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Avoid allocating for all message buffers, expose querying in no-std
[dnssec-prover] / src / query.rs
1 //! This module exposes utilities for building DNSSEC proofs by directly querying a recursive
2 //! resolver.
3
4 use core::{cmp, ops};
5 use alloc::vec;
6 use alloc::vec::Vec;
7
8 #[cfg(feature = "std")]
9 use std::net::{SocketAddr, TcpStream};
10 #[cfg(feature = "std")]
11 use std::io::{Read, Write, Error, ErrorKind};
12
13 #[cfg(feature = "tokio")]
14 use tokio_crate::net::TcpStream as TokioTcpStream;
15 #[cfg(feature = "tokio")]
16 use tokio_crate::io::{AsyncReadExt, AsyncWriteExt};
17
18 use crate::rr::*;
19 use crate::ser::*;
20
21 // In testing use a rather small buffer to ensure we hit the allocation paths sometimes. In
22 // production, we should generally never actually need to go to heap as DNS messages are rarely
23 // larger than a KiB or two.
24 #[cfg(test)]
25 const STACK_BUF_LIMIT: u16 = 32;
26 #[cfg(not(test))]
27 const STACK_BUF_LIMIT: u16 = 2048;
28
29 /// A buffer for storing queries and responses.
30 #[derive(Clone, PartialEq, Eq)]
31 pub struct QueryBuf {
32         buf: [u8; STACK_BUF_LIMIT as usize],
33         heap_buf: Vec<u8>,
34         len: u16,
35 }
36 impl QueryBuf {
37         fn new_zeroed(len: u16) -> Self {
38                 let heap_buf = if len > STACK_BUF_LIMIT { vec![0; len as usize] } else { Vec::new() };
39                 Self {
40                         buf: [0; STACK_BUF_LIMIT as usize],
41                         heap_buf,
42                         len
43                 }
44         }
45         pub(crate) fn extend_from_slice(&mut self, sl: &[u8]) {
46                 let new_len = self.len.saturating_add(sl.len() as u16);
47                 let was_heap = self.len > STACK_BUF_LIMIT;
48                 let is_heap = new_len > STACK_BUF_LIMIT;
49                 if was_heap != is_heap {
50                         self.heap_buf = vec![0; new_len as usize];
51                         self.heap_buf[..self.len as usize].copy_from_slice(&self.buf[..self.len as usize]);
52                 }
53                 let target = if is_heap {
54                         self.heap_buf.resize(new_len as usize, 0);
55                         &mut self.heap_buf[self.len as usize..]
56                 } else {
57                         &mut self.buf[self.len as usize..new_len as usize]
58                 };
59                 target.copy_from_slice(sl);
60                 self.len = new_len;
61         }
62 }
63 impl ops::Deref for QueryBuf {
64         type Target = [u8];
65         fn deref(&self) -> &[u8] {
66                 if self.len > STACK_BUF_LIMIT {
67                         &self.heap_buf
68                 } else {
69                         &self.buf[..self.len as usize]
70                 }
71         }
72 }
73 impl ops::DerefMut for QueryBuf {
74         fn deref_mut(&mut self) -> &mut [u8] {
75                 if self.len > STACK_BUF_LIMIT {
76                         &mut self.heap_buf
77                 } else {
78                         &mut self.buf[..self.len as usize]
79                 }
80         }
81 }
82
83 // We don't care about transaction IDs as we're only going to accept signed data. Thus, we use
84 // this constant instead of a random value.
85 const TXID: u16 = 0x4242;
86
87 fn build_query(domain: &Name, ty: u16) -> QueryBuf {
88         let mut query = QueryBuf::new_zeroed(0);
89         let query_msg_len: u16 = 2 + 2 + 8 + 2 + 2 + name_len(domain) + 11;
90         query.extend_from_slice(&query_msg_len.to_be_bytes());
91         query.extend_from_slice(&TXID.to_be_bytes());
92         query.extend_from_slice(&[0x01, 0x20]); // Flags: Recursive, Authenticated Data
93         query.extend_from_slice(&[0, 1, 0, 0, 0, 0, 0, 1]); // One question, One additional
94         write_name(&mut query, domain);
95         query.extend_from_slice(&ty.to_be_bytes());
96         query.extend_from_slice(&1u16.to_be_bytes()); // INternet class
97         query.extend_from_slice(&[0, 0, 0x29]); // . OPT
98         query.extend_from_slice(&0u16.to_be_bytes()); // 0 UDP payload size
99         query.extend_from_slice(&[0, 0]); // EDNS version 0
100         query.extend_from_slice(&0x8000u16.to_be_bytes()); // Accept DNSSEC RRs
101         query.extend_from_slice(&0u16.to_be_bytes()); // No additional data
102         query
103 }
104
105 #[cfg(fuzzing)]
106 /// Read some input and parse it as if it came from a server, for fuzzing.
