f "$output"
@@ -421,6 +422,16 @@ HOME="$here/.build/home" xvfb-run -a java -Duser.language=de -Duser.country=DE -
     "$root/packages/core/test/scenarios/mail-lan.scenario.json" "$output" 2>&1 | grep -v 'logback\|^$\|^\s*at ' || true
 test -s "$output"
 
+# FILIUS' echo server and generic client windows used as a person does —
+# the port typed (also one that is no number), "Verbinden", "Senden" (also
+# nothing), the server stopped while connected, failures (EchoWindowRun): the
+# room's echo windows (packages/sim/test/echoWindow.test.ts).
+output="$root/packages/sim/test/echoWindow.java.json"
+rm -f "$output"
+HOME="$here/.build/home" xvfb-run -a java -Duser.language=de -Duser.country=DE -cp "$classpath:$here/.build" EchoWindowRun \
+    "$root/packages/core/test/scenarios/mail-lan.scenario.json" "$output" 2>&1 | grep -v 'logback\|^$\|^\s*at ' || true
+test -s "$output"
+
 # FILIUS' own examples as Java FILIUS runs them, opened and started as FILIUS
 # does (ExampleRun): the acceptance of F2 (packages/fls/test/examplesJava.test.ts)
 # and the classics of F3 (web, email, gnutella; packages/fls/test/classicsJava.test.ts).

