Peter M. Groen / libmodbus

With the previous value UT_REGISTERS_NB, the server sent two
consecutives and identical responses to the client. These requests
could be confusing for the human reader!

The _modbus_receive_confirmation()_ function shall receive a
request via the socket of the context 'ctx'. This function must be
used for debugging purposes because the received response isn't
checked against the initial request. This function can be
convenient to receive request not handled by the library.

The _modbus_send_raw_request()_ function shall send a request via
the socket of the context 'ctx'. This function must be used for
debugging purposes because you have to take care to make a valid
request by hand. The function only adds to the message, the header
or CRC of the selected backend, so 'raw_req' must start and contain
at least a slave/unit identifier and a function code. This function
can be used to send request not handled by the library.

Reported by Allan Cornet.

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.

Related to 49d6f4a71f686de64e5c28d6dd8acd2c98c5038d.

Page 38 in the document Modbus_Application_Protocol_V1_1b.pdf:
6.17 23 (0x17) Read/Write Multiple registers

This function code performs a combination of one read operation
and one write operation in a single MODBUS transaction. The write
operation is performed before the read.

The unit test has been updated.

Contributed by Dominic Storey.
- new function modbus_reply_exception
- unit test

- MODBUS_GET_INT32_FROM_INT16
- MODBUS_GET_INT16_FROM_INT8
- MODBUS_SET_INT16_TO_INT8
- check the trame length before indexing in unit-test-server

- new public function
- change unit-test-server.c to be transport layer independant (query
  and header_length)

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

- removed comment not required anymore with -Wall -Werror

Reported by Ivan Giuliani <giuliani.v@gmail.com>
It was not possible to use libmodbus outside of projects without
config.h file.

The inclusion has been removed from the public header.

Signed-off-by: Stéphane Raimbault <stephane.raimbault@gmail.com>

These functions have no meaning in RTU so it's better to specialize
the names and remove them from the backend.

- remove the functions from the backend
- update tests to handle RTU mode (master and slave)
- add command line options to tests (rtu or tcp)

- check strlcpy in configure.ac
- test for empty device string
- test truncated device string

modbus_set_slave must be used to set the slave ID of the remote
device to talk in master mode and to set the internal slave ID in
slave mode.

If you talk to several devices, you need to call modbus_set_slave
each time the following requests must be sent to another device.

- move termios header in RTU backend
- move TCP headers in TCP backend
- use native serial on Win32 for Cygwin
- avoid too many defines

Added support for native Win32 based on
https://code.launchpad.net/~thepyper/libmodbus/win32-native
This mainly affects the RTU implementation as the TCP/IP socket
interface is the same thanks to the winsocks library. The interface
for using the serial port is completely different on Win32 and is now
implemented accordingly.

Signed-off-by: Stéphane Raimbault <stephane.raimbault@gmail.com>

All private functions and constants are now prefixed by _.
The modbus protocol uses entry points to call specific functions.

- return only useful data client side
- available in TCP when a gateway to RTU is used
- need to add isolated handling of indication/confirmation messages

- more coherent
- namespace
- opaque and smaller context
- usual wording

A new API will be committed to remove the slave in TCP communication.