107 pub fn fuzz_response(response: &[u8]) {
108         let (mut proof, mut names) = (Vec::new(), Vec::new());
109         let _ = handle_response(response, &mut proof, &mut names);
110 }
111
112 fn handle_response(resp: &[u8], proof: &mut Vec<u8>, rrsig_key_names: &mut Vec<Name>) -> Result<u32, ()> {
113         let mut read: &[u8] = resp;
114         if read_u16(&mut read)? != TXID { return Err(()); }
115         // 2 byte transaction ID
116         let flags = read_u16(&mut read)?;
117         if flags & 0b1000_0000_0000_0000 == 0 {
118                 return Err(());
119         }
120         if flags & 0b0111_1010_0000_0111 != 0 {
121                 return Err(());
122         }
123         if flags & 0b10_0000 == 0 {
124                 return Err(());
125         }
126         let questions = read_u16(&mut read)?;
127         if questions != 1 { return Err(()); }
128         let answers = read_u16(&mut read)?;
129         if answers == 0 { return Err(()); }
130         let _authorities = read_u16(&mut read)?;
131         let _additional = read_u16(&mut read)?;
132
133         for _ in 0..questions {
134                 read_wire_packet_name(&mut read, resp)?;
135                 read_u16(&mut read)?; // type
136                 read_u16(&mut read)?; // class
137         }
138
139         // Only read the answers (skip authorities and additional) as that's all we care about.
140         let mut min_ttl = u32::MAX;
141         for _ in 0..answers {
142                 let (rr, ttl) = parse_wire_packet_rr(&mut read, &resp)?;
143                 write_rr(&rr, ttl, proof);
144                 min_ttl = cmp::min(min_ttl, ttl);
145                 if let RR::RRSig(rrsig) = rr { rrsig_key_names.push(rrsig.key_name); }
146         }
147         Ok(min_ttl)
148 }
149
150 const MAX_REQUESTS: usize = 10;
151 /// A simple state machine which will generate a series of queries and process the responses until
152 /// it has built a DNSSEC proof.
153 ///
154 /// A [`ProofBuilder`] driver starts with [`ProofBuilder::new`], fetching the state machine and
155 /// initial query. As long as [`ProofBuilder::awaiting_responses`] returns true, responses should
156 /// be read from the resolver. For each query response read from the DNS resolver,
157 /// [`ProofBuilder::process_response`] should be called, and each fresh query returned should be
158 /// sent to the resolver. Once [`ProofBuilder::awaiting_responses`] returns false,
159 /// [`ProofBuilder::finish_proof`] should be called to fetch the resulting proof.
160 pub struct ProofBuilder {
161         proof: Vec<u8>,
162         min_ttl: u32,
163         dnskeys_requested: Vec<Name>,
164         pending_queries: usize,
165         queries_made: usize,
166 }
167
168 impl ProofBuilder {
169         /// Constructs a new [`ProofBuilder`] and an initial query to send to the recursive resolver to
170         /// begin the proof building process.
171         ///
172         /// Given a correctly-functioning resolver the proof will ultimately be able to prove the
173         /// contents of any records with the given `ty`pe at the given `name` (as long as the given
174         /// `ty`pe is supported by this library).
175         ///
176         /// You can find constants for supported standard types in the [`crate::rr`] module.
177         pub fn new(name: &Name, ty: u16) -> (ProofBuilder, QueryBuf) {
178                 let initial_query = build_query(name, ty);
179                 (ProofBuilder {
180                         proof: Vec::new(),
181                         min_ttl: u32::MAX,
182                         dnskeys_requested: Vec::with_capacity(MAX_REQUESTS),
183                         pending_queries: 1,
184                         queries_made: 1,
185                 }, initial_query)
186         }
187
188         /// Returns true as long as further responses are expected from the resolver.
