xref: /lsquic/CHANGELOG

2019-10-31
    - 2.5.0
    - [API] lsquic_engine_connect() can now be passed QUIC version to use.
    - [OPTIMIZATION] Queue opportunistic ACKs if there is data to be sent.
    - [BUGFIX] Don't evict streams from priority iterator if there is
      only one queue.
    - [OPTIMIZATION, BUGFIX] Several other optimizations and bug fixes.
    - Use ls-qpack v0.10.7.

2019-10-24
    - 2.4.10
    - [BUGFIX] IETF QUIC server: fix uninitialized variable use.
    - [BUGFIX] make sure TLSv1.3 is not disabled in SSL object.
    - [BUGFIX] Use issuer name and serial number to cache certs (SKID
      values are not unique).
    - [BUGFIX] Always set the idle alarm in IETF connection so that it
      can time out.
    - Use ls-qpack v0.10.6, as it silences some warnings.

2019-10-21
    - 2.4.8
    - [OPTIMIZATION, BUGFIX] Use ls-qpack v0.10.5.

2019-10-15
    - 2.4.7
    - Add echo client and server to the distibution.
    - Add MD5 client and server to the distibution.
    - Fix http_client: check command-line arguments better, prevent crash.
    - Fix IETF conn: can_write_ack() should only care about APP PNS.
    - Client: delay stream creation until handshake succeds.
    - Reset HTTP stream whose write end is closed prematurely.
    - Fix tickable(): mirror behavior of tick() wrt buffered packets.
    - Log reason why engine is tickable.

2019-10-11
    - 2.4.6
    - Minor code cleanup and logging improvements.
    - Server and client programs: include library version (e.g. 2.4.6)
      into `server' and `user-agent' headers.

2019-10-08
    - 2.4.5
    - [OPTIMIZATION]: flush encoder stream only when necessary.
    - [BUGFIX] Use ls-qpack v0.10.2 for new API -- and for a bug fix.
    - [BUGFIX] Typo in IETF conn SETTINGS writer.
    - Use latest BoringSSL.

2019-10-08
    - 2.4.4
    - [API] Add lsquic_alpn2ver() to aid parsing Alt-Svc header.
    - [BUGFIX] NULL dereference when H3 frame header would be split.
    - [BUGFIX] Do not close fixed-size H3 frame prematurely.
    - [BUGFIX] Allow PING frames in IETF mini conn.
    - [BUGFIX] Mini conns: don't send any packets after receiving
      CONNECTION_CLOSE.
    - [BUGFIX] Client migration: reserve slot for DCID from transport params.
    - [BUGFIX] Allow max_early_data_size=0 -- early_data might not be there.
    - [BUGFIX] Use an invalid stream number to reset BPT cache (zero is now a
      valid stream number).
    - [SPEC] Use FINAL_SIZE_ERROR when FIN mismatch is detected.
    - [OPTIMIZATION] Closed connection only gets one chance to send packets.
    - [OPTIMIZATION] Flush headers stream before packetizing stream data.
    - [OPTIMIZATION] process QPACK encoder STREAM frames immediately.
    - Update ls-qpack to v0.10.1.

2019-09-30
    - 2.4.3
    - Add GQUIC versions to the list of h3 ALPNs for Alt-Svc header.
      For example, h3-Q043.  Chrome will switch to using this format at
      some point in the future.
    - [BUGFIX] Send correct value in max_streams_uni transport param
    - [SPEC] Abort IETF QUIC connection if max_early_data_size is not set
      to 0xFFFFFFFF

2019-09-23
    - 2.4.2
    - [BUGFIX] H3 framing: fix zero-byte write when space is available
    - [BUGFIX] Don't send STREAM frame when incoming unidirectgional stream
      is closed
    - [BUGFIX] Cancel all pending writes by stream reset by a GOAWAY
    - [BUGFIX] Fix use-after-free in IETF full conn
    - [OPTIMIZATION] Wait for session tickets for two seconds and then drop
      SSL object and crypto streams.

