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
use crate::session::{Session, SessionCommon, MiddleboxCCS};
use crate::keylog::{KeyLog, NoKeyLog};
use crate::suites::{SupportedCipherSuite, ALL_CIPHERSUITES};
use crate::msgs::enums::ContentType;
use crate::msgs::enums::SignatureScheme;
use crate::msgs::enums::{AlertDescription, HandshakeType, ProtocolVersion};
use crate::msgs::handshake::ServerExtension;
use crate::msgs::message::Message;
use crate::error::TLSError;
use crate::sign;
use crate::verify;
use crate::key;
#[cfg(feature = "logging")]
use crate::log::trace;

use webpki;

use std::sync::Arc;
use std::io::{self, IoSlice};
use std::fmt;

#[macro_use]
mod hs;
mod tls12;
mod tls13;
mod common;
pub mod handy;

/// A trait for the ability to store server session data.
///
/// The keys and values are opaque.
///
/// Both the keys and values should be treated as
/// **highly sensitive data**, containing enough key material
/// to break all security of the corresponding sessions.
///
/// Implementations can be lossy (in other words, forgetting
/// key/value pairs) without any negative security consequences.
///
/// However, note that `take` **must** reliably delete a returned
/// value.  If it does not, there may be security consequences.
///
/// `put` and `take` are mutating operations; this isn't expressed
/// in the type system to allow implementations freedom in
/// how to achieve interior mutability.  `Mutex` is a common
/// choice.
pub trait StoresServerSessions : Send + Sync {
    /// Store session secrets encoded in `value` against `key`,
    /// overwrites any existing value against `key`.  Returns `true`
    /// if the value was stored.
    fn put(&self, key: Vec<u8>, value: Vec<u8>) -> bool;

    /// Find a value with the given `key`.  Return it, or None
    /// if it doesn't exist.
    fn get(&self, key: &[u8]) -> Option<Vec<u8>>;

    /// Find a value with the given `key`.  Return it and delete it;
    /// or None if it doesn't exist.
    fn take(&self, key: &[u8]) -> Option<Vec<u8>>;
}

/// A trait for the ability to encrypt and decrypt tickets.
pub trait ProducesTickets : Send + Sync {
    /// Returns true if this implementation will encrypt/decrypt
    /// tickets.  Should return false if this is a dummy
    /// implementation: the server will not send the SessionTicket
    /// extension and will not call the other functions.
    fn enabled(&self) -> bool;

    /// Returns the lifetime in seconds of tickets produced now.
    /// The lifetime is provided as a hint to clients that the
    /// ticket will not be useful after the given time.
    ///
    /// This lifetime must be implemented by key rolling and
    /// erasure, *not* by storing a lifetime in the ticket.
    ///
    /// The objective is to limit damage to forward secrecy caused
    /// by tickets, not just limiting their lifetime.
    fn get_lifetime(&self) -> u32;

    /// Encrypt and authenticate `plain`, returning the resulting
    /// ticket.  Return None if `plain` cannot be encrypted for
    /// some reason: an empty ticket will be sent and the connection
    /// will continue.
    fn encrypt(&self, plain: &[u8]) -> Option<Vec<u8>>;

    /// Decrypt `cipher`, validating its authenticity protection
    /// and recovering the plaintext.  `cipher` is fully attacker
    /// controlled, so this decryption must be side-channel free,
    /// panic-proof, and otherwise bullet-proof.  If the decryption
    /// fails, return None.
    fn decrypt(&self, cipher: &[u8]) -> Option<Vec<u8>>;
}

/// How to choose a certificate chain and signing key for use
/// in server authentication.
pub trait ResolvesServerCert : Send + Sync {
    /// Choose a certificate chain and matching key given simplified
    /// ClientHello information.
    /// 
    /// Return `None` to abort the handshake.
    fn resolve(&self, client_hello: ClientHello) -> Option<sign::CertifiedKey>;
}

/// A struct representing the received Client Hello
pub struct ClientHello<'a> {
    server_name: Option<webpki::DNSNameRef<'a>>,
    sigschemes: &'a [SignatureScheme],
    alpn: Option<&'a[&'a[u8]]>,
}

impl<'a> ClientHello<'a> {
    /// Creates a new ClientHello
    fn new(server_name: Option<webpki::DNSNameRef<'a>>,
           sigschemes:  &'a [SignatureScheme],
           alpn: Option<&'a[&'a[u8]]>) -> Self {
        ClientHello {server_name, sigschemes, alpn}
    }

