others-How to parse nginx request parameter dynamically?

1. Purpose

In this post, I would demonstrate how to parse the nginx quuery parameter using nginx directives. Just as the following picture shows:

2. The solution

2.1 The nginx config file

You can include this content in nginx:

server {
    listen          81;
    access_log /dev/stdout;
    error_log /dev/stdout debug;

    location /foo {
        set $a 'hello $arg_name';
        return 200 'a=$a';
    }

}

Then we can test it:

 ⚡ root@launch-advisor-20191120  /etc/nginx  curl http://localhost:81/foo\?name\=world
a=hello world#

There is very common built-in variable that does not have a fixed variable name. Instead, It has infinite variations. That is, all those variables whose names have the prefix arg_, like $arg_foo and $arg_bar. Let’s just call it the $arg_XXX “variable group”. For example, the $arg_name variable is evaluated to the value of the name URI argument for the current request. Also, the URI argument’s value obtained here is not decoded yet, potentially containing the %XX sequences.

For example:

location /test {
    echo "name: $arg_name";
    echo "class: $arg_class";
}

Then we test this interface with various different URI argument combinations:

$ curl 'http://localhost:8080/test'
name:
class:

$ curl 'http://localhost:8080/test?name=Tom&class=3'
name: Tom
class: 3

$ curl 'http://localhost:8080/test?name=hello%20world&class=9'
name: hello%20world
class: 9

3. Summary

In this post, I demonstrated how to parse request parameters using $arg_xxx variable group. That’s it, thanks for your reading.