Some code style improvements: removed redundant parentheses, added const, joined declaration and assignment of local variables

Solution: add some msg helpers to parse commands, and check for
subscribe or cancel commands and process them accordingly in the xpub
and xsub classes.

Solution: use UCHAR_MAX constant instead

Problem: inconsistent naming style for private data members, conflicts with naming of local variables and member functions

Solution: apply and check _lower_case naming style for private data members

Solution: remove else

Solution: define and apply parameter naming style: lower_case_

Solution: add const

Solution: replace by C++-style casts

Solution: if a PING message contains a context, echo it back in the
PONG message. In order to do so, create the PONG message when PING
is received and store it in the engine.
After the PING the engine goes straight to encoding and sending, so
there can always be at most one pending PING.
Add tests for various contexts.

Solution: treat the first byte of the command body as the size of the
command name, rather than as an id, to comply with ZMTP 3.1.
This was not an actual problem at runtime since both heartbeat
commands have a size of 4, which was treated like an id.
But once SUBSCRIBE/UNSUBSCRIBE get implemented it needs to be checked.

Solution: do it explicitly to fix build on Solaris 10/11 with the Sun
compiler

* Fixes issue 2963, ref stream_engine.cpp:981

* Fixes issue 2963, ref socks_connecter.cpp:158

* Fixes issue 2963, ref tcp_listener.cpp:144

* Fixes issue 2963, ref tcp_connecter.cpp:423

* Fixes issue 2963, ref socks_connecter.cpp:436

* Fixes issue 2963, ref tcp_listener.cpp:179

* Fixes issue 2963, ref tcp_listener.cpp:268

* Fixes issue 2963, ref tcp_connecter.cpp:160

The zero copy decoding strategy implemented for 4.2.0 can lead to a large
increase of main memory usage in some cases (I have seen one program go up to
40G from 10G after upgrading from 4.1.4). This commit adds a new option to
contexts, called ZMQ_ZERO_COPY_RECV, which allows one to switch to the old
decoding strategy.

Solution: applied clang-format

Solution: use std::map::emplace instead, where available

* Problem: excessive memory allocations around blob_t

Solution: redefine blob_t as a custom type, and use reference/move
semantics where possible

On FreeBSD the sysmbol __FreeBSD_kernel__ is only defines if a
specific param.h file is included, unlike Debian/kFreeBSD where this
symbol is always defined.  So also compile the FreeBSD specific code
if __FreeBSD__ is defined for FreeBSD 11 & 12 compatibility.
Signed-off-by: Christopher Hall <hsw@ms2.hinet.net>

Solution: renamed routing_id fields in pipe_t, renamed ZMQ_CONNECT_RID to ZMQ_CONNECT_ROUTING_ID

Solution: replace by "routing id"

Solution: renamed routing_id fields in pipe_t, renamed ZMQ_CONNECT_RID to ZMQ_CONNECT_ROUTING_ID

Solution: replace by "routing id"

Solution: emit events at appropriate places

Solution: use check_basic_command_structure in curve_client_t::decode, also prepare other client mechanisms to use that method by rearranging inheritance hierarchy

Solution: add handshake failure events to curve_client_t

Solution: redesign ZMQ_HANDSHAKE_FAILED_* events, introduce new class of ZMQ_HANDSHAKE_FAILED_AUTH events

* Problem: missing test for status code 300, inadequate assertion for status code 500

Solution: add test, change assertion (currently test fails)

* Problem: gcc compiler error deprecated conversion from string constant

Solution: declare variable as const

* Problem: in case of ZAP handler returning a status code other than 200, no appropriate event is emitted

Solution: immediately emit event after receiving reply from ZAP handler

* Problem: endpoint address is not included in zap-reply monitor event

Solution: added functions to retrieve endpoint address in zmq::i_engine and zmq::session_base_t
removed unused code block in zmq::stream_engine_t::next_handshake_command

* Problem: wrong formatting

Solution: fix formatting

* Problem: test fails because of EPIPE

Solution: add EPIPE/ECONNRESET/ECONNAGAIN handling for more test cases

Solution: Define them in zmq.h and use them (currently in DRAFT API)

* Fixing #2002 one way of doing it

 * Mechanisms can implement a new method `error_detail()`
 * This error detail have three values for the moment: no_detail
 (default), protocol, encryption.
    + generic enough to make sense for all mechanisms.
    - low granularity level on information.

* Fixing #2002: implementation of the error details

The ZMQ_EVENT_HANDSHAKE_FAILED event carries the error details
as value.

* Removed Microsoft extenstion for enum member access

This was leading to compilation error under linux.

* Adaptation of CURVE test cases

* Monitoring event: changed API for detailed events

Removed ZMQ_EVENT_HANDSHAKE_FAILED and replaced it by:
- ZMQ_EVENT_HANDSHAKE_FAILED_NO_DETAIL,
- ZMQ_EVENT_HANDSHAKE_FAILED_PROTOCOL,
- ZMQ_EVENT_HANDSHAKE_FAILED_ENCRYPTION

Adaptation of text case `security_curve`

* Removed event value comparison

This was introduced for the previous API model adaptation

* Removed the prints in std output and added missing details

`current_error_detail` was not set in every protocol error cases

* Fixed initialization of current_error_detail

* Fixed error in greeting test case

The handshake failure due to mechanism mismatch in greeting is actually
a protocol error. The error handling method consider it like so and
send a protocol handshake failure monitoring event instead of no_detail.

Fixed the test_security_curve expectation as well.