    /// Get the server name indicator.
    /// 
    /// Returns `None` if the client did not supply a SNI.
    pub fn server_name(&self) -> Option<webpki::DNSNameRef> {
        self.server_name
    }

    /// Get the compatible signature schemes.
    /// 
    /// Returns standard-specified default if the client omitted this extension.
    pub fn sigschemes(&self) -> &[SignatureScheme] {
        self.sigschemes
    }

    /// Get the alpn.
    /// 
    /// Returns `None` if the client did not include an ALPN extension
    pub fn alpn(&self) -> Option<&'a[&'a[u8]]> {
        self.alpn
    }
}

/// Common configuration for a set of server sessions.
///
/// Making one of these can be expensive, and should be
/// once per process rather than once per connection.
#[derive(Clone)]
pub struct ServerConfig {
    /// List of ciphersuites, in preference order.
    pub ciphersuites: Vec<&'static SupportedCipherSuite>,

    /// Ignore the client's ciphersuite order. Instead,
    /// choose the top ciphersuite in the server list
    /// which is supported by the client.
    pub ignore_client_order: bool,

    /// Our MTU.  If None, we don't limit TLS message sizes.
    pub mtu: Option<usize>,

    /// How to store client sessions.
    pub session_storage: Arc<dyn StoresServerSessions + Send + Sync>,

    /// How to produce tickets.
    pub ticketer: Arc<dyn ProducesTickets>,

    /// How to choose a server cert and key.
    pub cert_resolver: Arc<dyn ResolvesServerCert>,

    /// Protocol names we support, most preferred first.
    /// If empty we don't do ALPN at all.
    pub alpn_protocols: Vec<Vec<u8>>,

    /// Supported protocol versions, in no particular order.
    /// The default is all supported versions.
    pub versions: Vec<ProtocolVersion>,

    /// How to verify client certificates.
    verifier: Arc<dyn verify::ClientCertVerifier>,

    /// How to output key material for debugging.  The default
    /// does nothing.
    pub key_log: Arc<dyn KeyLog>,

    /// Amount of early data to accept; 0 to disable.
    #[cfg(feature = "quic")]    // TLS support unimplemented
    #[doc(hidden)]
    pub max_early_data_size: u32,
}

impl ServerConfig {
    /// Make a `ServerConfig` with a default set of ciphersuites,
    /// no keys/certificates, and no ALPN protocols.  Session resumption
    /// is enabled by storing up to 256 recent sessions in memory. Tickets are
    /// disabled.
    ///
    /// Publicly-available web servers on the internet generally don't do client
    /// authentication; for this use case, `client_cert_verifier` should be a
    /// `NoClientAuth`. Otherwise, use `AllowAnyAuthenticatedClient` or another
    /// implementation to enforce client authentication.
    ///
    /// We don't provide a default for `client_cert_verifier` because the safest
    /// default, requiring client authentication, requires additional
    /// configuration that we cannot provide reasonable defaults for.
    pub fn new(client_cert_verifier: Arc<dyn verify::ClientCertVerifier>) -> ServerConfig {
        ServerConfig::with_ciphersuites(client_cert_verifier, &ALL_CIPHERSUITES)
    }

