Peter M. Groen / libmodbus

Thanks to Petr Gladkiy

Thanks to oldfaber and endrelovas.

It will better to code something such as:
https://github.com/crossroads-io/libxs/blob/master/src/err.cpp

I don't intend to rewrite glib neither :(

Thanks to oldfaber

Thanks to Thomas Stalder and Torello Querci for the report.

Original patch for new connect function by Thomas Stalder.

- export new symbols to create specific behavior (RTU)
- the flag can't only be set by slaves
- new tests

Warning, modbus_receive returns 0 when a query is ignored.

- function removed from TCP and RTU code and from backend structure
- updated documentation
- updated examples

- remove static variable in the library

libabc is a really good source of inspiration!
https://git.kernel.org/?p=linux/kernel/git/kay/libabc.git

Thanks to Pavel Mazniker for the report.

Avoid incompatibility with GPLv2 program. This change has been approved by
Tobias Doerffel, Florian octo Forster and Hannu Vuolasaho.

The two modes are complementary, MODBUS_ERROR_RECOVERY_LINK handles
errors at data link level (bad file descriptor, timeout, etc) and
MODBUS_ERROR_RECOVERY_PROTOCOL checks Modbus error (eg. invalid
function code or trame length).

This change introduces the use of the Sleep function for Windows.
Some duplicated code has been moved from backends to modbus core.
A new debug message is now available when a flush occurs.

The unit tests are now based on this error recovery code.

The loop test ought to iterate again to end the loop but this is
only required if the socket contained more data than read.

The error reported by #9 was already fixed in master but this change
scrupulously respects the definition of DWORD.

Each function is decribed in one txt file. The file libmodbus.txt
offers an overview of the library.

It's possible to generate HTML and man outputs from the txt file.
The documentation can be generated only if you have the required
tools (asciidoc and xmlto).

Better results are obtained with AsciiDoc v8.6+

To avoid to duplicate the documentation between source and
documentation. The information already available in documentation
is removed from source.

Reported by Allan Cornet.

- removed ENOTCONN errno not supported
- set WINVER to Windows XP (and above) and add ws2_32.dll. So older
  Windows versions aren't supported.

Reported by Patsy Kaye.
Removed useless asignment at the same time.

Inspired by the branch ff/ipv6 of Florian Forster but this version uses
a specific PI backend to isolate the IPv4 and IPv6 implementations.

The existing TCP/IPv4 implementation has been kept intact (not rebased
on the PI one) because its data backend requires fewer bytes than the PI.

New functions modbus_new_tcp_pi, modbus_tcp_pi_listen and
modbus_tcp_pi_accept and new backend called modbus_tcp_pi_t.

In modbus-tcp.c:
- Needed to include <signal.h>
- Added Jay's fix for __OpenBSD__
- SIGPIPE ignore handler needs to return a pointer instead of an integer.

Patch provided bu Barry Grumbine and Jason Oster.

Original patch by Jason Oster

Win32 uses a specific function to close socket.
Reported by Petr Parýzek.

Reported by Antti Manninen and according to Page6 in the document
"MODBUS Messaging on TCP/IP Implementation Guide V1.0b",
------------------------
Unit Identifier – This field is used for intra-system routing purpose.
It is typically used to communicate to a MODBUS+ or a MODBUS serial
line slave through a gateway between an Ethernet TCP-IP network and
a MODBUS serial line. This field is set by the MODBUS Client in the
request and must be returned with the same value in the response by
the server.
------------------------

The goal of this rewriting is to avoid the timeouts on the receiving
of exceptions and to be more robust on bad requests. Some devices
use the exception MODBUS_EXCEPTION_ACKNOWLEDGE to response to some
valid requests, so in this case, you'll really appreciate this
change!

- Slower! More system calls are used.
- The code is cleaner and easier to understand.
- Really faster when an exception occurs.
- Fix unit test of bad request in RTU