1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
// Copyright 2015-2021 Benjamin Fry <benjaminfry@me.com>
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.

//! SVCB records, see [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03)

use std::{
    cmp::{Ord, Ordering, PartialOrd},
    convert::TryFrom,
    fmt,
    net::Ipv4Addr,
    net::Ipv6Addr,
};

#[cfg(feature = "serde-config")]
use serde::{Deserialize, Serialize};

use enum_as_inner::EnumAsInner;

use crate::error::*;
use crate::rr::Name;
use crate::serialize::binary::*;

///  [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-2.2)
///
/// ```text
/// 2.2.  RDATA wire format
///
///   The RDATA for the SVCB RR consists of:
///
///   *  a 2 octet field for SvcPriority as an integer in network byte
///      order.
///   *  the uncompressed, fully-qualified TargetName, represented as a
///      sequence of length-prefixed labels as in Section 3.1 of [RFC1035].
///   *  the SvcParams, consuming the remainder of the record (so smaller
///      than 65535 octets and constrained by the RDATA and DNS message
///      sizes).
///
///   When the list of SvcParams is non-empty (ServiceMode), it contains a
///   series of SvcParamKey=SvcParamValue pairs, represented as:
///
///   *  a 2 octet field containing the SvcParamKey as an integer in
///      network byte order.  (See Section 14.3.2 for the defined values.)
///   *  a 2 octet field containing the length of the SvcParamValue as an
///      integer between 0 and 65535 in network byte order (but constrained
///      by the RDATA and DNS message sizes).
///   *  an octet string of this length whose contents are in a format
///      determined by the SvcParamKey.
///
///   SvcParamKeys SHALL appear in increasing numeric order.
///
///   Clients MUST consider an RR malformed if:
///
///   *  the end of the RDATA occurs within a SvcParam.
///   *  SvcParamKeys are not in strictly increasing numeric order.
///   *  the SvcParamValue for an SvcParamKey does not have the expected
///      format.
///
///   Note that the second condition implies that there are no duplicate
///   SvcParamKeys.
///
///   If any RRs are malformed, the client MUST reject the entire RRSet and
///   fall back to non-SVCB connection establishment.
/// ```
#[cfg_attr(feature = "serde-config", derive(Deserialize, Serialize))]
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
pub struct SVCB {
    svc_priority: u16,
    target_name: Name,
    svc_params: Vec<(SvcParamKey, SvcParamValue)>,
}

impl SVCB {
    /// Create a new SVCB record from parts
    ///
    /// It is up to the caller to validate the data going into the record
    pub fn new(
        svc_priority: u16,
        target_name: Name,
        svc_params: Vec<(SvcParamKey, SvcParamValue)>,
    ) -> Self {
        Self {
            svc_priority,
            target_name,
            svc_params,
        }
    }

    ///  [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-2.4.1)
    /// ```text
    /// 2.4.1.  SvcPriority
    ///
    ///   When SvcPriority is 0 the SVCB record is in AliasMode
    ///   (Section 2.4.2).  Otherwise, it is in ServiceMode (Section 2.4.3).
    ///
    ///   Within a SVCB RRSet, all RRs SHOULD have the same Mode.  If an RRSet
    ///   contains a record in AliasMode, the recipient MUST ignore any
    ///   ServiceMode records in the set.
    ///
    ///   RRSets are explicitly unordered collections, so the SvcPriority field
    ///   is used to impose an ordering on SVCB RRs.  SVCB RRs with a smaller
    ///   SvcPriority value SHOULD be given preference over RRs with a larger
    ///   SvcPriority value.
    ///
    ///   When receiving an RRSet containing multiple SVCB records with the
    ///   same SvcPriority value, clients SHOULD apply a random shuffle within
    ///   a priority level to the records before using them, to ensure uniform
    ///   load-balancing.
    /// ```
    pub fn svc_priority(&self) -> u16 {
        self.svc_priority
    }

    ///  [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-2.5)
    /// ```text
    /// 2.5.  Special handling of "." in TargetName
    ///
    ///   If TargetName has the value "." (represented in the wire format as a
    ///    zero-length label), special rules apply.
    ///
    /// 2.5.1.  AliasMode
    ///
    ///    For AliasMode SVCB RRs, a TargetName of "." indicates that the
    ///    service is not available or does not exist.  This indication is
    ///    advisory: clients encountering this indication MAY ignore it and
    ///    attempt to connect without the use of SVCB.
    ///
    /// 2.5.2.  ServiceMode
    ///
    ///    For ServiceMode SVCB RRs, if TargetName has the value ".", then the
    ///    owner name of this record MUST be used as the effective TargetName.
    ///
    ///    For example, in the following example "svc2.example.net" is the
    ///    effective TargetName:
    ///
    ///    example.com.      7200  IN HTTPS 0 svc.example.net.
    ///    svc.example.net.  7200  IN CNAME svc2.example.net.
    ///    svc2.example.net. 7200  IN HTTPS 1 . port=8002 echconfig="..."
    ///    svc2.example.net. 300   IN A     192.0.2.2
    ///    svc2.example.net. 300   IN AAAA  2001:db8::2
    /// ```
    pub fn target_name(&self) -> &Name {
        &self.target_name
    }

    /// See [`SvcParamKey`] for details on each parameter
    pub fn svc_params(&self) -> &[(SvcParamKey, SvcParamValue)] {
        &self.svc_params
    }
}

