Opal - the OPA not quite standard library

Opal is a collection of common functions for OPA/Rego as found in the standard library of many popular programming languages. While OPA itself includes many useful built-ins and constructs for policy authoring, the provided "stdlib" is kept quite minimal. Opal aims to complement that with a batteries included package of functions recognizable from languages such as Python, Go or Java. While the library is ready to be used as it, it is just as much meant as an educational resource answering the occasional "how would I write function X in rego?" that may come up while authoring Rego policies. Copy-pasting highly encouraged!

If you are rather looking for examples, policies and rules for working with systems like Kubernetes, Terraform or AWS, checkout the Open Policy Agent Library.

Using Opal

1. git clone the repository and copy the lib directory to wherver you keep your Rego policies. Import and use.

or

2. Simply copy and paste the functions you may want to use into your policies and use them directly.

Functions

Strings

Function	Description
strings.capitalize(word)	Capitalize provided word
strings.repeat(str, x)	Returns str repeated x number of times
strings.lines(str)	Returns a list of all lines in str
strings.char_at(str, x)	Get character from str at position x
strings.pad_left(str, length, char)	Pad str to the left with char up to length
strings.pad_right(str, length, char)	Pad str to the right with char up to length
strings.is_blank(str)	True if str is empty or contains only whitespace characters
strings.startswith_any(str, list)	True if str starts with any item in list
strings.endswith_any(str, list)	True if str ends with any item in list

Lists / Arrays

Function	Description
lists.append(l, x)	Returns list l with value x appended (added last)
lists.insert(l, x, pos)	Return list l with value x inserted at position pos
lists.index(l, x)	Provides the position of first occurrence of value x in list, or -1 if not found
lists.index_last	Provides the position of last occurrence of value x in list, or -1 if not found
lists.reverse(l)	Reverse provided list
lists.count_value(l, v)	Count the number of occurrences of provided value v in list l

Objects

Function	Description
objects.keys(o)	Returns a list of (top level) keys in object o
objects.values(o)	Returns a list of (top level) values in object o
objects.put(o, k, v)	Return a new object with the provided key/value added (overwritten if exists)
objects.put_if_absent(o, k, v)	Return a new object with the provided key/value added (if not exists)
objects.select(o, path)	Return the value at provided path (separated by '.') in nested object o

Math

Function	Description
math.ceil(x)	Returns x rounded up to the closest integer
math.floor(x)	Returns x rounded down to the closest integer

Contributing

If you have a function you'd like to add, that's great! Just remember to submit a unit test or two along with your PR.