Function

Functions in matchers

You can even specify functions in a matcher to make it more powerful. You can use the built-in functions or specify your own function. The built-in key-matching functions take such a format:

bool function_name(string url, string pattern)

It returns a boolean indicating whether url matches pattern.

The supported built-in functions are:

Function	url	pattern	Example
keyMatch	a URL path like /alice_data/resource1	a URL path or a * pattern like /alice_data/*	keymatch_model.conf/keymatch_policy.csv
keyMatch2	a URL path like /alice_data/resource1	a URL path or a : pattern like /alice_data/:resource	keymatch2_model.conf/keymatch2_policy.csv
keyMatch3	a URL path like /alice_data/resource1	a URL path or a {} pattern like /alice_data/{resource}	https://github.com/casbin/casbin/blob/277c1a2b85698272f764d71a94d2595a8d425915/util/builtin_operators_test.go#L171-L196
keyMatch4	a URL path like /alice_data/123/book/123	a URL path or a {} pattern like /alice_data/{id}/book/{id}	https://github.com/casbin/casbin/blob/277c1a2b85698272f764d71a94d2595a8d425915/util/builtin_operators_test.go#L208-L222
regexMatch	any string	a regular expression pattern	keymatch_model.conf/keymatch_policy.csv
ipMatch	an IP address like 192.168.2.123	an IP address or a CIDR like 192.168.2.0/24	ipmatch_model.conf/ipmatch_policy.csv
globMatch	a path-like path like /alice_data/resource1	a glob pattern like /alice_data/*	https://github.com/casbin/casbin/blob/277c1a2b85698272f764d71a94d2595a8d425915/util/builtin_operators_test.go#L426-L466

For key-getting functions, they usually take three parameters(except keyGet):

bool function_name(string url, string pattern, string key_name)

They will return the value of the key key_name if it matches the pattern, and return "" if nothing is matched.

For example, KeyGet2("/resource1/action", "/:res/action, "res") will return "resource1", KeyGet3("/resource1_admin/action", "/{res}_admin/*", "res") will return "resource1". As for KeyGet, which takes two parameters, KeyGet("/resource1/action", "/*) will return "resource1/action".

Function	url	pattern	key_name	example
keyGet	a URL path like /proj/resource1	a URL path or a * pattern like /proj/*	\	keyget_model.conf/keymatch_policy.csv
keyGet2	a URL path like /proj/resource1	a URL path or : pattern like /prooj/:resource	key name specified in the pattern	keyget2_model.conf/keymatch2_policy.csv
keyGet3	a URL path like /proj/res3_admin/	a URL path or {} pattern like /proj/{resource}_admin/*	key name specified in the pattern	https://github.com/casbin/casbin/blob/7bd496f94f5a2739a392d333a9aaaa10ae397673/util/builtin_operators_test.go#L209-L247

See details for above functions at: https://github.com/casbin/casbin/blob/master/util/builtin_operators_test.go

How to add a customized function

First prepare your function. It takes several parameters and return a bool:

func KeyMatch(key1 string, key2 string) bool {
    i := strings.Index(key2, "*")
    if i == -1 {
        return key1 == key2
    }

    if len(key1) > i {
        return key1[:i] == key2[:i]
    }
    return key1 == key2[:i]
}

Then wrap it with interface{} types:

func KeyMatchFunc(args ...interface{}) (interface{}, error) {
    name1 := args[0].(string)
    name2 := args[1].(string)

    return (bool)(KeyMatch(name1, name2)), nil
}

At last, register the function to the Casbin enforcer:

e.AddFunction("my_func", KeyMatchFunc)

Now, you can use the function in your model CONF like this:

[matchers]
m = r.sub == p.sub && my_func(r.obj, p.obj) && r.act == p.act