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[appendix]
== Migrating from Cowboy 2.5 to 2.6

Cowboy 2.6 greatly refactored the HTTP/2 code, a large
part of which was moved to Cowlib and is now used by
both the Cowboy server and the Gun client.

A large number of tickets were also closed which
resulted in many bugs fixed and many features and
options added, although some of them are still
experimental.

=== Features added

* Add support for the PROXY protocol header.
  It can be enabled via the `proxy_header` option.
  The proxy information can then be found under
  the `proxy_info` key in the Req object.

* Allow using sendfile tuples in `cowboy_req:stream_body/3`
  and in the data command in stream handlers. The only
  caveat is that when using `cowboy_compress_h` the
  sendfile tuples may have to be converted to in-memory
  data in order to compress them. This is the case for
  gzip compression.

* The stream handlers `cowboy_stream_h` and
  `cowboy_compress_h` are now documented.

* Add the `chunked` option to allow disabling chunked
  transfer-encoding for HTTP/1.1 connections.

* Add the `http10_keepalive` option to allow disabling
  keep-alive for HTTP/1.0 connections.

* Add the `idle_timeout` option for HTTP/2.

* Add the `sendfile` option to both HTTP/1.1 and HTTP/2.
  It allows disabling the sendfile syscall entirely for
  all connections. It is recommended to disable sendfile
  when using VirtualBox shared folders.

* Add the `rate_limited/2` callback to REST handlers.

* Add the `deflate_opts` option to Websocket handlers that
  allows configuring deflate options for the
  permessage-deflate extension.

* Add the `charset` option to `cowboy_static`.

* Add support for the SameSite cookie attribute.

* Update Ranch to 1.7.0

* Update Cowlib to 2.7.0

=== Experimental features added

* Add support for range requests (RFC7233) in REST handlers.
  This adds two new callbacks: `ranges_accepted/2` and
  `range_satisfiable/2` along with the user-specified
  `ProvideRangeCallback/2`.

* Add automatic handling of range requests to REST handlers
  that return the callback `auto` from `ranges_accepted/2`.
  Cowboy will call the configured `ProvideCallback` and
  then split the ouput automatically for the ranged response.

* Enable range requests support in `cowboy_static`.

* Add the `{deflate, boolean()}` Websocket handler
  command to disable permessage-deflate compression
  temporarily.

* Add the `compress_threshold` option which allows
  configuring how much data must be present in a
  response body to compress it. This only applies
  to non-streamed bodies at this time.

* Add the `compress_buffering` option which allows
  controlling whether some buffering may be done
  when streaming a response body. Change the default
  behavior to not buffer to make sure it works by
  default in all scenarios.

* Add the `{set_options, map()}` command to stream
  handlers and Websocket handlers. This can be used
  to update options on a per-request basis. Allow
  overriding the `idle_timeout` option for both
  HTTP/1.1 and Websocket, the `cowboy_compress_h`
  options for HTTP/1.1 and HTTP/2 and the `chunked`
  option for HTTP/1.1.

=== Bugs fixed

* Do not send a content-length automatically with
  304 responses. This status code allows a content-length
  that corresponds to what would have been sent for a 200
  response, but is never followed by a body.

* HTTP/2 streams are now terminated once the body
  has been sent fully, instead of immediately once
  the stop command is returned (by default when the
  request process exits). Metrics will therefore
  more accurately represent when a stream ended.

* Terminate connection processes gracefully when the
  parent process exists or when sys:terminate/2,3
  is called.

* Automatically ignore the boundary parameter of multipart
  media types when using REST handlers. This is a special
  parameter that may change with all requests and cannot
  be predicted.

* Fix parsing of the accept header when it contains charset
  parameters. They are case insensitive and will now be
  lowercased, like for accept-charset and content-type.

* Handle the charset parameter using `charsets_provided`
  when it is present in the accept header when using
  REST handlers.

* Don't select charsets when the q-value is 0 in REST
  handlers.

* Handle accept-charset headers that include a wildcard
  in REST handlers.

* Only send a charset header when the content-type
  negotiated is of type text in REST handlers.

* Remove the default charset iso-8859-1 from REST
  handlers when no other is provided. This has been
  removed from the HTTP specifications for a long time.

* Many cases where a content-type header was sent
  unnecessarily in the REST handlers response have
  been fixed.

* Handle error_response commands in `cowboy_metrics_h`.

* A number of types and function specifications were
  fixed or improved. Dialyzer is now run against both
  the code and tests to help uncover issues.

* An undefined `cowboy_router` behavior has been
  documented.