It doesn't benefit us much as the connection could get closed at
any time, and also by checking we lose the ability to determine
if the socket was closed by reading zero bytes.

Reported-by: Michael Kaufmann

Closes https://github.com/curl/curl/pull/1134

In order to make the code style more uniform everywhere

Adds access to the effectively used protocol/scheme to both libcurl and
curl, both in string and numeric (CURLPROTO_*) form.

Note that the string form will be uppercase, as it is just the internal
string.

As these strings are declared internally as const, and all other strings
returned by curl_easy_getinfo() are de-facto const as well, string
handling in getinfo.c got const-ified.

Closes #1137

* HTTPS proxies:

An HTTPS proxy receives all transactions over an SSL/TLS connection.
Once a secure connection with the proxy is established, the user agent
uses the proxy as usual, including sending CONNECT requests to instruct
the proxy to establish a [usually secure] TCP tunnel with an origin
server. HTTPS proxies protect nearly all aspects of user-proxy
communications as opposed to HTTP proxies that receive all requests
(including CONNECT requests) in vulnerable clear text.

With HTTPS proxies, it is possible to have two concurrent _nested_
SSL/TLS sessions: the "outer" one between the user agent and the proxy
and the "inner" one between the user agent and the origin server
(through the proxy). This change adds supports for such nested sessions
as well.

A secure connection with a proxy requires its own set of the usual SSL
options (their actual descriptions differ and need polishing, see TODO):

  --proxy-cacert FILE        CA certificate to verify peer against
  --proxy-capath DIR         CA directory to verify peer against
  --proxy-cert CERT[:PASSWD] Client certificate file and password
  --proxy-cert-type TYPE     Certificate file type (DER/PEM/ENG)
  --proxy-ciphers LIST       SSL ciphers to use
  --proxy-crlfile FILE       Get a CRL list in PEM format from the file
  --proxy-insecure           Allow connections to proxies with bad certs
  --proxy-key KEY            Private key file name
  --proxy-key-type TYPE      Private key file type (DER/PEM/ENG)
  --proxy-pass PASS          Pass phrase for the private key
  --proxy-ssl-allow-beast    Allow security flaw to improve interop
  --proxy-sslv2              Use SSLv2
  --proxy-sslv3              Use SSLv3
  --proxy-tlsv1              Use TLSv1
  --proxy-tlsuser USER       TLS username
  --proxy-tlspassword STRING TLS password
  --proxy-tlsauthtype STRING TLS authentication type (default SRP)

All --proxy-foo options are independent from their --foo counterparts,
except --proxy-crlfile which defaults to --crlfile and --proxy-capath
which defaults to --capath.

Curl now also supports %{proxy_ssl_verify_result} --write-out variable,
similar to the existing %{ssl_verify_result} variable.

Supported backends: OpenSSL, GnuTLS, and NSS.

* A SOCKS proxy + HTTP/HTTPS proxy combination:

If both --socks* and --proxy options are given, Curl first connects to
the SOCKS proxy and then connects (through SOCKS) to the HTTP or HTTPS
proxy.

TODO: Update documentation for the new APIs and --proxy-* options.
Look for "Added in 7.XXX" marks.

Visual C++ now complains about implicitly casting time_t (64-bit) to
long (32-bit). Fix this by changing some variables from long to time_t,
or explicitly casting to long where the public interface would be
affected.

Closes #1131

Curl_select_ready() was the former API that was replaced with
Curl_select_check() a while back and the former arg setup was provided
with a define (in order to leave existing code unmodified).

Now we instead offer SOCKET_READABLE and SOCKET_WRITABLE for the most
common shortcuts where only one socket is checked. They're also more
visibly macros.

This fixes a merge error in commit 7f3df804 caused by commit 332e8d61.

Additionally, this changes Curl_verify_windows_version for Windows App
builds to assume to always be running on the target Windows version.
There seems to be no way to determine the Windows version from a
UWP app. Neither GetVersion(Ex), nor VerifyVersionInfo, nor the
Version Helper functions are supported.

Bug: https://github.com/curl/curl/pull/820#issuecomment-250889878
Reported-by: Paul Joyce

Closes https://github.com/curl/curl/pull/1048

CURLDEBUG is for the memory debugging

DEBUGBUILD is for the extra debug stuff

Pointed-out-by: Steve Holme

With HTTP/2 each transfer is made in an indivial logical stream over the
connection, making most previous errors that caused the connection to get
forced-closed now instead just kill the stream and not the connection.

Fixes #941

Closes #820

- Linux TFO + TLS is not implemented yet.

Bug: https://github.com/curl/curl/issues/907

connect.c:952:5: warning: suggest explicit braces to avoid ambiguous 'else'

Closes #845

Sometimes, in systems with both ipv4 and ipv6 addresses but where the
network doesn't support ipv6, Curl_is_connected returns an error
(intermittently) even if the ipv4 socket connects successfully.

