R/pvsRequest3.R

In umatter/pvsR: Interact with the Project Vote Smart API for Scientific Research

pvsRequest3 <-
	function (request,inputs) {
		pvs.key <- getPVS_key()
		pvs.url <- paste("http://api.votesmart.org/",request,"key=",pvs.key,inputs,sep="") #generate url for request
		
		# Handle slow connection (try max. 3 times to get data from PVS, otherwhise move on)
		httpresp <- try(GET(url=pvs.url, timeout(5)), silent=TRUE)
		timedout <- any(grepl("OPERATION_TIMEDOUT", x=class(attributes(httpresp)$condition)))
		t <- 0
		while (timedout & t<3) {
			httpresp <- try(GET(url=pvs.url, timeout(5)), silent=TRUE)
			timedout <- any(grepl("OPERATION_TIMEDOUT", x=class(attributes(httpresp)$condition)))
			t <- t +1
		}
		

		# in rare cases, the transaction still fails
		xmltext <- try(content(x=httpresp, as="text"), silent = TRUE)
		# ensure that code does not break and empty result is shown
			if (class(httpresp)[1]!="try-error"){
			  
			errors <-  getXMLErrors(xmltext) # check if xml can be parsed properly
			if (length(errors) != 0) {
				if (names(errors[[1]]$code) == "XML_ERR_CDATA_NOT_FINISHED") { # if not, try to fix 
					xmltext <- gsub(pattern="\003", replacement="", x=xmltext, fixed=TRUE)
				}
			}
			
			# in case of (still) malformed XML, force parsing problems into an empty function (does not
			# break parsing process. parser might still work.)
			output.base <- xmlRoot(xmlTreeParse(xmltext, useInternalNodes=TRUE, error=function(...){}))
			output <- xmlSApply(output.base, function(x) data.frame(t(xmlSApply(x, xmlValue)), stringsAsFactors = FALSE))
			
			return(output)
			
		} else {
			
			return(data.frame(V1="NA"))
		}
		
  	
  }