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Concept and Grammar

Basic Concepts

Condition Primitive

  • A condition primitive is a basic and built-in function which check some specified condition matched or not.
// return true if the request Host is "www.bfe-networks.com" or "bfe-networks.com"
req_host_in("www.bfe-networks.com|bfe-networks.com")

Condition Expression

  • A condition expression is a series of condition primitives combined with operators (e.g. AND, OR, NOT, etc).
// return ture if the request host is "bfe-networks.com" and the request method is "GET"
req_host_in("bfe-networks.com") && req_method_in("GET")
  • The supported operators are described in another section below.

Condition Variable

  • You can define a variable and assign a condition expression to it.
// define a condition variable
bfe_host = req_host_in("bfe-networks.com")

Advanced Condition Expression

  • An advanced condition expression is a series of condition primitives and condition variables combined with operators (e.g. AND, OR, NOT, etc).

  • In an advanced condition expression, the condition variable is identified by "$" prefix

// return true if the value of new_host is true and the request method is GET
$new_host && req_method_in("GET")

Grammar

Condition Primitive Grammar

A condition primitive is shown as follows:

func_name(params)
  • func_name is the name of condition primitive
  • params are the parameters condition primitive
  • The type of return value is bool

Condition Expression Grammar

Condition Expression(CE) grammar is defined as follows:

CE = CE && CE
   | CE || CE
   | ( CE )
   | ! CE
   | ConditionPrimitive

Advanced Condition Expression Grammar

Advanced Condition Expression(ACE) grammar is defined as follows:

ACE = ACE && ACE
    | ACE || ACE
    | ( ACE)
    | ! ACE
    | ConditionPrimitive
    | ConditionVariable

Operator Precedence

The precedence and associativity of operators are similar to the C language. The following table lists the precedence and associativity of all operators. Operators are listed top to bottom, in descending precedence.

Precedence Operator Description Associativity
1 () parentheses (grouping) Left-to-right
2 ! logical NOT Right-to-left
3 && logical AND Left-to-right
4 || logical OR Left-to-right