[Rd] Issues with libcurl + HTTP status codes (eg. 403, 404)

Martin Morgan mtmorgan at fredhutch.org
Thu Aug 27 17:27:58 CEST 2015

On 08/27/2015 08:16 AM, Martin Maechler wrote:
>>>>>> "DM" == Duncan Murdoch <murdoch.duncan at gmail.com>
>>>>>>      on Wed, 26 Aug 2015 19:07:23 -0400 writes:
>      DM> On 26/08/2015 6:04 PM, Jeroen Ooms wrote:
>      >> On Tue, Aug 25, 2015 at 10:33 PM, Martin Morgan <mtmorgan at fredhutch.org> wrote:
>      >>>
>      >>> actually I don't know that it does -- it addresses the symptom but I think there should be an error from libcurl on the 403 / 404 rather than from read.dcf on error page...
>      >>
>      >> Indeed, the only correct behavior is to turn the protocol error code
>      >> into an R exception. When the server returns a status code >= 400, it
>      >> indicates that the request was unsuccessful and the response body does
>      >> not contain the content the client had requested, but should instead
>      >> be interpreted as an error message/page. Ignoring this fact and
>      >> proceeding with parsing the body as usual is incorrect and leads to
>      >> all kind of strange errors downstream.
>      DM> Yes.  I haven't been following this long thread.  Is it only in R-devel,
>      DM> or is this happening in 3.2.2 or R-patched?
>      DM> If the latter, please submit a bug report.  If it is only R-devel,
>      DM> please just be patient.  When R-devel becomes R-alpha next year, if the
>      DM> bug still exists, please report it.
>      DM> Duncan Murdoch
> Probably I'm confused now...
> Both R-patched and R-devel give an error (after a *long* wait!)
> for
>         download.file("https://someserver.com/mydata.csv", "mydata.csv")
> So that problem is I think  solved now.
> Ideally, it would nice to set the *timeout* as an R function
> argument ourselves.. though.
> Kevin Ushey's original problem however is still in R-patched and
> R-devel:
> ap <- available.packages("http://www.stats.ox.ac.uk/pub/RWin", method="libcurl")
> ap
> giving
>> ap <- available.packages("http://www.stats.ox.ac.uk/pub/RWin", method="libcurl")Warning: unable to access index for repository http://www.stats.ox.ac.uk/pub/RWin:
>    Line starting '<!DOCTYPE HTML PUBLI ...' is malformed!
>> ap
>       Package Version Priority Depends Imports LinkingTo Suggests Enhances License License_is_FOSS License_restricts_use OS_type Archs
>       MD5sum NeedsCompilation File Repository
> and the resulting 'ap' is the same as e.g., with the the default
> method which also gives a warning and then an empty list (well
> "data.frame") of packages.
> I don't see a big problem with the above.
> It would be better if the warning did not contain the extra
>     "Line starting '<!DOCTYPE HTML PUBLI ...' is malformed!"
> part, but apart from that I'd say the behavior is not bogous:
> We ask for the available package get as answer 'zero packages'
> which is correct.

In Kevin's original post, he was using an earlier version of R, and the code in 
available.packages was returning an error.

The code had been updated (by me) in the version that you are using to return a 
warning, which was the original design and intention (to convert errors during 
repository queries into warnings, so other repositories could be queried; this 
was Kevin's original point).

The fix I provided does not address the underlying problem, which is that

                 fl <- tempfile(), method="libcurl")

actually downloads the error file, without throwing an error

 >   download.file("http://www.stats.ox.ac.uk/pub/RWin/PACKAGES.gz",   fl <- 
tempfile(), method="libcurl")
trying URL 'http://www.stats.ox.ac.uk/pub/RWin/PACKAGES.gz'
Content type 'text/html; charset=iso-8859-1' length 302 bytes
downloaded 302 bytes

 > cat(paste(readLines(fl), collapse="\n"))
<title>404 Not Found</title>
<h1>Not Found</h1>
<p>The requested URL /pub/RWin/PACKAGES.gz was not found on this server.</p>
<address>Apache/2.2.22 (Debian) Server at www.stats.ox.ac.uk Port 80</address>

I do have a patch for this, which I will share off-list before committing.

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