CHANGELOG revision 662de5e1
12019-10-08
2    - 2.4.4
3    - [API] Add lsquic_alpn2ver() to aid parsing Alt-Svc header.
4    - [BUGFIX] NULL dereference when H3 frame header would be split.
5    - [BUGFIX] Do not close fixed-size H3 frame prematurely.
6    - [BUGFIX] Allow PING frames in IETF mini conn.
7    - [BUGFIX] Mini conns: don't send any packets after receiving
8      CONNECTION_CLOSE.
9    - [BUGFIX] Client migration: reserve slot for DCID from transport params.
10    - [BUGFIX] Allow max_early_data_size=0 -- early_data might not be there.
11    - [BUGFIX] Use an invalid stream number to reset BPT cache (zero is now a
12      valid stream number).
13    - [SPEC] Use FINAL_SIZE_ERROR when FIN mismatch is detected.
14    - [OPTIMIZATION] Closed connection only gets one chance to send packets.
15    - [OPTIMIZATION] Flush headers stream before packetizing stream data.
16    - [OPTIMIZATION] process QPACK encoder STREAM frames immediately.
17    - Update ls-qpack to v0.10.1.
18
192019-09-30
20    - 2.4.3
21    - Add GQUIC versions to the list of h3 ALPNs for Alt-Svc header.
22      For example, h3-Q043.  Chrome will switch to using this format at
23      some point in the future.
24    - [BUGFIX] Send correct value in max_streams_uni transport param
25    - [SPEC] Abort IETF QUIC connection if max_early_data_size is not set
26      to 0xFFFFFFFF
27
282019-09-23
29    - 2.4.2
30    - [BUGFIX] H3 framing: fix zero-byte write when space is available
31    - [BUGFIX] Don't send STREAM frame when incoming unidirectgional stream
32      is closed
33    - [BUGFIX] Cancel all pending writes by stream reset by a GOAWAY
34    - [BUGFIX] Fix use-after-free in IETF full conn
35    - [OPTIMIZATION] Wait for session tickets for two seconds and then drop
36      SSL object and crypto streams.
37
382019-09-18
39    - 2.4.0
40    - [FEATURE] QUIC and HTTP/3 Internet Draft 23 support
41
422019-09-13
43    - 2.3.1
44    - [BUGFIX] Fix memory leaks
45    - [BUGFIX] Fix unit tests
46
472019-09-12
48    - 2.3.0
49    - [FEATURE] BBR congestion control is on by default
50    - [BUGFIX] BBR app-limited logic
51    - [BUGFIX] Fix uninitialized warnings in IETF
52    - [BUGFIX] Update ls-qpack to v0.9.14
53    - [CLEANUP] Code cleanup
54
552019-09-11
56    - 2.2.0
57    - [FEATURE] Server code is included in the library
58    - [FEATURE] IETF QUIC and HTTP/3 Support (ID-22)
59
602019-05-13
61    - 1.21.2
62    - [OPTIMIZATION] HPACK: use history to improve compression performance
63
642019-05-06
65    - 1.21.1
66    - [BUGFIX] If FIN or RST not received, don't delay stream destruction.
67    - [OPTIMIZATION] Speed up HPACK encoder by using same hash value to
68      search static and dynamic tables.
69
702019-04-12
71    - 1.21.0
72    - [FEATURE] Add qlog log module.
73
742019-04-01
75    - 1.20.0
76    - [FEATURE] Add support for Q046.
77
782019-03-19
79    - 1.19.6
80    - [BUGFIX] Ensure that Largest Observed does not decrease in ACKs we
81      send.  ACK frames placed in packets in buffered queues (optimization
82      introduced in 1.17.15) can be preceded by an ACK frame generated later.
83      In this case, the older ACK frame should not be sent out, as Chromium-
84      based servers flags decrease in the ACK frame's Largest Observed value
85      as an error.
86
872019-03-05
88    - 1.19.5
89    - [BUGFIX] Use correct public key from PUBS based on KEXS index.
90    - [BUGFIX] Check flags before dispatching writes, avoiding assert.
91    - [BUGFIX] Set :scheme to "https" (instead of "HTTP").