/// ```text
/// 14.3.2.  Initial contents
///
///   The "Service Binding (SVCB) Parameter Registry" shall initially be
///   populated with the registrations below:
///
///   +=============+=================+======================+===========+
///   | Number      | Name            | Meaning              | Reference |
///   +=============+=================+======================+===========+
///   | 0           | mandatory       | Mandatory keys in    | (This     |
///   |             |                 | this RR              | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 1           | alpn            | Additional supported | (This     |
///   |             |                 | protocols            | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 2           | no-default-alpn | No support for       | (This     |
///   |             |                 | default protocol     | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 3           | port            | Port for alternative | (This     |
///   |             |                 | endpoint             | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 4           | ipv4hint        | IPv4 address hints   | (This     |
///   |             |                 |                      | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 5           | echconfig       | Encrypted            | (This     |
///   |             |                 | ClientHello info     | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 6           | ipv6hint        | IPv6 address hints   | (This     |
///   |             |                 |                      | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 65280-65534 | keyNNNNN        | Private Use          | (This     |
///   |             |                 |                      | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 65535       | key65535        | Reserved ("Invalid   | (This     |
///   |             |                 | key")                | document) |
///   +-------------+-----------------+----------------------+-----------+
///
/// parsing done via:
///   *  a 2 octet field containing the SvcParamKey as an integer in
///      network byte order.  (See Section 14.3.2 for the defined values.)
/// ```
#[cfg_attr(feature = "serde-config", derive(Deserialize, Serialize))]
#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
pub enum SvcParamKey {
    /// Mandatory keys in this RR
    Mandatory,
    /// Additional supported protocols
    Alpn,
    /// No support for default protocol
    NoDefaultAlpn,
    /// Port for alternative endpoint
    Port,
    /// IPv4 address hints
    Ipv4Hint,
    /// Encrypted ClientHello info
    EchConfig,
    /// IPv6 address hints
    Ipv6Hint,
    /// Private Use
    Key(u16),
    /// Reserved ("Invalid key")
    Key65535,
    /// Unknown
    Unknown(u16),
}

impl From<u16> for SvcParamKey {
    fn from(val: u16) -> Self {
        match val {
            0 => Self::Mandatory,
            1 => Self::Alpn,
            2 => Self::NoDefaultAlpn,
            3 => Self::Port,
            4 => Self::Ipv4Hint,
            5 => Self::EchConfig,
            6 => Self::Ipv6Hint,
            65280..=65534 => Self::Key(val),
            65535 => Self::Key65535,
            _ => Self::Unknown(val),
        }
    }
}

impl From<SvcParamKey> for u16 {
    fn from(val: SvcParamKey) -> Self {
        match val {
            SvcParamKey::Mandatory => 0,
            SvcParamKey::Alpn => 1,
            SvcParamKey::NoDefaultAlpn => 2,
            SvcParamKey::Port => 3,
            SvcParamKey::Ipv4Hint => 4,
            SvcParamKey::EchConfig => 5,
            SvcParamKey::Ipv6Hint => 6,
            SvcParamKey::Key(val) => val,
            SvcParamKey::Key65535 => 65535,
            SvcParamKey::Unknown(val) => val,
        }
    }
}

impl<'r> BinDecodable<'r> for SvcParamKey {
    // a 2 octet field containing the SvcParamKey as an integer in
    //      network byte order.  (See Section 14.3.2 for the defined values.)
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        Ok(decoder.read_u16()?.unverified(/*any u16 is valid*/).into())
    }
}

impl BinEncodable for SvcParamKey {
    // a 2 octet field containing the SvcParamKey as an integer in
    //      network byte order.  (See Section 14.3.2 for the defined values.)
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        encoder.emit_u16((*self).into())
    }
}

impl fmt::Display for SvcParamKey {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        match *self {
            SvcParamKey::Mandatory => f.write_str("mandatory")?,
            SvcParamKey::Alpn => f.write_str("alpn")?,
            SvcParamKey::NoDefaultAlpn => f.write_str("no-default-alpn")?,
            SvcParamKey::Port => f.write_str("port")?,
            SvcParamKey::Ipv4Hint => f.write_str("ipv4hint")?,
            SvcParamKey::EchConfig => f.write_str("echconfig")?,
            SvcParamKey::Ipv6Hint => f.write_str("ipv6hint")?,
            SvcParamKey::Key(val) => write!(f, "key{}", val)?,
            SvcParamKey::Key65535 => f.write_str("key65535")?,
            SvcParamKey::Unknown(val) => write!(f, "unknown{}", val)?,
        }

        Ok(())
    }
}

impl std::str::FromStr for SvcParamKey {
    type Err = ProtoError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        /// keys are in the format of key#, e.g. key12344, with a max value of u16
        fn parse_unknown_key(key: &str) -> Result<SvcParamKey, ProtoError> {
            let key_value = key.strip_prefix("key").ok_or_else(|| {
                ProtoError::from(ProtoErrorKind::Msg(format!(
                    "bad formatted key ({}), expected key1234",
                    key
                )))
            })?;

            let key_value = u16::from_str(key_value)?;
            let key = SvcParamKey::from(key_value);
            Ok(key)
        }

        let key = match s {
            "mandatory" => Self::Mandatory,
            "alpn" => Self::Alpn,
            "no-default-alpn" => Self::NoDefaultAlpn,
            "port" => Self::Port,
            "ipv4hint" => Self::Ipv4Hint,
            "echconfig" => Self::EchConfig,
            "ipv6hint" => Self::Ipv6Hint,
            "key65535" => Self::Key65535,
            _ => parse_unknown_key(s)?,
        };

        Ok(key)
    }
}

impl Ord for SvcParamKey {
    fn cmp(&self, other: &Self) -> Ordering {
        u16::from(*self).cmp(&u16::from(*other))
    }
}

impl PartialOrd for SvcParamKey {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