    /// Make a `ServerConfig` with a custom set of ciphersuites,
    /// no keys/certificates, and no ALPN protocols.  Session resumption
    /// is enabled by storing up to 256 recent sessions in memory. Tickets are
    /// disabled.
    ///
    /// Publicly-available web servers on the internet generally don't do client
    /// authentication; for this use case, `client_cert_verifier` should be a
    /// `NoClientAuth`. Otherwise, use `AllowAnyAuthenticatedClient` or another
    /// implementation to enforce client authentication.
    ///
    /// We don't provide a default for `client_cert_verifier` because the safest
    /// default, requiring client authentication, requires additional
    /// configuration that we cannot provide reasonable defaults for.
    pub fn with_ciphersuites(client_cert_verifier: Arc<dyn verify::ClientCertVerifier>,
                             ciphersuites: &[&'static SupportedCipherSuite]) -> ServerConfig {
        ServerConfig {
            ciphersuites: ciphersuites.to_vec(),
            ignore_client_order: false,
            mtu: None,
            session_storage: handy::ServerSessionMemoryCache::new(256),
            ticketer: Arc::new(handy::NeverProducesTickets {}),
            alpn_protocols: Vec::new(),
            cert_resolver: Arc::new(handy::FailResolveChain {}),
            versions: vec![ ProtocolVersion::TLSv1_3, ProtocolVersion::TLSv1_2 ],
            verifier: client_cert_verifier,
            key_log: Arc::new(NoKeyLog {}),
            #[cfg(feature = "quic")]
            max_early_data_size: 0,
        }
    }

    #[doc(hidden)]
    /// We support a given TLS version if it's quoted in the configured
    /// versions *and* at least one ciphersuite for this version is
    /// also configured.
    pub fn supports_version(&self, v: ProtocolVersion) -> bool {
        self.versions.contains(&v) && self.ciphersuites.iter().any(|cs| cs.usable_for_version(v))
    }

    #[doc(hidden)]
    pub fn get_verifier(&self) -> &dyn verify::ClientCertVerifier {
        self.verifier.as_ref()
    }

    /// Sets the session persistence layer to `persist`.
    pub fn set_persistence(&mut self, persist: Arc<dyn StoresServerSessions + Send + Sync>) {
        self.session_storage = persist;
    }

    /// Sets a single certificate chain and matching private key.  This
    /// certificate and key is used for all subsequent connections,
    /// irrespective of things like SNI hostname.
    ///
    /// Note that the end-entity certificate must have the
    /// [Subject Alternative Name](https://tools.ietf.org/html/rfc6125#section-4.1)
    /// extension to describe, e.g., the valid DNS name. The `commonName` field is
    /// disregarded.
    ///
    /// `cert_chain` is a vector of DER-encoded certificates.
    /// `key_der` is a DER-encoded RSA, ECDSA, or Ed25519 private key.
    ///
    /// This function fails if `key_der` is invalid.
    pub fn set_single_cert(&mut self,
                           cert_chain: Vec<key::Certificate>,
                           key_der: key::PrivateKey) -> Result<(), TLSError> {
        let resolver = handy::AlwaysResolvesChain::new(cert_chain, &key_der)?;
        self.cert_resolver = Arc::new(resolver);
        Ok(())
    }

    /// Sets a single certificate chain, matching private key and OCSP
    /// response.  This certificate and key is used for all subsequent
    /// connections, irrespective of things like SNI hostname.
    ///
    /// `cert_chain` is a vector of DER-encoded certificates.
    /// `key_der` is a DER-encoded RSA, ECDSA, or Ed25519 private key.
    /// `ocsp` is a DER-encoded OCSP response.  Ignored if zero length.
    /// `scts` is an `SignedCertificateTimestampList` encoding (see RFC6962)
    /// and is ignored if empty.
    ///
    /// This function fails if `key_der` is invalid.
    pub fn set_single_cert_with_ocsp_and_sct(&mut self,
                                             cert_chain: Vec<key::Certificate>,
                                             key_der: key::PrivateKey,
                                             ocsp: Vec<u8>,
                                             scts: Vec<u8>) -> Result<(), TLSError> {
        let resolver = handy::AlwaysResolvesChain::new_with_extras(cert_chain,
                                                                   &key_der,
                                                                   ocsp,
                                                                   scts)?;
        self.cert_resolver = Arc::new(resolver);
        Ok(())
    }

    /// Set the ALPN protocol list to the given protocol names.
    /// Overwrites any existing configured protocols.
    ///
    /// The first element in the `protocols` list is the most
    /// preferred, the last is the least preferred.
    pub fn set_protocols(&mut self, protocols: &[Vec<u8>]) {
        self.alpn_protocols.clear();
        self.alpn_protocols.extend_from_slice(protocols);
    }