92
932019-02-25
94    - 1.19.4
95    - [BUGFIX] Check buffer bounds when looking up version in 0-RTT blob.
96    - [BUGFIX] http_client: don't fetch 0-rtt info if handshake failed.
97    - Log number of pacer calls at DEBUG, rather than NOTICE, level.
98
992019-02-18
100    - 1.19.3
101    - [BUGFIX] Q044: don't encode packet number in 6 bytes.  Six-byte
102      packet number encoding does not exist in Q044.  This fixes a
103      regression introduced in '[BUGFIX] Buffered packets can contain
104      ACK frames' -- we need to keep QUIC version in mind when selecting
105      the longest possible packet number encoding used for the buffered
106      packet that carries the ACK.
107    - [BUGFIX] Do not increase CWND when timeout occurs.
108    - http_client: support setting handshake timeout on command line.
109      Use -o handshake_to=timeout.
110    - http_client: use -k to connect UDP socket to pick up ICMP errors.
111    - http_client: allow pathless mode, when only handshake is performed
112      without issuing any requests.  This can be done by simply not
113      specifying a -p flag on the command line.
114
1152019-02-11
116    - 1.19.2
117    - [BUGFIX] Begin negotiation with version provided in 0-RTT info.
118    - [BUGFIX] Version checking in zero_rtt deserialize function.
119
1202019-02-04
121    - 1.19.1
122    - [BUGFIX] Fix Windows build.
123
1242019-02-04
125    - 1.19.0
126    - [FEATURE, API Change] 0-RTT support.  Add function to export 0-RTT
127      information; it can be supplied to a subsequent connect() call.
128    - [FEATURE] Add -0 flag to http_client to exercise 0-RTT support.
129    - [BUGFIX] Resuscitate the Windows build.
130    - [BUGFIX] Send HTTP settings (max header list size) if necessary.
131    - [BUGFIX] Buffered packets can contain ACK frames.
132    - [BUGFIX] Make packet writeable once all STREAM frames are elided.
133    - [BUGFIX] Fix potential null dereference when realloc fails.
134    - cmake: simplify build configuration.
135
1362019-01-28
137    - 1.18.0
138    - [API Change] Can specify clock granularity in engine settings.
139    - [BUGFIX] Pacer uses fixed clock granularity.  Since the change on
140      2018-04-09, it is not necessary to try to approximate the next tick
141      time in the pacer: it can use fix clock granularity specified by
142      the user.
143    - [BUGFIX] Do not tick constantly before handshake is done.
144    - [BUGFIX] Do not exit tick prematurely: reuse packet with ACK.  Even
145      if we cannot allocate *more* packets, we could still be able to write
146      to one already allocated.
147    - [BUGFIX] Do not schedule pacer if there are no lost packets.
148
1492019-01-17
150    - 1.17.15
151    - [BUGFIX] http_client: make sure only one read per on_read() callback
152      is performed in the header conversion bypass (-B) mode.
153    - http_client: with -E, assign random priority when stream is created.
154    - [OPTIMIZATION] On immediate write, place an ACK frame into the first
155      buffered packet if an ACK is queued.  This reduces the number of
156      standalone ACK packets.
157    - [OPTIMIZATION] Allow placing more than one STREAM frame from the same
158      stream into an outgoing packet.  This change minimizes the number of
159      buffered packets required to store several small HTTP messages by
160      virtue of allowing more than one STREAM frame from HEADERS stream in
161      the same packet.
162    - [OPTIMIZATION] Flush headers when writing to buffered packets.  This
163      causes the headers to be written to the same buffered packet queue,
164      thereby improving packet utilization, especially for small HTTP
165      messages.
166
1672019-01-16
168    - 1.17.14
169    - [FEATURE] http_client can now collect stats: time to connect, TTFB,
170      time to download, requests per seconds, and bandwidth.  See -t flag.
171    - [BUGFIX] http_client: -B, -K, and -r can be used at the same time.
172    - [BUGFIX] http_client: do not display cert chain before each request.
173      Now this is only done once per connection, if the handshake is
174      successful and -a option is given.