/// Warning, it is currently up to users of this type to validate the data against that expected by the key
///
/// ```text
///   *  a 2 octet field containing the length of the SvcParamValue as an
///      integer between 0 and 65535 in network byte order (but constrained
///      by the RDATA and DNS message sizes).
///   *  an octet string of this length whose contents are in a format
///      determined by the SvcParamKey.
/// ```
#[cfg_attr(feature = "serde-config", derive(Deserialize, Serialize))]
#[derive(Debug, PartialEq, Eq, Hash, Clone, EnumAsInner)]
pub enum SvcParamValue {
    ///    In a ServiceMode RR, a SvcParamKey is considered "mandatory" if the
    ///    RR will not function correctly for clients that ignore this
    ///    SvcParamKey.  Each SVCB protocol mapping SHOULD specify a set of keys
    ///    that are "automatically mandatory", i.e. mandatory if they are
    ///    present in an RR.  The SvcParamKey "mandatory" is used to indicate
    ///    any mandatory keys for this RR, in addition to any automatically
    ///    mandatory keys that are present.
    ///
    /// see `Mandatory`
    Mandatory(Mandatory),
    /// The "alpn" and "no-default-alpn" SvcParamKeys together indicate the
    ///    set of Application Layer Protocol Negotiation (ALPN) protocol
    ///    identifiers [Alpn] and associated transport protocols supported by
    ///    this service endpoint.
    Alpn(Alpn),
    /// For "no-default-alpn", the presentation and wire format values MUST
    ///    be empty.
    /// See also `Alpn`
    NoDefaultAlpn,
    /// ```text
    ///    6.2.  "port"
    ///
    ///   The "port" SvcParamKey defines the TCP or UDP port that should be
    ///   used to reach this alternative endpoint.  If this key is not present,
    ///   clients SHALL use the authority endpoint's port number.
    ///
    ///   The presentation "value" of the SvcParamValue is a single decimal
    ///   integer between 0 and 65535 in ASCII.  Any other "value" (e.g. an
    ///   empty value) is a syntax error.  To enable simpler parsing, this
    ///   SvcParam MUST NOT contain escape sequences.
    ///
    ///   The wire format of the SvcParamValue is the corresponding 2 octet
    ///   numeric value in network byte order.
    ///
    ///   If a port-restricting firewall is in place between some client and
    ///   the service endpoint, changing the port number might cause that
    ///   client to lose access to the service, so operators should exercise
    ///   caution when using this SvcParamKey to specify a non-default port.
    /// ```
    Port(u16),
    ///   The "ipv4hint" and "ipv6hint" keys convey IP addresses that clients
    ///   MAY use to reach the service.  If A and AAAA records for TargetName
    ///   are locally available, the client SHOULD ignore these hints.
    ///   Otherwise, clients SHOULD perform A and/or AAAA queries for
    ///   TargetName as in Section 3, and clients SHOULD use the IP address in
    ///   those responses for future connections.  Clients MAY opt to terminate
    ///   any connections using the addresses in hints and instead switch to
    ///   the addresses in response to the TargetName query.  Failure to use A
    ///   and/or AAAA response addresses could negatively impact load balancing
    ///   or other geo-aware features and thereby degrade client performance.
    ///
    /// see `IpHint`
    Ipv4Hint(IpHint<Ipv4Addr>),
    /// ```text
    /// 6.3.  "echconfig"
    ///
    ///   The SvcParamKey to enable Encrypted ClientHello (ECH) is "echconfig".
    ///   Its value is defined in Section 9.  It is applicable to most TLS-
    ///   based protocols.
    ///
    ///   When publishing a record containing an "echconfig" parameter, the
    ///   publisher MUST ensure that all IP addresses of TargetName correspond
    ///   to servers that have access to the corresponding private key or are
    ///   authoritative for the public name.  (See Section 7.2.2 of [ECH] for
    ///   more details about the public name.)  This yields an anonymity set of
    ///   cardinality equal to the number of ECH-enabled server domains
    ///   supported by a given client-facing server.  Thus, even with an
    ///   encrypted ClientHello, an attacker who can enumerate the set of ECH-
    ///   enabled domains supported by a client-facing server can guess the
    ///   correct SNI with probability at least 1/K, where K is the size of
    ///   this ECH-enabled server anonymity set.  This probability may be
    ///   increased via traffic analysis or other mechanisms.
    /// ```
    EchConfig(EchConfig),
    /// See `IpHint`
    Ipv6Hint(IpHint<Ipv6Addr>),
    /// Unparsed network data. Refer to documents on the associated key value
    ///
    /// This will be left as is when read off the wire, and encoded in bas64
    ///    for presentation.
    Unknown(Unknown),
}

impl SvcParamValue {
    // a 2 octet field containing the length of the SvcParamValue as an
    //      integer between 0 and 65535 in network byte order (but constrained
    //      by the RDATA and DNS message sizes).
    fn read(key: SvcParamKey, decoder: &mut BinDecoder<'_>) -> ProtoResult<Self> {
        let len: usize = decoder
            .read_u16()?
            .verify_unwrap(|len| *len as usize <= decoder.len())
            .map(|len| len as usize)
            .map_err(|u| {
                ProtoError::from(format!(
                    "length of SvcParamValue ({}) exceeds remainder in RDATA ({})",
                    u,
                    decoder.len()
                ))
            })?;

        let param_data = decoder.read_slice(len)?.unverified(/*verification to be done by individual param types*/);
        let mut decoder = BinDecoder::new(param_data);

        let value = match key {
            SvcParamKey::Mandatory => Self::Mandatory(Mandatory::read(&mut decoder)?),
            SvcParamKey::Alpn => Self::Alpn(Alpn::read(&mut decoder)?),
            // should always be empty
            SvcParamKey::NoDefaultAlpn => {
                if len > 0 {
                    return Err(ProtoError::from("Alpn expects at least one value"));
                }

                Self::NoDefaultAlpn
            }
            // The wire format of the SvcParamValue is the corresponding 2 octet
            // numeric value in network byte order.
            SvcParamKey::Port => {
                let port = decoder.read_u16()?.unverified(/*all values are legal ports*/);
                Self::Port(port)
            }
            SvcParamKey::Ipv4Hint => Self::Ipv4Hint(IpHint::<Ipv4Addr>::read(&mut decoder)?),
            SvcParamKey::EchConfig => Self::EchConfig(EchConfig::read(&mut decoder)?),
            SvcParamKey::Ipv6Hint => Self::Ipv6Hint(IpHint::<Ipv6Addr>::read(&mut decoder)?),
            SvcParamKey::Key(_) | SvcParamKey::Key65535 | SvcParamKey::Unknown(_) => {
                Self::Unknown(Unknown::read(&mut decoder)?)
            }
        };

