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Rule expressions are written using a simple expression language. It provides a rich set of operators and builtin functions, and allows you to create flexible conditions and criteria. You can use available data fields with available operators and functions.

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Data fields

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Operators

LHS stands for left-hand side of the operation, RHS stands for right-hand side of the operation.

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Equality

  • LHS == RHS - returns true if both sides are equal
  • LHS != RHS - returns true if both sides are different

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Numerical

When LHS and RHSare numerical values.
  • LHS < RHS - returns true if LHS is less than RHS
  • LHS > RHS - returns true if LHS is more than RHS
  • LHS <= RHS - returns true if LHS is less than or equal to RHS
  • LHS >= RHS - returns true if LHS is more than or equal to RHS

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Logical

When LHS and RHSare boolean values.
  • !LHS - returns the opposite boolean value of LHS
  • LHS && RHS - returns true if both LHS and RHS are true
  • LHS || RHS - returns true if either LHS or RHS are true

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Strings

When LHS and RHSare strings.
  • LHS contains RHS - returns true if RHS is a contained in LHS
  • LHS not contains RHS - returns true if RHS is not contained in LHS

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RegEx matching

When LHS is a string, and RHS is a string literal with a RegEx pattern. Pattern needs to be enclosed with backticks (`).
  • LHS matches RHS - returns true if LHS matches the regular expression in the RHS
  • LHS not matches RHS - returns true if LHS does not match the regular expression in the RHS

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Arrays

When LHSis an array.
  • LHS in RHS - returns true whether LHS is in (or belongs to) RHS
  • LHS not in RHS - returns the opposite of LHS in RHS
  • LHS[RHS] - returns the value at numeric index RHS in the array LHS, returns nil for missing values

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Objects

When LHSis an object.
  • LHS in RHS - returns true whether LHS is in (or belongs to)
  • RHS:LHS not in RHS - returns the opposite of LHS in RHS.
  • LHS[RHS] - returns the value at string field RHS in the object LHS. Returns nil for missing values
  • LHS.RHS is equivalent to LHS[RHS] where LHS is an object, and RHS is an unquoted string literal that can be used as an identifier.
Examples:
  1. http.request is equivalent to http["request"].
  2. http.request.headers.origin.0 produces an error because the unquoted string literal 0 cannot be used as an identifier.

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Functions and custom data types

Describes additional functions and special data types available during rule evaluation.

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Strings

  • upper(string) -> string - transforms the string to all uppercase characters
  • lower(string) -> string - - transforms the string to all lowercase characters
  • starts_with(source string, substring string) -> bool
  • ends_with(source string, substring string) -> bool

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HTTP headers

The Custom Type http_headers behaves similar to an object, but it’s keys are normalized to be in MIME Header format in all operations (so usage is case-insensitive), and its values are of type array and contain the values for the given header name, preserving the original order.

Examples:
  1. Check if a header was set: "cOnTeNt-TyPe" in http.request.headers
  2. Get the first cookie that was set: http.request.headers["accept"][0]

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IP address and CIDR

The Custom Type ip represents an IPv4 or IPv6 address. The Custom Type cidr represents an IPv4 or IPv6 CIDR range.
  • cidr(string) -> cidr parses an IPv4 or IPv6 CIDR.
    • The in operator can be used to check if an ip is in a given cidr.
Example:
  1. Check if IP address belongs to a CIDR range: http.request.ip in cidr("1.1.1.1/10")

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Semantic versioning

  • semver_is_valid(string) -> bool - checks if given string is a valid semver string
  • semver_compare(s1, s2) -> int - compares two semver strings
    • returns -1 if s2 < s1, 1 if s2 > s1, or 0 if they are equal