2019-09-18
    - 2.4.0
    - [FEATURE] QUIC and HTTP/3 Internet Draft 23 support

2019-09-13
    - 2.3.1
    - [BUGFIX] Fix memory leaks
    - [BUGFIX] Fix unit tests

2019-09-12
    - 2.3.0
    - [FEATURE] BBR congestion control is on by default
    - [BUGFIX] BBR app-limited logic
    - [BUGFIX] Fix uninitialized warnings in IETF
    - [BUGFIX] Update ls-qpack to v0.9.14
    - [CLEANUP] Code cleanup

2019-09-11
    - 2.2.0
    - [FEATURE] Server code is included in the library
    - [FEATURE] IETF QUIC and HTTP/3 Support (ID-22)

2019-05-13
    - 1.21.2
    - [OPTIMIZATION] HPACK: use history to improve compression performance

2019-05-06
    - 1.21.1
    - [BUGFIX] If FIN or RST not received, don't delay stream destruction.
    - [OPTIMIZATION] Speed up HPACK encoder by using same hash value to
      search static and dynamic tables.

2019-04-12
    - 1.21.0
    - [FEATURE] Add qlog log module.

2019-04-01
    - 1.20.0
    - [FEATURE] Add support for Q046.

2019-03-19
    - 1.19.6
    - [BUGFIX] Ensure that Largest Observed does not decrease in ACKs we
      send.  ACK frames placed in packets in buffered queues (optimization
      introduced in 1.17.15) can be preceded by an ACK frame generated later.
      In this case, the older ACK frame should not be sent out, as Chromium-
      based servers flags decrease in the ACK frame's Largest Observed value
      as an error.

2019-03-05
    - 1.19.5
    - [BUGFIX] Use correct public key from PUBS based on KEXS index.
    - [BUGFIX] Check flags before dispatching writes, avoiding assert.
    - [BUGFIX] Set :scheme to "https" (instead of "HTTP").

2019-02-25
    - 1.19.4
    - [BUGFIX] Check buffer bounds when looking up version in 0-RTT blob.
    - [BUGFIX] http_client: don't fetch 0-rtt info if handshake failed.
    - Log number of pacer calls at DEBUG, rather than NOTICE, level.

2019-02-18
    - 1.19.3
    - [BUGFIX] Q044: don't encode packet number in 6 bytes.  Six-byte
      packet number encoding does not exist in Q044.  This fixes a
      regression introduced in '[BUGFIX] Buffered packets can contain
      ACK frames' -- we need to keep QUIC version in mind when selecting
      the longest possible packet number encoding used for the buffered
      packet that carries the ACK.
    - [BUGFIX] Do not increase CWND when timeout occurs.
    - http_client: support setting handshake timeout on command line.
      Use -o handshake_to=timeout.
    - http_client: use -k to connect UDP socket to pick up ICMP errors.
    - http_client: allow pathless mode, when only handshake is performed
      without issuing any requests.  This can be done by simply not
      specifying a -p flag on the command line.

2019-02-11
    - 1.19.2
    - [BUGFIX] Begin negotiation with version provided in 0-RTT info.
    - [BUGFIX] Version checking in zero_rtt deserialize function.

2019-02-04
    - 1.19.1
    - [BUGFIX] Fix Windows build.

2019-02-04
    - 1.19.0
    - [FEATURE, API Change] 0-RTT support.  Add function to export 0-RTT
      information; it can be supplied to a subsequent connect() call.
    - [FEATURE] Add -0 flag to http_client to exercise 0-RTT support.
    - [BUGFIX] Resuscitate the Windows build.
    - [BUGFIX] Send HTTP settings (max header list size) if necessary.
    - [BUGFIX] Buffered packets can contain ACK frames.
    - [BUGFIX] Make packet writeable once all STREAM frames are elided.
    - [BUGFIX] Fix potential null dereference when realloc fails.
    - cmake: simplify build configuration.

