v1.11.3
--------------------------------------------------------------------------------
 * Adding defensive code for stream EOS handling, in case the request handler somehow
   missed to signal it the normal way. Should address #167 and #170. 
 
v1.11.2
--------------------------------------------------------------------------------
 * Fixed configure to no longer require ```libcurl-devel```, but only the ```curl```
   command with h2 support for testing.

v1.11.1
--------------------------------------------------------------------------------
 * added test/Makefile.in to the release tar ball, so that peopl just need
   automake to build (reported in #169 by @uhliarik, fix proposed by @notroj)
 * added  -avoid-version to the linker flags (thanks to Oden Erikson, @odeneriksson)
 * added tests for 100 interim responses
 * added tests for trailers
 * added tests for conditional request header
 * added tests for invalid characters in response header
 * added Upgrade: response header tests
 * added vars require configuration tests
 * added ssl renegotiation tests

v1.11.0
--------------------------------------------------------------------------------
 * connection IO event handling reworked. Instead of reacting on incoming bytes, the
   state machine now acts on incoming frames that are affecting it. This reduces
   state transitions.
 * pytest suite now covers some basic tests on h2 selection, GET and POST
 * started to add pytest suite from existing bash tests

v1.10.21
--------------------------------------------------------------------------------
 * Code cleanups from Apache subversion
 * New optional function to query the number of h2 workers from Apache branch

v1.10.20
--------------------------------------------------------------------------------
 * Restore keepalive handling of v1.10.16. Idle connections are kept open
   for the duration.

v1.10.19
--------------------------------------------------------------------------------
 * adding regular memory cleanup when transferring large response bodies. This
   reduces memory footprint and avoids memory exhaustion when transferring large files
   on 32-bit architectures.

v1.10.18
--------------------------------------------------------------------------------
 * fixes a race condition where aborting streams triggers an unnecessary timeout.

v1.10.17
--------------------------------------------------------------------------------
 * accurate reporting of h2 data input/output per request via mod_logio. Fixes
   an issue where output sizes where counted n-times on reused slave connections. See #158.
 * normalized connection prefix logging when trace2 is enabled for direct h2 connection
   detection.

v1.10.16
--------------------------------------------------------------------------------
 * Removed no longer used code in stream cleanup, disabled beam events
   during pool shutdown, discouraged content-encoding filter from applying
   themselves to http2_status responses.

v1.10.15
--------------------------------------------------------------------------------
 * discourage gzip/brotli content encoding on http2-status responses as
   they are inserted into the reponse when filters are already done.

v1.10.14
--------------------------------------------------------------------------------
  * fixed unfair scheduling when number of active connections
     exceeded the scheduling fifo capacity.

v1.10.13
--------------------------------------------------------------------------------
  * avoid unnecessary data retrieval for a trace log. Allow certain
    information retrievals on null bucket beams where it makes sense.
  * Fixed configure to check first for libs and then add compiler flags

v1.10.12
--------------------------------------------------------------------------------
  * Reverting 1.10.11 change since showed no effect on issue #120
  * Fixes a race condition on request body handling.

v1.10.11
--------------------------------------------------------------------------------
  * DoS flow control protection is less agressive as long as active tasks stay
    below worker capacity. Intended to fix problems with media streaming.

v1.10.10
--------------------------------------------------------------------------------
  * adding signalling of data available before waiting on beam buffer to drain. Missing this causes suspended streams to stall and time out.

v1.10.9
--------------------------------------------------------------------------------
  * cleanup of bucket beam change signaling to track down issue #143

v1.10.8
--------------------------------------------------------------------------------
  * a stream could stall and not send any more output to the client which in the end aborts the connection due to a timeout.

v1.10.7
--------------------------------------------------------------------------------
  * disable and give warning when mpm_prefork is encountered. The server will
    continue to work, but HTTP/2 will no longer be negotiated.
  * improved implementation of ready queue.

v1.10.6
--------------------------------------------------------------------------------
  * Fix for possible CPU busy loop introduced in v1.10.3 where a stream may keep
    the session in continuous check for state changes that never happen.

v1.10.5
--------------------------------------------------------------------------------
  * fail requests without ERROR log in case we need to read interim
    responses and see only garbage. This can happen if proxied servers send
    data where none should be, e.g. a body for a HEAD request.

v1.10.4
--------------------------------------------------------------------------------
  * mod_proxy_http2: adding support for Reverse Proxy Request headers.

v1.10.3
--------------------------------------------------------------------------------
  * fixed possible deadlock that could occur when connections were 
     terminated early with ongoing streams. Fixed possible hanger with timeout
     on race when connection considers itself idle. 

v1.10.2
--------------------------------------------------------------------------------
  * MaxKeepAliveRequests now limits the number of times a 
    slave connection gets reused.
  * Client streams that lack the EOF flag get now forcefully
    closed with a RST_STREAM (NO_ERROR) when the request has been answered.
  * Only when 'HttpProtocolOptions Unsafe' is configured, will
    control characters in response headers or trailers be forwarded to the
    client. Otherwise, in the default configuration, a request will eiher 
    fail with status 500 or the stream will be reset by a RST_STREAM frame. 
     
v1.10.1
--------------------------------------------------------------------------------
  * Fixed bug in re-attempting proxy requests after connection error. 
    Reliability of reconnect handling improved.
  * Fixed two rare deadlocks with new non-nested mutex use.
  * No longer mapping Link: header urls in proxy requests when preserve host
    is set.

