How can I parse \'relaxed\' JSON without using eval and maintaining security?

Parsing "Relaxed" JSON without Resorting to Eval

In an effort to facilitate a more user-friendly JSON parsing experience, developers often resort to the infamous eval function. However, this practice raises concerns about security vulnerabilities. This article explores an alternative approach to parsing "relaxed" JSON without compromising safety, providing a solution that satisfies both convenience and security requirements.

The Issue:

The standard JSON parsing method, JSON.parse, strictly adheres to the correct JSON syntax, requiring keys to be enclosed in quotes. However, in practice, developers often encounter JSON data with "relaxed" syntax, where keys may not be quoted. This poses a challenge for parsing such data securely.

The Solution:

Instead of using eval, which indiscriminately executes code, a safer and equally effective method involves employing a regular expression to sanitize the JSON data. This technique involves replacing unquoted keys with properly quoted equivalents, allowing the data to be successfully parsed by JSON.parse.

Step-by-Step Process:

1. Sanitize the JSON:
   Use a regular expression to scan the JSON data for unquoted keys. For each unquoted key, replace it with its quoted counterpart.
2. Evaluate the Sanitized JSON:
   Once the data is sanitized, it can be passed to JSON.parse to parse it safely into a JavaScript object.

Code Example:

Consider the following "relaxed" JSON:

{muh: 2}

To parse this data using the sanitized approach:

var badJson = "{muh: 2}";
var correctJson = badJson.replace(/(['"])?([a-z0-9A-Z_]+)(['"])?:/g, '"": ');
var resultObject = JSON.parse(correctJson);

After the sanitization process, the correctJson variable will contain valid JSON:

{"muh": 2}

Which can then be parsed safely by JSON.parse, resulting in the desired JavaScript object.

Conclusion:

By adopting this sanitization technique, developers can securely parse "relaxed" JSON data without resorting to eval. This approach provides a practical solution that ensures both data integrity and adherence to secure programming practices.

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