2019-01-28
    - 1.18.0
    - [API Change] Can specify clock granularity in engine settings.
    - [BUGFIX] Pacer uses fixed clock granularity.  Since the change on
      2018-04-09, it is not necessary to try to approximate the next tick
      time in the pacer: it can use fix clock granularity specified by
      the user.
    - [BUGFIX] Do not tick constantly before handshake is done.
    - [BUGFIX] Do not exit tick prematurely: reuse packet with ACK.  Even
      if we cannot allocate *more* packets, we could still be able to write
      to one already allocated.
    - [BUGFIX] Do not schedule pacer if there are no lost packets.

2019-01-17
    - 1.17.15
    - [BUGFIX] http_client: make sure only one read per on_read() callback
      is performed in the header conversion bypass (-B) mode.
    - http_client: with -E, assign random priority when stream is created.
    - [OPTIMIZATION] On immediate write, place an ACK frame into the first
      buffered packet if an ACK is queued.  This reduces the number of
      standalone ACK packets.
    - [OPTIMIZATION] Allow placing more than one STREAM frame from the same
      stream into an outgoing packet.  This change minimizes the number of
      buffered packets required to store several small HTTP messages by
      virtue of allowing more than one STREAM frame from HEADERS stream in
      the same packet.
    - [OPTIMIZATION] Flush headers when writing to buffered packets.  This
      causes the headers to be written to the same buffered packet queue,
      thereby improving packet utilization, especially for small HTTP
      messages.

2019-01-16
    - 1.17.14
    - [FEATURE] http_client can now collect stats: time to connect, TTFB,
      time to download, requests per seconds, and bandwidth.  See -t flag.
    - [BUGFIX] http_client: -B, -K, and -r can be used at the same time.
    - [BUGFIX] http_client: do not display cert chain before each request.
      Now this is only done once per connection, if the handshake is
      successful and -a option is given.
    - [BUGFIX] Do not wait to dispatch on_close() after reading.  If a
      stream is scheduled to be closed after on_read() callback returns,
      close it immediately instead of waiting until the end of the tick.
      If client creates new request from on_close() event, they will be
      processed in the same tick instead of waiting for the next one.
    - [BUGFIX] HEADERS stream is critical: always treat it with highest
      priority.

2019-01-10
    - 1.17.12
    - [FEATURE] http_client can now issue parallel requests in the context
      of a single connection.  See -w option.

2019-01-03
    - 1.17.11
    - Fix strict aliasing warning in optimized compilation.

2018-12-27
    - 1.17.10
    - Fix the example program to be able to use parallel connections
      again.  (See the -n argument.)

2018-12-18
    - 1.17.9
    - [BUGFIX] Engine: reduce minimum batch size from 256 to 4

2018-12-10
    - 1.17.8
    - [BUGFIX] Fix compilation on FreeBSD and 32-bit Linux

2018-12-03
    - 1.17.7
    - [BUGFIX] Do not unset PING alarm before ringing expired alarms.
      This prevented PING from ever being sent.

2018-11-29
    - 1.17.6
    - Add failsafe: resume sending packets after some time

      The change puts a 1-second limit on the amount of time the engine
      will not send packets after some packets are delayed.  This makes
      the library robust in case the user does not unblock the engine
      explicitly using lsquic_engine_send_unsent_packets() call.

    - [BUGFIX] Handle corner cases in send controller when packets are
      a) delayed or b) dropped during repackaging.
    - [BUGFIX] Memory leak: destroy buffered packets during controller
      cleanup.

2018-11-16
    - 1.17.3
    - [BUGFIX] Do not send STOP_WAITING frames when using Q044

2018-10-19
    - 1.17.2
    - [BUGFIX] Memory leak in test_frame_rw unit test.
    - [BUGFIX] Parsing packets with short IETF header: do not overwrite
      flags.  (Only a problem in unit tests -- benign otherwise.)

