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>
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Claude Opus 5.5
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// Java's reading of /dns/hosts (DNSServer.leseRecordListe): every case in
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// dns-hosts.cases.txt was run through Java (dns-hosts.java.json) and through
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// Swift's hosts-file codec (dns-hosts.swift.json, tools/swift-oracle). The
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// Java view must match Java exactly; the records the model keeps must match
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// Swift except where Java answers differently — each case named below.
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import { readFileSync } from 'node:fs';
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import { dirname, join } from 'node:path';
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import { fileURLToPath } from 'node:url';
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import { describe, expect, it } from 'vitest';
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import type { FlsFileTree } from '../src/index.js';
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import { dnsRecordsOf, javaHostsFileContent, readJavaDnsHosts } from '../src/dnsHosts.js';
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const here = dirname(fileURLToPath(import.meta.url));
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type Row = [string, string, number, string];
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const javaMeasured = JSON.parse(readFileSync(join(here, 'dns-hosts.java.json'), 'utf8')) as [string, Row[]][];
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const swiftMeasured = JSON.parse(readFileSync(join(here, 'dns-hosts.swift.json'), 'utf8')) as [string, Row[]][];
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/** The cases file's escapes: a backslash, `u` and four hex digits for one UTF-16 unit. */
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function unescape(line: string): string {
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return line.replace(/\\u([0-9a-fA-F]{4})/g, (_, hex: string) => String.fromCharCode(Number.parseInt(hex, 16)));
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}
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function modelRows(line: string, warnings: string[] = []): Row[] {
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return dnsRecordsOf(readJavaDnsHosts(unescape(line)), (message) => warnings.push(message)).map((record) => [
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record.name,
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record.type,
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record.ttlSeconds,
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record.target,
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]);
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}
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/** Lines Swift reads as records that Java never answers. */
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const SWIFT_READS_JAVA_NEVER_ANSWERS: { reason: string; lines: string[] }[] = [
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{
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reason: 'a type in lower case is another type in Java, which never answers',
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lines: [
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String.raw`www.filius.de a 3600 1.2.3.4\u000A`,
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String.raw`filius.de mx 3600 mail.filius.de\u000A`,
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],
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},
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{
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reason: 'Java splits fields at single spaces only: a tab or NBSP is part of a field',
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lines: [
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String.raw`www.filius.de\u0009A\u00093600\u00091.2.3.4\u000A`,
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String.raw`www.filius.de\u00A0A 3600 1.2.3.4\u000A`,
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String.raw`www.filius.de A 3600 1.2.3.4\u00A0\u000A`,
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String.raw`www.filius.de \u0009 A 3600 1.2.3.4\u000A`,
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String.raw`www.filius.de A \u0009 3600 1.2.3.4\u000A`,
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],
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},
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{
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reason: 'Java splits lines at LF only: CR, LS and NEL stay in the line',
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lines: [
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String.raw`www.filius.de A 3600 1.2.3.4\u000Dmail.filius.de A 3600 1.2.3.5\u000D`,
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String.raw`www.filius.de A 3600 1.2.3.4\u2028mail.filius.de A 3600 1.2.3.5\u000A`,
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String.raw`www.filius.de A 3600 1.2.3.4\u0085\u000A`,
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],
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},
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{
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reason: 'Java has no comments, no "IN" and no zone-file order',
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lines: [
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String.raw`www.filius.de A 3600 1.2.3.4#x\u000A`,
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String.raw`www.filius.de A IN 3600 1.2.3.4\u000A`,
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String.raw`www.filius.de 3600 IN A 1.2.3.4\u000A`,
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],
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},
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{
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reason: 'a label that starts with a digit, or two final dots, make the name empty in Java',
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lines: [
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String.raw`1und1.de A 3600 1.2.3.4\u000A`,
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String.raw`www.1und1.de A 3600 1.2.3.4\u000A`,
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String.raw`www.filius.de.. A 3600 1.2.3.4\u000A`,
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],
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},
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{
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reason: 'an MX or NS target must be a name Java accepts: no preference, no address, one final dot',
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lines: [
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String.raw`filius.de MX 3600 10 mail.filius.de\u000A`,
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String.raw`filius.de MX 3600 1.2.3.4\u000A`,
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String.raw`filius.de NS 3600 dns.filius.de..\u000A`,
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],
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},
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];
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/** Lines Java answers that Swift drops or reads otherwise. */
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const JAVA_ANSWERS_SWIFT_DROPS: { reason: string; lines: string[] }[] = [
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{
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reason: 'a TTL that is no Java int is 3600',
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lines: [
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String.raw`www.filius.de A x 1.2.3.4\u000A`,
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String.raw`www.filius.de A 4294967295 1.2.3.4\u000A`,
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String.raw`www.filius.de A 99999999999 1.2.3.4\u000A`,
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String.raw`www.filius.de A 2147483648 1.2.3.4\u000A`,
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],
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},
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{
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reason: 'a TTL is Java\'s Integer.parseInt: negative, and in any script\'s digits',
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lines: [
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String.raw`www.filius.de A -5 1.2.3.4\u000A`,
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String.raw`www.filius.de A -2147483648 1.2.3.4\u000A`,
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String.raw`www.filius.de A \u0661\u0660 1.2.3.4\u000A`,
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],
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},
