fix(fls): Gnutella's peer limit is random in Java, not a default

PeerToPeerAnwendung's constructor rolls its peer limit (3, 4 or 5). The
getter defaults measured it once each run — 4, then 5 — and c48d15d
committed 5 as a default. GetterDefaults now constructs every class 64
times and writes a value that varies as {"random": [...]}; the decoder
answers a reference to it as unresolved, and the topology layer reports
a peer limit the file does not set as null.

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

packages/fls/src/javaDefaults.json

@@ -11,7 +11,13 @@
   "JSidebarButton#iconTextGap": 4,
   "JSidebarButton#verticalTextPosition": 3,
   "Notebook#maxLayerOfOperation": 4,
-  "PeerToPeerAnwendung#maxTeilnehmerZahl": 5,
+  "PeerToPeerAnwendung#maxTeilnehmerZahl": {
+    "random": [
+      "3",
+      "4",
+      "5"
+    ]
+  },
   "RIPServer#port": 520,
   "Rechner#maxLayerOfOperation": 4,
   "ServerBaustein#aktiv": false,

packages/fls/src/javabeans.ts

@@ -217,15 +217,30 @@ export function decodeXmlBytes(bytes: Uint8Array): string {
 // ── Decoder ────────────────────────────────────────────────────────────────
 
 const PRIMITIVE_ID_PREFIXES = new Set(['Integer', 'Boolean', 'Long', 'Short', 'Byte', 'Float', 'Double', 'Character']);
-const DEFAULTS = javaDefaults as Readonly<Record<string, string | number | boolean | null>>;
+type MeasuredValue = string | number | boolean | null;
+/** A value a constructor rolls at random: measured as the set of values seen, never a default. */
+type RandomValue = { random: string[] };
+const MEASURED = javaDefaults as Readonly<Record<string, MeasuredValue | RandomValue>>;
+
+/** The measured constant under `key`; undefined if nothing was measured or Java rolls it. */
+function measuredConstant(key: string): MeasuredValue | undefined {
+  if (!Object.hasOwn(MEASURED, key)) return undefined;
+  const value = MEASURED[key]!;
+  return typeof value === 'object' && value !== null ? undefined : value;
+}
+
+function isRandomInJava(key: string): boolean {
+  const value = MEASURED[key];
+  return typeof value === 'object' && value !== null;
+}
 
 /**
  * What a getter returns on a freshly constructed object of `simpleClass`, as
- * measured (javaDefaults.json) — undefined where nothing was measured.
+ * measured (javaDefaults.json) — undefined where nothing was measured or
+ * where Java's constructor rolls the value.
  */
 export function javaDefault(simpleClass: string, property: string): string | number | boolean | null | undefined {
-  const key = `${simpleClass}#${property}`;
+  return measuredConstant(`${simpleClass}#${property}`);
-  return Object.hasOwn(DEFAULTS, key) ? DEFAULTS[key] : undefined;
 }
 
 /** `getFoo`/`isFoo` → `foo`, as java.beans.Introspector derives it. */
@@ -356,7 +371,8 @@ class Decoder {
       // A static constant: XMLEncoder writes a shared Integer 0 as
       // SwingConstants.CENTER when that was the first 0 it met.
       const constantKey = `${simpleClassName(className)}.${attributes.field}`;
-      if (Object.hasOwn(DEFAULTS, constantKey)) return this.primitive(element, DEFAULTS[constantKey]!);
+      const constant = measuredConstant(constantKey);
+      if (constant !== undefined) return this.primitive(element, constant);
     }
     const args = element.children.filter((child) => child.name !== 'void');
     const object = newObject({
@@ -457,7 +473,9 @@ class Decoder {
     }
     if (target.properties.has(property)) return target.properties.get(property)!;
     const defaultKey = `${simpleClassName(target.className)}#${property}`;
-    if (Object.hasOwn(DEFAULTS, defaultKey)) return DEFAULTS[defaultKey]!;
+    const measured = measuredConstant(defaultKey);
+    if (measured !== undefined) return measured;
+    if (isRandomInJava(defaultKey)) return { kind: 'unresolved', reason: `${defaultKey} is random in Java` };
     const prefix = id?.replace(/\d+$/, '');
     if (prefix !== undefined && PRIMITIVE_ID_PREFIXES.has(prefix)) {
       return { kind: 'unresolved', reason: `no measured default for ${defaultKey}` };