    /// Overrides the default `ClientCertVerifier` with something else.
    pub fn set_client_certificate_verifier(&mut self, verifier: Arc<dyn verify::ClientCertVerifier>) {
        self.verifier = verifier;
    }
}

pub struct ServerSessionImpl {
    pub config: Arc<ServerConfig>,
    pub common: SessionCommon,
    sni: Option<webpki::DNSName>,
    pub alpn_protocol: Option<Vec<u8>>,
    pub quic_params: Option<Vec<u8>>,
    pub received_resumption_data: Option<Vec<u8>>,
    pub resumption_data: Vec<u8>,
    pub error: Option<TLSError>,
    pub state: Option<Box<dyn hs::State + Send + Sync>>,
    pub client_cert_chain: Option<Vec<key::Certificate>>,
    /// Whether to reject early data even if it would otherwise be accepted
    pub reject_early_data: bool,
}

impl fmt::Debug for ServerSessionImpl {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("ServerSessionImpl").finish()
    }
}

impl ServerSessionImpl {
    pub fn new(server_config: &Arc<ServerConfig>, extra_exts: Vec<ServerExtension>)
               -> ServerSessionImpl {
        ServerSessionImpl {
            config: server_config.clone(),
            common: SessionCommon::new(server_config.mtu, false),
            sni: None,
            alpn_protocol: None,
            quic_params: None,
            received_resumption_data: None,
            resumption_data: Vec::new(),
            error: None,
            state: Some(Box::new(hs::ExpectClientHello::new(server_config, extra_exts))),
            client_cert_chain: None,
            reject_early_data: false,
        }
    }

    pub fn wants_read(&self) -> bool {
        // We want to read more data all the time, except when we
        // have unprocessed plaintext.  This provides back-pressure
        // to the TCP buffers.
        //
        // This also covers the handshake case, because we don't have
        // readable plaintext before handshake has completed.
        !self.common.has_readable_plaintext()
    }

    pub fn wants_write(&self) -> bool {
        !self.common.sendable_tls.is_empty()
    }

    pub fn is_handshaking(&self) -> bool {
        !self.common.traffic
    }

    pub fn set_buffer_limit(&mut self, len: usize) {
        self.common.set_buffer_limit(len)
    }

    pub fn process_msg(&mut self, mut msg: Message) -> Result<(), TLSError> {
        // TLS1.3: drop CCS at any time during handshaking
        if let MiddleboxCCS::Drop = self.common.filter_tls13_ccs(&msg)? {
            trace!("Dropping CCS");
            return Ok(());
        }

        // Decrypt if demanded by current state.
        if self.common.record_layer.is_decrypting() {
            let dm = self.common.decrypt_incoming(msg)?;
            msg = dm;
        }

        // For handshake messages, we need to join them before parsing
        // and processing.
        if self.common.handshake_joiner.want_message(&msg) {
            self.common.handshake_joiner.take_message(msg)
                .ok_or_else(|| {
                            self.common.send_fatal_alert(AlertDescription::DecodeError);
                            TLSError::CorruptMessagePayload(ContentType::Handshake)
                            })?;
            return self.process_new_handshake_messages();
        }

        // Now we can fully parse the message payload.
        msg.decode_payload();

        if msg.is_content_type(ContentType::Alert) {
            return self.common.process_alert(msg);
        }

        self.process_main_protocol(msg)
    }

    pub fn process_new_handshake_messages(&mut self) -> Result<(), TLSError> {
        while let Some(msg) = self.common.handshake_joiner.frames.pop_front() {
            self.process_main_protocol(msg)?;
        }

        Ok(())
    }

    fn queue_unexpected_alert(&mut self) {
        self.common.send_fatal_alert(AlertDescription::UnexpectedMessage);
    }

    fn maybe_send_unexpected_alert(&mut self, rc: hs::NextStateOrError) -> hs::NextStateOrError {
        match rc {
            Err(TLSError::InappropriateMessage { .. }) |
            Err(TLSError::InappropriateHandshakeMessage { .. }) => {
                self.queue_unexpected_alert();
            }
            _ => {}
        };
        rc
    }

    pub fn process_main_protocol(&mut self, msg: Message) -> Result<(), TLSError> {
        if self.common.traffic && !self.common.is_tls13() &&
           msg.is_handshake_type(HandshakeType::ClientHello) {
            self.common.send_warning_alert(AlertDescription::NoRenegotiation);
            return Ok(());
        }

        let state = self.state.take().unwrap();
        let maybe_next_state = state.handle(self, msg);
        let next_state = self.maybe_send_unexpected_alert(maybe_next_state)?;
        self.state = Some(next_state);