v1.10.0
--------------------------------------------------------------------------------
  * better performance, eliminated need for nested locks and
    thread privates. Moving request setups from the main connection to the
    worker threads. Increase number of spare connections kept.
  * input buffering and dynamic flow windows for increased 
    throughput. Requires nghttp2 >= v1.5.0 features. Announced at startup
    in mod_http2 INFO log as feature 'DWINS'.
  * h2 workers with improved scalability for better scheduling
    performance. There are H2MaxWorkers threads created at start and the
    number is kept constant for now.
  * obsoleted option H2SessionExtraFiles, will be ignored and
    just log a warning.
  * fixed PR60869 by making h2 workers exit explicitly waking up
    all threads to exit in a defined way.
     
v1.9.3
--------------------------------------------------------------------------------
  * moving session cleanup to pre_close hook to avoid races with
    modules already shut down and slave connections still operating.
  * stream timeouts now change to vhost values once the request
    is parsed and processing starts. Initial values are taken from base
    server or SNI host as before. [Stefan Eissing]
  * fixed retry behaviour for http2 proxy connections when frontend 
    connection uses http/1.1.     
  * separate mutex instances for each bucket beam, resulting in 
    less lock contention. input beams only created when necessary.

v1.9.2
--------------------------------------------------------------------------------
  * mod_http2: adding allocator mutex to session pool due to reports of rare
    crashes.
    
v1.9.1
--------------------------------------------------------------------------------
  * mod_proxy_http2: support for ProxyPreserveHost directive

v1.9.0
--------------------------------------------------------------------------------
  * not counting file buckets again stream max buffer limits. 
    Effectively transfering static files in one step from slave to master 
    connection.    
  * mod_http2: comforting ap_check_pipeline() on slave connections
    to facilitate reuse (see https://github.com/icing/mod_h2/issues/128).
    [reported by Armin Abfalterer]
  * mod_http2: http/2 streams now with state handling/transitions as defined
    in RFC7540. Stream cleanup/connection shutdown reworked to become easier
    to understand/maintain/debug. Added many asserts on state and cleanup 
    transitions.
 
v1.8.11
--------------------------------------------------------------------------------
  * regression fix on bugzilla PR 59348, on graceful restart, ongoing 
    streams are finished normally before the final GOAWAY is sent.
  * do not attempt to generated a response on an already aborted slave connection
  * fix potential double cleanup of bucket beam memory

v1.8.10
--------------------------------------------------------------------------------
  * fixes bugzilla PR60599, sending proper response for conditional requests
    answered by mod_cache. (orignal patch by Jeff Wheelhouse)

v1.8.9
--------------------------------------------------------------------------------
  * rework of stream resource cleanup to avoid a crash in a close
    of a lingering connection. Prohibit special file bucket beaming for
    shared buckets. Files sent in stream output now use the stream pool
    as read buffer, reducing memory footprint of connections.
    (much help from Yann Ylavic)

v1.8.8
--------------------------------------------------------------------------------
  * streaming of request output now reacts timely to data
    from other streams becoming available. Same for new incoming requests.
 
v1.8.7
--------------------------------------------------------------------------------
  * fix for possible page fault when stream is resumed during session shutdown. 
    (Patch by sidney-j-r-m, github)
  * fix for h2 session ignoring new responses while already
    open streams continue to have data available.
     
v1.8.6
--------------------------------------------------------------------------------
  * adding support for MergeTrailers directive. 
  * limiting DATA frame sizes by TLS record sizes in use on the     
    connection. Flushing outgoing frames earlier.

v1.8.5
--------------------------------------------------------------------------------
  * Removed debug log statements left over in 1.8.4 release.
  
v1.8.4
--------------------------------------------------------------------------------
  * Cleanup beamer registry on server reload, Fixes Apache bugzilla PR60510.
    Patch by Pavel Mateja <pavel@verotel.cz>
  * Fixes #126 e.g. beam bucket lifetime handling when data is sent 
    over temporary pools.

v1.8.3
--------------------------------------------------------------------------------
  * CVE-2016-8740: Mitigate DoS memory exhaustion via endless
    CONTINUATION frames. Reported by Naveen Tiwari <naveen.tiwari@asu.edu> and 
    CDF/SEFCOM at Arizona State University
  * Removing some warning when streams are cleaned up that were never scheduled


v1.8.2
--------------------------------------------------------------------------------
  * new directive 'H2EarlyHints' to enable sending of HTTP status 103 interim
    responses. Off by default since some browser still choke on them.
  * mod_proxy_http2 will, when used on top of a HTTP/1.x connection, only 
    forward 100 responses from the backend if the client expects them. All
    other responses in the 100 range are filtered.

v1.8.0
--------------------------------------------------------------------------------
  * mod_http2: new directive 'H2PushResource' to enable early pushes before 
    processing of the main request starts. Resources are announced to the 
    client in Link headers on a 103 early hint response. 
    All responses with status code <400 are inspected for Link header and
    trigger pushes accordingly. 304 still does prevent pushes.
    'H2PushResource' can mark resources as 'critical' which gives them higher
    priority than the main resource. This leads to preferred scheduling for
    processing and, when content is available, will send it first. 'critical'
    is also recognized on Link headers.
  * mod_proxy_http2: uris in Link headers are now mapped back to a suitable
    local url when available. Relative uris with an absolute path are mapped
    as well. This makes reverse proxy mapping available for resources
    announced in this header. 
    With 103 interim responses being forwarded to the main client connection,
    this effectively allows early pushing of resources by a reverse proxied
    backend server.
  * mod_proxy_http2: adding support for 103 status code, as proposed by
    Kazuho Oku.