packages/fls/src/systemSoftware.ts

@@ -129,8 +129,11 @@ export interface FlsApplication {
   recursiveResolutionEnabled?: boolean;
   /** WebServer: serve by host name (Java's useVHost). */
   useVirtualHosts?: boolean;
-  /** PeerToPeerAnwendung: how many peers it keeps (Java's maxTeilnehmerZahl). */
+  /**
-  maxPeers?: number;
+   * PeerToPeerAnwendung: how many peers it keeps (Java's maxTeilnehmerZahl);
+   * null when the file has none — Java's constructor rolls 3, 4 or 5.
+   */
+  maxPeers?: number | null;
   /** Firewall: the personal firewall. */
   firewall?: FlsFirewall;
   /** The application's JavaBean, for the e-mail layer. */
@@ -269,7 +272,8 @@ function applications(map: JavaValue | undefined, warn: Warn): FlsApplication[]
         entry.useVirtualHosts = boolean(at('useVHost'), measured('useVHost') === true, 'WebServer useVHost', warn);
         break;
       case 'filius.software.dateiaustausch.PeerToPeerAnwendung':
-        entry.maxPeers = integer(at('maxTeilnehmerZahl'), Number(measured('maxTeilnehmerZahl')), 'Gnutella peers', warn);
+        entry.maxPeers =
+          at('maxTeilnehmerZahl') === undefined ? null : integer(at('maxTeilnehmerZahl'), 0, 'Gnutella peers', warn);
         break;
       case 'filius.software.firewall.Firewall':
         entry.firewall = firewallOf([application], true, warn);

packages/fls/test/javabeans.test.ts

@@ -240,6 +240,17 @@ describe('XMLDecoder rules', () => {
     expect(isUnresolved(listItems(holder)[0])).toBe(true);
   });
 
+  it('does not take a value Java rolls in its constructor as a default', () => {
+    // Gnutella's peer limit is 3, 4 or 5 at random (measured by constructing it 64 times).
+    const [, holder] = decodeJavaBeans(
+      doc(`<object class="filius.software.dateiaustausch.PeerToPeerAnwendung"><void id="Integer0" property="maxTeilnehmerZahl"/></object>
+           <object class="java.util.ArrayList"><void method="add"><object idref="Integer0"/></void></object>`),
+    );
+
+    const [item] = listItems(holder);
+    expect(item).toEqual({ kind: 'unresolved', reason: 'PeerToPeerAnwendung#maxTeilnehmerZahl is random in Java' });
+  });
+
   it('reports an idref to an id that was never defined', () => {
     const [value] = decodeJavaBeans(doc('<object idref="Missing0"/>'));
 

packages/fls/test/topology.test.ts

@@ -416,7 +416,8 @@ describe('readTopology rules', () => {
 
     expect(byClass.get('filius.software.www.WebServer')).toMatchObject({ isActive: false, port: 80, useVirtualHosts: false });
     expect(byClass.get('filius.software.clientserver.ClientBaustein')).toMatchObject({ targetAddress: null, targetPort: 55_555 });
-    expect(byClass.get('filius.software.dateiaustausch.PeerToPeerAnwendung')).toMatchObject({ maxPeers: 4 });
+    // Java rolls it: no default.
+    expect(byClass.get('filius.software.dateiaustausch.PeerToPeerAnwendung')).toMatchObject({ maxPeers: null });
     expect(byClass.get('filius.software.firewall.Firewall')?.firewall).toMatchObject({ activated: true, defaultPolicy: 0 });
     expect(byClass.get('filius.software.dns.DNSServer')).toMatchObject({ isActive: true, port: 5353, recursiveResolutionEnabled: false });
     expect(Object.keys(byClass.get('filius.software.lokal.Terminal')!).sort()).toEqual(['javaClass', 'key', 'source']);

tools/java-oracle/src/GetterDefaults.java

@@ -34,12 +34,20 @@ public class GetterDefaults {
             String property = key.substring(key.indexOf('#') + 1);
             String simpleName = className.substring(className.lastIndexOf('.') + 1);
             try {
-                Object value = className.equals("java.lang.ThreadGroup")
+                // Constructed many times: a constructor may roll its value (Gnutella's
-                        // A Thread's uncaughtExceptionHandler is its group; XMLDecoder runs
+                // peer limit is 3, 4 or 5 at random). Such a value is no default and is
-                        // in the main thread, so that is the group asked.
+                // written as {"random": [the values seen]}.
-                        ? read(Thread.currentThread().getThreadGroup(), property)
+                java.util.TreeSet<String> seen = new java.util.TreeSet<>();
-                        : read(Class.forName(className).getDeclaredConstructor().newInstance(), property);
+                Object value = null;
-                result.put(simpleName + "#" + property, value);
+                for (int attempt = 0; attempt < 64; attempt++) {
+                    value = className.equals("java.lang.ThreadGroup")
+                            // A Thread's uncaughtExceptionHandler is its group; XMLDecoder runs
+                            // in the main thread, so that is the group asked.
+                            ? read(Thread.currentThread().getThreadGroup(), property)
+                            : read(Class.forName(className).getDeclaredConstructor().newInstance(), property);
+                    seen.add(String.valueOf(value));
+                }
+                result.put(simpleName + "#" + property, seen.size() == 1 ? value : Map.of("random", new java.util.ArrayList<>(seen)));
             } catch (Throwable error) {
                 Throwable cause = error.getCause() != null ? error.getCause() : error;
                 result.put(simpleName + "#" + property, Map.of("error", cause.toString()));