feat(fls): write the file systems of a .fls, loaded by Java as the original

topologyWriter.ts adds each node's file tree to the root its constructor
makes, as XMLEncoder does (arbeitsVerzeichnis, files as new Datei(name,
typ, inhalt)); a root of its own is set anew.

The reader now reads the files of routers and home routers too: their
constructor makes files from templates (the web interface), and the file
adds to them (a web server's www.conf). systemSoftware.ts keeps what the
file adds, and templateFiles says whether the constructor's files stay in
front (false when the file sets a root of its own). The topology test finds
our part at the end of Java's tree and the template in front, the same for
every router of a class across the corpus.

Checked by Java against Java: every corpus file, read and written again,
loads with the same file systems as the original. The synthetic topology
adds a nested tree with a renamed root, a nameless directory, a file
without type, content with CR, CRLF and beyond-BMP characters, router files
after the template and a home router with a root of its own. 9 mutation
probes, each loaded by Java, were all caught.

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

packages/fls/src/systemSoftware.ts

@@ -11,11 +11,12 @@
 // table (port forwarding) and a modem's connection settings.
 // Java counterparts as well: filius.software.dhcp.DHCPServer, ModemFirmware.
 //
-// And the file system of a PC or notebook: Java's tree of
-// DefaultMutableTreeNodes, a directory's user object its name, a file's a
-// filius.software.system.Datei. Routers and home routers have files too, but
-// Java's constructor makes them from its own templates (the start page of
-// the firewall's web interface); they are not in the file.
+// And the file system: Java's tree of DefaultMutableTreeNodes, a
+// directory's user object its name, a file's a filius.software.system.Datei.
+// A PC's or notebook's constructor leaves the root empty. A router's or home
+// router's makes files from its own templates (the start page of the
+// firewall's web interface), which are not in the file; what the file adds
+// to that root (a web server's www.conf) comes after them.
 //
 // Checked against Java (corpus.java.json, `system`). Applications are a
 // later layer.
@@ -198,8 +199,17 @@ export interface FlsSystemSoftware {
   modem?: FlsModem;
   /** Rechner, Notebook: the installed applications, in the file's order. */
   applications?: FlsApplication[];
-  /** Rechner, Notebook: the root directory (named "root" by Java's constructor). */
+  /**
+   * Every node with an IP stack: the root directory (named "root" by Java's
+   * constructor) as the file has it. A router's or home router's holds only
+   * what the file adds to the constructor's, see `templateFiles`.
+   */
   fileSystem?: FlsFileTree;
+  /**
+   * Vermittlungsrechner, Gateway: whether the files the constructor makes
+   * stay in front of the file's — false when the file sets a root of its own.
+   */
+  templateFiles?: boolean;
 }
 
 type Warn = (message: string) => void;
@@ -231,6 +241,10 @@ export function readSystemSoftware(device: JavaObject, javaClass: FlsNodeClass,
     case 'Modem':
       break;
   }
+  if (javaClass === 'Vermittlungsrechner' || javaClass === 'Gateway') {
+    result.fileSystem = fileSystem(value('dateisystem'), warn);
+    result.templateFiles = constructedRoot(value('dateisystem'));
+  }
   if (javaClass !== 'Switch' && javaClass !== 'Modem') {
     result.manualRoutes = manualRoutes(value('weiterleitungstabelle'), warn);
     result.dhcpClient = boolean(value('DHCPKonfiguration'), false, 'DHCPKonfiguration', warn);
@@ -343,12 +357,23 @@ function applications(map: JavaValue | undefined, root: FlsFileTree, warn: Warn)
  * file makes with `new DefaultMutableTreeNode()` has no user object.
  */
 function fileSystem(system: JavaValue | undefined, warn: Warn): FlsFileTree {
-  const at = (property: string) => (isJavaObject(system) ? system.properties.get(property) : undefined);
-  const root = at('root') ?? at('arbeitsVerzeichnis');
+  const root = fileSystemRoot(system);
   if (root === undefined) return { kind: 'directory', name: 'root', children: [] };
   return fileTreeNode(root, true, warn);
 }
 
