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
use super::{
    store, Buffer, Codec, Config, Counts, Frame, Prioritize, Prioritized, Store, Stream, StreamId,
    StreamIdOverflow, WindowSize,
};
use crate::codec::UserError;
use crate::frame::{self, Reason};
use crate::proto::{self, Error, Initiator};

use bytes::Buf;
use tokio::io::AsyncWrite;

use std::cmp::Ordering;
use std::io;
use std::task::{Context, Poll, Waker};

/// Manages state transitions related to outbound frames.
#[derive(Debug)]
pub(super) struct Send {
    /// Stream identifier to use for next initialized stream.
    next_stream_id: Result<StreamId, StreamIdOverflow>,

    /// Any streams with a higher ID are ignored.
    ///
    /// This starts as MAX, but is lowered when a GOAWAY is received.
    ///
    /// > After sending a GOAWAY frame, the sender can discard frames for
    /// > streams initiated by the receiver with identifiers higher than
    /// > the identified last stream.
    max_stream_id: StreamId,

    /// Initial window size of locally initiated streams
    init_window_sz: WindowSize,

    /// Prioritization layer
    prioritize: Prioritize,

    is_push_enabled: bool,

    /// If extended connect protocol is enabled.
    is_extended_connect_protocol_enabled: bool,
}

/// A value to detect which public API has called `poll_reset`.
#[derive(Debug)]
pub(crate) enum PollReset {
    AwaitingHeaders,
    Streaming,
}

impl Send {
    /// Create a new `Send`
    pub fn new(config: &Config) -> Self {
        Send {
            init_window_sz: config.remote_init_window_sz,
            max_stream_id: StreamId::MAX,
            next_stream_id: Ok(config.local_next_stream_id),
            prioritize: Prioritize::new(config),
            is_push_enabled: true,
            is_extended_connect_protocol_enabled: false,
        }
    }

    /// Returns the initial send window size
    pub fn init_window_sz(&self) -> WindowSize {
        self.init_window_sz
    }

    pub fn open(&mut self) -> Result<StreamId, UserError> {
        let stream_id = self.ensure_next_stream_id()?;
        self.next_stream_id = stream_id.next_id();
        Ok(stream_id)
    }

    pub fn reserve_local(&mut self) -> Result<StreamId, UserError> {
        let stream_id = self.ensure_next_stream_id()?;
        self.next_stream_id = stream_id.next_id();
        Ok(stream_id)
    }

    fn check_headers(fields: &http::HeaderMap) -> Result<(), UserError> {
        // 8.1.2.2. Connection-Specific Header Fields
        if fields.contains_key(http::header::CONNECTION)
            || fields.contains_key(http::header::TRANSFER_ENCODING)
            || fields.contains_key(http::header::UPGRADE)
            || fields.contains_key("keep-alive")
            || fields.contains_key("proxy-connection")
        {
            tracing::debug!("illegal connection-specific headers found");
            return Err(UserError::MalformedHeaders);
        } else if let Some(te) = fields.get(http::header::TE) {
            if te != "trailers" {
                tracing::debug!("illegal connection-specific headers found");
                return Err(UserError::MalformedHeaders);
            }
        }
        Ok(())
    }

    pub fn send_push_promise<B>(
        &mut self,
        frame: frame::PushPromise,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        task: &mut Option<Waker>,
    ) -> Result<(), UserError> {
        if !self.is_push_enabled {
            return Err(UserError::PeerDisabledServerPush);
        }

        tracing::trace!(
            "send_push_promise; frame={:?}; init_window={:?}",
            frame,
            self.init_window_sz
        );

        Self::check_headers(frame.fields())?;

        // Queue the frame for sending
        self.prioritize
            .queue_frame(frame.into(), buffer, stream, task);

        Ok(())
    }

    pub fn send_headers<B>(
        &mut self,
        frame: frame::Headers,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        counts: &mut Counts,
        task: &mut Option<Waker>,
    ) -> Result<(), UserError> {
        tracing::trace!(
            "send_headers; frame={:?}; init_window={:?}",
            frame,
            self.init_window_sz
        );

        Self::check_headers(frame.fields())?;

        let end_stream = frame.is_end_stream();

        // Update the state
        stream.state.send_open(end_stream)?;

        let mut pending_open = false;
        if counts.peer().is_local_init(frame.stream_id()) && !stream.is_pending_push {
            self.prioritize.queue_open(stream);
            pending_open = true;
        }