v1.7.9
--------------------------------------------------------------------------------
  * fixed a crash in stream shutdown introduced in 1.7.8

v1.7.8
--------------------------------------------------------------------------------
  * unannounced and multiple interim responses (status code < 200)
    are parsed and forwarded to client until a final response arrives.
  * mod_proxy_http2: improved robustness when main connection is closed early
    by resetting all ongoing streams against the backend.
  * mod_http2: allocators from slave connections are released earlier, resulting
    in less overall memory use on busy, long lived connections.

v1.7.6
--------------------------------------------------------------------------------
  * fixed crash in beam memory handling introduced in 1.7.x changes

v1.7.5
--------------------------------------------------------------------------------
  * properly implemented 100-continue handling for proxy setups, be it
    mod_proxy_http or mod_proxy_http2
  * reusing backend HTTP/2 connections more than a second old will hold back
    request bodies until a PING response is received. Headers are still sent
    right away since those are repeatable on a new connection.
  
  
v1.7.3
--------------------------------------------------------------------------------
  * reverts some int -> apr_uint32_t changes made in 1.7.0 to address possible
    crashes.
    
v1.7.2
--------------------------------------------------------------------------------
  * fixes compilation error on 32 bit systems when generating slave connection id.

v1.7.1
--------------------------------------------------------------------------------
  * fix for build issues on Windows platforms

v1.7.0
--------------------------------------------------------------------------------
  * rewrite of how responses and trailers are transferred between master and 
    slave connections.
  * Reduction of internal states for tasks and streams, reducing complexity
    for increased stability. 
  * Heuristic id generation for slave connections to better keep promise of 
    connection ids unique at given point in time. This fixes problems with
    mod_cgid in high load situtations. 
  * Fix for handling of incoming trailers when no request body is sent.

v1.6.2
--------------------------------------------------------------------------------
  * fixes a race that led to output blocking (stream not finishing)

v1.6.1
--------------------------------------------------------------------------------
  * if configured with nghttp2 1.14.0 and onward, invalid request
    headers will immediately reset the stream with a PROTOCOL error. Feature
    logged by module on startup as 'INVHD' in info message.
  * fixed handling of stream buffers during shutdown.
     
v1.6.0
--------------------------------------------------------------------------------
 * handling graceful shutdown gracefully, e.g. processing existing streams to the end.
 * h2 status resource follows latest draft, see
   http://www.ietf.org/id/draft-benfield-http2-debug-state-01.txt
   Configure it as
   <Location "/.well-known/h2/state">
        SetHandler http2-status
    </Location>
 * support for 'Expect: 100-continue' handling

v1.5.13
--------------------------------------------------------------------------------
 * new H2CopyFiles directive that changes treatment of file handles in 
   responses. Necessary in order to fix broken lifetime handling in modules 
   such as mod_wsgi. Use 'H2CopyFiles off' where ever you need it.
 * removing timeouts on master connection while requests are being processed. 
   Requests may timeout, but the master only times out when no more requests 
   are active.

v1.5.12
--------------------------------------------------------------------------------
 * fixed connection flushing when handling SETTINGS and no stream is open.
   (thanks @summerwind)
 * fix for request abort when connections drops, introduced in 1.5.8
 * more rigid error handling in DATA frame assembly, leading
   to deterministic connection errors if assembly fails.

v1.5.10
--------------------------------------------------------------------------------
 * fixed bug in error handling when passing DATA frames.

v1.5.9
--------------------------------------------------------------------------------
 * more strict error handling and logging in DATA frame assembly.

v1.5.8
--------------------------------------------------------------------------------
 * mod_http2: improved cleanup of connection/streams/tasks to always
   have deterministic order regardless of event initiating it. Addresses
   reported crashes due to memory read after free issues. 
  
v1.5.7
--------------------------------------------------------------------------------
 * fixed read after free on certain conditions when clients abort connections
 * fixed connection shutdown when stream tasks block on reads

v1.5.6
--------------------------------------------------------------------------------
 * fixed possible null pointer reference in new bucket beams during read on an 
   aborted beam
 * improved event handling on master connection (idle/submit/wait) to increase 
   performance
 
v1.5.5
-------------------------------------------------------------------------------- 
 * Fix async write issue that sometimes led to selection of wrong timeout
   vs. keepalive timeout selection for idle sessions.
 * Checking LimitRequestLine, LimitRequestFields and 
   LimitRequestFieldSize configurated values for incoming streams. Returning
   HTTP status 431 for too long/many headers fields and 414 for a too long
   pseudo header.
 * Tracking conn_rec->current_thread on slave connections, so
   that mod_lua finds the correct one. Fixes PR 59542.

v1.5.3
-------------------------------------------------------------------------------- 
 * slave connections have conn_rec->aborted flag set when a stream
   has been reset by the client.
 * Small fixes in bucket beams when forwarding file buckets. Output handling
   on master connection uses less FLUSH and passes automatically when more
   than half of H2StreamMaxMemSize bytes have accumulated.
   Workaround for http: when forwarding partial file buckets to keep the
   output filter from closing these too early.
 * elimination of fixed master connectin buffer for TLS connections. New 
   scratch bucket handling optimized for TLS write sizes. 
   File bucket data read directly into scratch buffers, avoiding one
   copy. Non-TLS connections continue to pass buckets unchanged to the core
   filters to allow sendfile() usage.
 * h2_request.c is no longer shared between these modules. This simplifies 
   building on platforms such as Windows, as module reference used in 
   logging is now clear.
     