        Ok(value)
    }
}

impl BinEncodable for SvcParamValue {
    // a 2 octet field containing the length of the SvcParamValue as an
    //      integer between 0 and 65535 in network byte order (but constrained
    //      by the RDATA and DNS message sizes).
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        // set the place for the length...
        let place = encoder.place::<u16>()?;

        match self {
            SvcParamValue::Mandatory(mandatory) => mandatory.emit(encoder)?,
            SvcParamValue::Alpn(alpn) => alpn.emit(encoder)?,
            SvcParamValue::NoDefaultAlpn => (),
            SvcParamValue::Port(port) => encoder.emit_u16(*port)?,
            SvcParamValue::Ipv4Hint(ip_hint) => ip_hint.emit(encoder)?,
            SvcParamValue::EchConfig(ech_config) => ech_config.emit(encoder)?,
            SvcParamValue::Ipv6Hint(ip_hint) => ip_hint.emit(encoder)?,
            SvcParamValue::Unknown(unknown) => unknown.emit(encoder)?,
        }

        // go back and set the length
        let len = u16::try_from(encoder.len_since_place(&place))
            .map_err(|_| ProtoError::from("Total length of SvcParamValue exceeds u16::MAX"))?;
        place.replace(encoder, len)?;

        Ok(())
    }
}

impl fmt::Display for SvcParamValue {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        match self {
            SvcParamValue::Mandatory(mandatory) => write!(f, "{}", mandatory)?,
            SvcParamValue::Alpn(alpn) => write!(f, "{}", alpn)?,
            SvcParamValue::NoDefaultAlpn => (),
            SvcParamValue::Port(port) => write!(f, "{}", port)?,
            SvcParamValue::Ipv4Hint(ip_hint) => write!(f, "{}", ip_hint)?,
            SvcParamValue::EchConfig(ech_config) => write!(f, "{}", ech_config)?,
            SvcParamValue::Ipv6Hint(ip_hint) => write!(f, "{}", ip_hint)?,
            SvcParamValue::Unknown(unknown) => write!(f, "{}", unknown)?,
        }

        Ok(())
    }
}

/// ```text
/// 7.  ServiceMode RR compatibility and mandatory keys
///
///    In a ServiceMode RR, a SvcParamKey is considered "mandatory" if the
///    RR will not function correctly for clients that ignore this
///    SvcParamKey.  Each SVCB protocol mapping SHOULD specify a set of keys
///    that are "automatically mandatory", i.e. mandatory if they are
///    present in an RR.  The SvcParamKey "mandatory" is used to indicate
///    any mandatory keys for this RR, in addition to any automatically
///    mandatory keys that are present.
///
///    A ServiceMode RR is considered "compatible" with a client if the
///    client recognizes all the mandatory keys, and their values indicate
///    that successful connection establishment is possible.  If the SVCB
///    RRSet contains no compatible RRs, the client will generally act as if
///    the RRSet is empty.
///
///    The presentation "value" SHALL be a comma-separated list
///    (Appendix A.1) of one or more valid SvcParamKeys, either by their
///    registered name or in the unknown-key format (Section 2.1).  Keys MAY
///    appear in any order, but MUST NOT appear more than once.  For self-
///    consistency (Section 2.4.3), listed keys MUST also appear in the
///    SvcParams.
///
///    To enable simpler parsing, this SvcParamValue MUST NOT contain escape
///    sequences.
///
///    For example, the following is a valid list of SvcParams:
///
///    echconfig=... key65333=ex1 key65444=ex2 mandatory=key65444,echconfig
///
///    In wire format, the keys are represented by their numeric values in
///    network byte order, concatenated in ascending order.
///
///    This SvcParamKey is always automatically mandatory, and MUST NOT
///    appear in its own value-list.  Other automatically mandatory keys
///    SHOULD NOT appear in the list either.  (Including them wastes space
///    and otherwise has no effect.)
/// ```
#[cfg_attr(feature = "serde-config", derive(Deserialize, Serialize))]
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
#[repr(transparent)]
pub struct Mandatory(pub Vec<SvcParamKey>);

impl<'r> BinDecodable<'r> for Mandatory {
    /// This expects the decoder to be limited to only this field, i.e. the end of input for the decoder
    ///   is the end of input for the fields
    ///
    /// ```text
    ///    In wire format, the keys are represented by their numeric values in
    ///    network byte order, concatenated in ascending order.
    /// ```
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        let mut keys = Vec::with_capacity(1);

        while decoder.peek().is_some() {
            keys.push(SvcParamKey::read(decoder)?);
        }

        if keys.is_empty() {
            return Err(ProtoError::from("Mandatory expects at least one value"));
        }

        Ok(Self(keys))
    }
}

impl BinEncodable for Mandatory {
    /// This expects the decoder to be limited to only this field, i.e. the end of input for the decoder
    ///   is the end of input for the fields
    ///
    /// ```text
    ///    In wire format, the keys are represented by their numeric values in
    ///    network byte order, concatenated in ascending order.
    /// ```
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        if self.0.is_empty() {
            return Err(ProtoError::from("Alpn expects at least one value"));
        }

        // TODO: order by key value
        for key in self.0.iter() {
            key.emit(encoder)?
        }

        Ok(())
    }
}

impl fmt::Display for Mandatory {
    ///    The presentation "value" SHALL be a comma-separated list
    ///    (Appendix A.1) of one or more valid SvcParamKeys, either by their
    ///    registered name or in the unknown-key format (Section 2.1).  Keys MAY
    ///    appear in any order, but MUST NOT appear more than once.  For self-
    ///    consistency (Section 2.4.3), listed keys MUST also appear in the
    ///    SvcParams.
    ///
    ///    To enable simpler parsing, this SvcParamValue MUST NOT contain escape
    ///    sequences.
    ///
    ///    For example, the following is a valid list of SvcParams:
    ///
    ///    echconfig=... key65333=ex1 key65444=ex2 mandatory=key65444,echconfig
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        for key in self.0.iter() {
            // TODO: confirm in the RFC that trailing commas are ok
            write!(f, "{},", key)?;
        }

