scan-style iteration over redis list in ruby, making multiple roundtrips

ruby-redis-utils.rb

# useful if k is a very large list, and you don't want to do it all in one request
# note that consistency will not be guaranteed here (i.e. list can change during iteration)
def scan_list(k, range=1000, &block)
  i = 0
  result = []
  while l = HLR.lrange(k, i, i+range)
    break if l.size == 0
    if block_given?
      yield l
    else
      result.concat(l)
    end
    i += range + 1
  end
  result unless block_given?
end

# hackily dump set contents to JSON file
# probably won't work if set contains values with unescaped single quotes
def dump_set_to_json(filename, setname)
  File.open(filename, 'w+') do |file|
    file.write("[")
    HLR.sscan_each(setname) do |item|
      file.write(item)
      file.write(',')
    end
    file.pos = file.pos - 1 # jump back to overwrite last ','
    file.write("]")
  end
end