189         ///
190         /// As long as this returns true, responses should be read from the resolver and passed to
191         /// [`Self::process_response`]. Once this returns false, [`Self::finish_proof`] should be used
192         /// to (possibly) get the final proof.
193         pub fn awaiting_responses(&self) -> bool {
194                 self.pending_queries > 0 && self.queries_made <= MAX_REQUESTS
195         }
196
197         /// Processes a query response from the recursive resolver, returning a list of new queries to
198         /// send to the resolver.
199         pub fn process_response(&mut self, resp: &QueryBuf) -> Result<Vec<QueryBuf>, ()> {
200                 if self.pending_queries == 0 { return Err(()); }
201
202                 let mut rrsig_key_names = Vec::new();
203                 let min_ttl = handle_response(&resp, &mut self.proof, &mut rrsig_key_names)?;
204                 self.min_ttl = cmp::min(self.min_ttl, min_ttl);
205                 self.pending_queries -= 1;
206
207                 rrsig_key_names.sort_unstable();
208                 rrsig_key_names.dedup();
209
210                 let mut new_queries = Vec::with_capacity(2);
211                 for key_name in rrsig_key_names.drain(..) {
212                         if !self.dnskeys_requested.contains(&key_name) {
213                                 new_queries.push(build_query(&key_name, DnsKey::TYPE));
214                                 self.pending_queries += 1;
215                                 self.queries_made += 1;
216                                 self.dnskeys_requested.push(key_name.clone());
217
218                                 if key_name.as_str() != "." {
219                                         new_queries.push(build_query(&key_name, DS::TYPE));
220                                         self.pending_queries += 1;
221                                         self.queries_made += 1;
222                                 }
223                         }
224                 }
225                 if self.queries_made <= MAX_REQUESTS {
226                         Ok(new_queries)
227                 } else {
228                         Ok(Vec::new())
229                 }
230         }
231
232         /// Finalizes the proof, if one is available, and returns it as well as the TTL that should be
233         /// used to cache the proof (i.e. the lowest TTL of all records which were used to build the
234         /// proof).
235         pub fn finish_proof(self) -> Result<(Vec<u8>, u32), ()> {
236                 if self.pending_queries > 0 || self.queries_made > MAX_REQUESTS {
237                         Err(())
238                 } else {
239                         Ok((self.proof, self.min_ttl))
240                 }
241         }
242 }
243
244 #[cfg(feature = "std")]
245 fn send_query(stream: &mut TcpStream, query: &[u8]) -> Result<(), Error> {
246         stream.write_all(&query)?;
247         Ok(())
248 }
249
250 #[cfg(feature = "tokio")]
251 async fn send_query_async(stream: &mut TokioTcpStream, query: &[u8]) -> Result<(), Error> {
252         stream.write_all(&query).await?;
253         Ok(())
254 }
255
256 #[cfg(feature = "std")]
257 fn read_response(stream: &mut TcpStream) -> Result<QueryBuf, Error> {
258         let mut len_bytes = [0; 2];
259         stream.read_exact(&mut len_bytes)?;
260         let mut buf = QueryBuf::new_zeroed(u16::from_be_bytes(len_bytes));
261         stream.read_exact(&mut buf)?;
262         Ok(buf)
263 }
264
265 #[cfg(feature = "tokio")]
266 async fn read_response_async(stream: &mut TokioTcpStream) -> Result<QueryBuf, Error> {
267         let mut len_bytes = [0; 2];
268         stream.read_exact(&mut len_bytes).await?;
269         let mut buf = QueryBuf::new_zeroed(u16::from_be_bytes(len_bytes));
270         stream.read_exact(&mut buf).await?;
271         Ok(buf)
272 }
273
274 #[cfg(feature = "std")]
275 macro_rules! build_proof_impl {
276         ($stream: ident, $send_query: ident, $read_response: ident, $domain: expr, $ty: expr $(, $async_ok: tt)?) => { {
277                 // We require the initial query to have already gone out, and assume our resolver will
278                 // return any CNAMEs all the way to the final record in the response. From there, we just
279                 // have to take any RRSIGs in the response and walk them up to the root. We do so
280                 // iteratively, sending DNSKEY and DS lookups after every response, deduplicating requests
281                 // using `dnskeys_requested`.
