feat(fls): DNS records from /dns/hosts, as Java's server answers them

Java's DNS server reads its records from the text file /dns/hosts on every
query. dnsHosts.ts ports that reading (DNSServer.leseRecordListe,
ResourceRecord, Dateisystem.holeDatei) and keeps in the model the records
Java answers: type exactly A, MX or NS, and a name Java accepted. The file
stays in the file system as it is.

Both oracles read 76 hand-picked hosts files (dns-hosts.cases.txt): the
Java oracle through DNSServer.holeResourceRecords (DnsHostsCases), the
Swift oracle through TopologyDNSHostsFileCodec (--dns-hosts). The Java view
matches Java on every case; the model matches Swift except for 33 named
cases in twelve reasons: Java splits at single spaces and LF only, has no
comments or "IN", turns a TTL that is no int into 3600, keeps duplicates,
and empties names with a leading digit. The Swift dump now carries each
server's records; the corpus comparison covers them on 16 files.

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

tools/java-oracle/README.md

@@ -64,3 +64,16 @@ Java-Filius schickt jede IP-Adresse und Maske beim Laden durch
 zählen nicht (`10..0.0.1`), Vorzeichen und führende Nullen gehen, ebenso
 Ziffern jeder Schrift in der BMP (Thai, Devanagari, Vollbreite) — aber kein
 Leerzeichen und kein 𝟏 (Ersatzpaar).
+
+## `/dns/hosts`
+
+Javas DNS-Server liest seine Einträge bei jeder Anfrage aus der Textdatei
+`/dns/hosts`. `DnsHostsCases` legt für jede Zeile von
+`packages/fls/test/dns-hosts.cases.txt` (eine ganze Datei je Zeile, ASCII,
+Zeilenumbruch als `\u000A`) einen Rechner mit dieser Datei an und schreibt,
+was `DNSServer.holeResourceRecords()` liefert, nach `dns-hosts.java.json`.
+Gemessen: Felder trennt nur ein einzelnes Leerzeichen (Tab und NBSP nicht),
+Zeilen nur LF; ein Name, den Javas Muster ablehnt (`1und1.de`, `müller.de`),
+wird leer, der Eintrag bleibt trotzdem; Typen außer A/MX/NS (auch `a`,
+`CNAME`, eine Kommentarzeile) gelten als gültig; eine TTL, die kein `int`
+ist, wird still 3600.

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" "$here/src/IpCheckCases.java"
+javac -encoding UTF-8 -d "$here/.build" -cp "$classpath" "$here/src/FlsOracle.java" "$here/src/GetterDefaults.java" "$here/src/IpCheckCases.java" "$here/src/DnsHostsCases.java"
 # 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.
@@ -66,3 +66,10 @@ ipcheck="$root/packages/fls/test/ip-check.java.json"
 rm -f "$ipcheck"
 HOME="$here/.build/home" java -cp "$classpath:$here/.build" IpCheckCases "$cases" "$ipcheck" 2>&1 | grep -v 'logback\|^$' || true
 test -s "$ipcheck"
+
+# DNSServer's own reading of /dns/hosts on hand-picked files (packages/fls/src/dnsHosts.ts).
+cases="$root/packages/fls/test/dns-hosts.cases.txt"
+dnshosts="$root/packages/fls/test/dns-hosts.java.json"
+rm -f "$dnshosts"
+HOME="$here/.build/home" xvfb-run -a java -cp "$classpath:$here/.build" DnsHostsCases "$cases" "$dnshosts" 2>&1 | grep -v 'logback\|^$' || true
+test -s "$dnshosts"

tools/java-oracle/src/DnsHostsCases.java

@@ -0,0 +1,50 @@
+// Runs FILIUS's own reading of /dns/hosts (DNSServer.holeResourceRecords)
+// on every case of a list and writes the records Java keeps — the reference
+// for packages/fls/src/dnsHosts.ts. One case per line: a whole hosts file,
+// ASCII with Java-style unicode escapes (backslash, u, four hex digits), so
+// line breaks and odd spaces survive editors and hooks.
+//
+// Usage: java -cp filius.jar:lib/*:classes DnsHostsCases <cases txt> <output json>
+
+import filius.hardware.knoten.Rechner;
+import filius.software.dns.DNSServer;
+import filius.software.dns.ResourceRecord;
+import filius.software.system.Datei;
+import filius.software.system.Dateisystem;
+import filius.software.system.InternetKnotenBetriebssystem;
+
+import java.io.FileOutputStream;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class DnsHostsCases {
+
+    public static void main(String[] args) throws Exception {
+        List<Object> result = new ArrayList<>();
+        for (String line : Files.readAllLines(Path.of(args[0]), StandardCharsets.US_ASCII)) {
+            InternetKnotenBetriebssystem system = (InternetKnotenBetriebssystem) new Rechner().getSystemSoftware();
+            Dateisystem fileSystem = system.getDateisystem();
+            fileSystem.erstelleVerzeichnis(fileSystem.getRoot(), "dns");
+            Datei hosts = new Datei();
+            hosts.setName("hosts");
+            hosts.setDateiInhalt(IpCheckCases.unescape(line));
+            fileSystem.speicherDatei(fileSystem.holeRootPfad() + Dateisystem.FILE_SEPARATOR + "dns", hosts);
+            DNSServer server = new DNSServer();
+            server.setSystemSoftware(system);
+            List<Object> records = new ArrayList<>();
+            for (ResourceRecord record : server.holeResourceRecords()) {
+                records.add(Arrays.asList(record.getDomainname(), record.getType(), record.getTtl(), record.getRdata()));
+            }
+            result.add(Arrays.asList(line, records));
+        }
+        try (FileOutputStream out = new FileOutputStream(args[1])) {
+            out.write((FlsOracle.Json.write(result, "") + "\n").getBytes(StandardCharsets.UTF_8));
+        }
+        System.out.println("dns hosts cases: " + result.size());
+        System.exit(0);
+    }
+}