v1.5.2
-------------------------------------------------------------------------------- 
 * fixed connection shutdown deadlock on linux when client closed early
 * beam shutdown does now wait on endpoint to finish using buckets in flight,
   hopefully addressing crash issues completely 
 * Since 1.5.1 the internal HTTP/2 protocol is reported as "HTTP/2.0" for
   better compatibility and since CGI's SERVER_PROTOCOL seems to require this
   format
    
v1.5.1
-------------------------------------------------------------------------------- 
 * fixed segmentation fault when connections where aborted by client in new
   bucket beam code
 * eliminated one more memory pool per stream
 
v1.5.0
-------------------------------------------------------------------------------- 
 * mod_proxy_http2 for backend HTTP/2 connections, currently cleartext only
 * new "bucket beam" technology to transport buckets across threads without 
   buffer copy. 
 * delaying response start until flush or enough body data has been accumulated.
 * all fixed up to and including 1.4.7
     
v1.4.7
-------------------------------------------------------------------------------- 
 * disabling file mmap handling as this leads to segmentation faults when files
   are truncates while being streamed out. 
 * Some additional trace1 logging when connections give unexpected errors, e.g.
   clients close connection without final GOAWAY frame. 
 
v1.4.6 (as released in Apache httpd 2.4.20)
-------------------------------------------------------------------------------- 
 * incrementing keepalives on each request started so that logging %k gives 
   increasing numbers per master http2 connection. New documented variables 
   in env, usable in custom log formats: H2_PUSH, H2_PUSHED, H2_PUSHED_ON, 
   H2_STREAM_ID and H2_STREAM_TAG.
 * more efficient passing of response bodies with less contention
     and file bucket forwarding.
 * fix for missing score board updates on request count, fix for memory leak 
   on slave connection reuse.
 * disabling PUSH when client sends GOAWAY. Slave connections are reused for 
   several requests, improved performance and better memory use. 
 * fixes problem with wrong lifetime of file buckets on main connection.
 * fixes incorrect denial of requests without :authority header.
 * give control to async mpm for keepalive timeouts only when no streams are 
   open and even if only after 1 sec delay. Under load, event mpm discards 
   connections otherwise too quickly.
 * fixed possible read after free when streams were cancelled early by the 
   client.
 * fixed possible deadlock during connection shutdown. Thanks to @FrankStolle 
   for reporting and getting the necessary data.
 * fixed apr_uint64_t formatting in a log statement to user proper APR def, 
   thanks to @Sp1l.
 * number of worker threads allowed to a connection is adjusting 
   dynamically. Starting with 4, the number is doubled when streams can be 
   served without block on http/2 connection flow. The number is halfed, when
   the server has to wait on client flow control grants. 
   This can happen with a maximum frequency of 5 times per second. 
   When a connection occupies too many workers, repeatable requests 
   (GET/HEAD/OPTIONS) are cancelled and placed back in the queue. Should that 
   not suffice and a stream is busy longer than the server timeout, the 
   connection will be aborted with error code ENHANCE_YOUR_CALM.
   This does *not* limit the number of streams a client may open, rather the
   number of server threads a connection might use.
 * allowing link header to specify multiple "rel" values, space-separated 
   inside a quoted string. Prohibiting push when Link parameter "nopush" is 
   present.
 * reworked connection state handling. Idle connections accept a GOAWAY from 
   the client without further reply. Otherwise the module makes a best effort 
   to send one last GOAWAY to the client.
 * the values from standard directives Timeout and KeepAliveTimeout properly 
   are applied to http/2 connections.
 * idle connections are returned to async mpms. new hook "pre_close_connection" 
   used to send GOAWAY frame when not already done. Setting event mpm server 
   config "by hand" for the main connection to the correct negotiated server.
 * keep-alive blocking reads are done with 1 second timeouts to check for MPM 
   stopping. Will announce early GOAWAY and finish processing open streams, 
   then close.
 * bytes read/written on slave connections are reported via the optional 
   mod_logio functions. Fixes PR 58871.
 * connections how keep a "push diary" where hashes of already pushed resources 
   are kept. See directive H2PushDiarySize for managing this. Push diaries can 
   be initialized by clients via the "Cache-Digest" request header. 
   This carries a base64url encoded. compressed Golomb set as described
   in https://datatracker.ietf.org/doc/draft-kazuho-h2-cache-digest/
   Introduced a status handler for HTTP/2 connections, giving various counters
   and statistics about the current connection, plus its cache digest value
   in a JSON record. Not a replacement for more HTTP/2 in the server status. 
   Configured as
   <Location "/http2-status">
       SetHandler http2-status
   </Location>
 * Fixed flushing of last GOAWAY frame. Previously, that frame did not always 
   reach the client, causing some to fail the next request.
   Fixed calculation of last stream id accepted as described in rfc7540. 
   Reading in KEEPALIVE state now correctly shown in scoreboard. 
   Fixed possible race in connection shutdown after review by Ylavic. 
   Fixed segfault on connection shutdown, callback ran into a semi dismantled session. 
 * Added support for experimental accept-push-policy draft
   (https://tools.ietf.org/html/draft-ruellan-http-accept-push-policy-00). Clients
   may now influence server pushes by sending accept-push-policy headers.
 * new r->subprocess_env variables HTTP2 and H2PUSH, set to "on"
   when available for request.
 * mod_status/scoreboard: showing connection protocol in new column, new 
   ap_update_child_status methods for updating server/description. mod_ssl
   sets vhost negotiated by servername directly.

v1.2.8
-------------------------------------------------------------------------------- 
 * Requests without ':authority' header, using 'Host' instead, are no longer
   denied.
   
v1.2.7
-------------------------------------------------------------------------------- 
 * Adding logio fix from apache trunk so that resource sizes are correcly 
   reported in access logs.

v1.2.6
-------------------------------------------------------------------------------- 
 * Adding 'accept-encoding' to headers used in PUSHed resources - as sent by
   the initiating request.

v1.2.5
-------------------------------------------------------------------------------- 
 * fixes a deadlock that caused connections to get stuck in output, locking
   up the connection and a server thread forever. Thanks to @FrankStolle for
   reporting and getting the necessary data.
 