175    - [BUGFIX] Do not wait to dispatch on_close() after reading.  If a
176      stream is scheduled to be closed after on_read() callback returns,
177      close it immediately instead of waiting until the end of the tick.
178      If client creates new request from on_close() event, they will be
179      processed in the same tick instead of waiting for the next one.
180    - [BUGFIX] HEADERS stream is critical: always treat it with highest
181      priority.
182
1832019-01-10
184    - 1.17.12
185    - [FEATURE] http_client can now issue parallel requests in the context
186      of a single connection.  See -w option.
187
1882019-01-03
189    - 1.17.11
190    - Fix strict aliasing warning in optimized compilation.
191
1922018-12-27
193    - 1.17.10
194    - Fix the example program to be able to use parallel connections
195      again.  (See the -n argument.)
196
1972018-12-18
198    - 1.17.9
199    - [BUGFIX] Engine: reduce minimum batch size from 256 to 4
200
2012018-12-10
202    - 1.17.8
203    - [BUGFIX] Fix compilation on FreeBSD and 32-bit Linux
204
2052018-12-03
206    - 1.17.7
207    - [BUGFIX] Do not unset PING alarm before ringing expired alarms.
208      This prevented PING from ever being sent.
209
2102018-11-29
211    - 1.17.6
212    - Add failsafe: resume sending packets after some time
213
214      The change puts a 1-second limit on the amount of time the engine
215      will not send packets after some packets are delayed.  This makes
216      the library robust in case the user does not unblock the engine
217      explicitly using lsquic_engine_send_unsent_packets() call.
218
219    - [BUGFIX] Handle corner cases in send controller when packets are
220      a) delayed or b) dropped during repackaging.
221    - [BUGFIX] Memory leak: destroy buffered packets during controller
222      cleanup.
223
2242018-11-16
225    - 1.17.3
226    - [BUGFIX] Do not send STOP_WAITING frames when using Q044
227
2282018-10-19
229    - 1.17.2
230    - [BUGFIX] Memory leak in test_frame_rw unit test.
231    - [BUGFIX] Parsing packets with short IETF header: do not overwrite
232      flags.  (Only a problem in unit tests -- benign otherwise.)
233
2342018-10-16
235    - 1.17.0
236    - [API Change] Packet out Memory Interface (PMI) update:
237      - Split PMI pool return into pmi_release and pmi_return
238      - PMI callbacks take peer_ctx and is_ipv6 arguments
239    - [BUGFIX] Fix use-after-free when certificate is updated
240    - Silence gcc warning in optimized mode by performing useless
241      initialization
242    - cmake: use the standard variable CMAKE_BUILD_TYPE instead of
243      DEVEL_MODE
244
2452018-10-03
246    - 1.16.0
247    - [API Change] Add lsquic_conn_n_avail_streams()
248    - [BUGFIX] only dispatch crypto stream read events if WANT_READ is on
249
2502018-09-27
251    - 1.15.0
252    - [API Change] Add LSCONN_ST_PEER_GOING_AWAY to the list of conn statuses
253    - [BUGFIX] free uncompressed headers correctly when error occurs
254
2552018-09-12
256    - 1.14.3
257    - [BUGFIX] Do not abort conn on STREAM frame for a reset stream
258    - [BUGFIX] Drop packets that would become empty due to repackaging.
259      Packets on the scheduled queue may be marked for repackaging.
260      Frames such as ACK frame that are never resent are removed from
261      repackaged packets.  We must check that the newly repackaged packet
262      would not be empty.  If it would be, it is destroyed instead and
263      the next packet on the scheduled queue is used.  Note that this
264      change only affects the logic to return the next packet to be sent.
265      Lost packets that are being rescheduled are already processed in
266      this fashion.
267    - Byteswap CID before logging it - this makes it match Chrome CIDs.
268      (Except Q035, which is the last little-endian GQUIC version we
269      support.)
270
2712018-09-06
272    - 1.14.0
273    - [API Change] Disable packet sending if full batch cannot be sent
274      If lsquic_packets_out_f() cannot send the whole batch, disable
275      packet sending until lsquic_engine_send_unsent_packets() is called.