2018-10-16
    - 1.17.0
    - [API Change] Packet out Memory Interface (PMI) update:
      - Split PMI pool return into pmi_release and pmi_return
      - PMI callbacks take peer_ctx and is_ipv6 arguments
    - [BUGFIX] Fix use-after-free when certificate is updated
    - Silence gcc warning in optimized mode by performing useless
      initialization
    - cmake: use the standard variable CMAKE_BUILD_TYPE instead of
      DEVEL_MODE

2018-10-03
    - 1.16.0
    - [API Change] Add lsquic_conn_n_avail_streams()
    - [BUGFIX] only dispatch crypto stream read events if WANT_READ is on

2018-09-27
    - 1.15.0
    - [API Change] Add LSCONN_ST_PEER_GOING_AWAY to the list of conn statuses
    - [BUGFIX] free uncompressed headers correctly when error occurs

2018-09-12
    - 1.14.3
    - [BUGFIX] Do not abort conn on STREAM frame for a reset stream
    - [BUGFIX] Drop packets that would become empty due to repackaging.
      Packets on the scheduled queue may be marked for repackaging.
      Frames such as ACK frame that are never resent are removed from
      repackaged packets.  We must check that the newly repackaged packet
      would not be empty.  If it would be, it is destroyed instead and
      the next packet on the scheduled queue is used.  Note that this
      change only affects the logic to return the next packet to be sent.
      Lost packets that are being rescheduled are already processed in
      this fashion.
    - Byteswap CID before logging it - this makes it match Chrome CIDs.
      (Except Q035, which is the last little-endian GQUIC version we
      support.)

2018-09-06
    - 1.14.0
    - [API Change] Disable packet sending if full batch cannot be sent
      If lsquic_packets_out_f() cannot send the whole batch, disable
      packet sending until lsquic_engine_send_unsent_packets() is called.
    - [BUGFIX] Handle case when STREAM frame does not fit.
    - [BUGFIX] Always allow incoming STREAM frames to overlap.  Peers
      may send overlapping STREAM frames even if using versions older
      than Q043.
    - Custom header set fixes:
      - set "FIN reached" flag when custom header with FIN flag is
        claimed;
      - do not return custom header set for a reset stream.

2018-08-27

    - 1.13.0
    - [FEATURE, API Change] Add ability to create custom header set
      objects via callbacks.  This avoids reading and re-parsing
      headers from the stream.

2018-08-27

    - 1.12.4
    - Fix memory leak when engine is destroyed
    - Fix memory leak in http_client
    - Fix gcc warning in unit tests

2018-08-22

    - 1.12.3
    - [BUGFIX] Fix duplicate STREAM frame detection

2018-08-20

    - 1.12.2
    - [BUGFIX] Update count of scheduled bytes when adjusting size of
      an already-scheduled packet.
    - Emit info instead of warning messages when stream is used in
      unexpected ways.

2018-08-17

    - 1.12.0
    - [FEATURE, API Change] Add support for certificate verification

2018-08-16

    - 1.11.1
    - [BUGFIX] Fix STOP_WAITING frame processing in the new Q044 code

2018-08-15

    - 1.11.0
    - [FEATURE] Add support for Q044.

2018-08-09

    - 1.10.2
    - [BUGFIX] Don't go over limit when creating delayed streams

2018-07-10

    - 1.10.1
    - [BUGFIX]  process connections after each batch of packets is read
      This avoids a problem of accumulating a very large list of packets
      (possible when speeds are high and socket's receive buffer is large)
      and processing it all at once.
    - If glibc is older than 2.17, link with rt.  This is necessary for
      clock_getres(2).
    - Add version macros to lsquic.h; remove unnecessary includes.

2018-06-13

    - [BUGFIX] allow multiple parallel connections by default

      Use the original method of tracking connections by CIDs by default.
      If zero-sized CID support is turned on, connections are tracked by
      the address.  A new connection is not created if another connection
      is using the same network address

2018-05-30

    - [FEATURE, API CHANGE] Support zero-sized CIDs in received packets

2018-05-24

    - Close connection properly when packet encryption fails

2018-05-23

    - [BUGFIX] Do not produce packet sequence gaps due to delayed packets

2018-05-21

    - [API Change] Add optional callback to call when handshake is done
    - [API Change, BUGFIX] After send failure, wait until transport available

2018-05-18

    - [API] Expose useful lsquic_ver2str[] in lsquic.h
    - [BUGFIX] Do not produce packet sequence gaps due to STREAM frame elision
    - Improve checks of number of incoming streams limit and associated
      error reporting.
    - [BUGFIX] Command-line option `-6` now works correctly.

