[Gambas-user] Working with .so library

[Benoît Minisini]

Le 31/05/2017 à 06:48, Admin a écrit :
> So, I am writing a programm for my business that would basically be a 
> cash register. Don't know for other countries but here in Russia the tax 
> law works like this: you have to form a check for a customer in a 
> spicific way spicified by the law, so some hardware manufacturers are 
> making certified cash registers/check printers that simply form the 
> check needed and automatically send tax info to authorities, very simple 
> and easy to integrate with ERP systems. The only problem is that most of 
> accounting software that is compatible with those registers is written 
> for Windows. Now that Windows becomes more and more monstrous, many 
> businesses turn to Linux, at least on those computers that are only a 
> cashier's workstation that does not need to do much in terms of 
> performance power. But the problem is, there's only one or two cashier's 
> programms for linux exist for now, that are compatible with that 
> certified hardware, and it's not open source or free.
> 
> 
> First of all I want to make my own for myself, and second - I want to 
> share it. Gambas is a great language in this case because of many 
> aspects. In small buisnesses usually there are not a lot of qualified 
> programmers to make some apps in C or C++, but instead there usually is 
> just a single sysadmin, who is servicing the IT stuff wich usually is 
> just one or two PCs and a router/switch. So, Gambas is much more 
> accessible to those people as I see it. Programs written on it are easy 
> to understand and modify to the needs of a small business.
> 
> 
> And what is great - the manufacturers of that certified hardware are 
> willing to help: ofcourse they mostly do business with Windows stuff, 
> they only work directly with big businesses and they don't produce 
> accounting software themselves, but they are kind enough to provide at 
> least a binary libraries (they call those - drivers, but i'm not shure 
> if it's technically correct) for their hardware even for Linux as a x86 
> and x64 .so files. What those binary libraries do is simple conversion 
> of easy commands to hex codes that are then passed to a hardware via USB 
> or RS232 or Ethernet. It is MUCH easier to work with those commands then 
> implement the whole communication protocol from scratch. Ofcourse I am 
> not the only one who is interested in those devices to work under linux, 
> and as I can tell from different forums in the internet - programmers 
> successfully use this libraries and thank the developers. There's not a 
> lot of documentation out there, but yeah, on paper it seems to be simple 
> enough... if you write your code in C or C++.
> 
> 
> Things get much different when you try to use the library in Gambas. 
> What I was able to understand from the documentation is that you need to 
> "initialize the interface" with the library, which will create a 
> "virtual class" and than you can pass your data to it. So, in C (using 
> QT) that would look something like this:
> 
> 
>   typedef IFptr * (*_CreateFptrInterface)(int ver);
> 
>      bool init() {
>          QLibrary *lib = new QLibrary("fptr");
>          lib->load();
>          if(lib->isLoaded()) {
>              _CreateFptrInterface CreateFptrInterface = 
> (_CreateFptrInterface)lib->resolve("CreateFptrInterface");
>              if(CreateFptrInterface) {
>                  IFptr * iface = CreateFptrInterface(12);
>                  iface->put_DeviceEnabled(true);
>                  int result = 0;
>                  iface->get_ResultCode(&result);
>                  qDebug() << result;
>                  wchar_t bfr[1000];
>                  int length = iface->get_ResultDescription(bfr,1000);
>                  qDebug() << QString::fromWCharArray(bfr,length);
>              }
>          }
>      }
> 
> 
> So, as I understand we create a pointer called IFptr by calling 
> CreateFptrInterface() and then we pass any other pointer through this 
> one. Pardon my terminology, I am new to this stuff.
> 
> I wrote some simple code that basically initializes this driver just so 
> I can see some output in the driver logs which are kindly created in 
> ~/.atol. It also sends some data to driver which must change just one 
> setting:
> 
> -----
> 
> Library "~/ATOL/linux-x64/libfptr"
> 
> Extern CreateFptrInterface(ver As Integer) As Pointer
> Extern put_DeviceSingleSettingAsInt(p As Pointer, s1 As String, s2 As 
> Integer) As Integer
> Extern ApplySingleSettings(p As Pointer) As Pointer
> 
> [...]
> 
> Public Sub Button1_Click()
> Dim IFptr As Pointer
> 
> IFptr = CreateFptrInterface(12)
> put_DeviceSingleSettingAsInt(IFptr, "Model", 63)
> 
> ApplySingleSettings(IFptr)
> 
> End
> 
> -----
> 
> When I click Button1, the driver surely initializes, I see in logs that 
> IFptr object is created. If I provide the wrong version in 
> CreateFptrInterface it fails, saying in logs that there's missmatch in 
> interface version, so no doubt the argument is passed correctly. I also 
> can see that put_DeviceSingleSetting is being called, but the 
> configuration does not actually change. The commercial software that 
> uses this very same driver and works fine - leaves mostly the same trace 
> in driver's log except that I see what arguments are passed to 
> DeviceSingleSetting. And in my case I only see that the procedure is 
> envoked but with no arguments. I was trying to use many other procedures 
> (or methods, or pointers, or what are they?) with the same effect - they 
> surely are called and executed, but I can't pass any arguments to them. 
> I was experimenting with variable types I send them, and if I, for 
> example, send an integer as an argument when the library expects a 
> string - it crashes. If I do not use IFptr pointer - it crashes. So I 
> think I figured out the syntax correctly, but I still can't get the 
> desired result.
> 
> 
> My question is basically this: Should I continue experimenting, or is it 
> simply impossible to work with this kind of library from Gambas?
> 
> 
> Here is the link to the library and some other libraries it uses itself: 
> http://allunix.ru/back/atol.tar.gz - there's also a binary executable 
> that is a test program, unfortunately it's in Russian, but it still 
> shows what logs must look like when everything is correct, just for a 
> comparison.
> 
> 
> There's simple experiment you can make: it has a pointer 
> ShowProperties() which must show a window with driver's settings using 
> it's own library libgui_engine.so. When I call ShowProperties(IFptr) it 
> prints to log that it can't find this lib, which is expectable, because 
> first I must provide the path to it using 
> put_DeviceSingleSettingAsBuff(IFptr, "SearchDir", 
> "/home/bocha/ATOL/linux-x64/") and AplySingleSettings(IFptr), but when I 
> pass this setting, I, as always, see that it passes no arguments, so the 
> result stays the same.
> 
> I do understand that I ask a lot of invovement, there's no simple way to 
> understand what's needed to be done to make this whole thing work so not 
> many people would even read this message to the end, but I still hope 
> for some answers, they would be much appriciated. Thank you!
> 
> Best Regards.
> 
> Dmitry Bachilo.
> 

Apparently all that black box is written in C++ with QT, and without the 
header of the library interface , I can't tell you if it is possible to 
use the library with Gambas, and how.

Regards,

-- 
Benoît Minisini