        Ok(())
    }
}

///  [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-6.1)
///
/// ```text
/// 6.1.  "alpn" and "no-default-alpn"
///
///   The "alpn" and "no-default-alpn" SvcParamKeys together indicate the
///   set of Application Layer Protocol Negotiation (ALPN) protocol
///   identifiers [ALPN] and associated transport protocols supported by
///   this service endpoint.
///
///   As with Alt-Svc [AltSvc], the ALPN protocol identifier is used to
///   identify the application protocol and associated suite of protocols
///   supported by the endpoint (the "protocol suite").  Clients filter the
///   set of ALPN identifiers to match the protocol suites they support,
///   and this informs the underlying transport protocol used (such as
///   QUIC-over-UDP or TLS-over-TCP).
///
///   ALPNs are identified by their registered "Identification Sequence"
///   ("alpn-id"), which is a sequence of 1-255 octets.
///
///   alpn-id = 1*255OCTET
///
///   The presentation "value" SHALL be a comma-separated list
///   (Appendix A.1) of one or more "alpn-id"s.
///
///   The wire format value for "alpn" consists of at least one "alpn-id"
///   prefixed by its length as a single octet, and these length-value
///   pairs are concatenated to form the SvcParamValue.  These pairs MUST
///   exactly fill the SvcParamValue; otherwise, the SvcParamValue is
///   malformed.
///
///   For "no-default-alpn", the presentation and wire format values MUST
///   be empty.  When "no-default-alpn" is specified in an RR, "alpn" must
///   also be specified in order for the RR to be "self-consistent"
///   (Section 2.4.3).
///
///   Each scheme that uses this SvcParamKey defines a "default set" of
///   supported ALPNs, which SHOULD NOT be empty.  To determine the set of
///   protocol suites supported by an endpoint (the "SVCB ALPN set"), the
///   client adds the default set to the list of "alpn-id"s unless the "no-
///   default-alpn" SvcParamKey is present.  The presence of an ALPN
///   protocol in the SVCB ALPN set indicates that this service endpoint,
///   described by TargetName and the other parameters (e.g. "port") offers
///   service with the protocol suite associated with this ALPN protocol.
///
///   ALPN protocol names that do not uniquely identify a protocol suite
///   (e.g. an Identification Sequence that can be used with both TLS and
///   DTLS) are not compatible with this SvcParamKey and MUST NOT be
///   included in the SVCB ALPN set.
///
///   To establish a connection to the endpoint, clients MUST
///
///   1.  Let SVCB-ALPN-Intersection be the set of protocols in the SVCB
///       ALPN set that the client supports.
///
///   2.  Let Intersection-Transports be the set of transports (e.g.  TLS,
///       DTLS, QUIC) implied by the protocols in SVCB-ALPN-Intersection.
///
///   3.  For each transport in Intersection-Transports, construct a
///       ProtocolNameList containing the Identification Sequences of all
///       the client's supported ALPN protocols for that transport, without
///       regard to the SVCB ALPN set.
///
///   For example, if the SVCB ALPN set is ["http/1.1", "h3"], and the
///   client supports HTTP/1.1, HTTP/2, and HTTP/3, the client could
///   attempt to connect using TLS over TCP with a ProtocolNameList of
///   ["http/1.1", "h2"], and could also attempt a connection using QUIC,
///   with a ProtocolNameList of ["h3"].
///
///   Once the client has constructed a ClientHello, protocol negotiation
///   in that handshake proceeds as specified in [ALPN], without regard to
///   the SVCB ALPN set.
///
///   With this procedure in place, an attacker who can modify DNS and
///   network traffic can prevent a successful transport connection, but
///   cannot otherwise interfere with ALPN protocol selection.  This
///   procedure also ensures that each ProtocolNameList includes at least
///   one protocol from the SVCB ALPN set.
///
///   Clients SHOULD NOT attempt connection to a service endpoint whose
///   SVCB ALPN set does not contain any supported protocols.  To ensure
///   consistency of behavior, clients MAY reject the entire SVCB RRSet and
///   fall back to basic connection establishment if all of the RRs
///   indicate "no-default-alpn", even if connection could have succeeded
///   using a non-default alpn.
///
///   For compatibility with clients that require default transports, zone
///   operators SHOULD ensure that at least one RR in each RRSet supports
///   the default transports.
/// ```
#[cfg_attr(feature = "serde-config", derive(Deserialize, Serialize))]
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
#[repr(transparent)]
pub struct Alpn(pub Vec<String>);

impl<'r> BinDecodable<'r> for Alpn {
    /// This expects the decoder to be limited to only this field, i.e. the end of input for the decoder
    ///   is the end of input for the fields
    ///
    /// ```text
    ///   The wire format value for "alpn" consists of at least one "alpn-id"
    ///   prefixed by its length as a single octet, and these length-value
    ///   pairs are concatenated to form the SvcParamValue.  These pairs MUST
    ///   exactly fill the SvcParamValue; otherwise, the SvcParamValue is
    ///   malformed.
    /// ```
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        let mut alpns = Vec::with_capacity(1);

        while decoder.peek().is_some() {
            let alpn = decoder.read_character_data()?.unverified(/*will rely on string parser*/);
            let alpn = String::from_utf8(alpn.to_vec())?;
            alpns.push(alpn);
        }

        if alpns.is_empty() {
            return Err(ProtoError::from("Alpn expects at least one value"));
        }

        Ok(Self(alpns))
    }
}

impl BinEncodable for Alpn {
    ///   The wire format value for "alpn" consists of at least one "alpn-id"
    ///   prefixed by its length as a single octet, and these length-value
    ///   pairs are concatenated to form the SvcParamValue.  These pairs MUST
    ///   exactly fill the SvcParamValue; otherwise, the SvcParamValue is
    ///   malformed.
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        if self.0.is_empty() {
            return Err(ProtoError::from("Alpn expects at least one value"));
        }

        for alpn in self.0.iter() {
            encoder.emit_character_data(alpn)?
        }