v1.2.4
-------------------------------------------------------------------------------- 
 * removed all H2*Timeout directives. HTTP/2 uses not the same Timeout and
   KeepAliveTimeout as HTTP/1.1.
 * enforcing the Timeout value on read and write operations from the selected
   virtual host (TLS+SNI). httpd was wrongly using the defaults set in the
   base server config.
 * add DEBUG logging to see if writing properly returns to catch a connection
   hanger reported in #79
 
v1.2.3
-------------------------------------------------------------------------------- 
 * connection timeout handling when requests do not report back
 * setting correct server config for event mpm on main connection, so that
   timeouts, keepalives use the correct values
 * fixes event hack to match changes in structures

v1.2.2
-------------------------------------------------------------------------------- 
 * removed unused code
 
v1.2.1
-------------------------------------------------------------------------------- 
 * fixed compilation error because of stupid own log2n function
 * fixed cache digest calculation to spit out same values as Kazuho Oku's
   reference implementation (https://github.com/kazuho/h2-cache-digest).
 
v1.2.0
-------------------------------------------------------------------------------- 
 * Each connection now has a push diary where already pushed resources are
   recorded (as 64-bit subsets sha256 URL hashes). The maximum size of a diary
   can be configured with the new directive 'H2PushDiarySize'. The default is 256.
 * The module recognizes the request header 'Cache-Digest', carrying a base64url
   encoded set of hash values using Golomb set encoding as described in
      https://datatracker.ietf.org/doc/draft-kazuho-h2-cache-digest/
   This is highly experimental and will most likely change in format and
   interpretation as the draft evolves. For now, this value is used to replace
   the current push diary. This allows clients to inform the server about
   which resources they already have cached.
 * module configuration now looks to the crypto library (because it wants SHA256
   from it). If it is not found, a replacement hash is used, however this is
   not interoperable with cache digests from clients, e.g. hits will be missed.
 * the module has a new handler named "http2-status" which exposes certain
   properties and statistics of the *current* HTTP/2 connection. It can be 
   configured just like:
       <Location "/http2-status">
         SetHandler http2-status
       </Location>
   The usual precautions about exposing some internals of your server to the
   outside world apply. Just as for "server-status"."
 * Due to more test cases and new functions, more bugs have been exposed,
   examined and exterminated.

v1.1.0
-------------------------------------------------------------------------------- 
 * GOAWAY will be sent when a HTTP/2 connection is shutdown, whenever the
   connection still allows it. Calculation of the last stream id has been
   corrected to include streams started, not only streams finished processing.
 * several issues fixed with new fuzzing tests that simulate random closes 
   and delays/timeouts
 * H2SessionExtraFiles are now shared between all sessions in the same process.
   It now works like this:
   H2MaxWorkers * H2SessionFiles is assumed to be the total number of file
   handles that can be safely used for HTTP/2 transfers without other parts
   of the server running out of handles. This number is shared between all
   HTTP/2 connections in the same server process.
   The default is set to 2. With H2MaxWorkers on most platforms/mpms
   defaulting to 25 that gives a maximum of 50 handles that can be invoved in
   transfers. 
   I think I have to write a blog post one day of how this works and affects
   performance. tl;dr the more handles http2 may use, the faster static files
   can be served.
 * KeepAlive is not correctly visible on the server status page for HTTP/2
   connections. (Would like more info there, need to extend the scoreboard
   for it.)
 * KeepAlive connections are *not* set aside in async MPMs such as event. This
   is a very desirable feature, but I could not get it to work reliably with
   the existing MPM interface. Will work on that for the next Apache release.
   (The main problem is that event will silently close such connections and
    http2 has no chance to send a last GOAWAY frame. That makes clients fail
    requests which they have just started.)

v1.0.18
-------------------------------------------------------------------------------- 
 * fixed race condition in connnection shutdown that could cause indefinite 
   hang, fixed cleanup of http2 worker threads, thanks to Yann Ylavic
 
v1.0.17
-------------------------------------------------------------------------------- 
 * H2Timeout/H2KeepAliveTimeout now defaults to what ever is set for HTTP/1
   connections via Timeout/KeepAliveTimeout
 * fixes in calculating remaining timeout values

v1.0.16
-------------------------------------------------------------------------------- 
 * simplified connection shutdown and worker join for robustness
 * improved performance for small requests due to less locking
 * http2 connections work in event with normal server KeepAliveTimeout setting
 
v1.0.15
-------------------------------------------------------------------------------- 
 * fixed busy loops on random connection errors
 * fixed connection state for event MPM that shutdown child with 'G' status
 * changed default for H2KeepAliveTimeout. For async MPMs (event), will leave
   keepalive handling to the MPM. For sync (worker, prefork), will default to
   whatever is set for H2Timeout.
 
v1.0.14
-------------------------------------------------------------------------------- 
 * fixed segfault on connection shutdown
 * added support for accept-push-policy headers, see
   https://tools.ietf.org/html/draft-ruellan-http-accept-push-policy-00
 
v1.0.13
-------------------------------------------------------------------------------- 
 * reworked connection state handling. Improved scoreboard update (server-status).
   Default on H2KeepAliveTimeout same as H2Timeout, 5 seconds. After that, 
   connections are closed.
   On asynchronous MPMs (event), keep-alive connections no longer block threads,
   but exact timeout handling is then up to the MPM. In these MPMs, having a
   longer H2KeepAliveTimeout may be suitable.
 * new CGI environment variables HTTP2 and H2PUSH. With former "on", the 
   connection uses HTTP/2. With latter "on", the request may trigger Server Push
   via Link headers, as both server and clients support it.