+function fileSystemRoot(system: JavaValue | undefined): JavaValue | undefined {
+  const at = (property: string) => (isJavaObject(system) ? system.properties.get(property) : undefined);
+  return at('root') ?? at('arbeitsVerzeichnis');
+}
+
+/** Whether the root is the one the constructor made: none set, or reached through the getter. */
+function constructedRoot(system: JavaValue | undefined): boolean {
+  if (system !== undefined && !(isJavaObject(system) && system.fromGetter)) return false;
+  const root = fileSystemRoot(system);
+  return root === undefined || (isJavaObject(root) && root.fromGetter);
+}
+
 function fileTreeNode(node: JavaValue, constructorRoot: boolean, warn: Warn): FlsFileTree {
   if (!isJavaObject(node)) {
     warn(`file system: a node is ${describe(node)}, left empty`);

packages/fls/src/topologyWriter.ts

@@ -12,8 +12,9 @@
 // are set through getters. A router's or home router's firewall is reached
 // the way XMLEncoder reaches it: through the web server's `konfig` plug-in,
 // which holds the same object (its key among the installed applications
-// differs: Firewall on a router, NatGateway on a home router). Files and
-// applications are later layers.
+// differs: Firewall on a router, NatGateway on a home router). Files are
+// added to the constructor's root, as XMLEncoder adds them — on a router
+// after the files its constructor makes. Applications are a later layer.
 //
 // Checked by Java: every corpus file, read and written again, loads in Java
 // FILIUS to the same topology and system software (topologyWriter.test.ts,
@@ -31,14 +32,14 @@ import {
   type BeanValue,
   short,
 } from './javaBeansWriter.js';
-import type { FlsFirewall, FlsSystemSoftware } from './systemSoftware.js';
+import type { FlsFileTree, FlsFirewall, FlsSystemSoftware } from './systemSoftware.js';
 import type { FlsDocumentationItem, FlsInterface, FlsLink, FlsNode, FlsNodeClass } from './topology.js';
 
 /** The version line of the files this writer makes: the format of FILIUS 2.14. */
 export const WRITTEN_VERSION_LINE = 'Filius version: 2.14.0 (mdg-filius)';
 
-/** The system software's settings; its files and applications are later layers. */
-export type SystemToWrite = Omit<FlsSystemSoftware, 'fileSystem' | 'applications'>;
+/** The system software's settings and files; its applications are a later layer. */
+export type SystemToWrite = Omit<FlsSystemSoftware, 'applications'>;
 
 export type NodeToWrite = Pick<
   FlsNode,
@@ -165,6 +166,7 @@ function systemStatements(system: SystemToWrite, javaClass: FlsNodeClass): BeanS
       ],
     });
   }
+  if (system.fileSystem !== undefined) statements.push(fileSystemStatement(system.fileSystem, system.templateFiles !== false));
   if (system.dhcpServer !== undefined) {
     const server = system.dhcpServer;
     statements.push({
@@ -205,6 +207,35 @@ function systemStatements(system: SystemToWrite, javaClass: FlsNodeClass): BeanS
   return statements;
 }
 
+/**
+ * The file system: the root's children added to the constructor's root
+ * (named "root", empty on a PC or notebook), or a root of its own that
+ * replaces it with the files a router's constructor makes. `arbeitsVerzeichnis`
+ * is the property Java writes; `root` names the same field.
+ */
+function fileSystemStatement(root: FlsFileTree, constructedRoot: boolean): BeanStatement {
+  if (!constructedRoot) return { get: 'dateisystem', statements: [{ set: 'arbeitsVerzeichnis', value: treeNode(root) }] };
+  const statements: BeanStatement[] = [];
+  if (!(root.kind === 'directory' && root.name === 'root')) statements.push({ set: 'userObject', value: userObject(root) });
+  statements.push(...childStatements(root));
+  return { get: 'dateisystem', statements: [{ get: 'arbeitsVerzeichnis', statements }] };
+}
+
+function childStatements(tree: FlsFileTree): BeanStatement[] {
+  return tree.children.map((child) => ({ call: 'add', args: [treeNode(child)] }));
+}
+
+/** A DefaultMutableTreeNode; one of another kind than directory or file is written without a user object. */
+function treeNode(tree: FlsFileTree): BeanObject {
+  return object('javax.swing.tree.DefaultMutableTreeNode', childStatements(tree), tree.kind === 'other' ? [] : [userObject(tree)]);
+}
+
+/** A directory's name, or a file as `new Datei(name, typ, inhalt)`. */
+function userObject(tree: FlsFileTree): BeanValue {
+  if (tree.kind === 'file') return object('filius.software.system.Datei', [], [tree.name, tree.type, tree.content]);
+  return tree.kind === 'directory' ? tree.name : null;
+}
+
 /** A LinkedList of String arrays: routes, static NAT. */
 function rows(table: readonly (readonly (string | null)[])[]): BeanObject {
   return listOf(table.map((row) => ({ kind: 'array', componentClass: 'java.lang.String', items: [...row] })));