        Ok(())
    }
}

impl fmt::Display for Alpn {
    ///   The presentation "value" SHALL be a comma-separated list
    ///   (Appendix A.1) of one or more "alpn-id"s.
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        for alpn in self.0.iter() {
            // TODO: confirm in the RFC that trailing commas are ok
            write!(f, "{},", alpn)?;
        }

        Ok(())
    }
}

/// ```text
/// 9.  SVCB/HTTPS RR parameter for ECH configuration
///
///   The SVCB "echconfig" parameter is defined for conveying the ECH
///   configuration of an alternative endpoint.  In wire format, the value
///   of the parameter is an ECHConfigs vector [ECH], including the
///   redundant length prefix.  In presentation format, the value is a
///   single ECHConfigs encoded in Base64 [base64].  Base64 is used here to
///   simplify integration with TLS server software.  To enable simpler
///   parsing, this SvcParam MUST NOT contain escape sequences.
///
///   When ECH is in use, the TLS ClientHello is divided into an
///   unencrypted "outer" and an encrypted "inner" ClientHello.  The outer
///   ClientHello is an implementation detail of ECH, and its contents are
///   controlled by the ECHConfig in accordance with [ECH].  The inner
///   ClientHello is used for establishing a connection to the service, so
///   its contents may be influenced by other SVCB parameters.  For
///   example, the requirements on the ProtocolNameList in Section 6.1
///   apply only to the inner ClientHello.  Similarly, it is the inner
///   ClientHello whose Server Name Indication identifies the desired
/// ```
#[cfg_attr(feature = "serde-config", derive(Deserialize, Serialize))]
#[derive(PartialEq, Eq, Hash, Clone)]
#[repr(transparent)]
pub struct EchConfig(pub Vec<u8>);

impl<'r> BinDecodable<'r> for EchConfig {
    /// In wire format, the value
    ///   of the parameter is an ECHConfigs vector (ECH), including the
    ///   redundant length prefix (a 2 octet field containing the length of the SvcParamValue
    ///   as an integer between 0 and 65535 in network byte order).
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        let redundant_len = decoder
            .read_u16()?
            .map(|len| len as usize)
            .verify_unwrap(|len| *len <= decoder.len())
            .map_err(|_| ProtoError::from("ECH value length exceeds max size of u16::MAX"))?;

        let data =
            decoder.read_vec(redundant_len)?.unverified(/*up to consumer to validate this data*/);

        Ok(Self(data))
    }
}

impl BinEncodable for EchConfig {
    /// In wire format, the value
    ///   of the parameter is an ECHConfigs vector (ECH), including the
    ///   redundant length prefix (a 2 octet field containing the length of the SvcParamValue
    ///   as an integer between 0 and 65535 in network byte order).
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        let len = u16::try_from(self.0.len())
            .map_err(|_| ProtoError::from("ECH value length exceeds max size of u16::MAX"))?;

        // redundant length...
        encoder.emit_u16(len)?;
        encoder.emit_vec(&self.0)?;

        Ok(())
    }
}

impl fmt::Display for EchConfig {
    /// As the documentation states, the presentation format (what this function outputs) must be a BASE64 encoded string.
    ///   trust-dns will encode to BASE64 during formatting of the internal data, and output the BASE64 value.
    ///
    /// [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-9)
    /// ```text
    /// In presentation format, the value is a
    ///   single ECHConfigs encoded in Base64 [base64].  Base64 is used here to
    ///   simplify integration with TLS server software.  To enable simpler
    ///   parsing, this SvcParam MUST NOT contain escape sequences.
    /// ```
    ///
    /// *note* while the on the wire the EchConfig has a redundant length,
    ///   the RFC is not explicit about including it in the BASE64 encoded value,
    ///   trust-dns will encode the data as it is stored, i.e. without the length encoding.
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        write!(f, "\"{}\"", data_encoding::BASE64.encode(&self.0))
    }
}

impl fmt::Debug for EchConfig {
    /// The debug format for EchConfig will output the value in BASE64 like Display, but will the addition of the type-name.
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        write!(
            f,
            "\"EchConfig ({})\"",
            data_encoding::BASE64.encode(&self.0)
        )
    }
}

/// ```text
///    6.4.  "ipv4hint" and "ipv6hint"
///
///   The "ipv4hint" and "ipv6hint" keys convey IP addresses that clients
///   MAY use to reach the service.  If A and AAAA records for TargetName
///   are locally available, the client SHOULD ignore these hints.
///   Otherwise, clients SHOULD perform A and/or AAAA queries for
///   TargetName as in Section 3, and clients SHOULD use the IP address in
///   those responses for future connections.  Clients MAY opt to terminate
///   any connections using the addresses in hints and instead switch to
///   the addresses in response to the TargetName query.  Failure to use A
///   and/or AAAA response addresses could negatively impact load balancing
///   or other geo-aware features and thereby degrade client performance.
///
///   The presentation "value" SHALL be a comma-separated list
///   (Appendix A.1) of one or more IP addresses of the appropriate family
///   in standard textual format [RFC5952].  To enable simpler parsing,
///   this SvcParamValue MUST NOT contain escape sequences.
///
///   The wire format for each parameter is a sequence of IP addresses in
///   network byte order.  Like an A or AAAA RRSet, the list of addresses
///   represents an unordered collection, and clients SHOULD pick addresses
///   to use in a random order.  An empty list of addresses is invalid.
///
///   When selecting between IPv4 and IPv6 addresses to use, clients may
///   use an approach such as Happy Eyeballs [HappyEyeballsV2].  When only
///   "ipv4hint" is present, IPv6-only clients may synthesize IPv6
///   addresses as specified in [RFC7050] or ignore the "ipv4hint" key and
///   wait for AAAA resolution (Section 3).  Recursive resolvers MUST NOT
///   perform DNS64 ([RFC6147]) on parameters within a SVCB record.  For
///   best performance, server operators SHOULD include an "ipv6hint"
///   parameter whenever they include an "ipv4hint" parameter.
///
///   These parameters are intended to minimize additional connection
///   latency when a recursive resolver is not compliant with the
///   requirements in Section 4, and SHOULD NOT be included if most clients
///   are using compliant recursive resolvers.  When TargetName is the
///   origin hostname or the owner name (which can be written as "."),
///   server operators SHOULD NOT include these hints, because they are
///   unlikely to convey any performance benefit.
/// ```
#[cfg_attr(feature = "serde-config", derive(Deserialize, Serialize))]
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
#[repr(transparent)]
pub struct IpHint<T>(pub Vec<T>);

