detect overlapping CIDR ranges in SQL, prevent duplicate ranges using triggers

overlap_cidr.py

from sqlalchemy import event
from sqlalchemy import DDL

def mysql_cidr_overlap(engine, metadata):
    @event.listens_for(metadata, "after_create")
    def _create_mysql_proc(target, connection, **kw):
        if connection.engine.name != 'mysql':
            return

        if connection.scalar(
            "SELECT ROUTINE_NAME FROM INFORMATION_SCHEMA.ROUTINES "
            "WHERE ROUTINE_TYPE='FUNCTION' AND ROUTINE_SCHEMA=DATABASE() AND "
            "ROUTINE_NAME=%s",
            ("cidr_overlap", )
        ):
            connection.execute("DROP FUNCTION cidr_overlap")

        connection.execute(
            DDL("""
        CREATE FUNCTION cidr_overlap (cidr1 VARCHAR(30), cidr2 VARCHAR(30))
        RETURNS TINYINT
        BEGIN
        DECLARE bitmask INT;
        -- note - Mike is semi-guessing on the math here, needs tests!  don't stick
        -- into production pls :)
        SET bitmask = pow(
            2,
            (32 - least(
                cast(substring_index(cidr1, '/', -1) as integer),
                cast(substring_index(cidr2, '/', -1) as integer)
            ))
        ) - 1;

        RETURN
            inet_aton(substring_index(cidr1, '/', 1)) & ~bitmask =
            inet_aton(substring_index(cidr2, '/', 1)) & ~bitmask;
        END
        """)
        )




if __name__ == '__main__':
    from sqlalchemy import Column, Integer, String, create_engine, func
    from sqlalchemy.ext.declarative import declarative_base
    from sqlalchemy.orm import Session, aliased
    from sqlalchemy import event

    Base = declarative_base()

    class A(Base):
        __tablename__ = 'a'
        id = Column(Integer, primary_key=True)
        subnet = Column(String(30))

    event.listen(
        A.__table__, "after_create",
        DDL("""
    CREATE TRIGGER no_overlap_cidr_a
    BEFORE INSERT ON a
    FOR EACH ROW
    BEGIN
      DECLARE msg VARCHAR(200);
      IF (EXISTS(SELECT * FROM a WHERE cidr_overlap(subnet, NEW.subnet))) THEN
        SET msg = CONCAT(
            'inserted subnet ', NEW.subnet,
            ' conflicts with existing subnets');
        SIGNAL sqlstate '45000'
            SET MESSAGE_TEXT = msg;
      END IF;
    END
        """)
    )

    e = create_engine("mysql://scott:tiger@localhost/test", echo=True)

    mysql_cidr_overlap(e, Base.metadata)

    Base.metadata.drop_all(e)
    Base.metadata.create_all(e)

    s = Session(e)

    with s.begin_nested():
        s.add(A(subnet='192.168.1.0/24'))

    with s.begin_nested():
        s.add(A(subnet='192.168.2.0/24'))

    try:
        with s.begin_nested():
            s.add(A(subnet='192.168.2.0/25'))
    except Exception as e:
        print "Error! %s" % e

    s.commit()

    a1, a2 = aliased(A), aliased(A)

    # return all non-overlapping CIDR pairs
    for a, b in s.query(a1.subnet, a2.subnet).\
        filter(~func.cidr_overlap(a1.subnet, a2.subnet)).\
            filter(a1.id > a2.id):
            print a, b