276    - [BUGFIX] Handle case when STREAM frame does not fit.
277    - [BUGFIX] Always allow incoming STREAM frames to overlap.  Peers
278      may send overlapping STREAM frames even if using versions older
279      than Q043.
280    - Custom header set fixes:
281      - set "FIN reached" flag when custom header with FIN flag is
282        claimed;
283      - do not return custom header set for a reset stream.
284
2852018-08-27
286
287    - 1.13.0
288    - [FEATURE, API Change] Add ability to create custom header set
289      objects via callbacks.  This avoids reading and re-parsing
290      headers from the stream.
291
2922018-08-27
293
294    - 1.12.4
295    - Fix memory leak when engine is destroyed
296    - Fix memory leak in http_client
297    - Fix gcc warning in unit tests
298
2992018-08-22
300
301    - 1.12.3
302    - [BUGFIX] Fix duplicate STREAM frame detection
303
3042018-08-20
305
306    - 1.12.2
307    - [BUGFIX] Update count of scheduled bytes when adjusting size of
308      an already-scheduled packet.
309    - Emit info instead of warning messages when stream is used in
310      unexpected ways.
311
3122018-08-17
313
314    - 1.12.0
315    - [FEATURE, API Change] Add support for certificate verification
316
3172018-08-16
318
319    - 1.11.1
320    - [BUGFIX] Fix STOP_WAITING frame processing in the new Q044 code
321
3222018-08-15
323
324    - 1.11.0
325    - [FEATURE] Add support for Q044.
326
3272018-08-09
328
329    - 1.10.2
330    - [BUGFIX] Don't go over limit when creating delayed streams
331
3322018-07-10
333
334    - 1.10.1
335    - [BUGFIX]  process connections after each batch of packets is read
336      This avoids a problem of accumulating a very large list of packets
337      (possible when speeds are high and socket's receive buffer is large)
338      and processing it all at once.
339    - If glibc is older than 2.17, link with rt.  This is necessary for
340      clock_getres(2).
341    - Add version macros to lsquic.h; remove unnecessary includes.
342
3432018-06-13
344
345    - [BUGFIX] allow multiple parallel connections by default
346
347      Use the original method of tracking connections by CIDs by default.
348      If zero-sized CID support is turned on, connections are tracked by
349      the address.  A new connection is not created if another connection
350      is using the same network address
351
3522018-05-30
353
354    - [FEATURE, API CHANGE] Support zero-sized CIDs in received packets
355
3562018-05-24
357
358    - Close connection properly when packet encryption fails
359
3602018-05-23
361
362    - [BUGFIX] Do not produce packet sequence gaps due to delayed packets
363
3642018-05-21
365
366    - [API Change] Add optional callback to call when handshake is done
367    - [API Change, BUGFIX] After send failure, wait until transport available
368
3692018-05-18
370
371    - [API] Expose useful lsquic_ver2str[] in lsquic.h
372    - [BUGFIX] Do not produce packet sequence gaps due to STREAM frame elision
373    - Improve checks of number of incoming streams limit and associated
374      error reporting.
375    - [BUGFIX] Command-line option `-6` now works correctly.
376
3772018-05-16
378
379    - [FEATURE] DNS resolution
380    - [BUGFIX] Frame insertion mis-ID as overlap instead of dup
381    - http_client: fix priority range generated by -E flag
382
3832018-05-09
384
385    - [FEATURE] Add support for Q043.
386    - Support for versions Q037, Q038, Q041, and Q042 has been removed.
387    - Fix typo in debug message.
388    - Fix code indentation.
389    - Add /* fallthru */ comment to stop newer gcc from complaining.
390    - Logger: fix compilation of optimized Windows build.
391
3922018-05-04
393
394    - [FEATURE] Add support for Q042.