v1.0.12
-------------------------------------------------------------------------------- 
 * alpha release on top of Apache httpd 2.4.18
 * removed sandbox from build, needs installed 2.4.18 + apxs
 * new directives:
   - H2Timeout           timeout of a http/2 connection (seconds), default 5
   - H2KeepAliveTimeout  timeout of an idle http/2 connection (seconds), default 300
   - H2StreamTimeout     timeout on individual streams (seconds), default 120
   you can set them to `0` in which case no timeout may apply. You may try that
   for the stream timeouts if you have problems. This is the very experimental
   part right now...
 * improved handling of connection closes to make a better effort on freeing
   worker threads still involved in streams.
 * worker numbers are constant MaxThreadsPerChild by default
 * fixed bug on handling large input without content length
   
v1.0.3
-------------------------------------------------------------------------------- 
 * copy from https://svn.apache.org/repos/asf/httpd/httpd/trunk
 * includes proposed backport patch for Apache httpd 2.4.17
   * improved https:// throughput
   * vastly improved http:// throughput
   * several stability and logging improvements
   * connection reuse: virtual hosts that have exactly the same TLS setup
     (certificates, protocol, ciphers and all) allow using a single HTTP/2
     connection.
   * h2c: first HTTP/1.1 request on a connection will announce additionally
     available and more preferred protocols in the ```Upgrade``` response
     header.
   * H2Direct is by default on for cleartext connections where h2c is an
     allowed protocol. Or, the other way around, it is always disabled unless
     h2/h2c is configured.
   * TLS handshake is triggered earlier, allowing all connection hooks which
     register behind mod_ssl to see negotiated values.
   * new experimental directives ```H2TLSWarmUpSize``` and ```H2TLSCoolDownSecs```
     that specify how TLS record sizes should used during the lifetime of a
     connection.
     * H2TLSWarmUpSize: amount of bytes to send in small (~1300 bytes) chunks,
       so that packets fit inside a single MTU. After this many bytes have
       been sent, data is written with max size of 16 KB when possible.
     * H2TLSCoolDownSecs: number of idle seconds to pass before a warmed
       up TLS connection falls back to small chunks again.
     Set both to 0 to always write max chunks. Defaults are 1 MB and 1 second.
   * HTTP/2 priorities are now respected when scheduling streams for handling.
     This effects which queued task is handled first whenever a worker becomes
     available.
   * New directive ```H2ModernTLSOnly on|off``` that checks connections for
     TLS protocol version and negotiated ciphers, so that HTTP/2 connections
     only happen on ```modern``` TLS and none of the ciphers in the black
     list from RFC 7540 are used.
   * 'HTTP/2.0' is written in log files when requests are served via mod_http2.
     
 * updated test cases from Apache tests
 * configure now builds the sandbox by default, too many user problems
   otherwise


v0.9.9 - 1.0.2
-------------------------------------------------------------------------------- 
never happened here, but at http://httpd.apache.org

v0.9.8
-------------------------------------------------------------------------------- 
 * server protocol of requests served via mod_h2 is now `HTTP/2`
 * directive `H2SerializeHeaders` had no effect any longer, fixed.
 * requests served in `H2SerializeHeaders on` hosts, report `HTTP/1.1` as
   protocol. This is the mode to enabled when having compatiblity issues.

v0.9.7
-------------------------------------------------------------------------------- 
 * update of core-protocols.patch to v4
 * "Protocols" default changed. servers/vhosts need to explicitly enable h2/h2c 
   now. For example with `Protocols h2 http/1.1`
 * adding test cases for "Protocols" ordering
 * configuration option -enable-werror now sets compiler flags to go for Apache
   httpd standard code restrictions.

v0.9.6
-------------------------------------------------------------------------------- 
 * for closed h2 connections proper state is set. Fixes resource/worker handling
   issues in mpm_event
 * upgrade the core-protocols patch to the latest relevant apache changes
 * if not explicitly configured, H2SessionExtraFiles gets a default usable in
   proecsses with 256 max file handles and depending on mpm used.
 * upgraded sandbox to nghttp2 1.3.0

v0.9.5
-------------------------------------------------------------------------------- 
 * fix for resource management when running with mpm_event

v0.9.4
-------------------------------------------------------------------------------- 
 * mod_h2 is a copy of the module in Apache httpd trunk
 * requires a patched httpd for new Protocols feature. Patch applied in sandbox,
   available for own use in sandbox/httpd/patches/core_protocols_release.patch.
 * See README.me about changes, especially the chapter about Migration
 * Several H2* directives have disappeared, also see Migration in README.md
 * This version should be close to the release candidate. Report any issues
   here at github or on the apache httpd dev mailing list

v0.8.3
-------------------------------------------------------------------------------- 
 * Fixed typo in module setup during installation that broke enabling the module
   via a2enmod.

v0.8.2
-------------------------------------------------------------------------------- 
 * In case "H2SerializeHeaders On" is configured, errorneous requests led to
   500 responses. Fixed by installing post_read hooks really early now.