tools/java-oracle/src/EchoWindowRun.java

@@ -0,0 +1,197 @@
+// Uses FILIUS' own echo server and generic client windows
+// (GUIApplicationServerBausteinWindow, GUIApplicationClientBausteinWindow on
+// their GUIDesktopPanels) on mail-lan's network as a person does: the
+// server's port field and start button, the client's address and port
+// fields, "Verbinden"/"Trennen", the message field and "Senden" — a port
+// that is no number too, an empty message, the server stopped while the
+// client is connected, a port nobody listens on, a name nobody knows. After
+// each step it writes what both windows show: the buttons' texts, the
+// fields (and whether they can be typed into), the lines. The reference for
+// the editor's echo windows (packages/sim/test/echoWindow.test.ts).
+//
+// Usage: java -cp filius.jar:lib/*:classes EchoWindowRun <scenario.json> <output json>
+
+import filius.gui.anwendungssicht.GUIApplicationClientBausteinWindow;
+import filius.gui.anwendungssicht.GUIApplicationServerBausteinWindow;
+import filius.gui.anwendungssicht.GUIDesktopPanel;
+import filius.software.system.Betriebssystem;
+
+import java.awt.FlowLayout;
+import java.io.FileOutputStream;
+import java.lang.reflect.Field;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import javax.swing.JButton;
+import javax.swing.JFrame;
+import javax.swing.JTextArea;
+import javax.swing.JTextField;
+import javax.swing.SwingUtilities;
+
+public class EchoWindowRun {
+    static final String CLIENT = "00000000-0000-0000-0000-000000000201";
+    static final String SERVER = "00000000-0000-0000-0000-000000000203";
+
+    static final List<Object> steps = new ArrayList<>();
+    static GUIApplicationServerBausteinWindow server;
+    static GUIApplicationClientBausteinWindow client;
+    /** Exceptions the windows' buttons threw on the event thread since the last step. */
+    static final List<String> thrown = new ArrayList<>();
+
+    static Object field(Class<?> owner, Object object, String name) throws Exception {
+        Field field = owner.getDeclaredField(name);
+        field.setAccessible(true);
+        return field.get(object);
+    }
+
+    static void onEdt(Runnable action) throws Exception {
+        SwingUtilities.invokeLater(() -> {
+            try {
+                action.run();
+            } catch (RuntimeException error) {
+                synchronized (thrown) {
+                    thrown.add(error.getClass().getSimpleName() + ": " + error.getMessage());
+                }
+            }
+        });
+        Thread.sleep(400);
+    }
+
+    static Map<String, Object> textField(JTextField field) {
+        Map<String, Object> shown = new LinkedHashMap<>();
+        shown.put("text", field.getText());
+        shown.put("editable", field.isEditable());
+        return shown;
+    }
+
+    static void step(String name) throws Exception {
+        Class<?> s = GUIApplicationServerBausteinWindow.class;
+        Class<?> c = GUIApplicationClientBausteinWindow.class;
+        Map<String, Object> result = new LinkedHashMap<>();
+        result.put("step", name);
+        Map<String, Object> serverShown = new LinkedHashMap<>();
+        serverShown.put("button", ((JButton) field(s, server, "bStartStop")).getText());
+        serverShown.put("port", textField((JTextField) field(s, server, "tfPort")));
+        serverShown.put("log", ((JTextArea) field(s, server, "taLog")).getText());
+        result.put("server", serverShown);
+        Map<String, Object> clientShown = new LinkedHashMap<>();
+        clientShown.put("connect", ((JButton) field(c, client, "btVerbinden")).getText());
+        clientShown.put("sendEnabled", ((JButton) field(c, client, "btSenden")).isEnabled());
+        clientShown.put("address", textField((JTextField) field(c, client, "tfServerAdresse")));
+        clientShown.put("port", textField((JTextField) field(c, client, "tfServerPort")));
+        clientShown.put("message", ((JTextArea) field(c, client, "taSenden")).getText());
+        clientShown.put("output", ((JTextArea) field(c, client, "taAusgabe")).getText());
+        result.put("client", clientShown);
+        synchronized (thrown) {
+            result.put("thrown", new ArrayList<>(thrown));
+            thrown.clear();
+        }
+        steps.add(result);
+    }
+
+    static void type(Class<?> owner, Object window, String name, String text) throws Exception {
+        Object component = field(owner, window, name);
+        onEdt(() -> ((javax.swing.text.JTextComponent) component).setText(text));
+    }
+
+    static void press(Class<?> owner, Object window, String name, long wait) throws Exception {
+        JButton button = (JButton) field(owner, window, name);
+        onEdt(button::doClick);
+        Thread.sleep(wait);
+    }
+
+    public static void main(String[] args) throws Exception {
+        try {
+            run(args);
+        } catch (Throwable error) {
+            error.printStackTrace();
+            System.exit(1);
+        }
+        System.exit(0);
+    }
+
+    static void run(String[] args) throws Exception {
+        ScenarioNetwork network = ScenarioNetwork.read(args[0]);
+        Betriebssystem serverSystem = (Betriebssystem) network.nodes.get(SERVER).getSystemSoftware();
+        Betriebssystem clientSystem = (Betriebssystem) network.nodes.get(CLIENT).getSystemSoftware();
+        serverSystem.installApp("filius.software.clientserver.ServerBaustein", false);
+        clientSystem.installApp("filius.software.clientserver.ClientBaustein", false);
+        network.start();
+        Thread.sleep(500);
+
+        JFrame frame = new JFrame();
+        GUIDesktopPanel serverDesktop = new GUIDesktopPanel(serverSystem);
+        GUIDesktopPanel clientDesktop = new GUIDesktopPanel(clientSystem);
+        frame.getContentPane().setLayout(new FlowLayout());
+        frame.getContentPane().add(serverDesktop);
+        frame.getContentPane().add(clientDesktop);
+        server = (GUIApplicationServerBausteinWindow) serverDesktop.starteAnwendung("filius.software.clientserver.ServerBaustein");
+        client = (GUIApplicationClientBausteinWindow) clientDesktop.starteAnwendung("filius.software.clientserver.ClientBaustein");
+        SwingUtilities.invokeAndWait(() -> {
+            frame.pack();
+            frame.setVisible(true);
+        });
+        Thread.sleep(500);
+        Class<?> s = GUIApplicationServerBausteinWindow.class;
+        Class<?> c = GUIApplicationClientBausteinWindow.class;
+        step("open");
+
+        type(s, server, "tfPort", "abc");
+        press(s, server, "bStartStop", 500);
+        step("server: start with port abc");
+        type(s, server, "tfPort", "55555");
+        press(s, server, "bStartStop", 1000);
+        step("server: start with port 55555");
+
+        type(c, client, "tfServerAdresse", "192.168.0.30");
+        type(c, client, "tfServerPort", "x");
+        press(c, client, "btVerbinden", 500);
+        step("client: connect with port x");
+        type(c, client, "tfServerAdresse", "192.168.0.30");
+        type(c, client, "tfServerPort", "55555");
+        press(c, client, "btVerbinden", 6000);
+        step("client: connect to 192.168.0.30:55555");
+        type(c, client, "taSenden", "Hallo Echo");
+        press(c, client, "btSenden", 4000);
+        step("client: send Hallo Echo");
+        type(c, client, "taSenden", "");
+        press(c, client, "btSenden", 4000);
+        step("client: send nothing");
+        type(c, client, "taSenden", "Zeile 1\nZeile 2");
+        press(c, client, "btSenden", 4000);
+        step("client: send two lines");
+
+        press(s, server, "bStartStop", 4000);
+        step("server: stop while connected");
+        type(c, client, "taSenden", "noch da?");
+        press(c, client, "btSenden", 8000);
+        step("client: send after the server stopped");
+        press(c, client, "btVerbinden", 3000);
+        step("client: Trennen");
+
+        press(s, server, "bStartStop", 1000);
+        step("server: start again");
+        press(c, client, "btVerbinden", 6000);
+        step("client: connect again");
+        press(c, client, "btVerbinden", 3000);
+        step("client: Trennen again");
+
+        type(c, client, "tfServerPort", "4711");
+        press(c, client, "btVerbinden", 12000);
+        step("client: connect to a port nobody listens on");
+        type(c, client, "tfServerAdresse", "gibtsnicht");
+        type(c, client, "tfServerPort", "55555");
+        press(c, client, "btVerbinden", 12000);
+        step("client: connect to a name nobody knows");
+
+        Map<String, Object> output = new LinkedHashMap<>();
+        output.put("steps", steps);
+        try (FileOutputStream out = new FileOutputStream(args[1])) {
+            out.write((FlsOracle.Json.write(output, "") + "\n").getBytes(StandardCharsets.UTF_8));
+        }
+        network.stop();
+        System.out.println("echo window steps: " + steps.size());
+    }
+}

