Json parsing with iRules

JSON is now the format of choice for most APIs. It's time we were able to parse JSON with F5 iRules too, as simple string matching is not always good enough. That's why I wrote a simple JSON parser for iRules. It is a validating single pass parser that processes the JSON string char by char until the JsonPath expression matches, no recursion or any other fancy stuff. As I do not wanted to reinvent the wheel, it is basically a rewrite of the JSON parser found in the mongoose webserver project in plain TCL.

The usage is very simple:

set token [call json::json_get_tok { $json $path }]

• $json is the json string to parse
• $path is a JsonPath expression, following operators are implemented:

Example

Simple JSON:

{
    "aud": "audience \"test\"",
    "iss": "https://issuer.de/issuer/",
    "iat": 1701422123,
    "roles": [
        "role1",
        "role2"
    ],
    "obj": {
        "sub": "adcad2b8",
    },
    "ver": "2.0"
}

JsonPath expression to parse this simple JSON:

To decode the extracted JSON string:

set decoded [call json::json_decode_str { $token }]

This removes the enclosing quotes from a string and decodes JSON escapes.

Code

You can find the code and further documentation in my GitHub repository: https://github.com/JuergenMang/f5-irules-json