282                 let (mut builder, initial_query) = ProofBuilder::new($domain, $ty);
283                 $send_query(&mut $stream, &initial_query)
284                         $(.await?; $async_ok)??; // Either await?; Ok(())?, or just ?
285                 while builder.awaiting_responses() {
286                         let response = $read_response(&mut $stream)
287                                 $(.await?; $async_ok)??; // Either await?; Ok(())?, or just ?
288                         let new_queries = builder.process_response(&response)
289                                 .map_err(|()| Error::new(ErrorKind::Other, "Bad response"))?;
290                         for query in new_queries {
291                                 $send_query(&mut $stream, &query)
292                                         $(.await?; $async_ok)??; // Either await?; Ok(())?, or just ?
293                         }
294                 }
295
296                 builder.finish_proof()
297                         .map_err(|()| Error::new(ErrorKind::Other, "Too many requests required"))
298         } }
299 }
300
301 #[cfg(feature = "std")]
302 fn build_proof(resolver: SocketAddr, domain: &Name, ty: u16) -> Result<(Vec<u8>, u32), Error> {
303         let mut stream = TcpStream::connect(resolver)?;
304         build_proof_impl!(stream, send_query, read_response, domain, ty)
305 }
306
307 #[cfg(feature = "tokio")]
308 async fn build_proof_async(resolver: SocketAddr, domain: &Name, ty: u16) -> Result<(Vec<u8>, u32), Error> {
309         let mut stream = TokioTcpStream::connect(resolver).await?;
310         build_proof_impl!(stream, send_query_async, read_response_async, domain, ty, { Ok::<(), Error>(()) })
311 }
312
313 /// Builds a DNSSEC proof for an A record by querying a recursive resolver, returning the proof as
314 /// well as the TTL for the proof provided by the recursive resolver.
315 ///
316 /// Note that this proof is NOT verified in any way, you need to use the [`crate::validation`]
317 /// module to validate the records contained.
318 #[cfg(feature = "std")]
319 pub fn build_a_proof(resolver: SocketAddr, domain: &Name) -> Result<(Vec<u8>, u32), Error> {
320         build_proof(resolver, domain, A::TYPE)
321 }
322
323 /// Builds a DNSSEC proof for an AAAA record by querying a recursive resolver, returning the proof
324 /// as well as the TTL for the proof provided by the recursive resolver.
325 ///
326 /// Note that this proof is NOT verified in any way, you need to use the [`crate::validation`]
327 /// module to validate the records contained.
328 #[cfg(feature = "std")]
329 pub fn build_aaaa_proof(resolver: SocketAddr, domain: &Name) -> Result<(Vec<u8>, u32), Error> {
330         build_proof(resolver, domain, AAAA::TYPE)
331 }
332
333 /// Builds a DNSSEC proof for an TXT record by querying a recursive resolver, returning the proof
334 /// as well as the TTL for the proof provided by the recursive resolver.
335 ///
336 /// Note that this proof is NOT verified in any way, you need to use the [`crate::validation`]
337 /// module to validate the records contained.
338 #[cfg(feature = "std")]
339 pub fn build_txt_proof(resolver: SocketAddr, domain: &Name) -> Result<(Vec<u8>, u32), Error> {
340         build_proof(resolver, domain, Txt::TYPE)
341 }
342
343 /// Builds a DNSSEC proof for an TLSA record by querying a recursive resolver, returning the proof
344 /// as well as the TTL for the proof provided by the recursive resolver.
345 ///
346 /// Note that this proof is NOT verified in any way, you need to use the [`crate::validation`]
347 /// module to validate the records contained.
348 #[cfg(feature = "std")]
349 pub fn build_tlsa_proof(resolver: SocketAddr, domain: &Name) -> Result<(Vec<u8>, u32), Error> {
350         build_proof(resolver, domain, TLSA::TYPE)
351 }
352
353
354 /// Builds a DNSSEC proof for an A record by querying a recursive resolver, returning the proof as
355 /// well as the TTL for the proof provided by the recursive resolver.
356 ///
357 /// Note that this proof is NOT verified in any way, you need to use the [`crate::validation`]
358 /// module to validate the records contained.