2018-05-16

    - [FEATURE] DNS resolution
    - [BUGFIX] Frame insertion mis-ID as overlap instead of dup
    - http_client: fix priority range generated by -E flag

2018-05-09

    - [FEATURE] Add support for Q043.
    - Support for versions Q037, Q038, Q041, and Q042 has been removed.
    - Fix typo in debug message.
    - Fix code indentation.
    - Add /* fallthru */ comment to stop newer gcc from complaining.
    - Logger: fix compilation of optimized Windows build.

2018-05-04

    - [FEATURE] Add support for Q042.
    - Remove comment: MSPC is obsolete (no code changes)
    - Prog: use lsquic_str2ver() when processing -o version flag
    - Remove unused CTIM and SRBF transport parameters
    - Disable QUIC versions Q037 and Q038 by default
    - Fix Windows compilation by including compat header file in
      lshpack.c
    - Address warnings produced by newer versions of gcc
    - Future-proof: turn off -Werror

2018-05-02

    - [BUGFIX] Make lsquic_conn_quic_version() available
    - Switch to using ls-hpack 1.1
    - [BUGFIX] Do not ignore stream resets after receiving FIN

2018-04-27

    - HPACK: do not allow header block to end with table size update.

2018-04-25

    - [BUGFIX] Do not create gap in sent packnos when squeezing delayed
      packets.
    - [BUGFIX] sendctl checks for all unacked bytes, not just retx bytes.
    - [BUGFIX] connections with blocked scheduled packets are not tickable
      for sending.
    - [BUGFIX] Conn is tickable if it wants to send a connection-level
      frame.

2018-04-23

    - Fix busy loop: tickable must make progress.  When connection is
      self-reporting as tickable, it must make progress when ticked.  There
      are two issues:
        1. If there are buffered packets, the connection is only tickable if
           they can be sent out.
        2. A connection is tickable if there are streams on the servicing
           queue.  When the tick occurs, we must service the stream
           independent of whether any packets are sent.
    - Fix assertion in pacer which can be incorrect under some
      conditions.
    - cmake: do not turn on address sanitizer if in Travis.

2018-04-20

    - [BUGFIX] Fix bug in lsquic_engine_connect() exposed by yesterday's
      changes.

2018-04-19

    - [BUGFIX] Add connection to Tickable Queue on stream write
    - cmake: use MSVC variable instead of trying to detect
    - engine: improve connection incref/decref logging
    - stream: don't ignore errors that may occur on triggered flush
    - connection: remove obsolete method
    - engine: indicate connection as tickable if previous call went
      over threshold

2018-04-09

    [API Change, OPTIMIZATION] Only process conns that need to be processed

    The API is simplified: do not expose the user code to several
    queues.  A "connection queue" is now an internal concept.
    The user processes connections using the single function
    lsquic_engine_process_conns().  When this function is called,
    only those connections are processed that need to be processed.
    A connection needs to be processed when:

        1. New incoming packets have been fed to the connection.
        2. User wants to read from a stream that is readable.
        3. User wants to write to a stream that is writeable.
        4. There are buffered packets that can be sent out.  (This
           means that the user wrote to a stream outside of the
           lsquic library callback.)
        5. A control frame (such as BLOCKED) needs to be sent out.
        6. A stream needs to be serviced or delayed stream needs to
           be created.
        7. An alarm rings.
        8. Pacer timer expires.

    To achieve this, the library places the connections into two
    priority queues (min heaps):

        1. Tickable Queue; and
        2. Advisory Tick Time queue (ATTQ).

    Each time lsquic_engine_process_conns() is called, the Tickable
    Queue is emptied.  After the connections have been ticked, they are
    queried again: if a connection is not being closed, it is placed
    either in the Tickable Queue if it is ready to be ticked again or
    it is placed in the Advisory Tick Time Queue.  It is assumed that
    a connection always has at least one timer set (the idle alarm).

    The connections in the Tickable Queue are arranged in the least
    recently ticked order.  This lets connections that have been quiet
    longer to get their packets scheduled first.

