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lua-resty-expr

Name

A tiny DSL to evaluate expressions which is used inside of APISIX.

License

This project has been working in microservices API gateway Apache APISIX.

The project is open sourced by Shenzhen ZhiLiu Technology Co., Ltd.

In addition to this open source version, our company also provides a more powerful and performing commercial version, and provides technical support. If you are interested in our commercial version, please contact us.

Table of Contents

Synopsis

 location / {
     content_by_lua_block {
        local expr = require("resty.expr.v1")
        local ex = expr.new({
            {"arg_name", "==", "json"},
            {"arg_weight", ">", 10},
            {"arg_weight", "!", ">", 15},
        })

        -- equal to
        -- 'ngx.say(ngx.var.arg_name == "json" and ngx.var.arg_weight > 10 and not ngx.var.arg_weight > 15)'
        ngx.say(ex:eval(ngx.var))
     }
 }
 location / {
     content_by_lua_block {
        local expr = require("resty.expr.v1")
        local ex = expr.new({
            "!AND",
            {"arg_name", "==", "json"},
            {
                "OR",
                {"arg_weight", ">", 10},
                {"arg_height", "!", ">", 15},
            }
        })

        -- equal to
        -- 'ngx.say(not (ngx.var.arg_name == "json" and
        --               (ngx.var.arg_weight > 10 or
        --                not ngx.var.arg_height > 15))'
        ngx.say(ex:eval(ngx.var))
     }
 }

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Methods

new

syntax: ex, err = expr.new(rule)

Create an expression object which can be evaluated later.

The syntax of rule is an array table of nodes.

The first node can be an expression or a logical operator. The remain nodes can be an expression or another array of nodes which contain its logical operator and expressions.

Each expression is an array table which has three or four elements:

{
    {"var name (aka. left value)", "optional '!' operator", "operator", "const value (aka. right value)"},
    ...
}

Comparison Operators

Operator Description Example
== equal ["arg_version", "==", "v2"]
~= not equal ["arg_version", "~=", "v2"]
> greater than ["arg_ttl", ">", 3600]
>= greater than or equal to ["arg_ttl", ">=", 3600]
< less than ["arg_ttl", "<", 3600]
<= less than or equal to ["arg_ttl", "<=", 3600]
~~ match RegEx ["arg_env", "~~", "[Dd]ev"]
~* match RegEx (case-insensitive) ["arg_env", "~~", "dev"]
in exist in the right-hand side ["arg_version", "in", ["v1","v2"]]
has contain item in the right-hand side ["graphql_root_fields", "has", "owner"]
! reverse the adjacent operator ["arg_env", "!", "~~", "[Dd]ev"]
ipmatch match IP address ["remote_addr", "ipmatch", ["192.168.102.40", "192.168.3.0/24"]]

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Logical Operators

Operator Explanation
AND AND(A,B) is true if both A and B are true.
OR OR(A,B) is true if either A or B is true.
!AND !AND(A,B) is true if either A or B is false.
!OR !OR(A,B) is true only if both A and B are false.

Example usage with comparison operators:

[
    "AND",
    ["arg_version", "==", "v2"],
    [
        "OR",
        ["arg_action", "==", "signup"],
        ["arg_action", "==", "subscribe"]
    ]
]

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eval

syntax: ok, err = ex:eval(ctx)

Evaluate the expression according to the ctx. If ctx is missing, ngx.var is used by default.

local ok = rx:eval()
if ok == nil then
    log_err("failed to eval expression: ", err)
    return false
end

return ok

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Install

Compile and install

make install

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DEV ENV

Install Dependencies

make deps

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