        // Queue the frame for sending
        //
        // This call expects that, since new streams are in the open queue, new
        // streams won't be pushed on pending_send.
        self.prioritize
            .queue_frame(frame.into(), buffer, stream, task);

        // Need to notify the connection when pushing onto pending_open since
        // queue_frame only notifies for pending_send.
        if pending_open {
            if let Some(task) = task.take() {
                task.wake();
            }
        }

        Ok(())
    }

    /// Send an explicit RST_STREAM frame
    pub fn send_reset<B>(
        &mut self,
        reason: Reason,
        initiator: Initiator,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        counts: &mut Counts,
        task: &mut Option<Waker>,
    ) {
        let is_reset = stream.state.is_reset();
        let is_closed = stream.state.is_closed();
        let is_empty = stream.pending_send.is_empty();
        let stream_id = stream.id;

        tracing::trace!(
            "send_reset(..., reason={:?}, initiator={:?}, stream={:?}, ..., \
             is_reset={:?}; is_closed={:?}; pending_send.is_empty={:?}; \
             state={:?} \
             ",
            reason,
            initiator,
            stream_id,
            is_reset,
            is_closed,
            is_empty,
            stream.state
        );

        if is_reset {
            // Don't double reset
            tracing::trace!(
                " -> not sending RST_STREAM ({:?} is already reset)",
                stream_id
            );
            return;
        }

        // Transition the state to reset no matter what.
        stream.set_reset(reason, initiator);

        // If closed AND the send queue is flushed, then the stream cannot be
        // reset explicitly, either. Implicit resets can still be queued.
        if is_closed && is_empty {
            tracing::trace!(
                " -> not sending explicit RST_STREAM ({:?} was closed \
                 and send queue was flushed)",
                stream_id
            );
            return;
        }

        // Clear all pending outbound frames.
        // Note that we don't call `self.recv_err` because we want to enqueue
        // the reset frame before transitioning the stream inside
        // `reclaim_all_capacity`.
        self.prioritize.clear_queue(buffer, stream);

        let frame = frame::Reset::new(stream.id, reason);

        tracing::trace!("send_reset -- queueing; frame={:?}", frame);
        self.prioritize
            .queue_frame(frame.into(), buffer, stream, task);
        self.prioritize.reclaim_all_capacity(stream, counts);
    }

    pub fn schedule_implicit_reset(
        &mut self,
        stream: &mut store::Ptr,
        reason: Reason,
        counts: &mut Counts,
        task: &mut Option<Waker>,
    ) {
        if stream.state.is_closed() {
            // Stream is already closed, nothing more to do
            return;
        }

        stream.state.set_scheduled_reset(reason);

        self.prioritize.reclaim_reserved_capacity(stream, counts);
        self.prioritize.schedule_send(stream, task);
    }

    pub fn send_data<B>(
        &mut self,
        frame: frame::Data<B>,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        counts: &mut Counts,
        task: &mut Option<Waker>,
    ) -> Result<(), UserError>
    where
        B: Buf,
    {
        self.prioritize
            .send_data(frame, buffer, stream, counts, task)
    }

    pub fn send_trailers<B>(
        &mut self,
        frame: frame::Headers,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        counts: &mut Counts,
        task: &mut Option<Waker>,
    ) -> Result<(), UserError> {
        // TODO: Should this logic be moved into state.rs?
        if !stream.state.is_send_streaming() {
            return Err(UserError::UnexpectedFrameType);
        }

        stream.state.send_close();

        tracing::trace!("send_trailers -- queuing; frame={:?}", frame);
        self.prioritize
            .queue_frame(frame.into(), buffer, stream, task);

        // Release any excess capacity
        self.prioritize.reserve_capacity(0, stream, counts);

        Ok(())
    }

    pub fn poll_complete<T, B>(
        &mut self,
        cx: &mut Context,
        buffer: &mut Buffer<Frame<B>>,
        store: &mut Store,
        counts: &mut Counts,
        dst: &mut Codec<T, Prioritized<B>>,
    ) -> Poll<io::Result<()>>
    where
        T: AsyncWrite + Unpin,
        B: Buf,
    {
        self.prioritize
            .poll_complete(cx, buffer, store, counts, dst)
    }

