Ignore unsupported resolution values

Since some time the print dialog of Google's Chrome browser send the
attribute "Resolution=96dpi" with its print jobs (job itself sent in
PDF format). This is a resolution which most modern printers do not
support and usually the print filters and drivers should ignore
unsupported values for any option or IPP attribute, so such an
attribute should not harm.

Unfortunately, in some cases the validity of the resolution value is
not checked and so the wrong value makes it through to the actual
rasterization, messing up the printouts as a raster with a much too
low, unsupported resolution is sent to the printer.

This commit solves the problem by actually checking the resolution
values. This is done in the raster_base_header() function which
generates a CUPS/PWG Raster header from scratch, solely based on
printer and job IPP attributes, and the option list supplied to the
filter functions. This function is called by the
cfRasterPrepareHeader() API function which creates a CUPS/PWG Raster
header for the filter functions, either as base for the page headers
in CUPS/PWG/Apple Raster output or to get a data structure with all
important page properties. He we add a check now, by passing
resolutions parsed from the options through the
cfIPPAttrResolutionForPrinter() function. This way wrong values get
ignored and the default value be used instead. If there are no printer
attributes available, any resolution value is accepted.

Fixes #29: #29

Author: tillkamppeter

cupsfilters/raster.c

@@ -1023,14 +1023,32 @@ raster_base_header(cups_page_header2_t *h, // O - Raster header
   else
     h->Duplex = CUPS_FALSE;
 
-  if ((val = cupsGetOption("printer-resolution", num_options,
-			   options)) != NULL ||
-      (val = cupsGetOption("Resolution", num_options, options)) != NULL)
+  // To avoid that a resolution provided in the option list and not as
+  // job IPP attribute is a supported resolution according to the
+  // printer IPP attributes, we want to use the
+  // cfIPPAttrResolutionForPrinter() function on it, to only accept it
+  // if it is supported and use the default if not, and also to accept it if
+  // there are no printer IPP attributes.
+  //
+  // Therefore we create a new IPP message for adding the resolution
+  // parsed from the option list, but only if we do not already have a
+  // "printer-resolution" in the job IPP attributes, which we use
+  // preferrably then.
+  int x = 0, y = 0;
+  if ((attr = ippFindAttribute(data->job_attrs, "printer-resolution",
+			       IPP_TAG_ZERO)) != NULL)
+    cfIPPAttrResolutionForPrinter(data->printer_attrs, data->job_attrs, NULL,
+				  &x, &y);
+  else if ((val = cupsGetOption("printer-resolution", num_options,
+				options)) != NULL ||
+	   (val = cupsGetOption("Resolution", num_options, options)) != NULL)
   {
     int	        xres,		// X resolution
                 yres;		// Y resolution
     char	*ptr;		// Pointer into value
+    ipp_t       *attrs;
 
+    attrs = ippNew();
     xres = yres = strtol(val, (char **)&ptr, 10);
     if (ptr > val && xres > 0)
     {
@@ -1050,33 +1068,22 @@ raster_base_header(cups_page_header2_t *h, // O - Raster header
 	xres = xres * 254 / 100;
 	yres = yres * 254 / 100;
       }
-      h->HWResolution[0] = xres;
-      h->HWResolution[1] = yres;
-    }
-    else
-    {
-      h->HWResolution[0] = 100; // Resolution invalid
-      h->HWResolution[1] = 100;
+      ippAddResolution(attrs, IPP_TAG_PRINTER, "printer-resolution",
+		       IPP_RES_PER_INCH, xres, yres);
     }
+    cfIPPAttrResolutionForPrinter(data->printer_attrs, attrs, NULL, &x, &y);
+    ippDelete(attrs);
+  }
+  if (x && y)
+  {
+    h->HWResolution[0] = x;
+    h->HWResolution[1] = y;
   }
   else
   {
     h->HWResolution[0] = 100; // Resolution invalid
     h->HWResolution[1] = 100;
   }
-
-  // Resolution from IPP attrs
-  if (h->HWResolution[0] == 100 && h->HWResolution[1] == 100)
-  {
-    int x = 0, y = 0;
-    cfIPPAttrResolutionForPrinter(data->printer_attrs, data->job_attrs,
-				  NULL, &x, &y);
-    if (x && y)
-    {
-      h->HWResolution[0] = x;
-      h->HWResolution[1] = y;
-    }
-  }
 
   // TODO - Support for insert sheets
   h->InsertSheet = CUPS_FALSE;