impl<'r, T> BinDecodable<'r> for IpHint<T>
where
    T: BinDecodable<'r>,
{
    ///   The wire format for each parameter is a sequence of IP addresses in
    ///   network byte order.  Like an A or AAAA RRSet, the list of addresses
    ///   represents an unordered collection, and clients SHOULD pick addresses
    ///   to use in a random order.  An empty list of addresses is invalid.
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        let mut ips = Vec::new();

        while decoder.peek().is_some() {
            ips.push(T::read(decoder)?)
        }

        Ok(Self(ips))
    }
}

impl<T> BinEncodable for IpHint<T>
where
    T: BinEncodable,
{
    ///   The wire format for each parameter is a sequence of IP addresses in
    ///   network byte order.  Like an A or AAAA RRSet, the list of addresses
    ///   represents an unordered collection, and clients SHOULD pick addresses
    ///   to use in a random order.  An empty list of addresses is invalid.
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        for ip in self.0.iter() {
            ip.emit(encoder)?;
        }

        Ok(())
    }
}

impl<T> fmt::Display for IpHint<T>
where
    T: fmt::Display,
{
    ///   The presentation "value" SHALL be a comma-separated list
    ///   (Appendix A.1) of one or more IP addresses of the appropriate family
    ///   in standard textual format [RFC 5952](https://tools.ietf.org/html/rfc5952).  To enable simpler parsing,
    ///   this SvcParamValue MUST NOT contain escape sequences.
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        for ip in self.0.iter() {
            write!(f, "{},", ip)?;
        }

        Ok(())
    }
}

/// [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-2.1)
/// ```text
/// Unrecognized keys are represented in presentation format as
///   "keyNNNNN" where NNNNN is the numeric value of the key type without
///   leading zeros.  A SvcParam in this form SHALL be parsed as specified
///   above, and the decoded "value" SHALL be used as its wire format
///   encoding.
///
///   For some SvcParamKeys, the "value" corresponds to a list or set of
///   items.  Presentation formats for such keys SHOULD use a comma-
///   separated list (Appendix A.1).
///
///   SvcParams in presentation format MAY appear in any order, but keys
///   MUST NOT be repeated.
/// ```
#[cfg_attr(feature = "serde-config", derive(Deserialize, Serialize))]
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
#[repr(transparent)]
pub struct Unknown(pub Vec<Vec<u8>>);

impl<'r> BinDecodable<'r> for Unknown {
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        let mut unknowns = Vec::new();

        while decoder.peek().is_some() {
            let data = decoder.read_character_data()?;
            let data = data.unverified(/*any data is valid here*/).to_vec();
            unknowns.push(data)
        }

        Ok(Self(unknowns))
    }
}

impl BinEncodable for Unknown {
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        for unknown in self.0.iter() {
            encoder.emit_character_data(unknown)?;
        }

        Ok(())
    }
}

impl fmt::Display for Unknown {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        for unknown in self.0.iter() {
            // TODO: this needs to be properly encoded
            write!(f, "\"{}\",", String::from_utf8_lossy(unknown))?;
        }

        Ok(())
    }
}

/// Reads the SVCB record from the decoder.
///
/// ```text
///   Clients MUST consider an RR malformed if:
///
///   *  the end of the RDATA occurs within a SvcParam.
///   *  SvcParamKeys are not in strictly increasing numeric order.
///   *  the SvcParamValue for an SvcParamKey does not have the expected
///      format.
///
///   Note that the second condition implies that there are no duplicate
///   SvcParamKeys.
///
///   If any RRs are malformed, the client MUST reject the entire RRSet and
///   fall back to non-SVCB connection establishment.
/// ```
pub fn read(decoder: &mut BinDecoder<'_>, rdata_length: Restrict<u16>) -> ProtoResult<SVCB> {
    let start_index = decoder.index();

    let svc_priority = decoder.read_u16()?.unverified(/*any u16 is valid*/);
    let target_name = Name::read(decoder)?;

    let mut remainder_len = rdata_length
        .map(|len| len as usize)
        .checked_sub(decoder.index() - start_index)
        .map_err(|len| format!("Bad length for RDATA of SVCB: {}", len))?
        .unverified(); // valid len
    let mut svc_params: Vec<(SvcParamKey, SvcParamValue)> = Vec::new();

    // must have at least 4 bytes left for the key and the length
    while remainder_len >= 4 {
        // a 2 octet field containing the SvcParamKey as an integer in
        //      network byte order.  (See Section 14.3.2 for the defined values.)
        let key = SvcParamKey::read(decoder)?;

        // a 2 octet field containing the length of the SvcParamValue as an
        //      integer between 0 and 65535 in network byte order (but constrained
        //      by the RDATA and DNS message sizes).
        let value = SvcParamValue::read(key, decoder)?;

        if let Some(last_key) = svc_params.last().map(|(key, _)| key) {
            if last_key >= &key {
                return Err(ProtoError::from("SvcParams out of order"));
            }
        }

        svc_params.push((key, value));
        remainder_len = rdata_length
            .map(|len| len as usize)
            .checked_sub(decoder.index() - start_index)
            .map_err(|len| format!("Bad length for RDATA of SVCB: {}", len))?
            .unverified(); // valid len
    }

