Message-ID: <399CF5DD-4403-4460-8749-24DE126B66D0@bigelow.org>
Date: 2013-03-06T21:59:34Z
From: Ben Tupper
Subject: how to get xmlToList() to retry if http fails
In-Reply-To: <A632B3F93D861843A3C966F3962C3F840111393CF7D9@EMAIL05.pnl.gov>
Hi,
On Mar 6, 2013, at 4:12 PM, Waichler, Scott R wrote:
> Hi,
>
> I am using xmlToList() in a loop with a call to a webservice, per the code below.
>
> # Loop thru target locs
> for(i in 1:num.target.locs) {
> url <- paste(sep="/", "http://www.earthtools.org/timezone", lat[i], lon[i])
> tmp <- xmlToList(url)
> df$time.offset[i] <- tmp$offset
> system("sleep 1") # wait 1 second per requirements of above web service
> } # end loop thru target locations
>
> Failure struck midway through my loop, with the message below.
>
> failed to load HTTP resource
> Error: 1: failed to load HTTP resource
>
You can wrap it in a try function as in the following (untested). I have made the thing stop if the second try fails, but you may want to do something more useful. Check out tryCatch, too.
for(i in 1:num.target.locs) {
url <- paste(sep="/", "http://www.earthtools.org/timezone", lat[i], lon[i])
tmp <- try(xmlToList(url))
if (inherits(tmp, "try-error")) {
Sys.sleep(2)
tmp <- try(xmlToList(url))
if (inherits(tmp, "try-error")) stop("Error fetching data")
}
df$time.offset[i] <- tmp$offset
system("sleep 1") # wait 1 second per requirements of above web service
} # end loop thru target locations
Cheers,
Ben
> I presume that the webservice failed to respond in this instance. How can I trap the error and have it retry after waiting a second or two, instead of exiting?
>
> Thanks. --Scott Waichler
> Pacific Northwest National Laboratory
> Richland, WA, USA
> scott.waichler at pnnl.gov
>
> ______________________________________________
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Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org