tools/java-oracle/src/SaveAfterRunRun.java

@@ -18,11 +18,17 @@
 //          domain set to senior.org
 //   dhcp   einfaches_rechnernetz_komplett: the notebooks get their
 //          addresses from the server (10 s)
+//   echo   email_komplett, with FILIUS' echo server installed on Rechner 2
+//          and its client on Rechner 1 before the start: the server on port
+//          7777 (as its window sets it), the client connected to it, a
+//          message sent, the client left connected
 
 import filius.gui.GUIContainer;
 import filius.gui.netzwerksicht.GUIKnotenItem;
 import filius.hardware.knoten.Knoten;
 import filius.rahmenprogramm.SzenarioVerwaltung;
+import filius.software.clientserver.ClientBaustein;
+import filius.software.clientserver.ServerBaustein;
 import filius.software.email.Email;
 import filius.software.email.EmailAnwendung;
 import filius.software.email.EmailKonto;
@@ -93,6 +99,10 @@ public class SaveAfterRunRun {
         if (story.equals("email")) {
             ((Betriebssystem) system("Rechner 1")).installAndStartAppIfAvailable("filius.software.lokal.Terminal");
         }
+        if (story.equals("echo")) {
+            ((Betriebssystem) system("Rechner 2")).installAndStartAppIfAvailable("filius.software.clientserver.ServerBaustein");
+            ((Betriebssystem) system("Rechner 1")).installAndStartAppIfAvailable("filius.software.clientserver.ClientBaustein");
+        }
         network.start();
         Thread.sleep(2000);
         switch (story) {
@@ -130,6 +140,22 @@ public class SaveAfterRunRun {
             case "dhcp":
                 Thread.sleep(10000);
                 break;
+            case "echo": {
+                // GUIApplicationServerBausteinWindow's start button, then its client's "Verbinden" and "Senden".
+                ServerBaustein server = (ServerBaustein) system("Rechner 2").holeSoftware("filius.software.clientserver.ServerBaustein");
+                server.setPort(7777);
+                server.setAktiv(true);
+                server.setPort(7777);
+                Thread.sleep(1000);
+                ClientBaustein client = (ClientBaustein) system("Rechner 1").holeSoftware("filius.software.clientserver.ClientBaustein");
+                client.setZielIPAdresse(system("Rechner 2").primaryIPAdresse());
+                client.setZielPort(7777);
+                client.verbinden();
+                Thread.sleep(6000);
+                client.senden("Hallo");
+                Thread.sleep(4000);
+                break;
+            }
             default:
                 throw new IllegalArgumentException("unknown story " + story);
         }