    Ok(SVCB {
        svc_priority,
        target_name,
        svc_params,
    })
}

/// Write the RData from the given Decoder
pub fn emit(encoder: &mut BinEncoder<'_>, svcb: &SVCB) -> ProtoResult<()> {
    svcb.svc_priority.emit(encoder)?;
    svcb.target_name.emit(encoder)?;

    let mut last_key: Option<SvcParamKey> = None;
    for (key, param) in svcb.svc_params.iter() {
        if let Some(last_key) = last_key {
            if key <= &last_key {
                return Err(ProtoError::from("SvcParams out of order"));
            }
        }

        key.emit(encoder)?;
        param.emit(encoder)?;

        last_key = Some(*key);
    }

    Ok(())
}

/// [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-10.3)
///
/// ```text
/// simple.example. 7200 IN HTTPS 1 . alpn=h3
/// pool  7200 IN HTTPS 1 h3pool alpn=h2,h3 echconfig="123..."
///               HTTPS 2 .      alpn=h2 echconfig="abc..."
/// @     7200 IN HTTPS 0 www
/// _8765._baz.api.example.com. 7200 IN SVCB 0 svc4-baz.example.net.
/// ```
impl fmt::Display for SVCB {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        write!(
            f,
            "{svc_priority} {target_name}",
            svc_priority = self.svc_priority,
            target_name = self.target_name,
        )?;

        for (key, param) in self.svc_params.iter() {
            write!(f, " {key}={param}", key = key, param = param)?
        }

        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn read_svcb_key() {
        assert_eq!(SvcParamKey::Mandatory, 0.into());
        assert_eq!(SvcParamKey::Alpn, 1.into());
        assert_eq!(SvcParamKey::NoDefaultAlpn, 2.into());
        assert_eq!(SvcParamKey::Port, 3.into());
        assert_eq!(SvcParamKey::Ipv4Hint, 4.into());
        assert_eq!(SvcParamKey::EchConfig, 5.into());
        assert_eq!(SvcParamKey::Ipv6Hint, 6.into());
        assert_eq!(SvcParamKey::Key(65280), 65280.into());
        assert_eq!(SvcParamKey::Key(65534), 65534.into());
        assert_eq!(SvcParamKey::Key65535, 65535.into());
        assert_eq!(SvcParamKey::Unknown(65279), 65279.into());
    }

    #[test]
    fn read_svcb_key_to_u16() {
        assert_eq!(u16::from(SvcParamKey::Mandatory), 0);
        assert_eq!(u16::from(SvcParamKey::Alpn), 1);
        assert_eq!(u16::from(SvcParamKey::NoDefaultAlpn), 2);
        assert_eq!(u16::from(SvcParamKey::Port), 3);
        assert_eq!(u16::from(SvcParamKey::Ipv4Hint), 4);
        assert_eq!(u16::from(SvcParamKey::EchConfig), 5);
        assert_eq!(u16::from(SvcParamKey::Ipv6Hint), 6);
        assert_eq!(u16::from(SvcParamKey::Key(65280)), 65280);
        assert_eq!(u16::from(SvcParamKey::Key(65534)), 65534);
        assert_eq!(u16::from(SvcParamKey::Key65535), 65535);
        assert_eq!(u16::from(SvcParamKey::Unknown(65279)), 65279);
    }

    #[track_caller]
    fn test_encode_decode(rdata: SVCB) {
        let mut bytes = Vec::new();
        let mut encoder: BinEncoder<'_> = BinEncoder::new(&mut bytes);
        emit(&mut encoder, &rdata).expect("failed to emit SVCB");
        let bytes = encoder.into_bytes();

        println!("svcb: {}", rdata);
        println!("bytes: {:?}", bytes);

        let mut decoder: BinDecoder<'_> = BinDecoder::new(bytes);
        let read_rdata =
            read(&mut decoder, Restrict::new(bytes.len() as u16)).expect("failed to read back");
        assert_eq!(rdata, read_rdata);
    }

    #[test]
    fn test_encode_decode_svcb() {
        test_encode_decode(SVCB::new(
            0,
            Name::from_utf8("www.example.com.").unwrap(),
            vec![],
        ));
        test_encode_decode(SVCB::new(
            0,
            Name::from_utf8(".").unwrap(),
            vec![(
                SvcParamKey::Alpn,
                SvcParamValue::Alpn(Alpn(vec!["h2".to_string()])),
            )],
        ));
        test_encode_decode(SVCB::new(
            0,
            Name::from_utf8("example.com.").unwrap(),
            vec![
                (
                    SvcParamKey::Mandatory,
                    SvcParamValue::Mandatory(Mandatory(vec![SvcParamKey::Alpn])),
                ),
                (
                    SvcParamKey::Alpn,
                    SvcParamValue::Alpn(Alpn(vec!["h2".to_string()])),
                ),
            ],
        ));
    }

    #[test]
    #[should_panic]
    fn test_encode_decode_svcb_bad_order() {
        test_encode_decode(SVCB::new(
            0,
            Name::from_utf8(".").unwrap(),
            vec![
                (
                    SvcParamKey::Alpn,
                    SvcParamValue::Alpn(Alpn(vec!["h2".to_string()])),
                ),
                (
                    SvcParamKey::Mandatory,
                    SvcParamValue::Mandatory(Mandatory(vec![SvcParamKey::Alpn])),
                ),
            ],
        ));
    }

    #[test]
    fn test_no_panic() {
        const BUF: &[u8] = &[
            255, 121, 0, 0, 0, 0, 40, 255, 255, 160, 160, 0, 0, 0, 64, 0, 1, 255, 158, 0, 0, 0, 8,
            0, 0, 7, 7, 0, 0, 0, 0, 0, 0, 0,
        ];
        assert!(crate::op::Message::from_vec(BUF).is_err());
    }
}