v0.8.1
-------------------------------------------------------------------------------- 
 * added some defensive code for configurations at user that produced duplicate
   response headers
 * added httpd/trunk fix to allocate task memory pools under mplx locking

v0.8.0
-------------------------------------------------------------------------------- 
 * when serving static files, these are kept open longer (and buffer copied
   less). Use config "H2SessionExtraFiles" to change the value. The more you
   can give per connection, the better. But you may run out of open file 
   handles, if not careful. Default value is 5, which seems to work on my
   config with mpms worker, event and prefork. Basically, eaach httpd process
   needs at least #connections + #workers + (#conn * #extrafiles) available.
 * main connection buffering, buffer sizes and write sizes are configurable,
   see README.md for the list of options. buffer sizes and write sizes influence
   the TLS performance. Defaults seem reasonably, but ymmv.
 * general performance improved due to better handling of stream close and
   resource cleanup
 * prefork mpm confirmed working. Unless configured otherwise, each session
   will only have 1 worker thread. Raise this with "H2MaxWorkers"
 * changed sandbox cipher config to mozilla recommendation (thanks Lucas)
 * sandbox update to nghttp2 1.0.5

v0.7.3
--------------------------------------------------------------------------------
 * sandbox update to nghttp2 1.0.4
 * rework of stream scheduling and thread sync
 * test suite runs with mpm_prefork on OS X and Ubuntu (feedback welcome)

v0.7.2
--------------------------------------------------------------------------------
 * fixes crash with certain modules that (correctly) expected their 
   pre_connection hooks to work. Solves #28
 * fixes log statements and Makefile to compile sandbox on 32bit linux

v0.7.1
--------------------------------------------------------------------------------
 * h2_mplx now uses reference counting to enable a controlled destruction on
   session termination. If this fixes all the crashes reported, remains to
   be seen.

v0.7.0
--------------------------------------------------------------------------------
 * switching to nghttp2 v1.0.*, compilation + linkage with nghttp2 v0.7.* will
   not work any more as there have been changes in nghttp2's API. The sandbox
   builds against v1.0.2 and also pulls curl 7.43.0 which did the same version
   switch.
 * keeping support for h2-16/h2-14 ALPN identifiers until a 1.0 release
 * varying h2 support (on|off) among virtual hosts on the same port is now
   possible and should work correctly.
 * improved mod_ssl alpn patch to correctly select the proper virtual host
   even if the SSL library invokes SNI after ALPN callbacks.
 * Disabled NPN support in sandbox built. The patch for httpd 2.4.x is still
   there, but no longer applied.
 * KNOWN ISSUE: when using mpm_event, the error 
     "error scoreboard is full, not at MaxRequestWorkers" 
   sometimes happens. Under investigation. mpm_worker ist stable and recommended
   for now.


v0.6.6
--------------------------------------------------------------------------------
 * adding sni_misdirect.patch for httpd/mod_ssl that changes status code when 
   TLS connections are reused for other vhosts. 

v0.6.5
--------------------------------------------------------------------------------
 * httpd scoreboard fixups: scoreboard handles are still updated on the main
   connection from all stream request incoming from it, since it is not trivial
   to get new handles for h2 workers. Updating of scoreboard status has been 
   improved, no workers remain on "G"raceful shutdown in load tests any longer.
 * some refacoring to isolate tls/alpn/upgrade code
 * adding php-wrapper script to distribution, was missing

v0.6.4
--------------------------------------------------------------------------------
 * accepting "h2" on Upgrade: headers and allowing also Upgrade to work on TLS
   connections that talk HTTP/1.1.
 * logging WARNING once when mod_h2 is used in a "prefork" mpm configuration.
   There seem to be issues with mod_proxy/rewrite and dankging I/O.
 * added test suites for combinations with mod_proxy and mod_rewrite
 * added test for request with Host: header where h2 is not enabled
 * sandbox now builds local openssl 1.0.2 if 1.0.1 or older are installed
   on the system. Prior 1.0.1 was accepted, but NPN support will be disabled
   soon.
 * added "Known Problems" section in README
 * direct mode should also work with TLS connections, untested currently.

v0.6.3
--------------------------------------------------------------------------------
 * h2c direct mode is now enabled on http: virtual hosts. It can be disabled
   by configuring "H2Direct off" for the base server. This works for clients
   with prior knowledge that a http server supports h2c.

v0.6.2
--------------------------------------------------------------------------------
 * added "H2Direct (on|off)" as config directive. On a non-TLS host, it enables
   direct h2c communication without any Upgrade dance. Useful for testing, for
   example with h2load.
 * fixed concurrency issue observed on a mpm_event server when closing sessions

v0.6.1
--------------------------------------------------------------------------------
 * relaxing task finished sync due to segfaults with mpm_event
 * mod_reqtimeout enabled on stream processing again
 * merged pr from ecovener, fix for ap_update_vhost_from_headers use
 * tinkering with buffering on main connection

v0.6.0
--------------------------------------------------------------------------------
 * fiddling around with task/worker assignments to use the global h2_workers
   lock less, giving better parallelism
 * ./configure --enable-werror enables all sorts of compiler diagnostics, if
   the chosen compiler supports them
 * merged pull request with compiler warning fixes by LPardue and @samhurst 
   (Thanks!)
 * new config option "H2SerializeHeaders (On|Off)" that determines if request
   response headers should be serialized/parsed when converting from HTTP/2 to
   httpd's internal HTTP/1 processing or request_recs are manipulated directly.
   "Off" is default, "On" gives better compatibility.
 * new config options "H2HackMpmEvent (On|Off) that enables a hack to make
   internal connection work with the mpm_event module. Has no effect if other
   mpm modules have been configured. Defaults to "On"."
 * upgrading sandbox to nghttp2 0.7.15

v0.5.6
--------------------------------------------------------------------------------
 * making SSL variables available in subprocess (e.g. CGI) environments if
configured (fixes #19)

v0.5.5
--------------------------------------------------------------------------------
 * improved transfer of large resources by 50% by more efficient writes

v0.5.4
 --------------------------------------------------------------------------------
 * moving request handling and http/1 emulation into worker thread, offloading 
   main
 * some fixes in connection shutdown re race condition with still active workers
 * removing reqtimeout filters on stream connections
 * taking in latest alpn changes from httpd trunk, made separate npn patch for
   those who need to run with openssl 1.0.1
 * fixed handling of transient bucket in stream output data (led to corrupted
   responses)
 * reworked task join to eliminate race conditions during session shutdown
 * info logging is less verbose

