Once we know we are HTTP/2 enabled we know the server can multiplex.

Previously in Curl_http2_switched, we called nghttp2_session_mem_recv to
parse incoming data which were already received while curl was handling
upgrade.  But we didn't call nghttp2_session_send, and it led to make
curl not send any response to the received frames.  Most likely, we
received SETTINGS from server at this point, so we missed opportunity to
send SETTINGS + ACK.  This commit adds missing nghttp2_session_send call
in Curl_http2_switched to fix this issue.

Bug: https://github.com/bagder/curl/issues/192
Reported-by: Stefan Eissing

This header file must be included after all header files except
memdebug.h, as it does similar memory function redefinitions and can be
similarly affected by conflicting definitions in system or dependent
library headers.

... it would otherwise lead to memory leakage if we never actually do
the switch.

We prematurely changed protocol handler to HTTP/2 which made things very
slow (and wrong).

Reported-by: Stefan Eissing
Bug: https://github.com/bagder/curl/issues/169

Since we just started make use of free(NULL) in order to simplify code,
this change takes it a step further and:

- converts lots of Curl_safefree() calls to good old free()
- makes Curl_safefree() not check the pointer before free()

The (new) rule of thumb is: if you really want a function call that
frees a pointer and then assigns it to NULL, then use Curl_safefree().
But we will prefer just using free() from now on.

... by using the regular Curl_http_done() method which checks for
that. This makes test 1801 fail consistently with error 56 (which seems
fine) to that test is also updated here.

Reported-by: Ben Darnell
Bug: https://github.com/bagder/curl/issues/166

... and as a consequence, introduce curl_printf.h with that re-define
magic instead and make all libcurl code use that instead.

Previously, we just ignored error code passed to
on_stream_close_callback and just return 0 (success) after stream
closure even if stream was reset with error.  This patch records error
code in on_stream_close_callback, and return -1 and use CURLE_HTTP2
error code on abnormal stream closure.

Pointed-out-by: Tatsuhiro Tsujikawa
Bug: http://curl.haxx.se/bug/view.cgi?id=1487

Previously we don't ignore PUSH_PROMISE header fields in on_header
callback.  It makes header values mixed with following HEADERS,
resulting protocol error.

Previously if HTTP/2 traffic is appended to HTTP Upgrade response header
(thus they are in the same buffer), the trailing HTTP/2 traffic is not
processed and lost.  The appended data is most likely SETTINGS frame.
If it is lost, nghttp2 library complains server does not obey the HTTP/2
protocol and issues GOAWAY frame and curl eventually drops connection.
This commit fixes this problem and now trailing data is processed.

Previously we did not handle EOF from underlying transport socket and
wrongly just returned error code CURL_AGAIN from http2_recv, which
caused busy loop since socket has been closed.  This patch adds the
code to handle EOF situation and tells the upper layer that we got
EOF.

To prevent infinite loop in readwrite_data() function when stream is
reset before any response body comes, reset closed flag to false once
it is evaluated to true.

"Expect: 100-continue", which was once deprecated in HTTP/2, is now
resurrected in HTTP/2 draft 14.  This change adds its support to
HTTP/2 code.  This change also includes stricter header field
checking.

This is now used by the http2 code. It has two different symbols at the
end of the base64 table to make the output "url safe".

Bug: https://github.com/tatsuhiro-t/nghttp2/issues/62

1 - fixes the warnings when built without http2 support

2 - adds CURLE_HTTP2, a new error code for errors detected by nghttp2
basically when they are about http2 specific things.

This regression was introduced when *init was split into *init and
*setup...

Http2 connections would wrongly get closed after each individual
request.

Co-authored-by: Tatsuhiro Tsujikawa
Bug: http://curl.haxx.se/bug/view.cgi?id=1374

Now nghttp2_submit_request returns assigned stream ID, we don't have
to check stream ID using before_stream_send_callback.  The
adjust_priority_callback was removed.

commit 6d5f40238028f2d8c (Apr 27) or later nghttp2 is now required

This makes the findprotocol() function work as intended so that libcurl
can properly be restricted to not support HTTP while still supporting
HTTPS - since the HTTPS handler previously set both the HTTP and HTTPS
bits in the protocol field.

This fixes --proto and --proto-redir for most SSL protocols.

This is done by adding a few new convenience defines that groups HTTP
and HTTPS, FTP and FTPS etc that should then be used when the code wants
to check for both protocols at once. PROTO_FAMILY_[protocol] style.

Bug: https://github.com/bagder/curl/pull/97
Reported-by: drizzt

... and use Curl_safefree() instead of free()

For HTTP/2, we may read up everything including responde body with
header fields in Curl_http_readwrite_headers. If no content-length is
provided, curl waits for the connection close, which we emulate it
using conn->proto.httpc.closed = TRUE. The thing is if we read
everything, then http2_recv won't be called and we cannot signal the
HTTP/2 stream has closed. As a workaround, we return nonzero from
data_pending to call http2_recv.

nghttp2 has yet again extended its callback struct and this is an
attempt to make curl compile with nghttp2 from current git