Allow piping metrics into the conversion script

Prior to this commit, you could not pipe output into our conversion
script.  The conversion script could only read files.

After this commit, you can pipe output into the script OR you can
read a file.  You cannot pipe output in and read a file in the
same invocation of the conversion script.

Author: npwalker

json2graphite.rb

@@ -65,6 +65,10 @@ def close
 def parse_file(filename)
   data = JSON.parse(File.read(filename))
 
+  parse_input(data)
+end
+
+def parse_input( data )
   # Newer versions of the log tool insert a timestamp field into the JSON.
   if data['timestamp']
     timestamp = Time.parse(data.delete('timestamp'))
@@ -316,9 +320,17 @@ def influx_metrics(data, timestamp, parent_key = nil)
   $net_output = NetworkOutput.new(url)
 end
 
-data_files = ARGV
+data_files = []
 data_files += Dir.glob($options[:pattern]) if $options[:pattern]
 
+#http://ruby-doc.org/core-1.9.3/ARGF.html#method-i-filename
+while ARGF.filename != '-'
+  filename = ARGF.filename
+  data_files += [filename]
+  ARGF.skip
+  break if filename == ARGF.filename
+end
+
 data_files.each do |filename|
   begin
     converted_data = parse_file(filename)
@@ -333,4 +345,18 @@ def influx_metrics(data, timestamp, parent_key = nil)
   end
 end
 
+if ARGF.filename == '-'
+  begin
+    converted_data = parse_input( JSON.parse(ARGF.read) )
+
+    if $options[:host]
+      $net_output.write(converted_data)
+    else
+      STDOUT.write(converted_data)
+    end
+  rescue => e
+    STDERR.puts "ERROR: During read from STDIN: #{e.message}"
+  end
+end
+
 $net_output.close if $options[:host]