    /// Request capacity to send data
    pub fn reserve_capacity(
        &mut self,
        capacity: WindowSize,
        stream: &mut store::Ptr,
        counts: &mut Counts,
    ) {
        self.prioritize.reserve_capacity(capacity, stream, counts)
    }

    pub fn poll_capacity(
        &mut self,
        cx: &Context,
        stream: &mut store::Ptr,
    ) -> Poll<Option<Result<WindowSize, UserError>>> {
        if !stream.state.is_send_streaming() {
            return Poll::Ready(None);
        }

        if !stream.send_capacity_inc {
            stream.wait_send(cx);
            return Poll::Pending;
        }

        stream.send_capacity_inc = false;

        Poll::Ready(Some(Ok(self.capacity(stream))))
    }

    /// Current available stream send capacity
    pub fn capacity(&self, stream: &mut store::Ptr) -> WindowSize {
        stream.capacity(self.prioritize.max_buffer_size())
    }

    pub fn poll_reset(
        &self,
        cx: &Context,
        stream: &mut Stream,
        mode: PollReset,
    ) -> Poll<Result<Reason, crate::Error>> {
        match stream.state.ensure_reason(mode)? {
            Some(reason) => Poll::Ready(Ok(reason)),
            None => {
                stream.wait_send(cx);
                Poll::Pending
            }
        }
    }

    pub fn recv_connection_window_update(
        &mut self,
        frame: frame::WindowUpdate,
        store: &mut Store,
        counts: &mut Counts,
    ) -> Result<(), Reason> {
        self.prioritize
            .recv_connection_window_update(frame.size_increment(), store, counts)
    }

    pub fn recv_stream_window_update<B>(
        &mut self,
        sz: WindowSize,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        counts: &mut Counts,
        task: &mut Option<Waker>,
    ) -> Result<(), Reason> {
        if let Err(e) = self.prioritize.recv_stream_window_update(sz, stream) {
            tracing::debug!("recv_stream_window_update !!; err={:?}", e);

            self.send_reset(
                Reason::FLOW_CONTROL_ERROR,
                Initiator::Library,
                buffer,
                stream,
                counts,
                task,
            );

            return Err(e);
        }

        Ok(())
    }

    pub(super) fn recv_go_away(&mut self, last_stream_id: StreamId) -> Result<(), Error> {
        if last_stream_id > self.max_stream_id {
            // The remote endpoint sent a `GOAWAY` frame indicating a stream
            // that we never sent, or that we have already terminated on account
            // of previous `GOAWAY` frame. In either case, that is illegal.
            // (When sending multiple `GOAWAY`s, "Endpoints MUST NOT increase
            // the value they send in the last stream identifier, since the
            // peers might already have retried unprocessed requests on another
            // connection.")
            proto_err!(conn:
                "recv_go_away: last_stream_id ({:?}) > max_stream_id ({:?})",
                last_stream_id, self.max_stream_id,
            );
            return Err(Error::library_go_away(Reason::PROTOCOL_ERROR));
        }

        self.max_stream_id = last_stream_id;
        Ok(())
    }

    pub fn handle_error<B>(
        &mut self,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        counts: &mut Counts,
    ) {
        // Clear all pending outbound frames
        self.prioritize.clear_queue(buffer, stream);
        self.prioritize.reclaim_all_capacity(stream, counts);
    }

    pub fn apply_remote_settings<B>(
        &mut self,
        settings: &frame::Settings,
        buffer: &mut Buffer<Frame<B>>,
        store: &mut Store,
        counts: &mut Counts,
        task: &mut Option<Waker>,
    ) -> Result<(), Error> {
        if let Some(val) = settings.is_extended_connect_protocol_enabled() {
            self.is_extended_connect_protocol_enabled = val;
        }

