bug#33684: DocView bombs out upon password protected PDFs

[Tassilo Horn <tsdh@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

Hi Federico, Dan & Eli,

>> From: Federico Tedin <federicotedin@gmail.com>
>> Date: Sat, 26 Jan 2019 23:14:49 -0300
>
> Thanks.
>
> Tassilo, any comments on the proposal below? Should I push it?

It would be great if we could support opening password protected PDFs
also when we're using mupdf as a converter.  That has a "-p" option for
the very same sake which could be set analogously in
`doc-view-pdf->png-converter-mupdf'.

So, yes, please push it with that small addition.

Bye,
Tassilo

>> 積丹尼 Dan Jacobson <jidanni@jidanni.org> writes:
>> 
>> > When trying to view a password protected PDF:
>> > DocView: process pdf/ps->png changed status to exited abnormally with code 1.
>> > Maybe it should ask for the password.
>> > emacs-version "25.2.2"
>> 
>> Would something like this make sense? A short patch that adds
>> `doc-view-pdf-password-protected-p', and an extra option to pass to
>> Ghostscript (-sPDFPassword=) when the command is invoked (only when the
>> PDF file is password protected). I tried it out by creating a
>> password-protected PDF using LibreOffice Writer, and then opening it
>> with find-file.
>> 
>> 
>> diff --git a/lisp/doc-view.el b/lisp/doc-view.el
>> index df8a9fc70f..8691d2a3a6 100644
>> --- a/lisp/doc-view.el
>> +++ b/lisp/doc-view.el
>> @@ -183,11 +183,16 @@ doc-view-pdf->png-converter-function
>>  (defcustom doc-view-ghostscript-options
>>    '("-dSAFER" ;; Avoid security problems when rendering files from untrusted
>>      ;; sources.
>> -    "-dNOPAUSE" "-sDEVICE=png16m" "-dTextAlphaBits=4"
>> -    "-dBATCH" "-dGraphicsAlphaBits=4" "-dQUIET")
>> +    "-dNOPAUSE" "-dTextAlphaBits=4" "-dBATCH"
>> +    "-dGraphicsAlphaBits=4" "-dQUIET")
>>    "A list of options to give to ghostscript."
>>    :type '(repeat string))
>>  
>> +(defcustom doc-view-ghostscript-device "png16m"
>> +  "Output device to give to ghostscript."
>> +  :type 'string
>> +  :version "27.1")
>> +
>>  (defcustom doc-view-resolution 100
>>    "Dots per inch resolution used to render the documents.
>>  Higher values result in larger images."
>> @@ -950,16 +955,30 @@ doc-view-dvi->pdf
>>  			    (list "-o" pdf dvi)
>>  			    callback)))
>>  
>> +(defun doc-view-pdf-password-protected-p (pdf)
>> +  "Using Ghostscript, check if a PDF file is password-protected."
>> +  (with-temp-buffer
>> +    (apply #'call-process doc-view-ghostscript-program nil (current-buffer)
>> +           nil `(,@doc-view-ghostscript-options
>> +                 "-sNODISPLAY"
>> +                 ,pdf))
>> +    (goto-char (point-min))
>> +    (search-forward "This file requires a password for access." nil t)))
>> +
>>  (defun doc-view-pdf->png-converter-ghostscript (pdf png page callback)
>> -  (doc-view-start-process
>> -   "pdf/ps->png" doc-view-ghostscript-program
>> -   `(,@doc-view-ghostscript-options
>> -     ,(format "-r%d" (round doc-view-resolution))
>> -     ,@(if page `(,(format "-dFirstPage=%d" page)))
>> -     ,@(if page `(,(format "-dLastPage=%d" page)))
>> -     ,(concat "-sOutputFile=" png)
>> -     ,pdf)
>> -   callback))
>> +  (let ((pdf-passwd (if (doc-view-pdf-password-protected-p pdf)
>> +                        (read-passwd "Enter password for PDF file: "))))
>> +    (doc-view-start-process
>> +     "pdf/ps->png" doc-view-ghostscript-program
>> +     `(,@doc-view-ghostscript-options
>> +       ,(concat "-sDEVICE=" doc-view-ghostscript-device)
>> +       ,(format "-r%d" (round doc-view-resolution))
>> +       ,@(if page `(,(format "-dFirstPage=%d" page)))
>> +       ,@(if page `(,(format "-dLastPage=%d" page)))
>> +       ,@(if pdf-passwd `(,(format "-sPDFPassword=%s" pdf-passwd)))
>> +       ,(concat "-sOutputFile=" png)
>> +       ,pdf)
>> +     callback)))
>>  
>>  (defalias 'doc-view-ps->png-converter-ghostscript
>>    'doc-view-pdf->png-converter-ghostscript)
>