Re: [Pharo-dev] NativeBoost and WKHTML

[Henrik Johansen]

On 23 May 2014, at 2:36 , Torsten Bergmann <asta...@gmx.de> wrote:

> Hi, 
> 
> as there was no responded so far I tried to track the problem deeper and did 
> a short test
> client in C/C++ to verify if I can call WKHTMLTOPDF there and generate a PDF 
> and to 
> compare to the Pharo/NativeBoost client. 
> 
> Attached is the according CPP file which works and results in a PDF with the 
> google 
> homepage. 
> 
> I also additionally implemented the callback functions in the Pharo wrapper 
> and 
> using the error handling I noticed that the component returns "Failed loading 
> page http:// ..."
> 
> 
> With that info I compared the C/C++ calls to the Pharo/NativeBoost calls more 
> deeply and 
> found out that in C/C++ the following call for an object setting works (by 
> returning 1):
> 
> 
>        // this returns 1 in C/C++ which is OK
>       int a = wkhtmltopdf_set_object_setting(os, "page", 
> "http://www.google.de";);
>       printf("object set %i",a);
> 
> 
> while in Pharo the same call fails (by returning 0):
> 
>        "The following call failed and returns 0 instead of 1"
>       self setObjectSetting: 'page' to: 'http://www.google.de' in: os.

With argument type char * , NB does not 0-terminate your strings, but passes in 
the argument you provided raw.
ByteStrings have an internal representation size a multiplum of 4, thus ‘page’ 
will have no accidentally terminating 0, while ‘out’ does, and the call fails 
since whatever garbage bytes are in the image after the string instance 
(‘page’) leads to the it not being recognized as a valid property name.

Change the call definitions to use String as argument type instead, and NB will 
convert the args to zero-terminated strings for you:

NBFFICallout stdcall: #(int 
wkhtmltopdf_set_object_setting(wkhtmltopdf_object_settings* settings, String 
aName, String value)) module: 'wkhtmltox.dll'  

Alternatively, you need to provide null-terminated strings yourself:

x := self setObjectSetting: ('page' , (Character value: 0) asString) to: 
'http://www.google.de', (Character value: 0) asString) in: os.

Which also returns makes it return 1.

Cheers,
Henry

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