packages/fls/test/topology.test.ts

@@ -168,6 +168,7 @@ function asJavaView(topology: FlsTopology, javaBounds: (number[] | null)[]) {
             }),
         ...(node.system.modem === undefined ? {} : { modem: javaModem(node.system.modem) }),
         ...(node.system.fileSystem === undefined ? {} : { fileSystem: javaFileTree(node.system.fileSystem) }),
+        ...('templateFiles' in node.system ? { templateFiles: undefined } : {}),
         ...(node.system.applications === undefined ? {} : { applications: javaApplications(node.system.applications) }),
         ...(node.system.firewall === undefined
           ? {}
@@ -202,19 +203,33 @@ function asJavaView(topology: FlsTopology, javaBounds: (number[] | null)[]) {
   };
 }
 
+type JavaTree = { children: unknown[] };
+
 /**
- * Java's view without the file systems of routers and home routers: their
- * files come from Java's constructor (templates of the firewall's web
- * interface), not from the .fls file, and the reader does not claim them.
+ * The files a router's or home router's constructor makes, as Java loaded
+ * each one: they come first in its root, what the file adds follows. Each
+ * router's are cut off here and collected, and must be the same for every
+ * router of a class across the corpus.
  */
-function withoutTemplateFiles(view: unknown): unknown {
+const templateChildren = new Map<string, Set<string>>();
+
+function withoutTemplateFiles(view: unknown, topology: FlsTopology): unknown {
   const { nodes, ...rest } = view as { nodes: { class: string; system: Record<string, unknown> }[] };
   return {
     ...rest,
-    nodes: nodes.map((node) => {
-      if (node.class !== 'Vermittlungsrechner' && node.class !== 'Gateway') return node;
-      const { fileSystem: _templateFiles, ...system } = node.system;
-      return { ...node, system };
+    nodes: nodes.map((node, index) => {
+      const ours = topology.nodes[index]?.system;
+      if ((node.class !== 'Vermittlungsrechner' && node.class !== 'Gateway') || ours?.templateFiles !== true) return node;
+      const tree = node.system.fileSystem as JavaTree;
+      const added = ours.fileSystem?.children.length ?? 0;
+      const template = tree.children.slice(0, tree.children.length - added);
+      const seen = templateChildren.get(node.class) ?? new Set<string>();
+      seen.add(JSON.stringify(template));
+      templateChildren.set(node.class, seen);
+      return {
+        ...node,
+        system: { ...node.system, fileSystem: { ...tree, children: tree.children.slice(tree.children.length - added) } },
+      };
     }),
   };
 }
@@ -227,10 +242,18 @@ describe('corpus: the topology as Java loads it', () => {
       const topology = readTopology(values);
       const expected = javaView[name] as { nodes: { bounds: number[] | null }[] };
 
-      expect(asJavaView(topology, expected.nodes.map((node) => node.bounds))).toEqual(withoutTemplateFiles(expected));
+      expect(asJavaView(topology, expected.nodes.map((node) => node.bounds))).toEqual(withoutTemplateFiles(expected, topology));
       expect(topology.warnings).toEqual(EXPECTED_WARNINGS[name] ?? []);
     });
   }
+
+  it("a router's constructor makes the same files in every corpus file", () => {
+    for (const javaClass of ['Vermittlungsrechner', 'Gateway']) {
+      const templates = [...(templateChildren.get(javaClass) ?? [])].map((text) => JSON.parse(text) as { directory?: string }[]);
+      expect(templates, javaClass).toHaveLength(1);
+      expect(templates[0]!.map((child) => child.directory), javaClass).toEqual(['webserver']);
+    }
+  });
 });
 
 // ── Rules the corpus does not exercise ─────────────────────────────────────
@@ -433,6 +456,30 @@ describe('readTopology rules', () => {
     expect(warnings).toEqual(['node 2: file system: insert on a node is not read']);
   });
 
