GetDates <-
function(Lat, Long, Product)
{
  if(!any(Product == GetProducts())) stop("Product entered does not match any available products; see ?GetProducts.")

  if(!is.numeric(Lat) | !is.numeric(Long)) stop("Lat and Long inputs must be numeric.")

  if(length(Lat) != 1 | length(Long) != 1) stop("Incorrect number of Lats and Longs supplied (only 1 coordinate allowed).")

  if(abs(Lat) > 90 | abs(Long) > 180) stop("Detected a lat or long beyond the range of valid coordinates.")

  getdates.xml <- paste('
<soapenv:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:mod="https://modis.ornl.gov/MODIS_soapservice">
   <soapenv:Header/>
                         <soapenv:Body>
                         <mod:getdates soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
                         <Latitude xsi:type="xsd:float">', Lat, '</Latitude>
                         <Longitude xsi:type="xsd:float">', Long, '</Longitude>
                         <Product xsi:type="xsd:string">', Product, '</Product>
                         </mod:getdates>
                         </soapenv:Body>
                         </soapenv:Envelope>',
                         sep = "")

  header.fields <- c(Accept = "text/xml",
                     Accept = "multipart/*",
                     'Content-Type' = "text/xml; charset=utf-8",
                     SOAPAction = "")

  reader <- basicTextGatherer()
  header <- basicTextGatherer()

  curlPerform(url = paste0(daacmodis, "/cgi-bin/MODIS/soapservice/MODIS_soapservice.pl"),
              httpheader = header.fields,
              postfields = getdates.xml,
              writefunction = reader$update,
              verbose = FALSE)

  # Check the server is not down by insepcting the XML response for internal server error message.
  if(grepl("Internal Server Error", reader$value())){
    stop("Web service failure: the ORNL DAAC server seems to be down, please try again later.
         The online subsetting tool (https://daac.ornl.gov/cgi-bin/MODIS/GLBVIZ_1_Glb/modis_subset_order_global_col5.pl)
         will indicate when the server is up and running again.")
  }

  xmlres <- xmlRoot(xmlTreeParse(reader$value()))
  datesres <- xmlSApply(xmlres[[1]],
                        function(x) xmlSApply(x,
                            function(x) xmlSApply(x,
                                function(x) xmlSApply(x,xmlValue))))

  if(colnames(datesres) == "Fault"){
    if(length(datesres['faultstring.text', ][[1]]) == 0){
      stop("Downloading from the web service is currently not working. Please try again later.")
    }
    stop(datesres['faultstring.text', ])
  } else{
    return(as.vector(datesres))
  }
}