[cups] Can't detect file type / Not a PDF file

[Brian Potkin]

On Thu 02 May 2019 at 11:29:26 +0100, Henrik Morsing wrote:

> On Thu, May 02, 2019 at 10:38:15AM +0100, Brian Potkin wrote:
> > 
> > The job has undergone filtering on the client.
> > 
> [...]
> > 
> > It then gets filtered again on the server.
> > 
> > https://wiki.debian.org/PrintQueuesCUPS#Double_Filtering
> > 
> > might help to explain why this is not a good idea.
> 
> Well, yes, that has been one of my concerns ever since this stopped
> working, but I can't see a way around it. CUPS has abandoned raw
> queues, I found that documented somewehere, and Windows can't print
> without you going though which printer you have and doesn't have raw
> printing either. It does have a "print to PDF" printer but that
> appears to just print to a local file.
> 
> So I'm still stuck... But yes, the double-filtering has puzzled me
> ever since this broke...

I am completely unfamiliar with printing from Windows but, TBH, I cannot
see why the the server should not process a PostScript file. That's in
spite of pointing you in the direction of double filtering.

 > E [02/May/2019:07:13:46 +0100] [Job 278] Can\'t detect file type

That looks like a gstoraster message. I am also unfamiliar with coding
but gstoraster.c has

     parse_doc_type(FILE *fp)
     {
       char buf[5];

       /* get the first few bytes of the file */
       rewind(fp);
     /* skip until PDF/PS start header */
      while (fgets(buf,sizeof(buf),fp) != 0) {
        if (strncmp(buf,"%PDF",4) == 0) return GS_DOC_TYPE_PDF;
        if (strncmp(buf,"%!",2) == 0) return GS_DOC_TYPE_PS;
       }
       return GS_DOC_TYPE_UNKNOWN;
     }

and

     doc_type = parse_doc_type(fp);
     if (doc_type == GS_DOC_TYPE_UNKNOWN) {
      fprintf(stderr, "ERROR: Can't detect file type\n");
       goto out;
     }

It might be worth capturing the file sent to the server and looking at
the header.

https://wiki.debian.org/DissectingandDebuggingtheCUPSPrintingSystem#Capturing_the_File_Received_by_CUPS

-- 
Brian.