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{
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reason: 'labels after the first may hold a backslash (Java\'s domain pattern)',
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lines: [
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String.raw`www.a\u005Cb.de A 3600 1.2.3.4\u000A`,
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],
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},
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{
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reason: 'Java trims control characters off a line (String.trim)',
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lines: [
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String.raw`www.filius.de A 3600 1.2.3.4\u0001\u000A`,
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String.raw`\u001Fwww.filius.de A 3600 1.2.3.4\u000A`,
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],
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},
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{
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reason: 'an NS record may name the root',
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lines: [
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String.raw`de. NS 3600 .\u000A`,
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],
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},
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{
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reason: 'duplicates stay, as in Java\'s list',
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lines: [
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String.raw`www.filius.de A 3600 1.2.3.4\u000Awww.filius.de A 3600 1.2.3.4\u000A`,
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String.raw`www.filius.de A 3600 1.2.3.4\u000Awww.filius.de A 7200 1.2.3.4\u000A`,
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String.raw`www.filius.de A 3600 1.2.3.4\u000AWWW.filius.de. A 3600 1.2.3.4\u000A`,
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],
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},
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];
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const departures = new Map(
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[...SWIFT_READS_JAVA_NEVER_ANSWERS, ...JAVA_ANSWERS_SWIFT_DROPS].flatMap(({ reason, lines }) =>
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lines.map((line) => [line, reason] as const),
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),
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);
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describe('readJavaDnsHosts against Java', () => {
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it('covers every line of the cases file, in both oracles', () => {
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const lines = readFileSync(join(here, 'dns-hosts.cases.txt'), 'ascii').split('\n').slice(0, -1);
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expect(javaMeasured.map(([line]) => line)).toEqual(lines);
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expect(swiftMeasured.map(([line]) => line)).toEqual(lines);
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});
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for (const [line, expected] of javaMeasured) {
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it(JSON.stringify(line), () => {
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const records = readJavaDnsHosts(unescape(line));
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expect(records.map((record) => [record.domainName, record.type, record.ttl, record.rdata])).toEqual(expected);
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});
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}
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});
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describe('the records the model keeps, against Swift', () => {
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it('names only cases of the cases file as departures', () => {
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const lines = new Set(swiftMeasured.map(([line]) => line));
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expect([...departures.keys()].filter((line) => !lines.has(line))).toEqual([]);
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});
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for (const [line, swift] of swiftMeasured) {
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const reason = departures.get(line);
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it(reason === undefined ? JSON.stringify(line) : `${JSON.stringify(line)} (departs: ${reason})`, () => {
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if (reason === undefined) expect(modelRows(line)).toEqual(swift);
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else expect(modelRows(line)).not.toEqual(swift);
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});
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}
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});
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describe('the records Java answers', () => {
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it('leave out records Java never answers: an empty name, or a type other than A, MX, NS', () => {
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expect(modelRows(String.raw`1und1.de A 3600 1.2.3.4\u000Afilius.de CNAME 3600 www.filius.de\u000Afilius.de a 3600 1.2.3.4`)).toEqual([]);
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});
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it('take names in lower case without the final dot, A targets as FILIUS normalises addresses', () => {
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expect(modelRows(String.raw`WWW.Filius.DE. A 60 010.000.0.1\u000Afilius.de MX 3600 Mail.Filius.DE\u000A. NS 3600 dns-root`)).toEqual([
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['www.filius.de', 'A', 60, '10.0.0.1'],
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['filius.de', 'MX', 3600, 'mail.filius.de.'],
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['.', 'NS', 3600, 'dns-root.'],
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]);
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});
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it('warn about an A record Java answers with an address FILIUS cannot use', () => {
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const warnings: string[] = [];
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expect(modelRows(String.raw`www.filius.de A 3600 .1.2.3`, warnings)).toEqual([]);
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expect(warnings).toEqual(["DNS record 'www.filius.de A .1.2.3' has no usable IPv4 address, left out (it stays in /dns/hosts)"]);
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});
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});
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describe('javaHostsFileContent', () => {
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const file = (name: string, content: string | null): FlsFileTree => ({ kind: 'file', name, type: 'text', content, children: [] });
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const directory = (name: string, ...children: FlsFileTree[]): FlsFileTree => ({ kind: 'directory', name, children });
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it('finds /dns/hosts ignoring case, as Java does', () => {
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expect(javaHostsFileContent(directory('root', directory('DNS', file('Hosts', 'x'))))).toBe('x');
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expect(javaHostsFileContent(directory('root', directory('dns', file('ho\u017Fts', 'long s'))))).toBe('long s');
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});
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it('takes the first match in preorder, and nothing when that is a directory', () => {
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expect(javaHostsFileContent(directory('root', directory('dns', file('hosts', 'first')), directory('DNS', file('hosts', 'second'))))).toBe('first');
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expect(javaHostsFileContent(directory('root', directory('dns', directory('hosts'), file('HOSTS', 'later'))))).toBeUndefined();
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});
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it('is undefined without the file, and empty for a file without content', () => {
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expect(javaHostsFileContent(undefined)).toBeUndefined();
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expect(javaHostsFileContent(directory('root', file('hosts', 'x')))).toBeUndefined();
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expect(javaHostsFileContent(directory('root', directory('dns', file('hosts', null))))).toBe('');
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});
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});
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