v0.5.2
--------------------------------------------------------------------------------
 * rewrote the input handling
    * forwarding headers in camel case to HTTP/1 request prossing
    * merging duplicate headers into single line with proper separators
    * eliminated h2_bucket by using apr_bucket_brigades everywhere
    * added test cases and fixed chunked input processing
 * sandbox now uses curl 7.42.0
 * enhanced alpn patch slightly, compatible to old one, no need to repatch mod_ssl on existing installations
 * adding some tests with fcgi, for sandbox testing please install php5-cgi

v0.5.1
--------------------------------------------------------------------------------
 * ensuring HOST header is properly set for internal request handling
 * updated sandbox to latest nghttp2 release

v0.5.0
--------------------------------------------------------------------------------
 * improved resource handling and performance
 * fixes lookup of correct server config when several virtual hosts are 
   available

v0.4.5
--------------------------------------------------------------------------------
 * fixed base64 decoding to use correct dialect when upgrading to h2c

v0.4.4
--------------------------------------------------------------------------------
 * adds missing file in distribution tar, fixes #11
 * sandbox now uses nghttp2 0.7.11

v0.4.3
--------------------------------------------------------------------------------
 * heavy work on internal data transfers, use of apache bucket brigades for
   improved performance and parallelism
 * mod_h2 now performs proper flow-control on input. Uploads can no longer
   flood memory of the server.
 * changed mod_ssl patch to reflect current trunk changes in regard to NPN/ALPN
   support.
 * patched the trunk ALPN patch to make it do the right thing if no 
   ALPNPreference is configured
 * added DESTDIR support in Makefile as supplied by Hanno Böck.

v0.4.2
--------------------------------------------------------------------------------
 * adding more low-level logging to NPN/ALPN negotiation
 * added '-Werror' to module compiler flags (thanks @devurandom)
 * debugged and tcpdumped around h2c startup handling with curl on certain
   platforms. If you experience connection hangers, report pls with 'trace2'
   level error log.

v0.4.1
--------------------------------------------------------------------------------
 * fixing infinite loop when aborting session with tasks hanging in read

v0.4.0
--------------------------------------------------------------------------------
 * h2 + h2-16 will be negiotiated/upgraded. Priority handling is implemented
   in nghttp2, however assigning requests to workers has currently not the
   necessary information.
 * Alt-Svc support based on https://http2.github.io/http2-spec/alt-svc.html#indicator
   Configuration directives "H2AltSvc" and "H2AltSvcMaxAge" added. Configurable
   per virtual host.
 * reduced lock contention and eliminated broadcast signalling on internal 
   condition variables, improved multi-thread performance

v0.3.1
--------------------------------------------------------------------------------
 * defining _GNU_SOURCE to pull in proper features and make APR header files
   happy, fixes #7 

v0.3.0
--------------------------------------------------------------------------------
 * new directory structure, all sandbox related parts have been moved to 
   own sandbox dir
 * non-sandbox configuration no longer triggers building of sandbox stuff
 * cleanup up distribution builds to have smaller and working tar balls

v0.2.2
--------------------------------------------------------------------------------
 * optimizations on response reads
 * being more apacheeeish, using APR_RINGs for queue handling
 * using openssl latest.tar.gz to retrieve latest openssl for sandbox
 * fixed crash in large request header handling
 * better flushing of stream io resulting in performance improvements
 * added sandbox tests for chunked responses of various sizes
 * integrated fix (https://github.com/icing/mod_h2/pull/5) from 
   Jonathan (invader444) to fix chunked encoding when converting http/1
   responses to http2 unchunked data.

v0.2.1
--------------------------------------------------------------------------------
 * changed apr_pool usage to have more recycling, 50% performance increase in 
   loadtest
 * added hack to enable mod_h2 to run in mpm_event (experimental)
 * changed internal stream/data lookup from O(n/2) to O(log(n)) time
 * fixed index in http2 to http1 header conversion leading to segfaults
 * update openssl version downloaded for sandbox
 * using sha256 for self-signed sandbox certificates
 * sandbox certificate no longer announces itself as roo
   (last 3 thanks to michael.koeller at greenbytes.de)

v0.2.0
--------------------------------------------------------------------------------
 * merged pull request from Tatsuhiro Tsujikawa, removing code for CONTINUATION
   frames that are never seen by mod_h2
 * request/response headers are filtered when converting between HTTP/1.1 and
   HTTP/2 where they can only do harm (Expect/Connection/etc.)
 * added test cases for uploads
 * fixed handling of uploads ;-)
 * enabled h2c upgrade for "OPTIONS *" requests
 * changed h2_stream_set implementation to use sorted apr array
 * switched to nghttp2 v0.7.7 in sandbox

v0.1.1
--------------------------------------------------------------------------------
 * added cgi test cases (needs python installed)
 * fixed typo in configure.ac that did not set the CPP flags correctly (#3)
 * fixed handling of chunked encoding in responses
 * merged header macro pull request from MATSUMOTO, Ryosuke

v0.1.0
--------------------------------------------------------------------------------
 * first alpha release, see README on how to use it and what is all missing
 * h2 supported with openssl > 1.0.1 and patched mod_ssl (patch included and used in sandbox)
 * h2c supported
 * only usable in mpm_worker right now
 * configure --enable-sandbox for a local install of everything needed
 * tested with httpd 2.4.12 and nghttp2 0.7.5 on Ubuntu 14.04 and OS X 10.10
