Processing Australian BOM Weather XML Data

[admin]

Since Expat library is stream-oriented, xpath cannot be used. Here's an example that parses the XML and retrieves the required fields:

Code:

require('socket.ftp')
data = socket.ftp.get('ftp://ftp.bom.gov.au/anon/gen/fwo/IDV10450.xml')

if not data then
  log('Fetch failed to retrieve weather data')
  return
end

aac = 'VIC_PT042'
forecast = {}

function starttag(p, tag, attrs)
  if tag == 'area' and attrs.aac == aac then
    in_area = true
  elseif tag == 'forecast-period' and in_area then
    index = tonumber(attrs.index)

    if index then
      forecast[ index ] = {}
    end
  elseif index then
    prop = attrs.type
  end
end

function endtag(p, tag)
  if tag == 'area' then
    in_area = false
  elseif tag == 'forecast-period' then
    index = nil
  elseif index then
    prop = nil
  end
end

function text(p, txt)
  if in_area and index and prop then
    forecast[ index ][ prop ] = txt:trim()
  end
end

require('lxp').new({
  StartElement = starttag,
  EndElement = endtag,
  CharacterData = text,
}):parse(data)

Weather_Temp_Max = forecast[ 1 ].air_temperature_maximum
Weather_Temp_Min = forecast[ 1 ].air_temperature_minimum
Weather_Rain = forecast[ 1 ].probability_of_precipitation

-- remove percent sign from string
if Weather_Rain then
  Weather_Rain = Weather_Rain:gsub('%%', '')
end

grp.write('1/1/100', Weather_Temp_Max)
grp.write('1/1/101', Weather_Temp_Min)
grp.write('1/1/102', Weather_Rain)