    This change means that the library no longer needs to be ticked
    periodically.  The user code can query the library when is the
    next tick event and schedule it exactly.  When connections are
    processed, only the tickable connections are processed, not *all*
    the connections.  When there are no tick events, it means that no
    timer event is necessary -- only the file descriptor READ event
    is active.

    The following are improvements and simplifications that have
    been triggered:

        - Queue of connections with incoming packets is gone.
        - "Pending Read/Write Events" Queue is gone (along with its
          history and progress checks).  This queue has become the
          Tickable Queue.
        - The connection hash no longer needs to track the connection
          insertion order.

2018-04-02

    - [FEATURE] Windows support

    - Reduce stack use -- outgoing packet batch is now allocated on the heap.

2018-03-09

    - [OPTIMIZATION] Merge series of ACKs if possible

      Parsed single-range ACK frames (that is the majority of frames) are
      saved in the connection and their processing is deferred until the
      connection is ticked.  If several ACKs come in a series between
      adjacent ticks, we check whether the latest ACK is a strict superset
      of the saved ACK.  If it is, the older ACK is not processed.

      If ACK frames can be merged, they are merged and only one of them is
      either processed or saved.

    - [OPTIMIZATION] Speed up ACK verification by simplifying send history.

      Never generate a gap in the sent packet number sequence.  This reduces
      the send history to a single number instead of potentially a series of
      packet ranges and thereby speeds up ACK verification.

      By default, detecting a gap in the send history is not fatal: only a
      single warning is generated per connection.  The connection can continue
      to operate even if the ACK verification code is not able to detect some
      inconsistencies.

    - [OPTIMIZATION] Rearrange the lsquic_send_ctl struct

      The first part of struct lsquic_send_ctl now consists of members that
      are used in lsquic_send_ctl_got_ack() (in the absense of packet loss,
      which is the normal case).  To speed up reads and writes, we no longer
      try to save space by using 8- and 16-bit integers.  Use regular integer
      width for everything.

    - [OPTIMIZATION] Cache size of sent packet.

    - [OPTIMIZATION] Keep track of the largest ACKed in packet_out

      Instead of parsing our own ACK frames when packet has been acked,
      use the value saved in the packet_out structure when the ACK frame
      was generated.

    - [OPTIMIZATION] Take RTT sampling conditional out of ACK loop

    - [OPTIMIZATION] ACK processing: only call clock_gettime() if needed

    - [OPTIMIZATION] Several code-level optimizations to ACK processing.

    - Fix: http_client: fix -I flag; switch assert() to abort()

2018-02-26
    - [API Change] lsquic_engine_connect() returns pointer to the connection
      object.
    - [API Change] Add lsquic_conn_get_engine() to get engine object from
      connection object.
    - [API Change] Add lsquic_conn_status() to query connection status.
    - [API Change] Add add lsquic_conn_set_ctx().
    - [API Change] Add new timestamp format, e.g. 2017-03-21 13:43:46.671345
    - [OPTIMIZATION] Process handshake STREAM frames as soon as packet
      arrives.
    - [OPTIMIZATION] Do not compile expensive send controller sanity check
      by default.
    - [OPTIMIZATION] Add fast path to gquic_be_gen_reg_pkt_header.
    - [OPTIMIZATION] Only make squeeze function call if necessary.
    - [OPTIMIZATION] Speed up Q039 ACK frame parsing.
    - [OPTIMIZATION] Fit most used elements of packet_out into first 64 bytes.
    - [OPTIMIZATION] Keep track of scheduled bytes instead of calculating.
    - [OPTIMIZATION] Prefetch next unacked packet when processing ACK.
    - [OPTIMIZATION] Leverage fact that ACK ranges and unacked list are.
      ordered.
    - [OPTIMIZATION] Reduce function pointer use for STREAM frame generation
    - Fix: reset incoming streams that arrive after we send GOAWAY.
    - Fix: delay client on_new_conn() call until connection is fully set up.
    - Fixes to buffered packets logic: splitting, STREAM frame elision.
    - Fix: do not dispatch on_write callback if no packets are available.
    - Fix WINDOW_UPDATE send and resend logic.
    - Fix STREAM frame extension code.
    - Fix: Drop unflushed data when stream is reset.
    - Switch to tracking CWND using bytes rather than packets.
    - Fix TCP friendly adjustment in cubic.
    - Fix: do not generate invalid STOP_WAITING frames during high packet
      loss.
    - Pacer fixes.

