# SynchronizedSpider Development

SynchronizedSpider plugins use built-in connection methods along with global system configuration to change the behaviour of the connections.

## Connection Modes

The following connection types are built-in to PATHspider:

Name | Description
--- | ---
tcp | Perform a TCP handshake
http | Perform an HTTP GET request
https | Perform an HTTP GET request using TLS
dnsudp | Perform a DNS query using UDP
dnstcp | Perform a DNS query using TCP

To indicate the connection types that are supported by your plugin, use the `connect_supported` metadata variable. The first type listed in the variable will be the default connection type for the plugin.

For example, if your plugin supports all the TCP based connection types and you would like plain HTTP to be the default:

    class SynchronizedSpiderPlugin(SynchronizedSpider, PluggableSpider):
        connect_supported = ["http", "https", "tcp", "dnstcp"]

## Configuration Functions

Configuration functions are at the heart of a SynchronizedSpider plugin. These may make calls to `sysctl` or `iptables` to make changes to the way that traffic is generated.

One function should be written for each of the configurations and PATHspider will ensure that the configurations are set before the corresponding traffic is generated. It is the responsibility of plugin authors to ensure that any configuration is reset by the next configuration function if that is required.

By convention, functions should be prefixed with `config_` to ensure there are no conflicts. After declaring the functions, you must then set the `configurations` metadata variable with pointers to each of the configuration functions.

The following shows the relevant portions of the ECN plugin, which uses this framework:

    class ECN(SynchronizedSpider, PluggableSpider):
        def config_no_ecn(self): # pylint: disable=no-self-use
            """
            Disables ECN negotiation via sysctl.
            """

            logger = logging.getLogger('ecn')
            subprocess.check_call(
                ['/sbin/sysctl', '-w', 'net.ipv4.tcp_ecn=2'],
                stdout=subprocess.DEVNULL,
                stderr=subprocess.DEVNULL)
            logger.debug("Configurator disabled ECN")

        def config_ecn(self): # pylint: disable=no-self-use
            """
            Enables ECN negotiation via sysctl.
            """

            logger = logging.getLogger('ecn')
            subprocess.check_call(
                ['/sbin/sysctl', '-w', 'net.ipv4.tcp_ecn=1'],
                stdout=subprocess.DEVNULL,
                stderr=subprocess.DEVNULL)
            logger.debug("Configurator enabled ECN")

        configurations = [config_no_ecn, config_ecn]

Warning

You must have the `configurations` variable after the declaration of the functions, as otherwise you are attempting to reference functions that have not yet been defined.