[fix] @koa/router does not handle decoding URL with '+' character properly

[stixsg]

Describe the bug

Node.js version: v20.12.0

OS version: Ubuntu 22.04

Description: @koa/router does not handle decoding URL with '+' character properly. With reference to https://en.wikipedia.org/wiki/Percent-encoding:

When data that has been entered into HTML forms is submitted, the form field names and values are encoded and sent to the server in an HTTP request message using method GET or POST, or, historically, via email.[3] The encoding used by default is based on an early version of the general URI percent-encoding rules,[4] with a number of modifications such as newline normalization and replacing spaces with + instead of %20. The media type of data encoded this way is application/x-www-form-urlencoded, and it is currently defined in the HTML and XForms specifications. In addition, the CGI specification contains rules for how web servers decode data of this type and make it available to applications.

'+' characters in URL should be decoded as spaces.

Possible fix

According to https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/decodeURIComponent#decoding_query_parameters_from_a_url, decodeURIComponent() cannot be used directly to parse query parameters from a URL. It needs a bit of preparation. In function safeDecodeURIComponent(text) in layer.js, call to decodeURIComponent() should first replace all '+' with spaces:

function safeDecodeURIComponent(text) {
  try {
    return decodeURIComponent(text.replace(/\+/g, " "));
  } catch {
    return text;
  }
}

Checklist

• I have searched through GitHub issues for similar issues.
• I have completely read through the README and documentation.
• I have tested my code with the latest version of Node.js and this package and confirmed it is still not working.