359 #[cfg(feature = "tokio")]
360 pub async fn build_a_proof_async(resolver: SocketAddr, domain: &Name) -> Result<(Vec<u8>, u32), Error> {
361         build_proof_async(resolver, domain, A::TYPE).await
362 }
363
364 /// Builds a DNSSEC proof for an AAAA record by querying a recursive resolver, returning the proof
365 /// as well as the TTL for the proof provided by the recursive resolver.
366 ///
367 /// Note that this proof is NOT verified in any way, you need to use the [`crate::validation`]
368 /// module to validate the records contained.
369 #[cfg(feature = "tokio")]
370 pub async fn build_aaaa_proof_async(resolver: SocketAddr, domain: &Name) -> Result<(Vec<u8>, u32), Error> {
371         build_proof_async(resolver, domain, AAAA::TYPE).await
372 }
373
374 /// Builds a DNSSEC proof for an TXT record by querying a recursive resolver, returning the proof
375 /// as well as the TTL for the proof provided by the recursive resolver.
376 ///
377 /// Note that this proof is NOT verified in any way, you need to use the [`crate::validation`]
378 /// module to validate the records contained.
379 #[cfg(feature = "tokio")]
380 pub async fn build_txt_proof_async(resolver: SocketAddr, domain: &Name) -> Result<(Vec<u8>, u32), Error> {
381         build_proof_async(resolver, domain, Txt::TYPE).await
382 }
383
384 /// Builds a DNSSEC proof for an TLSA record by querying a recursive resolver, returning the proof
385 /// as well as the TTL for the proof provided by the recursive resolver.
386 ///
387 /// Note that this proof is NOT verified in any way, you need to use the [`crate::validation`]
388 /// module to validate the records contained.
389 #[cfg(feature = "tokio")]
390 pub async fn build_tlsa_proof_async(resolver: SocketAddr, domain: &Name) -> Result<(Vec<u8>, u32), Error> {
391         build_proof_async(resolver, domain, TLSA::TYPE).await
392 }
393
394 #[cfg(all(feature = "validation", feature = "std", test))]
395 mod tests {
396         use super::*;
397         use crate::validation::*;
398
399         use rand::seq::SliceRandom;
400
401         use std::net::ToSocketAddrs;
402         use std::time::SystemTime;
403
404         #[test]
405         fn test_cloudflare_txt_query() {
406                 let sockaddr = "8.8.8.8:53".to_socket_addrs().unwrap().next().unwrap();
407                 let query_name = "cloudflare.com.".try_into().unwrap();
408                 let (proof, _) = build_txt_proof(sockaddr, &query_name).unwrap();
409
410                 let mut rrs = parse_rr_stream(&proof).unwrap();
411                 rrs.shuffle(&mut rand::rngs::OsRng);
412                 let verified_rrs = verify_rr_stream(&rrs).unwrap();
413                 assert!(verified_rrs.verified_rrs.len() > 1);
414
415                 let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap().as_secs();
416                 assert!(verified_rrs.valid_from < now);
417                 assert!(verified_rrs.expires > now);
418         }
419
420         #[test]
421         fn test_sha1_query() {
422                 let sockaddr = "8.8.8.8:53".to_socket_addrs().unwrap().next().unwrap();
423                 let query_name = "benthecarman.com.".try_into().unwrap();
424                 let (proof, _) = build_a_proof(sockaddr, &query_name).unwrap();
425
426                 let mut rrs = parse_rr_stream(&proof).unwrap();
427                 rrs.shuffle(&mut rand::rngs::OsRng);
428                 let verified_rrs = verify_rr_stream(&rrs).unwrap();
429                 assert!(verified_rrs.verified_rrs.len() >= 1);
430
431                 let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap().as_secs();
432                 assert!(verified_rrs.valid_from < now);
433                 assert!(verified_rrs.expires > now);
434         }
435
436         #[test]
437         fn test_txt_query() {
438                 let sockaddr = "8.8.8.8:53".to_socket_addrs().unwrap().next().unwrap();
439                 let query_name = "matt.user._bitcoin-payment.mattcorallo.com.".try_into().unwrap();
440                 let (proof, _) = build_txt_proof(sockaddr, &query_name).unwrap();
441
442                 let mut rrs = parse_rr_stream(&proof).unwrap();
443                 rrs.shuffle(&mut rand::rngs::OsRng);
444                 let verified_rrs = verify_rr_stream(&rrs).unwrap();