2017-12-18

    - Fix: better follow cubic curve after idle period
    - Fix: add missing parts to outgoing packet splitting code
    - Fix: compilation using gcc 4.8.4

2017-10-31

    - Add APIs.txt -- describes LSQUIC APIs

2017-10-31

    - [API Change] Sendfile-like functionality is gone.  The stream no
      longer opens files and deals with file descriptors.  (Among other
      things, this makes the code more portable.)  Three writing functions
      are provided:

        lsquic_stream_write
        lsquic_stream_writev
        lsquic_stream_writef    (NEW)

      lsquic_stream_writef() is given an abstract reader that has function
      pointers for size() and read() functions which the user can implement.
      This is the most flexible way.  lsquic_stream_write() and
      lsquic_stream_writev() are now both implemented as wrappers around
      lsquic_stream_writef().

    - [OPTIMIZATION] When writing to stream, be it within or without the
      on_write() callback, place data directly into packet buffer,
      bypassing auxiliary data structures.  This reduces amount of memory
      required, for the amount of data that can be written is limited
      by the congestion window.

      To support writes outside the on_write() callback, we keep N
      outgoing packet buffers per connection which can be written to
      by any stream.  One half of these are reserved for the highest
      priority stream(s), the other half for all other streams.  This way,
      low-priority streams cannot write instead of high-priority streams
      and, on the other hand, low-priority streams get a chance to send
      their packets out.

      The algorithm is as follows:

      - When user writes to stream outside of the callback:
        - If this is the highest priority stream, place it onto the
          reserved N/2 queue or fail.
            (The actual size of this queue is dynamic -- MAX(N/2, CWND) --
             rather than N/2, allowing high-priority streams to write as
             much as can be sent.)
        - If the stream is not the highest priority, try to place the
          data onto the reserved N/2 queue or fail.
      - When tick occurs *and* more packets can be scheduled:
        - Transfer packets from the high N/2 queue to the scheduled
          queue.
        - If more scheduling is allowed:
          - Call on_write callbacks for highest-priority streams,
            placing resulting packets directly onto the scheduled queue.
        - If more scheduling is allowed:
          - Transfer packets from the low N/2 queue to the scheduled
            queue.
        - If more scheduling is allowed:
          - Call on_write callbacks for non-highest-priority streams,
            placing resulting packets directly onto the scheduled queue

      The number N is currently 20, but it could be varied based on
      resource usage.

    - If stream is created due to incoming headers, make headers readable
      from on_new.

    - Outgoing packets are no longer marked non-writeable to prevent placing
      more than one STREAM frame from the same stream into a single packet.
      This property is maintained via code flow and an explicit check.
      Packets for stream data are allocated using a special function.

    - STREAM frame elision is cheaper, as we only perform it if a reset
      stream has outgoing packets referencing it.

    - lsquic_packet_out_t is smaller, as stream_rec elements are now
      inside a union.

2017-10-12

    - Do not send RST_STREAM when stream is closed for reading
    - Raise maximum header size from 4K to 64K
    - Check header name and value lengths against maximum imposed by HPACK
    - Fix NULL dereference in stream flow controller

2017-10-09

    - Hide handshake implementation behind a set of function pointers
    - Use monotonically increasing clock
    - Make sure that retx delay is not larger than the max of 60 seconds

2017-09-29

    - A few fixes to code and README

2017-09-28

    - Add support for Q041; drop support for Q040

2017-09-27

    - Fix CMakeLists.txt: BoringSSL include and lib was mixed up

2017-09-26

    - Add support for Mac OS
    - Add support for Raspberry Pi
    - Fix BoringSSL compilation: include <openssl/hmac.h> explicitly

2017-09-22

    - Initial release