395    - Remove comment: MSPC is obsolete (no code changes)
396    - Prog: use lsquic_str2ver() when processing -o version flag
397    - Remove unused CTIM and SRBF transport parameters
398    - Disable QUIC versions Q037 and Q038 by default
399    - Fix Windows compilation by including compat header file in
400      lshpack.c
401    - Address warnings produced by newer versions of gcc
402    - Future-proof: turn off -Werror
403
4042018-05-02
405
406    - [BUGFIX] Make lsquic_conn_quic_version() available
407    - Switch to using ls-hpack 1.1
408    - [BUGFIX] Do not ignore stream resets after receiving FIN
409
4102018-04-27
411
412    - HPACK: do not allow header block to end with table size update.
413
4142018-04-25
415
416    - [BUGFIX] Do not create gap in sent packnos when squeezing delayed
417      packets.
418    - [BUGFIX] sendctl checks for all unacked bytes, not just retx bytes.
419    - [BUGFIX] connections with blocked scheduled packets are not tickable
420      for sending.
421    - [BUGFIX] Conn is tickable if it wants to send a connection-level
422      frame.
423
4242018-04-23
425
426    - Fix busy loop: tickable must make progress.  When connection is
427      self-reporting as tickable, it must make progress when ticked.  There
428      are two issues:
429        1. If there are buffered packets, the connection is only tickable if
430           they can be sent out.
431        2. A connection is tickable if there are streams on the servicing
432           queue.  When the tick occurs, we must service the stream
433           independent of whether any packets are sent.
434    - Fix assertion in pacer which can be incorrect under some
435      conditions.
436    - cmake: do not turn on address sanitizer if in Travis.
437
4382018-04-20
439
440    - [BUGFIX] Fix bug in lsquic_engine_connect() exposed by yesterday's
441      changes.
442
4432018-04-19
444
445    - [BUGFIX] Add connection to Tickable Queue on stream write
446    - cmake: use MSVC variable instead of trying to detect
447    - engine: improve connection incref/decref logging
448    - stream: don't ignore errors that may occur on triggered flush
449    - connection: remove obsolete method
450    - engine: indicate connection as tickable if previous call went
451      over threshold
452
4532018-04-09
454
455    [API Change, OPTIMIZATION] Only process conns that need to be processed
456
457    The API is simplified: do not expose the user code to several
458    queues.  A "connection queue" is now an internal concept.
459    The user processes connections using the single function
460    lsquic_engine_process_conns().  When this function is called,
461    only those connections are processed that need to be processed.
462    A connection needs to be processed when:
463
464        1. New incoming packets have been fed to the connection.
465        2. User wants to read from a stream that is readable.
466        3. User wants to write to a stream that is writeable.
467        4. There are buffered packets that can be sent out.  (This
468           means that the user wrote to a stream outside of the
469           lsquic library callback.)
470        5. A control frame (such as BLOCKED) needs to be sent out.
471        6. A stream needs to be serviced or delayed stream needs to
472           be created.
473        7. An alarm rings.
474        8. Pacer timer expires.
475
476    To achieve this, the library places the connections into two
477    priority queues (min heaps):
478
479        1. Tickable Queue; and
480        2. Advisory Tick Time queue (ATTQ).
481
482    Each time lsquic_engine_process_conns() is called, the Tickable
483    Queue is emptied.  After the connections have been ticked, they are
484    queried again: if a connection is not being closed, it is placed
485    either in the Tickable Queue if it is ready to be ticked again or
486    it is placed in the Advisory Tick Time Queue.  It is assumed that
487    a connection always has at least one timer set (the idle alarm).
488
489    The connections in the Tickable Queue are arranged in the least
490    recently ticked order.  This lets connections that have been quiet
491    longer to get their packets scheduled first.
492
493    This change means that the library no longer needs to be ticked
494    periodically.  The user code can query the library when is the
495    next tick event and schedule it exactly.  When connections are
496    processed, only the tickable connections are processed, not *all*
497    the connections.  When there are no tick events, it means that no
498    timer event is necessary -- only the file descriptor READ event
499    is active.
500
501    The following are improvements and simplifications that have
502    been triggered:
503
504        - Queue of connections with incoming packets is gone.
505        - "Pending Read/Write Events" Queue is gone (along with its
506          history and progress checks).  This queue has become the
507          Tickable Queue.
508        - The connection hash no longer needs to track the connection
509          insertion order.