        // Applies an update to the remote endpoint's initial window size.
        //
        // Per RFC 7540 ยง6.9.2:
        //
        // In addition to changing the flow-control window for streams that are
        // not yet active, a SETTINGS frame can alter the initial flow-control
        // window size for streams with active flow-control windows (that is,
        // streams in the "open" or "half-closed (remote)" state). When the
        // value of SETTINGS_INITIAL_WINDOW_SIZE changes, a receiver MUST adjust
        // the size of all stream flow-control windows that it maintains by the
        // difference between the new value and the old value.
        //
        // A change to `SETTINGS_INITIAL_WINDOW_SIZE` can cause the available
        // space in a flow-control window to become negative. A sender MUST
        // track the negative flow-control window and MUST NOT send new
        // flow-controlled frames until it receives WINDOW_UPDATE frames that
        // cause the flow-control window to become positive.
        if let Some(val) = settings.initial_window_size() {
            let old_val = self.init_window_sz;
            self.init_window_sz = val;

            match val.cmp(&old_val) {
                Ordering::Less => {
                    // We must decrease the (remote) window on every open stream.
                    let dec = old_val - val;
                    tracing::trace!("decrementing all windows; dec={}", dec);

                    let mut total_reclaimed = 0;
                    store.try_for_each(|mut stream| {
                        let stream = &mut *stream;

                        tracing::trace!(
                            "decrementing stream window; id={:?}; decr={}; flow={:?}",
                            stream.id,
                            dec,
                            stream.send_flow
                        );

                        // TODO: this decrement can underflow based on received frames!
                        stream
                            .send_flow
                            .dec_send_window(dec)
                            .map_err(proto::Error::library_go_away)?;

                        // It's possible that decreasing the window causes
                        // `window_size` (the stream-specific window) to fall below
                        // `available` (the portion of the connection-level window
                        // that we have allocated to the stream).
                        // In this case, we should take that excess allocation away
                        // and reassign it to other streams.
                        let window_size = stream.send_flow.window_size();
                        let available = stream.send_flow.available().as_size();
                        let reclaimed = if available > window_size {
                            // Drop down to `window_size`.
                            let reclaim = available - window_size;
                            stream
                                .send_flow
                                .claim_capacity(reclaim)
                                .map_err(proto::Error::library_go_away)?;
                            total_reclaimed += reclaim;
                            reclaim
                        } else {
                            0
                        };

                        tracing::trace!(
                            "decremented stream window; id={:?}; decr={}; reclaimed={}; flow={:?}",
                            stream.id,
                            dec,
                            reclaimed,
                            stream.send_flow
                        );

                        // TODO: Should this notify the producer when the capacity
                        // of a stream is reduced? Maybe it should if the capacity
                        // is reduced to zero, allowing the producer to stop work.

                        Ok::<_, proto::Error>(())
                    })?;

                    self.prioritize
                        .assign_connection_capacity(total_reclaimed, store, counts);
                }
                Ordering::Greater => {
                    let inc = val - old_val;

                    store.try_for_each(|mut stream| {
                        self.recv_stream_window_update(inc, buffer, &mut stream, counts, task)
                            .map_err(Error::library_go_away)
                    })?;
                }
                Ordering::Equal => (),
            }
        }

        if let Some(val) = settings.is_push_enabled() {
            self.is_push_enabled = val
        }

        Ok(())
    }

    pub fn clear_queues(&mut self, store: &mut Store, counts: &mut Counts) {
        self.prioritize.clear_pending_capacity(store, counts);
        self.prioritize.clear_pending_send(store, counts);
        self.prioritize.clear_pending_open(store, counts);
    }

    pub fn ensure_not_idle(&self, id: StreamId) -> Result<(), Reason> {
        if let Ok(next) = self.next_stream_id {
            if id >= next {
                return Err(Reason::PROTOCOL_ERROR);
            }
        }
        // if next_stream_id is overflowed, that's ok.

        Ok(())
    }

    pub fn ensure_next_stream_id(&self) -> Result<StreamId, UserError> {
        self.next_stream_id
            .map_err(|_| UserError::OverflowedStreamId)
    }

    pub fn may_have_created_stream(&self, id: StreamId) -> bool {
        if let Ok(next_id) = self.next_stream_id {
            // Peer::is_local_init should have been called beforehand
            debug_assert_eq!(id.is_server_initiated(), next_id.is_server_initiated(),);
            id < next_id
        } else {
            true
        }
    }

    pub(super) fn maybe_reset_next_stream_id(&mut self, id: StreamId) {
        if let Ok(next_id) = self.next_stream_id {
            // Peer::is_local_init should have been called beforehand
            debug_assert_eq!(id.is_server_initiated(), next_id.is_server_initiated());
            if id >= next_id {
                self.next_stream_id = id.next_id();
            }
        }
    }

    pub(crate) fn is_extended_connect_protocol_enabled(&self) -> bool {
        self.is_extended_connect_protocol_enabled
    }
}