How do I use logical functions in AScript - Server Load Balancer

AScript provides six logical functions for building conditions in forwarding rules: and(), or(), not(), eq(), ne(), and null().

Quick reference

Function	Signature	Returns	Short-circuit
`and`	`and(arg, ...) → Boolean`	`true` if all args are true	Stops at first `false`
`or`	`or(arg, ...) → Boolean`	`true` if any arg is true	Stops at first `true`
`not`	`not(arg) → Boolean`	Inverts truthiness of arg	N/A
`eq`	`eq(arg1, arg2) → Boolean`	`true` if arg1 equals arg2	N/A
`ne`	`ne(arg1, arg2) → Boolean`	`true` if arg1 does not equal arg2	N/A
`null`	`null(v) → Boolean`	`true` if v is empty (array, dict, or empty string)	N/A

and

Item	Description
Syntax	`and(arg, ...) → Boolean`
Description	Executes the AND logical operator. Supports short-circuit evaluation: when any argument evaluates to `false`, the remaining arguments are not evaluated.
Parameter	One or more values to evaluate. Data type: any type.
Return value	`true` if all arguments evaluate to true. `false` if any argument evaluates to false.
Example	See below.

if and($arg_mode, eq($arg_mode, 'set_header')) {
   add_rsp_header('USER-DEFINED-1','path1')
}

If the request includes the mode parameter and its value is set_header, the USER-DEFINED-1 response header is set.
If the request does not include the mode parameter, short-circuit evaluation stops execution. The eq comparison is not run, and USER-DEFINED-1 is not set because and() returns false.

or

Item	Description
Syntax	`or(arg, ...) → Boolean`
Description	Executes the OR logical operator. Supports short-circuit evaluation: when any argument evaluates to `true`, the remaining arguments are not evaluated.
Parameter	One or more values to evaluate. Data type: any type.
Return value	`true` if any argument evaluates to true. `false` if all arguments evaluate to false.
Example	See below.

if and($http_from, or(eq($http_from, 'wap'), eq($http_from, 'comos'))) {
    rewrite(concat('http://tech.com.cn/zt_d/we2015/', $http_from), 'enhance_redirect')
}

If the request includes the from header and its value is wap or comos, the HTTP 302 redirect returns and the request is redirected to http://tech.com.cn/zt_d/we2015/[wap|comos].
If the from header value is wap, short-circuit evaluation stops the eq('comos') check. or() returns true immediately.

not

Item	Description
Syntax	`not(arg) → Boolean`
Description	Executes the NOT logical operator. `undef` and `false` evaluate to false; all other values evaluate to true.
Parameter	Exactly one value to evaluate. Data type: any type.
Return value	`true` if the argument is falsy (`undef` or `false`). `false` if the argument is truthy.
Example	See below.

Boundary behavior:

Input	`not()` result
`undef` (variable not present)	`true`
`false`	`true`
`0`	`false`

if not($arg_key) {
    exit(403)
}
if not($cookie_user) {
    exit(403, 'not cookie user')
}
if not(0) {
    exit(403)
}
if not(false) {
    exit(403)
}

not($arg_key): if the request does not include the key parameter, the request is denied and HTTP 403 is returned.
not($cookie_user): if the request does not include cookie_user, the request is denied. HTTP 403 and the response body not cookie user are returned.
not(0) returns false.
not(false) returns true.

eq

Item	Description
Syntax	`eq(arg1, arg2) → Boolean`
Description	Checks whether two values are equal.
Parameters	`arg1`: the first value. Data type: any type. `arg2`: the second value. Data type: same as `arg1`.
Return value	`true` if the two values are equal. `false` if they are not equal.
Example	See below.

key1 = 'value1'
key2 = 'value2'
if and($arg_k1, $arg_k2, eq(key1, $arg_k1), ne(key2, $arg_k2)) {
    say('match condition')
}

If the request includes both the k1 and k2 parameters, the comparison operations run.
If the request does not include k1 or k2, short-circuit evaluation stops the comparisons.
eq(key1, $arg_k1): checks whether the value of k1 equals value1.
ne(key2, $arg_k2): checks whether the value of k2 does not equal value2.
The response body match condition is returned only when the request includes both k1 and k2, the value of k1 equals value1, and the value of k2 does not equal value2.

ne

Item	Description
Syntax	`ne(arg1, arg2) → Boolean`
Description	Checks whether two values are not equal.
Parameters	`arg1`: the first value. Data type: any type. `arg2`: the second value. Data type: same as `arg1`.
Return value	`true` if the two values are not equal. `false` if they are equal.
Example	See below.

key1 = 'value1'
key2 = 'value2'
if and($arg_k1, $arg_k2, eq(key1, $arg_k1), ne(key2, $arg_k2)) {
    say('match condition')
}

If the request includes both the k1 and k2 parameters, the comparison operations run.
If the request does not include k1 or k2, short-circuit evaluation stops the comparisons.
eq(key1, $arg_k1): checks whether the value of k1 equals value1.
ne(key2, $arg_k2): checks whether the value of k2 does not equal value2.
The response body match condition is returned only when the request includes both k1 and k2, the value of k1 equals value1, and the value of k2 does not equal value2.

null

Item	Description
Syntax	`null(v) → Boolean`
Description	Checks whether a value is empty. Returns `true` for an empty array, empty dictionary, or empty string. Returns `false` for all other types and non-empty values.
Parameter	`v`: the value to check. Data type: array, dictionary, or string. Returns `false` for other data types.
Return value	Data type: Boolean. See the boundary behavior table below.
Example	See below.

Boundary behavior:

Input	`null()` result
Empty array (`[]`)	`true`
Non-empty array	`false`
Empty dictionary (`{}`)	`true`
Non-empty dictionary	`false`
Empty string (`''`)	`true`
Non-empty string	`false`
Other data types	`false`

d = []
say(null(d))
set(d, 1, 'v1')
say(null(d))
say(tostring(null('x')))
say(tostring(null('')))

Output:

true
false
false
true