445                 assert_eq!(verified_rrs.verified_rrs.len(), 1);
446
447                 let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap().as_secs();
448                 assert!(verified_rrs.valid_from < now);
449                 assert!(verified_rrs.expires > now);
450         }
451
452         #[test]
453         fn test_cname_query() {
454                 for resolver in ["1.1.1.1:53", "8.8.8.8:53", "9.9.9.9:53"] {
455                         let sockaddr = resolver.to_socket_addrs().unwrap().next().unwrap();
456                         let query_name = "cname_test.matcorallo.com.".try_into().unwrap();
457                         let (proof, _) = build_txt_proof(sockaddr, &query_name).unwrap();
458
459                         let mut rrs = parse_rr_stream(&proof).unwrap();
460                         rrs.shuffle(&mut rand::rngs::OsRng);
461                         let verified_rrs = verify_rr_stream(&rrs).unwrap();
462                         assert_eq!(verified_rrs.verified_rrs.len(), 2);
463
464                         let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap().as_secs();
465                         assert!(verified_rrs.valid_from < now);
466                         assert!(verified_rrs.expires > now);
467
468                         let resolved_rrs = verified_rrs.resolve_name(&query_name);
469                         assert_eq!(resolved_rrs.len(), 1);
470                         if let RR::Txt(txt) = &resolved_rrs[0] {
471                                 assert_eq!(txt.name.as_str(), "txt_test.matcorallo.com.");
472                                 assert_eq!(txt.data, b"dnssec_prover_test");
473                         } else { panic!(); }
474                 }
475         }
476
477         #[cfg(feature = "tokio")]
478         use tokio_crate as tokio;
479
480         #[cfg(feature = "tokio")]
481         #[tokio::test]
482         async fn test_txt_query_async() {
483                 let sockaddr = "8.8.8.8:53".to_socket_addrs().unwrap().next().unwrap();
484                 let query_name = "matt.user._bitcoin-payment.mattcorallo.com.".try_into().unwrap();
485                 let (proof, _) = build_txt_proof_async(sockaddr, &query_name).await.unwrap();
486
487                 let mut rrs = parse_rr_stream(&proof).unwrap();
488                 rrs.shuffle(&mut rand::rngs::OsRng);
489                 let verified_rrs = verify_rr_stream(&rrs).unwrap();
490                 assert_eq!(verified_rrs.verified_rrs.len(), 1);
491
492                 let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap().as_secs();
493                 assert!(verified_rrs.valid_from < now);
494                 assert!(verified_rrs.expires > now);
495         }
496
497         #[cfg(feature = "tokio")]
498         #[tokio::test]
499         async fn test_cross_domain_cname_query_async() {
500                 for resolver in ["1.1.1.1:53", "8.8.8.8:53", "9.9.9.9:53"] {
501                         let sockaddr = resolver.to_socket_addrs().unwrap().next().unwrap();
502                         let query_name = "wildcard.x_domain_cname_wild.matcorallo.com.".try_into().unwrap();
503                         let (proof, _) = build_txt_proof_async(sockaddr, &query_name).await.unwrap();
504
505                         let mut rrs = parse_rr_stream(&proof).unwrap();
506                         rrs.shuffle(&mut rand::rngs::OsRng);
507                         let verified_rrs = verify_rr_stream(&rrs).unwrap();
508                         assert_eq!(verified_rrs.verified_rrs.len(), 2);
509
510                         let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap().as_secs();
511                         assert!(verified_rrs.valid_from < now);
512                         assert!(verified_rrs.expires > now);
513
514                         let resolved_rrs = verified_rrs.resolve_name(&query_name);
515                         assert_eq!(resolved_rrs.len(), 1);
516                         if let RR::Txt(txt) = &resolved_rrs[0] {
517                                 assert_eq!(txt.name.as_str(), "matt.user._bitcoin-payment.mattcorallo.com.");
518                                 assert!(txt.data.starts_with(b"bitcoin:"));
519                         } else { panic!(); }
520                 }
521         }
522 }