+  it("reads what a router's file adds to the constructor's files, or a root of its own", () => {
+    const folder = (name: string) =>
+      `<void method="add"><object class="javax.swing.tree.DefaultMutableTreeNode"><string>${name}</string></object></void>`;
+    const { nodes } = topologyOf(`<object class="java.util.LinkedList">
+        ${nodeItem('<object class="filius.hardware.knoten.Vermittlungsrechner"/>')}
+        ${nodeItem(`<object class="filius.hardware.knoten.Gateway"><void property="systemSoftware"><void property="dateisystem">
+          <void property="arbeitsVerzeichnis">${folder('www.conf')}</void>
+        </void></void></object>`)}
+        ${nodeItem(`<object class="filius.hardware.knoten.Vermittlungsrechner"><void property="systemSoftware"><void property="dateisystem">
+          <void property="arbeitsVerzeichnis"><object class="javax.swing.tree.DefaultMutableTreeNode"><string>root</string>${folder('own')}</object></void>
+        </void></void></object>`)}
+        ${nodeItem(`<object class="filius.hardware.knoten.Gateway"><void property="systemSoftware">
+          <void property="dateisystem"><object class="filius.software.system.Dateisystem"/></void>
+        </void></object>`)}</object>`);
+    const directory = (name: string, children: FlsFileTree[] = []): FlsFileTree => ({ kind: 'directory', name, children });
+
+    expect(nodes.map((node) => [node.system.fileSystem, node.system.templateFiles])).toEqual([
+      [directory('root'), true],
+      [directory('root', [directory('www.conf')]), true],
+      [directory('root', [directory('own')]), false],
+      [directory('root'), false],
+    ]);
+  });
+
   it("gives installed applications Java's measured defaults for what the file leaves out", () => {
     const put = (className: string, body = '') =>
       `<void method="put"><string>${className}</string><object class="${className}">${body}</object></void>`;

packages/fls/test/topologyWriter.test.ts

@@ -1,7 +1,7 @@
 // Every corpus file, read and written again: Java FILIUS loads the written
 // file (tools/java-oracle, written.java.json) to the same topology as the
 // original (corpus.java.json) — devices, names, positions, interfaces,
-// system software (without files and applications), cables and
+// system software and files (without applications), cables and
 // documentation. Java against Java: no mapping of this package stands
 // between the two.
 //
@@ -43,9 +43,9 @@ type JavaFile = { success: boolean; nodes: JavaNode[]; cables: unknown[]; docume
 const original = JSON.parse(readFileSync(join(corpusRoot, 'corpus.java.json'), 'utf8')) as Record<string, JavaFile>;
 const written = JSON.parse(readFileSync(join(here, 'written.java.json'), 'utf8')) as Record<string, JavaFile>;
 
-/** The system software without its files and applications, which are later layers. */
+/** The system software without its applications, which are a later layer. */
 function systemOf(system: Record<string, unknown>) {
-  const { fileSystem: _files, applications: _applications, ...settings } = system;
+  const { applications: _applications, ...settings } = system;
   return settings;
 }
 
@@ -89,6 +89,9 @@ describe('the topology written again, as Java loads it', () => {
   }
 });
 
+/** Text a file's content may hold: markup, CR and CRLF, a tab, beyond the BMP. */
+const FILE_CONTENT = '<p>a & b</p>\r\nline\rend\ttab Grüße 😀\n';
+
 /**
  * What the corpus does not have: a name set to null, useMACAsName, fewer
  * ports than the constructor makes, more interfaces; a PC's SSID, routes and
@@ -120,6 +123,21 @@ const SYNTHETIC: TopologyToWrite = {
           useOwnSettings: true,
           staticAssignedAddresses: [{ mac: 'AA:BB:CC:DD:EE:77', ip: '10.0.0.77' }],
         },
+        fileSystem: {
+          kind: 'directory',
+          name: '/',
+          children: [
+            {
+              kind: 'directory',
+              name: 'docs',
+              children: [
+                { kind: 'file', name: 'a.txt', type: 'text', content: FILE_CONTENT, children: [] },
+                { kind: 'directory', name: null, children: [] },
+              ],
+            },
+            { kind: 'file', name: 'untyped', type: null, content: null, children: [] },
+          ],
+        },
       },
     },
     {
@@ -150,6 +168,8 @@ const SYNTHETIC: TopologyToWrite = {
       portCount: 3,
       system: {
         ripEnabled: true,
+        fileSystem: { kind: 'directory', name: 'root', children: [{ kind: 'directory', name: 'www.conf', children: [] }] },
+        templateFiles: true,
         firewall: {
           activated: true,
           defaultPolicy: 1,
@@ -176,6 +196,26 @@ const SYNTHETIC: TopologyToWrite = {
       portCount: 1,
       system: { modem: { mode: 1, port: 4242, ipAddress: '192.168.1.5' } },
     },
+    {
+      javaClass: 'Gateway',
+      name: 'G',
+      x: 400,
+      y: 20,
+      useIpAsName: false,
+      useMacAsName: false,
+      interfaces: ['4', '5'].map((octet) => ({
+        ip: `10.0.${octet}.1`,
+        mask: '255.255.255.0',
+        mac: `AA:BB:CC:DD:EE:1${octet}`,
+        gateway: '',
+        dns: '',
+      })),
+      portCount: 2,
+      system: {
+        fileSystem: { kind: 'directory', name: 'own', children: [{ kind: 'file', name: 'x', type: 'text', content: 'y', children: [] }] },
+        templateFiles: false,
+      },
+    },
   ],
   links: [
     { ends: [{ node: 0, port: 0 }, { node: 1, port: 2 }], wireless: false, panel: [0, 1] },
@@ -195,6 +235,28 @@ const JAVA_DHCP_DEFAULTS = {
   staticAssignedAddresses: [],
 };
 