510
5112018-04-02
512
513    - [FEATURE] Windows support
514
515    - Reduce stack use -- outgoing packet batch is now allocated on the heap.
516
5172018-03-09
518
519    - [OPTIMIZATION] Merge series of ACKs if possible
520
521      Parsed single-range ACK frames (that is the majority of frames) are
522      saved in the connection and their processing is deferred until the
523      connection is ticked.  If several ACKs come in a series between
524      adjacent ticks, we check whether the latest ACK is a strict superset
525      of the saved ACK.  If it is, the older ACK is not processed.
526
527      If ACK frames can be merged, they are merged and only one of them is
528      either processed or saved.
529
530    - [OPTIMIZATION] Speed up ACK verification by simplifying send history.
531
532      Never generate a gap in the sent packet number sequence.  This reduces
533      the send history to a single number instead of potentially a series of
534      packet ranges and thereby speeds up ACK verification.
535
536      By default, detecting a gap in the send history is not fatal: only a
537      single warning is generated per connection.  The connection can continue
538      to operate even if the ACK verification code is not able to detect some
539      inconsistencies.
540
541    - [OPTIMIZATION] Rearrange the lsquic_send_ctl struct
542
543      The first part of struct lsquic_send_ctl now consists of members that
544      are used in lsquic_send_ctl_got_ack() (in the absense of packet loss,
545      which is the normal case).  To speed up reads and writes, we no longer
546      try to save space by using 8- and 16-bit integers.  Use regular integer
547      width for everything.
548
549    - [OPTIMIZATION] Cache size of sent packet.
550
551    - [OPTIMIZATION] Keep track of the largest ACKed in packet_out
552
553      Instead of parsing our own ACK frames when packet has been acked,
554      use the value saved in the packet_out structure when the ACK frame
555      was generated.
556
557    - [OPTIMIZATION] Take RTT sampling conditional out of ACK loop
558
559    - [OPTIMIZATION] ACK processing: only call clock_gettime() if needed
560
561    - [OPTIMIZATION] Several code-level optimizations to ACK processing.
562
563    - Fix: http_client: fix -I flag; switch assert() to abort()
564
5652018-02-26
566    - [API Change] lsquic_engine_connect() returns pointer to the connection
567      object.
568    - [API Change] Add lsquic_conn_get_engine() to get engine object from
569      connection object.
570    - [API Change] Add lsquic_conn_status() to query connection status.
571    - [API Change] Add add lsquic_conn_set_ctx().
572    - [API Change] Add new timestamp format, e.g. 2017-03-21 13:43:46.671345
573    - [OPTIMIZATION] Process handshake STREAM frames as soon as packet
574      arrives.
575    - [OPTIMIZATION] Do not compile expensive send controller sanity check
576      by default.
577    - [OPTIMIZATION] Add fast path to gquic_be_gen_reg_pkt_header.
578    - [OPTIMIZATION] Only make squeeze function call if necessary.
579    - [OPTIMIZATION] Speed up Q039 ACK frame parsing.
580    - [OPTIMIZATION] Fit most used elements of packet_out into first 64 bytes.
581    - [OPTIMIZATION] Keep track of scheduled bytes instead of calculating.
582    - [OPTIMIZATION] Prefetch next unacked packet when processing ACK.
583    - [OPTIMIZATION] Leverage fact that ACK ranges and unacked list are.
584      ordered.
585    - [OPTIMIZATION] Reduce function pointer use for STREAM frame generation
586    - Fix: reset incoming streams that arrive after we send GOAWAY.
587    - Fix: delay client on_new_conn() call until connection is fully set up.
588    - Fixes to buffered packets logic: splitting, STREAM frame elision.
589    - Fix: do not dispatch on_write callback if no packets are available.
590    - Fix WINDOW_UPDATE send and resend logic.
591    - Fix STREAM frame extension code.
592    - Fix: Drop unflushed data when stream is reset.
593    - Switch to tracking CWND using bytes rather than packets.
594    - Fix TCP friendly adjustment in cubic.
595    - Fix: do not generate invalid STOP_WAITING frames during high packet
596      loss.
