Ghostscript api requesting "press <return> to continue" - c++

Question

I am using GhostScript API to test if a PDF is user password protected (You can only open the document if you have the password, what is different from owner protection that only protects the content against unauthorized copying or printing)
I am using this code in Qt:
const bool PDFTools::isUserProtected(const QString &iFilePath)
{
void *minst;
const QString filePath = iFilePath.toUtf8();
const std::string inputFile = QString( "%1" ).arg(filePath).toStdString();
int initiationCode = 0;
int executionCode = 0;
// GhostScript arguments
const int gsArgumentCount = 2;
char * gsArgumentValues[gsArgumentCount];
gsArgumentValues[0] = "-dNODISPLAY";
gsArgumentValues[1] = const_cast<char*>( inputFile.c_str() );
initiationCode = gsapi_new_instance(&minst, NULL);
if(initiationCode < 0)
return true;
initiationCode = gsapi_set_arg_encoding(minst, GS_ARG_ENCODING_UTF8);
if (initiationCode < 0)
{
gsapi_delete_instance(minst);
return true;
}
executionCode = gsapi_init_with_args(minst, gsArgumentCount, gsArgumentValues);
if(executionCode < 0)
{
gsapi_exit(minst);
gsapi_delete_instance(minst);
return true;
}
gsapi_exit(minst);
gsapi_delete_instance(minst);
return false;
}
When the document is protected it returns true because it can't open without password and Ghostscript returns a execution error, this is OK.
The problem is when the document it's not protected it opens the first page and keeps waiting for the return key to be pressed so it can pass to the next page.
>>showpage, press <return> to continue<<
You can add the "-dNOPAUSE" and "-dBATCH" to the gsArgumentValues but this will cause another problem. If I have really big PDF with big number of pages this will take to much time to pass through all pages only after that it will return false.
Anyone knows how can I exit the process when the Ghostscript prompts for return? At that stage I already know that the PDF is not protected and I can exit and return false.
I have tried with the callback function but with no success.
Thanks in advance.

Answer 1

Try using -dFirstPage=1 -dLastPage=1 and -dNOPAUSE -dBATCH. Then it only processes the first page.
Otherwise you'll have to intercept the press any key and interrupt the process, or modify the device to throw an error after the first page or something.
NOTE although you can use these switches with other types of input than PDF, they still have to process the entire input file because, unlike PDF, there is no easy way to find the n'th page in a PostScript or PCL file.