+/** A file as the oracle describes it: its content as UTF-16 length and SHA-256 of its UTF-8 bytes. */
+function javaFile(name: string, type: string | null, content: string | null) {
+  return {
+    file: name,
+    type,
+    length: content === null ? null : content.length,
+    sha256: content === null ? null : createHash('sha256').update(content, 'utf8').digest('hex'),
+    children: [],
+  };
+}
+
+/** The files a router's constructor makes, as Java loaded them from the corpus. */
+function routerTemplate(): unknown[] {
+  const router = Object.values(original)
+    .flatMap((file) => file.nodes ?? [])
+    .find((node) => node.class === 'Vermittlungsrechner');
+  return ((router!.system.fileSystem as { children: unknown[] }).children).slice(0, 1);
+}
+
+/** A router's firewall as its constructor leaves it. */
+const JAVA_ROUTER_FIREWALL = { activated: false, defaultPolicy: 0, dropICMP: false, filterSYNSegmentsOnly: true, filterUdp: true, rules: [] };
+
 describe('a topology beyond the corpus, as Java loads it', () => {
   it('keeps what the corpus never sets', () => {
     const name = 'synthetic/synthetic.fls';
@@ -231,6 +293,13 @@ describe('a topology beyond the corpus, as Java loads it', () => {
               ownSettings: true,
               staticAssignedAddresses: ['AA:BB:CC:DD:EE:77 10.0.0.77'],
             },
+            fileSystem: {
+              directory: '/',
+              children: [
+                { directory: 'docs', children: [javaFile('a.txt', 'text', FILE_CONTENT), { directory: null, children: [] }] },
+                javaFile('untyped', null, null),
+              ],
+            },
           },
         },
         {
@@ -251,6 +320,7 @@ describe('a topology beyond the corpus, as Java loads it', () => {
           ports: ['1', '2', '3'].map(plainInterface),
           system: {
             ripEnabled: true,
+            fileSystem: { directory: 'root', children: [...routerTemplate(), { directory: 'www.conf', children: [] }] },
             manualRoutes: [],
             dhcpClient: false,
             dhcpServer: JAVA_DHCP_DEFAULTS,
@@ -278,6 +348,22 @@ describe('a topology beyond the corpus, as Java loads it', () => {
           ports: [{}],
           system: { modem: { mode: 1, port: 4242, ipAdresse: '192.168.1.5' } },
         },
+        {
+          class: 'Gateway',
+          name: 'G',
+          position: [400, 20],
+          useIpAsName: undefined,
+          useMacAsName: undefined,
+          ports: ['4', '5'].map(plainInterface),
+          system: {
+            fileSystem: { directory: 'own', children: [javaFile('x', 'text', 'y')] },
+            manualRoutes: [],
+            dhcpClient: false,
+            dhcpServer: JAVA_DHCP_DEFAULTS,
+            staticNAT: [],
+            firewall: JAVA_ROUTER_FIREWALL,
+          },
+        },
       ],
       cables: [
         { ends: [[0, 0], [1, 2]], wireless: false, panel: [0, 1] },