Users functions

[demiurg-spb]

Add new API function
int modbus_send_generic_request(modbus_t *ctx, const uint8_t *raw_req, int raw_req_length, int wanted_resp_data_length);
to enable the implementation of user-defined modbus functions (by standard in the range 65...72 and 100...110) with a predetermined number of requested bytes.
wanted_resp_data_length is number of data bytes between the function code and the checksum
(address, function, data[wanted_resp_data_length], crc).

[karlp]

I believe #140 would be a better solution to this problem, (and also solves many more)

[demiurg-spb]

Maybe so, but one does not interfere with the other. And it can be implemented in the code base at the same time.
If you look carefully, this commit does not change the initial behavior of the library, making only an additional wrapper over the function
int modbus_send_raw_request (modbus_t * ctx, const uint8_t * raw_req, int raw_req_length);

[demiurg-spb]

PS: Callbacks are convenient to use when you need to do something non-trivial. In your link #140 I see an implicit link to the size of the data. In my opinion, my solution is simple, convenient to use and very intelligible (solving a specific problem).
Custom user's functions are a typical part of the modbus protocol, which should be easily and intelligibly implemented. Which I suggest.
Callbacks are also a useful feature, but absolutely not related to the implementation of simple user-defined functions indicated by the STANDARD in the SPECIFIC range.

[demiurg-spb]

mazi thanx!
I fixed typos and comment style

[gbetous-swir]

I would need this improvement to implement user defined functions. What is missing for merging it ?

[demiurg-spb]

I've been asking the same question for a few years now.... (