597    - Pacer fixes.
598
5992017-12-18
600
601    - Fix: better follow cubic curve after idle period
602    - Fix: add missing parts to outgoing packet splitting code
603    - Fix: compilation using gcc 4.8.4
604
6052017-10-31
606
607    - Add APIs.txt -- describes LSQUIC APIs
608
6092017-10-31
610
611    - [API Change] Sendfile-like functionality is gone.  The stream no
612      longer opens files and deals with file descriptors.  (Among other
613      things, this makes the code more portable.)  Three writing functions
614      are provided:
615
616        lsquic_stream_write
617        lsquic_stream_writev
618        lsquic_stream_writef    (NEW)
619
620      lsquic_stream_writef() is given an abstract reader that has function
621      pointers for size() and read() functions which the user can implement.
622      This is the most flexible way.  lsquic_stream_write() and
623      lsquic_stream_writev() are now both implemented as wrappers around
624      lsquic_stream_writef().
625
626    - [OPTIMIZATION] When writing to stream, be it within or without the
627      on_write() callback, place data directly into packet buffer,
628      bypassing auxiliary data structures.  This reduces amount of memory
629      required, for the amount of data that can be written is limited
630      by the congestion window.
631
632      To support writes outside the on_write() callback, we keep N
633      outgoing packet buffers per connection which can be written to
634      by any stream.  One half of these are reserved for the highest
635      priority stream(s), the other half for all other streams.  This way,
636      low-priority streams cannot write instead of high-priority streams
637      and, on the other hand, low-priority streams get a chance to send
638      their packets out.
639
640      The algorithm is as follows:
641
642      - When user writes to stream outside of the callback:
643        - If this is the highest priority stream, place it onto the
644          reserved N/2 queue or fail.
645            (The actual size of this queue is dynamic -- MAX(N/2, CWND) --
646             rather than N/2, allowing high-priority streams to write as
647             much as can be sent.)
648        - If the stream is not the highest priority, try to place the
649          data onto the reserved N/2 queue or fail.
650      - When tick occurs *and* more packets can be scheduled:
651        - Transfer packets from the high N/2 queue to the scheduled
652          queue.
653        - If more scheduling is allowed:
654          - Call on_write callbacks for highest-priority streams,
655            placing resulting packets directly onto the scheduled queue.
656        - If more scheduling is allowed:
657          - Transfer packets from the low N/2 queue to the scheduled
658            queue.
659        - If more scheduling is allowed:
660          - Call on_write callbacks for non-highest-priority streams,
661            placing resulting packets directly onto the scheduled queue
662
663      The number N is currently 20, but it could be varied based on
664      resource usage.
665
666    - If stream is created due to incoming headers, make headers readable
667      from on_new.
668
669    - Outgoing packets are no longer marked non-writeable to prevent placing
670      more than one STREAM frame from the same stream into a single packet.
671      This property is maintained via code flow and an explicit check.
672      Packets for stream data are allocated using a special function.
673
674    - STREAM frame elision is cheaper, as we only perform it if a reset
675      stream has outgoing packets referencing it.
676
677    - lsquic_packet_out_t is smaller, as stream_rec elements are now
678      inside a union.
679
6802017-10-12
681
682    - Do not send RST_STREAM when stream is closed for reading
683    - Raise maximum header size from 4K to 64K
684    - Check header name and value lengths against maximum imposed by HPACK
685    - Fix NULL dereference in stream flow controller
686
6872017-10-09
688
689    - Hide handshake implementation behind a set of function pointers
690    - Use monotonically increasing clock
691    - Make sure that retx delay is not larger than the max of 60 seconds
692
6932017-09-29
694
695    - A few fixes to code and README
696
6972017-09-28
698
699    - Add support for Q041; drop support for Q040
700
7012017-09-27
702
703    - Fix CMakeLists.txt: BoringSSL include and lib was mixed up
704
7052017-09-26
706
707    - Add support for Mac OS
708    - Add support for Raspberry Pi
709    - Fix BoringSSL compilation: include <openssl/hmac.h> explicitly
710
7112017-09-22
712
713    - Initial release
714