fix: TXT decode preserves string-boundary info

Author: msimerson

CHANGELOG.md

@@ -4,6 +4,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/).
 
 ### Unreleased
 
+- **BREAKING** fix(packet): TXT decode preserves character-string boundaries (RFC 1035 §3.3.14); `data` is now always an array of strings
 - fix(packet): IPv6 `::` compression for leading-zero address #123
 - fix(packet): Name decode rejects pointer cycles (RFC 1035) #124
 - fix(packet): EDNS exposes extendedRcode/version/doFlag #124

packet.js

@@ -661,21 +661,24 @@ Packet.Resource.CNAME = {
  */
 Packet.Resource.SPF =
 Packet.Resource.TXT = {
+  // RFC 1035 §3.3.14: TXT RDATA is one or more length-prefixed
+  // <character-string> items. Preserve those boundaries by returning an
+  // array — joining them silently corrupts SPF/DKIM and other multi-string
+  // records whose semantics depend on segmentation.
   decode: function(reader, length) {
-    const parts = [];
-    let bytesRead = 0; let chunkLength;
-
+    const strings = [];
+    let bytesRead = 0;
     while (bytesRead < length) {
-      chunkLength = reader.read(8); // text length
+      const chunkLength = reader.read(8);
       bytesRead++;
-
-      while (chunkLength--) {
-        parts.push(reader.read(8));
+      const bytes = [];
+      for (let i = 0; i < chunkLength; i++) {
+        bytes.push(reader.read(8));
         bytesRead++;
       }
+      strings.push(Buffer.from(bytes).toString('utf8'));
     }
-
-    this.data = Buffer.from(parts).toString('utf8');
+    this.data = strings;
     return this;
   },
   encode: function(record, writer) {

test/packet.js

@@ -211,7 +211,8 @@ test('Packet#encode', function() {
     type  : Packet.TYPE.TXT,
     class : Packet.CLASS.IN,
     ttl   : 300,
-    data  : '#v=spf1 include:_spf.google.com ~all',
+    // TXT data is an array of <character-string> items (RFC 1035 §3.3.14).
+    data  : [ '#v=spf1 include:_spf.google.com ~all' ],
   });
 
   assert.deepEqual(Packet.parse(response.toBuffer()), response);
@@ -235,7 +236,7 @@ test('Packet#encode array of character strings', function() {
     data  : dkim,
   });
 
-  assert.equal(Packet.parse(response.toBuffer()).answers[0].data, dkim.join(''));
+  assert.deepEqual(Packet.parse(response.toBuffer()).answers[0].data, dkim);
 });
 
 test('EDNS.ECS#encode', function() {
@@ -394,9 +395,9 @@ test('Resource#TXT round-trip single string', function() {
     type  : Packet.TYPE.TXT,
     class : Packet.CLASS.IN,
     ttl   : 300,
-    data  : 'hello world',
+    data  : 'hello world', // encoder normalizes string → [string]
   });
-  assert.equal(out.data, 'hello world');
+  assert.deepEqual(out.data, [ 'hello world' ]);
 });
 
 test('Resource#TXT round-trip with utf-8', function() {
@@ -407,7 +408,20 @@ test('Resource#TXT round-trip with utf-8', function() {
     ttl   : 300,
     data  : 'café résumé 日本',
   });
-  assert.equal(out.data, 'café résumé 日本');
+  assert.deepEqual(out.data, [ 'café résumé 日本' ]);
+});
+
+test('Resource#TXT preserves character-string boundaries', function() {
+  // SPF/DKIM-style multi-string TXT records must not be merged on decode.
+  const chunks = [ 'part-one ', 'part-two ', 'part-three' ];
+  const out = roundTripAnswer({
+    name  : 'multi.example',
+    type  : Packet.TYPE.TXT,
+    class : Packet.CLASS.IN,
+    ttl   : 60,
+    data  : chunks,
+  });
+  assert.deepEqual(out.data, chunks);
 });
 
 test('Resource#SOA round-trip', function() {

test/server.js

@@ -119,7 +119,7 @@ test('server/udp-tcp#simple-request-async-response', async() => {
   assert.ok(servers.tcp.port > 1000);
   const tcpClient = TCPClient({ dns: '127.0.0.1', port: servers.tcp.port });
   const udpClient = UDPClient({ dns: '127.0.0.1', port: servers.udp.port });
-  const expected = [ { name: 'test.com', ttl: 300, type: 16, class: 1, data: 'Hello World' } ];
+  const expected = [ { name: 'test.com', ttl: 300, type: 16, class: 1, data: [ 'Hello World' ] } ];
   assert.deepEqual((await tcpClient('test.com')).answers, expected);
   assert.deepEqual((await udpClient('test.com')).answers, expected);
   await server.close();
@@ -207,7 +207,7 @@ test('server/doh#POST end-to-end', async() => {
       type  : Packet.TYPE.TXT,
       class : Packet.CLASS.IN,
       ttl   : 60,
-      data  : 'post-ok',
+      data  : [ 'post-ok' ],
     });
     send(response);
   });
@@ -243,7 +243,7 @@ test('server/doh#POST end-to-end', async() => {
   });
   const parsed = Packet.parse(body);
   assert.equal(parsed.answers.length, 1);
-  assert.equal(parsed.answers[0].data, 'post-ok');
+  assert.deepEqual(parsed.answers[0].data, [ 'post-ok' ]);
   server.close();
 });