        Ok(())
    }

    pub fn process_new_packets(&mut self) -> Result<(), TLSError> {
        if let Some(ref err) = self.error {
            return Err(err.clone());
        }

        if self.common.message_deframer.desynced {
            return Err(TLSError::CorruptMessage);
        }

        while let Some(msg) = self.common.message_deframer.frames.pop_front() {
            match self.process_msg(msg) {
                Ok(_) => {}
                Err(err) => {
                    self.error = Some(err.clone());
                    return Err(err);
                }
            }

        }

        Ok(())
    }

    pub fn get_peer_certificates(&self) -> Option<Vec<key::Certificate>> {
        let certs = self.client_cert_chain.as_ref()?;
        let mut r = Vec::new();

        for cert in certs {
            r.push(cert.clone());
        }

        Some(r)
    }

    pub fn get_alpn_protocol(&self) -> Option<&[u8]> {
        self.alpn_protocol.as_ref().map(AsRef::as_ref)
    }

    pub fn get_protocol_version(&self) -> Option<ProtocolVersion> {
        self.common.negotiated_version
    }

    pub fn get_negotiated_ciphersuite(&self) -> Option<&'static SupportedCipherSuite> {
        self.common.get_suite()
    }

    pub fn get_sni(&self)-> Option<&webpki::DNSName> {
        self.sni.as_ref()
    }

    pub fn set_sni(&mut self, value: webpki::DNSName) {
        // The SNI hostname is immutable once set.
        assert!(self.sni.is_none());
        self.sni = Some(value)
    }

    fn export_keying_material(&self,
                              output: &mut [u8],
                              label: &[u8],
                              context: Option<&[u8]>) -> Result<(), TLSError> {
        self.state
            .as_ref()
            .ok_or_else(|| TLSError::HandshakeNotComplete)
            .and_then(|st| st.export_keying_material(output, label, context))
    }

    fn send_some_plaintext(&mut self, buf: &[u8]) -> io::Result<usize> {
        let mut st = self.state.take();
        st.as_mut()
          .map(|st| st.perhaps_write_key_update(self));
        self.state = st;
        self.common.send_some_plaintext(buf)
    }
}

/// This represents a single TLS server session.
///
/// Send TLS-protected data to the peer using the `io::Write` trait implementation.
/// Read data from the peer using the `io::Read` trait implementation.
#[derive(Debug)]
pub struct ServerSession {
    // We use the pimpl idiom to hide unimportant details.
    pub(crate) imp: ServerSessionImpl,
}

impl ServerSession {
    /// Make a new ServerSession.  `config` controls how
    /// we behave in the TLS protocol.
    pub fn new(config: &Arc<ServerConfig>) -> ServerSession {
        ServerSession { imp: ServerSessionImpl::new(config, vec![]) }
    }

    /// Retrieves the SNI hostname, if any, used to select the certificate and
    /// private key.
    ///
    /// This returns `None` until some time after the client's SNI extension
    /// value is processed during the handshake. It will never be `None` when
    /// the connection is ready to send or process application data, unless the
    /// client does not support SNI.
    ///
    /// This is useful for application protocols that need to enforce that the
    /// SNI hostname matches an application layer protocol hostname. For
    /// example, HTTP/1.1 servers commonly expect the `Host:` header field of
    /// every request on a connection to match the hostname in the SNI extension
    /// when the client provides the SNI extension.
    ///
    /// The SNI hostname is also used to match sessions during session
    /// resumption.
    pub fn get_sni_hostname(&self)-> Option<&str> {
        self.imp.get_sni().map(|s| s.as_ref().into())
    }

    /// Application-controlled portion of the resumption ticket supplied by the client, if any.
    ///
    /// Recovered from the prior session's `set_resumption_data`. Integrity is guaranteed by rustls.
    ///
    /// Returns `Some` iff a valid resumption ticket has been received from the client.
    pub fn received_resumption_data(&self) -> Option<&[u8]> {
        self.imp.received_resumption_data.as_ref().map(|x| &x[..])
    }

