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A customizable parser/transpiler for SCIM2.0 filters

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Description

SCIM 2.0 defines queries that look like this:

'emails[type eq "work" and value co "@example.com"] or ims[type eq "xmpp" and value co "@foo.com"]'

These can be hard to work with and covert into SQL to run against a database.

That’s where SCIM 2.0 Filter Parser (SFP) can help.

SFP is broken up into four modules, each handling a different part of translating a SCIM call into a SQL query.

The first step is tokenization or lexical analysis where the filter query is broken down into many tokens that make it up.

sfp-lexer 'emails[type eq "work" and value co "@example.com"] or ims[type eq "xmpp" and value co "@foo.com"]'

Token(type='ATTRNAME', value='emails', lineno=1, index=0)
Token(type='LBRACKET', value='[', lineno=1, index=6)
Token(type='ATTRNAME', value='type', lineno=1, index=7)
Token(type='EQ', value='eq', lineno=1, index=12)
Token(type='COMP_VALUE', value='work', lineno=1, index=15)
Token(type='AND', value='and', lineno=1, index=22)
Token(type='ATTRNAME', value='value', lineno=1, index=26)
Token(type='CO', value='co', lineno=1, index=32)
Token(type='COMP_VALUE', value='@example.com', lineno=1, index=35)
Token(type='RBRACKET', value=']', lineno=1, index=49)
Token(type='OR', value='or', lineno=1, index=51)
Token(type='ATTRNAME', value='ims', lineno=1, index=54)
Token(type='LBRACKET', value='[', lineno=1, index=57)
Token(type='ATTRNAME', value='type', lineno=1, index=58)
Token(type='EQ', value='eq', lineno=1, index=63)
Token(type='COMP_VALUE', value='xmpp', lineno=1, index=66)
Token(type='AND', value='and', lineno=1, index=73)
Token(type='ATTRNAME', value='value', lineno=1, index=77)
Token(type='CO', value='co', lineno=1, index=83)
Token(type='COMP_VALUE', value='@foo.com', lineno=1, index=86)
Token(type='RBRACKET', value=']', lineno=1, index=96)

The second step is to convert that series of tokens into a abstract syntax tree.

sfp-parser 'emails[type eq "work" and value co "@example.com"] or ims[type eq "xmpp" and value co "@foo.com"]'

Filter(expr=LogExpr, negated=False, namespace=None)
    LogExpr(op='or', expr1=Filter, expr2=Filter)
        Filter(expr=Filter, negated=False, namespace=None)
            Filter(expr=Filter, negated=False, namespace=AttrPath)
                Filter(expr=LogExpr, negated=False, namespace=None)
                    LogExpr(op='and', expr1=Filter, expr2=Filter)
                        Filter(expr=AttrExpr, negated=False, namespace=None)
                            AttrExpr(value='eq', attr_path=AttrPath, comp_value=CompValue)
                                AttrPath(attr_name='type', sub_attr=None, uri=None)
                                CompValue(value='work')
                        Filter(expr=AttrExpr, negated=False, namespace=None)
                            AttrExpr(value='co', attr_path=AttrPath, comp_value=CompValue)
                                AttrPath(attr_name='value', sub_attr=None, uri=None)
                                CompValue(value='@example.com')
                AttrPath(attr_name='emails', sub_attr=None, uri=None)
        Filter(expr=Filter, negated=False, namespace=None)
            Filter(expr=Filter, negated=False, namespace=AttrPath)
                Filter(expr=LogExpr, negated=False, namespace=None)
                    LogExpr(op='and', expr1=Filter, expr2=Filter)
                        Filter(expr=AttrExpr, negated=False, namespace=None)
                            AttrExpr(value='eq', attr_path=AttrPath, comp_value=CompValue)
                                AttrPath(attr_name='type', sub_attr=None, uri=None)
                                CompValue(value='xmpp')
                        Filter(expr=AttrExpr, negated=False, namespace=None)
                            AttrExpr(value='co', attr_path=AttrPath, comp_value=CompValue)
                                AttrPath(attr_name='value', sub_attr=None, uri=None)
                                CompValue(value='@foo.com')
                AttrPath(attr_name='ims', sub_attr=None, uri=None)

The third step is to transpile this AST into a language of our choice. The above query is transpiled to SQL below.

sfp-transpiler 'emails[type eq "work" and value co "@example.com"] or ims[type eq "xmpp" and value co "@foo.com"]'

((emails.type = {0}) AND (emails.value LIKE {1})) OR ((ims.type = {2}) AND (ims.value LIKE {3}))
{0: 'work', 1: '%@example.com%', 2: 'xmpp', 3: '%@foo.com%'}

The fourth step is to take what is a segment of a SQL WHERE clause and complete the rest of the SQL query.

sfp-query 'emails[type eq "work" and value co "@example.com"] or ims[type eq "xmpp" and value co "@foo.com"]'

>>> DO NOT USE THIS OUTPUT DIRECTLY
>>> SQL INJECTION ATTACK RISK
>>> SQL PREVIEW:
    SELECT DISTINCT users.*
    FROM users
    LEFT JOIN emails ON emails.user_id = users.id
    LEFT JOIN schemas ON schemas.user_id = users.id
    WHERE ((emails.type = work) AND (emails.value LIKE %@example.com%)) OR ((ims.type = xmpp) AND (ims.value LIKE %@foo.com%));

Please note that SFP does not build SQL queries with parameters pre-injected. That would create a SQL injection attack vulnerability. Instead a Query object is created and can be forced to display itself as seen above by print ing the query object.

Use

Although command line shims are provided, the library is intended to be used programmatically. Users of the library should instantiate the scim2_filter_parser.query.Query class with an attribute map and optionally any joins necessary to make all required fields accessible in the query.

For example, if user information is stored in the users table and email information is stored in a different table emails, then the attribute map and the joins might be defined as so:

attr_map = {
    ('userName', None, None): 'users.username',
    ('name', 'familyName', None): 'users.family_name',
    ('meta', 'lastModified', None): 'users.update_ts',
    ('emails', None, None): 'emails.address',
    ('emails', 'value', None): 'emails.address',
}

joins = (
    'LEFT JOIN emails ON emails.user_id = users.id',
)

q = Query(filter, 'users', attr_map, joins)

q.sql # Will be equal to 'SELECT * FROM users ...
q.params # Will be equal to the paramters specific to the filter query.

The attribute_map (attr_map) is a mapping of SCIM attribute, subattribute, and schema uri to a table field. You will need to customize this to your particular database schema.

The Query.sql method returns SQL that can be used as the first argument in a call to cursor.execute() with your favorite DB engine. If you are using a database that requires a replacement character other than ‘%s’, then you can subclass the Query class and override the placeholder class level variable. See the query module and unit tests for an example of this subclassing with SQLite.

The Query.params method returns a list of items that can be used as the second argument in a call to cursor.execute().

Spped

SFP is pretty fast. Check out the speed_test.py script for details on the long and short filter queries tested. SFP transpiled a short filter query into SQL in under 54 microseconds. For a longer query, SFP only took 273 microseconds.

➜ scim2-filter-parser git:(master) ✗ python -m timeit -s “import speed_test” “speed_test.short()” 10000 loops, best of 3: 53.8 usec per loop ➜ scim2-filter-parser git:(master) ✗ python -m timeit -s “import speed_test” “speed_test.long()” 1000 loops, best of 3: 273 usec per loop

This project is still in its alpha stage of life and should be used accordingly.

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