* Upgraded tests of monitoring events

The tests check the number of monitoring events received

* Problem: does not build under Linux or without ZMQ_DRAFT_API

Solution:
- properly use ZMQ_DRAFT_API conditional compilation
- use receive timeouts instead of Sleep

* Problem: duplicate definition of variable 'timeout'

Solution: merged definitions

* Problem: inconsistent timing dependencies

Solution: reduce timing dependency by using timeouts at more places

* Problem: assertion failure under Linux due to unexpected monitor event

Solution: output event type to aid debugging

* Problem: erroneous assertion code

* Problem: assertion failure with a garbage server key due to an extra third event

Solution: changed assertion to expect three events (needs to be checked)

* Problem: extra include directive to non-existent file

Solution: removed include directive

* Problem: assertion failure on appveyor for unknown reason

Solution: improve debug output

* Problem: no build with libsodium and draft api

Solution: add build configurations with libsodium and draft api

* Problem: assertion failure on CI

Solution: change assertion to reflect actual behaviour on CI (at least temporarily)

* Problem: error in condition in assertion code

* Problem: assertion failure on CI

Solution: generalize assertion to match behavior on CI

* Problem: assertion failures on CI

Solution: removed inconsistent assertion on no monitor events before flushing
improved debuggability by converting function into macro

* Problem: diverging test code for three analogous test cases with garbage key

Solution: extract common code into function

* Problem: does not build without ZMQ_BUILD_DRAFT_API

Solution: introduce dummy variable

* Attempt to remove workaround regarding ZMQ_EVENT_HANDSHAKE_FAILED_NO_DETAIL again

* Problem: EAGAIN error after handshake complete if there is no more data in inbuffer

Solution: Skip tcp_read attempt in that case

* Problem: handshaking event emitted after handshaking failed

Solution: use stream_engine_t::handshaking instead of mechanism_t::status() to determine whether still handshaking

* Include error code in debug output

* Improve debugging output: output flushed events

* Split up ZMQ_EVENT_HANDSHAKE_FAILED_PROTOCOL into ZMQ_EVENT_HANDSHAKE_FAILED_ZMTP and ZMQ_EVENT_HANDSHAKE_FAILED_ZAP

* Fixed compilation without ZMQ_BUILD_DRAFT_API

* Renamed ZMQ_EVENT_HANDSHAKE_SUCCEED to ZMQ_EVENT_HANDSHAKE_SUCCEEDED for language consistency

* Renamed ZMQ_EVENT_HANDSHAKE_SUCCEED to ZMQ_EVENT_HANDSHAKE_SUCCEEDED for language consistency

* Renamed ZMQ_EVENT_HANDSHAKE_SUCCEED to ZMQ_EVENT_HANDSHAKE_SUCCEEDED for language consistency

* Fixed assert_monitor_event (require event instead of allowing no event)
Reverted erroneous change to handshaking condition
Renamed test_wrong_key to test_garbage_key
Generalized assumption in test_garbage_key to allow for ZMQ_EVENT_HANDSHAKE_FAILED_NO_DETAIL with error == EPIPE

* Better isolate test cases from each other by providing a fresh context & server for each

* Added diagnostic output

* Changed assertion to reflect actual behavior on CI

* Fixed formatting, observe maximum line length

* Fixed formatting, observe maximum line length

* Increase timeout to check if this fixes valgrind run

* Close server with close_zero_linger

* Increase timeout to check if this fixes valgrind run

* Increase timeout to check if this fixes valgrind run

* Generalize assertion to also work with valgrind

* Fixed formatting

* Add more diagnostic output

* Generalize assertion to also work with valgrind

Solution: Use the appropriate assertion macro.

Solution: setsockopt returns EINVAL if the connection was closed by
the peer after the accept returned a valid socket. This is a valid
network error and should not cause an assert.
To handle this we have to extract the setsockopt from the stream
engine, as there's no clean way to return an error from the
constructor. Instead, try to set this option before creating the
engine in the callers, and return immediately as if the accept
had failed to avoid churn. Do the same for the connect calls by
setting the option in open_socket, so that the option for that
case is set even before connecting, so there's no possible race
condition.
Since this has to be done in 4 places (tcp/ipc listener, socks
connecter and open_socket) add an utility function in ip.cpp.
Fixes #1442

The mechanism is instanciated during the handshake itself, when and
error happen before this, the error method shall work anyway.
An error handling with a NULL mechanism means the handshake fail, so the
handshake failure event is also raised in this case.

 - removed the previously added encryption_error, less changes less bug
 - handshake fail is now signaled when an error happen while the
   mechanism is still hanshaking

Solution: wrap the event triggering in the DRAFT ifdef as well as the
defines. This ensures that the event are returned only if the
library was built with DRAFTs enabled.

Also update the test case to expect the new events since it uses
the catch-all mask. Although the sequence of event is different and
this might be considered as an API breakage, using the catch-all
ZMQ_EVENT_ALL mask implies that, well, all events are monitored so
it's normal that new ones will be added.
Users that don't want this kind of behaviour to change can simply
monitor only the event that they care about.

 - Moved new events in draft section + added to zmq_draft.h
 - Removed the remainning tabs
 - Reverted the hard error (back to soft error) in curve_server.cpp

=> The feature doesn't works anymore

Added two new monitoring events:
 - ZMQ_EVENT_HANDSHAKE_SUCCEED is raised once the encryption handshake succeed
 - ZMQ_EVENT_HANDSHAKE_FAILED is raised when it failed
Both events are raised on server and client side.