# Re: Problems with Prisa 620S [snapscan] + BUG in xsane 0.76

From: Oliver Rauch (oliver.rauch@rauch-domain.de)
Date: Tue May 22 2001 - 09:02:50 PDT

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  Ben Stanley wrote:
  > I read the sane.ps API documentation, and by running xsane under a
  > debugger it appears that the scanner is sending too much data. I added a
  > check into xsane-preview.c, preview_increment_image_y, which checks if
  > p->image_y >= p->image_height. If this is true, the buffer will be
  > overrun. Perhaps this is legal on the last iteration in the read, but I
  > think that a check of this kind needs to be made. Perhaps there is
  > another place in the code where it would be more appropriate. At least
  > my xsane reports an error now instead of seg faulting :-).
  >

  Hi ben,

  I will think about that.
  The first step is to make the backend return the correct values.
  I think xsane should not read more data than given in sane_get_parameters
  so may be it is better to cancel the scan than to read more image data.

  > BTW, a BUG in xsane in increment_image_y: if there is an error, and
  > xsane_back_gtk_error is called, then preview_read_image_data will be
  > called (by gtk io scheduler), resulting in a seg fault. It seems that
  > calling preview_scan_done before calling xsane_back_gtk_error fixes this
  > problem, although the value of errno must be saved before calling
  > preview_scan_done() for use in generating the error message.

  Hm, I will take a look at that.

  > and redirecting the output. I checked the size inquiry before the scan
  > data was read, and from the get_parameters call which occurs just after
  > the scan started. It seems that these two are not returning the same
  > number of lines. should they be? I can post log output if you want.

  The sane standard says that after sane_start has called
  sane_get_parameters has to return exact values. So the first call
  has to return correct values, everything else is a backend bug.

  > I'm a C++ programmer, and I find the C way of doing this stuff to be a
  > bit 'messy' by comparison, but them's the breaks when you use other
  > people's software.

  A good written C code is not messy, but in fact some backends are messy
  (but you also can write messy code in C++ ;-))

  I suggest you contact the backend author and discuss the problem with him.

  Bye
  Oliver

      --
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  - Next message: Henning Meier-Geinitz: "Re: PNM device configuration"
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