Add an argument to pdf() that turns off the inclusion of a date

[hturner]

Another proposal from @pmur002: can we add an argument to pdf() that turns off the inclusion of a date in the PDF output?

I think we will need some help from Paul to navigate the C code that is called by pdf(), to work out which code would need modifying.

Not sure if access to the latest PDF standard is required, but here's a link in case: https://www.pdfa-inc.org/product/iso-32000-2-pdf-2-0-bundle-sponsored-access/.

[bastistician]

Thanks a lot for including this here @hturner. I had asked Paul if we could have such an option for reproducibility (and VCS-compatibility) of (uncompressed) PDF output and he said this could be something for the Dev Day. I think the relevant code that creates the timestamps in the PDF metadata, i.e. lines like

/CreationDate (D:20230118040050)
/ModDate (D:20230118040050)

is in the C function PDF_startfile in the source file src/library/grDevices/src/devPS.c (obviously I don't know this code).
One would indeed need to check the PDF specification (and their various versions) if these are required fields.

Code snippet:

pdf(f <- tempfile(), compress = FALSE); plot.new(); dev.off()
head(readLines(f))

[hadley]

Might also want to consider removing Producer so that https://github.com/r-devel/r-svn/blob/09f3acb92dcc180636a7c4e257491302e9a22ae8/src/library/tools/R/testing.R#L221 could be simplified.

[hadley]

Metadata added here: https://github.com/r-devel/r-svn/blob/main/src/library/grDevices/src/devPS.c#L8574-L8584

[edzer]

Thanks; @bastistician and I are on it.

[edzer]

We now have

> pdf(f <- tempfile(), compress = FALSE, useDate = FALSE); plot.new(); dev.off()
head(readLines(f), 12)
null device 
          1 
 [1] "%PDF-1.4"                          "%\x81\xe2\x81\xe3\x81ρ\xd3\\r"    
 [3] "1 0 obj"                           "<<"                               
 [5] "/Title (R Graphics Output)"        "/Creator (R)"                     
 [7] ">>"                                "endobj"                           
 [9] "2 0 obj"                           "<< /Type /Catalog /Pages 3 0 R >>"
[11] "endobj"                            "7 0 obj"                          
> pdf(f <- tempfile(), compress = FALSE, useDate = TRUE); plot.new(); dev.off()
head(readLines(f), 12)
null device 
          1 
 [1] "%PDF-1.4"                         "%\x81\xe2\x81\xe3\x81ρ\xd3\\r"   
 [3] "1 0 obj"                          "<<"                              
 [5] "/CreationDate (D:20240712104511)" "/ModDate (D:20240712104511)"     
 [7] "/Title (R Graphics Output)"       "/Producer (R 4.5.0)"             
 [9] "/Creator (R)"                     ">>"                              
[11] "endobj"                           "2 0 obj"                         
> pdf(f <- tempfile(), compress = FALSE, useDate = NA); plot.new(); dev.off()
head(readLines(f), 12)
Error in pdf(f <- tempfile(), compress = FALSE, useDate = NA) : 
  invalid value of 'useDate'

[edzer]

After discussion with @pmur002 and @bastistician we want to change to pdf():

• have a logical argument timestamp that can be set to FALSE to remove both datetime fields
• make sure that if title is set to "" the title field is removed (now not possible, against the standard)
• add a logical producer that, when FALSE, removes the producer field (because it contains version)
• (new) add a character variable author (similar to title) which adds the author metadata

[edzer]

> try(pdf(f <- tempfile(), compress = FALSE, timestamp = NA)) #error
Error in pdf(f <- tempfile(), compress = FALSE, timestamp = NA) : 
  invalid value of 'timestamp'
> try(pdf(f <- tempfile(), compress = FALSE, producer = NA))  #error
Error in pdf(f <- tempfile(), compress = FALSE, producer = NA) : 
  invalid value of 'producer'
> pdf(f <- tempfile(), compress = FALSE); plot.new(); dev.off() # old behaviour
null device 
          1 
> head(readLines(f), 12)
 [1] "%PDF-1.4"                         "%\x81\xe2\x81\xe3\x81ρ\xd3\\r"   
 [3] "1 0 obj"                          "<<"                              
 [5] "/CreationDate (D:20240712150049)" "/ModDate (D:20240712150049)"     
 [7] "/Title (R Graphics Output)"       "/Producer (R 4.5.0)"             
 [9] "/Creator (R)"                     ">>"                              
[11] "endobj"                           "2 0 obj"                         
> pdf(f <- tempfile(), compress = FALSE, timestamp = FALSE); plot.new(); dev.off() # remove 2 timestamp fields
null device 
          1 
> head(readLines(f), 12)
 [1] "%PDF-1.4"                          "%\x81\xe2\x81\xe3\x81ρ\xd3\\r"    
 [3] "1 0 obj"                           "<<"                               
 [5] "/Title (R Graphics Output)"        "/Producer (R 4.5.0)"              
 [7] "/Creator (R)"                      ">>"                               
 [9] "endobj"                            "2 0 obj"                          
[11] "<< /Type /Catalog /Pages 3 0 R >>" "endobj"                           
> pdf(f <- tempfile(), compress = FALSE, producer = FALSE); plot.new(); dev.off() # remove producer field
null device 
          1 
> head(readLines(f), 12)
 [1] "%PDF-1.4"                          "%\x81\xe2\x81\xe3\x81ρ\xd3\\r"    
 [3] "1 0 obj"                           "<<"                               
 [5] "/CreationDate (D:20240712150049)"  "/ModDate (D:20240712150049)"      
 [7] "/Title (R Graphics Output)"        "/Creator (R)"                     
 [9] ">>"                                "endobj"                           
[11] "2 0 obj"                           "<< /Type /Catalog /Pages 3 0 R >>"
> # remove title
> pdf(f <- tempfile(), compress = FALSE, title = ""); plot.new(); dev.off() # remove Title field
null device 
          1 
> head(readLines(f), 12)
 [1] "%PDF-1.4"                          "%\x81\xe2\x81\xe3\x81ρ\xd3\\r"    
 [3] "1 0 obj"                           "<<"                               
 [5] "/CreationDate (D:20240712150049)"  "/ModDate (D:20240712150049)"      
 [7] "/Producer (R 4.5.0)"               "/Creator (R)"                     
 [9] ">>"                                "endobj"                           
[11] "2 0 obj"                           "<< /Type /Catalog /Pages 3 0 R >>"
> pdf(f <- tempfile(), compress = FALSE, author = "Edzer Pebesma"); plot.new(); dev.off() # add author field
null device 
          1 
> head(readLines(f), 12)
 [1] "%PDF-1.4"                         "%\x81\xe2\x81\xe3\x81ρ\xd3\\r"   
 [3] "1 0 obj"                          "<<"                              
 [5] "/CreationDate (D:20240712150049)" "/ModDate (D:20240712150049)"     
 [7] "/Title (R Graphics Output)"       "/Producer (R 4.5.0)"             
 [9] "/Author (Edzer Pebesma)"          "/Creator (R)"                    
[11] ">>"                               "endobj"                       

[edzer]

pdf.zip

[bastistician]

Thanks a lot @edzer for helping with this. An amended version of the above patch (adding NEWS and tests, updating some more docs) has now been committed to the trunk (c86894).

[pmur002]

Thanks Sebastian and Edzer!