lua-resty-expr

Name

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

[!License](https://github.com/api7/lua-resty-expr/blob/main/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.

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))
         }
     }

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)"},
        ...
    }

Logical operator can be one of

• OR

• AND

• !OR: not (expr1 or expr2 or ...)

• !AND: not (expr1 and expr2 and ...)

Their combination can be like:

    [
        "AND",
        ["arg_name", "==", "json"],
        [
            "!OR",
            ["arg_weight", ">", 10],
            ["arg_height", "!", ">", 15]
        ]
    ]

Operator List

|operator|description|example| |--------|-----------|-------| |== |equal |{"arg_name", "==", "json"}| |~= |not equal |{"arg_name", "~=", "json"}| |> |greater than|{"arg_age", ">", 24}| |< |less than |{"arg_age", "<", 24}| |~~ |Regular match|{"arg_name", "~~", "[a-z]+"}| |~ |Case insensitive regular match|{"arg_name", "~", "[a-z]+"}| |in |find in array|{"arg_name", "in", {"1","2"}}| |has |left value array has value in the right |{"graphql_root_fields", "has", "repo"}| |! |reverse the result|{"arg_name", "!", "~~", "[a-z]+"}|

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

Install

Compile and install

    make install

DEV ENV

Install Dependencies

    make deps