In your modular input script, it is a good idea to validate the configuration of your input. Specify <use_external_validation>true</use_external_validation> in your introspection scheme to enable external validation.

If you provide an external validation routine and enable external validation the following occurs when a user creates or edits the configuration for a script:

1. Splunk software reads the configuration parameters from the user and creates an XML configuration of the parameters.

   The XML configuration looks something like this:

   <items>
       <server_host>myHost</server_host>
       <server_uri>https://127.0.0.1:8089</server_uri>
       <session_key>123102983109283019283</session_key>
       <checkpoint_dir>/opt/splunk/var/lib/splunk/modinputs</checkpoint_dir>
       <item name="myScheme">
           <param name="param1">value1</param>
           <param_list name="param2">
               <value>value2</value>
               <value>value3</value>
               <value>value4</value>
           </param_list>
       </item>
   </items>
   

   Notes: The <items> element can only contain one <item>. (This is because you can only operate on one item at a time.) The XML stream itself must be encoded in UTF-8.

   Refer to the Read XML configuration from splunkd section for a description of the XML configuration.

2. Splunk software invokes your script with the --validate-arguments option, passing in the XML configuration.
3. Your script validation routine determines if the configuration is valid.
   • If the configuration is valid, your script exits with return status of zero.
   • Otherwise the script exits with a non-zero status and a message indicating why configuration failed. Format the message in <error> tags so Splunk software can properly display the message in Splunk Web.

   <error>
       <message>Access is denied.</message>
   </error>
   

   The following snippets shows how the S3 example validates data returned from the Amazon S3 service. The snippet at the end shows how to provide the --validate-arguments option when invoking the script. This script has been made cross-compatible with Python 2 and Python 3 using python-future.

   Validation snippets

   . . .
   from builtins import str
   def get_validation_data():
       val_data = {}
   
       # read everything from stdin
       val_str = sys.stdin.read()
   
       # parse the validation XML
       doc = xml.dom.minidom.parseString(val_str)
       root = doc.documentElement
   
       logging.debug("XML: found items")
       item_node = root.getElementsByTagName("item")[0]
       if item_node:
           logging.debug("XML: found item")
   
           name = item_node.getAttribute("name")
           val_data["stanza"] = name
   
           params_node = item_node.getElementsByTagName("param")
           for param in params_node:
               name = param.getAttribute("name")
               logging.debug("Found param %s" % name)
               if name and param.firstChild and \
                  param.firstChild.nodeType == param.firstChild.TEXT_NODE:
                   val_data[name] = param.firstChild.data
   
       return val_data
   
   # make sure that the amazon credentials are good
   def validate_arguments():
       val_data = get_validation_data()
   
       try:
           url = "s3://" + val_data["stanza"]
           bucket, obj = read_from_s3_uri(url)
           conn = get_http_connection(val_data["key_id"], val_data["secret_key"], bucket, obj, method = "HEAD")
           resp = conn.getresponse()
           log_response(resp)
           if resp.status != 200:
               raise Exception("Amazon returned HTTP status code %d (%s): %s" % (resp.status, resp.reason, get_amazon_error(resp.read())))
   
       except Exception as e:
           print_error("Invalid configuration specified: %s" % str(e))
           sys.exit(1)
   . . .
   # Provide --validate-arguments arg on startup
   if __name__ == '__main__':
       if len(sys.argv) > 1:
           if sys.argv[1] == "--scheme":
               do_scheme()
           elif sys.argv[1] == "--validate-arguments":
               validate_arguments()
           elif sys.argv[1] == "--test":
               test()
           else:
               usage()
       else:
           # just request data from S3
           run()