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import os
import sys
import ConfigParser
from thrift.transport import TSSLSocket, TTransport

def ssl_transport_factory(host, port, env, config_file):
    """
    SSL Thrift transport factory function.

    Params:
    * host .........: hostname of Cassandra node.
    * port .........: port number to connect to.
    * env ..........: environment variables. SSL factory will use, if passed,
                      SSL_CERTFILE and SSL_VALIDATE variables.
    * config_file ..: path to cqlsh config file (usually ~/.cqlshrc).
                      SSL factory will use, if set, certfile and validate
                      options in [ssl] section, as well as host to certfile
                      mapping in [certfiles] section.

    [certfiles] section is optional, 'validate' setting in [ssl] section is
    optional too. If validation is enabled then SSL certfile must be provided
    either in the config file or as an environment variable.
    Environment variables override any options set in cqlsh config file.
    """
    configs = ConfigParser.SafeConfigParser()
    configs.read(config_file)

    def get_option(section, option):
        try:
            return configs.get(section, option)
        except ConfigParser.Error:
            return None

    ssl_validate = env.get('SSL_VALIDATE')
    if ssl_validate is None:
        ssl_validate = get_option('ssl', 'validate')
    ssl_validate = ssl_validate is None or ssl_validate.lower() != 'false'

    ssl_certfile = env.get('SSL_CERTFILE')
    if ssl_certfile is None:
        ssl_certfile = get_option('certfiles', host)
    if ssl_certfile is None:
        ssl_certfile = get_option('ssl', 'certfile')
    if ssl_validate and ssl_certfile is None:
        sys.exit("Validation is enabled; SSL transport factory requires a valid certfile "
                 "to be specified. Please provide path to the certfile in [ssl] section "
                 "as 'certfile' option in %s (or use [certfiles] section) or set SSL_CERTFILE "
                 "environment variable." % (config_file,))
    if not ssl_certfile is None:
        ssl_certfile = os.path.expanduser(ssl_certfile)

    tsocket = TSSLSocket.TSSLSocket(host, port, ca_certs=ssl_certfile,
                                    validate=ssl_validate)
    return TTransport.TFramedTransport(tsocket)