    /// Set the resumption data to embed in future resumption tickets supplied to the client.
    ///
    /// Defaults to the empty byte string. Must be less than 2^15 bytes to allow room for other
    /// data. Should be called while `is_handshaking` returns true to ensure all transmitted
    /// resumption tickets are affected.
    ///
    /// Integrity will be assured by rustls, but the data will be visible to the client. If secrecy
    /// from the client is desired, encrypt the data separately.
    pub fn set_resumption_data(&mut self, data: &[u8]) {
        assert!(data.len() < 2usize.pow(15));
        self.imp.resumption_data = data.into();
    }

    /// Explicitly discard early data, notifying the client
    ///
    /// Useful if invariants encoded in `received_resumption_data()` cannot be respected.
    ///
    /// Must be called while `is_handshaking` is true.
    pub fn reject_early_data(&mut self) {
        assert!(self.is_handshaking(), "cannot retroactively reject early data");
        self.imp.reject_early_data = true;
    }
}

impl Session for ServerSession {
    fn read_tls(&mut self, rd: &mut dyn io::Read) -> io::Result<usize> {
        self.imp.common.read_tls(rd)
    }

    /// Writes TLS messages to `wr`.
    fn write_tls(&mut self, wr: &mut dyn io::Write) -> io::Result<usize> {
        self.imp.common.write_tls(wr)
    }

    fn process_new_packets(&mut self) -> Result<(), TLSError> {
        self.imp.process_new_packets()
    }

    fn wants_read(&self) -> bool {
        self.imp.wants_read()
    }

    fn wants_write(&self) -> bool {
        self.imp.wants_write()
    }

    fn is_handshaking(&self) -> bool {
        self.imp.is_handshaking()
    }

    fn set_buffer_limit(&mut self, len: usize) {
        self.imp.set_buffer_limit(len)
    }

    fn send_close_notify(&mut self) {
        self.imp.common.send_close_notify()
    }

    fn get_peer_certificates(&self) -> Option<Vec<key::Certificate>> {
        self.imp.get_peer_certificates()
    }

    fn get_alpn_protocol(&self) -> Option<&[u8]> {
        self.imp.get_alpn_protocol()
    }

    fn get_protocol_version(&self) -> Option<ProtocolVersion> {
        self.imp.get_protocol_version()
    }

    fn export_keying_material(&self,
                              output: &mut [u8],
                              label: &[u8],
                              context: Option<&[u8]>) -> Result<(), TLSError> {
        self.imp.export_keying_material(output, label, context)
    }

    fn get_negotiated_ciphersuite(&self) -> Option<&'static SupportedCipherSuite> {
        self.imp.get_negotiated_ciphersuite()
    }
}

impl io::Read for ServerSession {
    /// Obtain plaintext data received from the peer over this TLS connection.
    ///
    /// If the peer closes the TLS session cleanly, this fails with an error of
    /// kind ErrorKind::ConnectionAborted once all the pending data has been read.
    /// No further data can be received on that connection, so the underlying TCP
    /// connection should closed too.
    ///
    /// Note that support close notify varies in peer TLS libraries: many do not
    /// support it and uncleanly close the TCP connection (this might be
    /// vulnerable to truncation attacks depending on the application protocol).
    /// This means applications using rustls must both handle ErrorKind::ConnectionAborted
    /// from this function, *and* unexpected closure of the underlying TCP connection.
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        self.imp.common.read(buf)
    }
}

impl io::Write for ServerSession {
    /// Send the plaintext `buf` to the peer, encrypting
    /// and authenticating it.  Once this function succeeds
    /// you should call `write_tls` which will output the
    /// corresponding TLS records.
    ///
    /// This function buffers plaintext sent before the
    /// TLS handshake completes, and sends it as soon
    /// as it can.  This buffer is of *unlimited size* so
    /// writing much data before it can be sent will
    /// cause excess memory usage.
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.imp.send_some_plaintext(buf)
    }

    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        let mut sz = 0;
        for buf in bufs {
            sz += self.imp.send_some_plaintext(buf)?;
        }
        Ok(sz)
    }

    fn flush(&mut self) -> io::Result<()> {
        self.imp.common.flush_plaintext();
        Ok(())
    }
}