This happens because there's a for-loop that iterates on the sockets but
the error variable is not resetted when the ipv4 is checked and is ok.

This patch fixes this problem by setting error to 0 when checking the
second socket and not having a result yet.

Fixes #794

curl_printf.h defines printf to curl_mprintf, etc. This can cause
problems with external headers which may use
__attribute__((format(printf, ...))) markers etc.

To avoid that they cause problems with system includes, we include
curl_printf.h after any system headers. That makes the three last
headers to always be, and we keep them in this order:

 curl_printf.h
 curl_memory.h
 memdebug.h

None of them include system headers, they all do funny #defines.

Reported-by: David Benjamin

Fixes #743

This commit fixes a Clang warning introduced in curl-7_48_0-190-g8f72b13:

Error: CLANG_WARNING:
lib/connect.c:1120:11: warning: The right operand of '==' is a garbage value
1118|       }
1119|
1120|->     if(-1 == rc)
1121|         error = SOCKERRNO;
1122|     }

Closes #660

Makes curl connect to the given host+port instead of the host+port found
in the URL.

warning C4189: 'data': local variable is initialized but not referenced

Closes #528

For a single-stream download from localhost, we managed to increase
transfer speed from 1.6MB/sec to around 400MB/sec, mostly because of
this single fix.

Closes #457

connect.c:953:5: warning: initializer element is not computable at load
                 time
connect.c:953:5: warning: missing initializer for field 'dwMinorVersion'
                 of 'OSVERSIONINFOEX'
curl_sspi.c:97:5: warning: initializer element is not computable at load
                  time
curl_sspi.c:97:5: warning: missing initializer for field 'szCSDVersion'
                  of 'OSVERSIONINFOEX'

- Fix the VerifyVersionInfo calls, which we use to test for the OS major
version, to also test for the minor version as well as the service pack
major and minor versions.

MSDN: "If you are testing the major version, you must also test the
minor version and the service pack major and minor versions."

https://msdn.microsoft.com/en-us/library/windows/desktop/ms725492.aspx

Bug: https://github.com/bagder/curl/pull/353#issuecomment-123493098


Reported-by: Marcel Raad <MarcelRaad@users.noreply.github.com>

When CURL_SOCKET_BAD is returned in the callback, it should be treated
as an error (CURLE_COULDNT_CONNECT) if no other socket is subsequently
created when trying to connect to a server.

Bug: http://curl.haxx.se/mail/lib-2015-06/0047.html

... by using plain structs instead of pointers for the connection cache,
we can avoid several dynamic allocations that weren't necessary.

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.

By making sure Curl_getconnectinfo() uses the correct connection cache
to find the last connection.

Bug: https://github.com/bagder/curl/pull/168

(trynextip)
- Don't try the "other" protocol family unless IPv6 is available. In an
IPv4-only build the other family can only be IPv6 which is unavailable.

This change essentially stops IPv4-only builds from attempting the
"happy eyeballs" secondary parallel connection that is supposed to be
used by the "other" address family.

Prior to this change in IPv4-only builds that secondary parallel
connection attempt could be erroneously used by the same family (IPv4)
which caused a bug where every address after the first for a host could
be tried twice, often in parallel. This change fixes that bug. An
example of the bug is shown below.

Assume MTEST resolves to 3 addresses 127.0.0.2, 127.0.0.3 and 127.0.0.4:

* STATE: INIT => CONNECT handle 0x64f4b0; line 1046 (connection #-5000)
* Rebuilt URL to: http://MTEST/
* Added connection 0. The cache now contains 1 members
* STATE: CONNECT => WAITRESOLVE handle 0x64f4b0; line 1083
(connection #0)
*   Trying 127.0.0.2...
* STATE: WAITRESOLVE => WAITCONNECT handle 0x64f4b0; line 1163
(connection #0)
*   Trying 127.0.0.3...
* connect to 127.0.0.2 port 80 failed: Connection refused
*   Trying 127.0.0.3...
* connect to 127.0.0.3 port 80 failed: Connection refused
*   Trying 127.0.0.4...
* connect to 127.0.0.3 port 80 failed: Connection refused
*   Trying 127.0.0.4...
* connect to 127.0.0.4 port 80 failed: Connection refused
* connect to 127.0.0.4 port 80 failed: Connection refused
* Failed to connect to MTEST port 80: Connection refused
* Closing connection 0
* The cache now contains 0 members
* Expire cleared
curl: (7) Failed to connect to MTEST port 80: Connection refused

The bug was born in commit bagder/curl@2d435c7.

In function Curl_closesocket() in connect.c the call to
Curl_multi_closed() was wrongly omitted if a socket close function
(CURLOPT_CLOSESOCKETFUNCTION) is registered.

That would lead to not removing the socket from the internal hash table
and not calling the multi socket callback appropriately.

Bug: http://curl.haxx.se/bug/view.cgi?id=1493

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

... even if the last IPv6 connection attempt has failed.

Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1187531#c4