Empty vs. null query parameters - wrong encoding in Uri about sdk HOT 5 OPEN

The other option is to treat a parameter of test1 as having no value, and test2= as having an empty value.
Then a URL of something?test1&test2=&test3=abc would encode the difference and parsing back in could recreate it. (If there was no way to represent the difference in text, it can't be round-tripped, but this may be a way.)

I'll have to check what the WhatWG URL spec does, because I still hope to one day migrate Dart Uri to that behavior.
If they don't distinguish the two cases, then Dart also won't.
If they do, then we may want to see if this is a breaking change worth making early, or is better to include it on a bigger update.
(Probably the latter, since we never noticed before.)

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Labels: area-core-library, type-bug
Summary: The Uri class encodes empty and null query parameters identically, making it impossible to distinguish between them after parsing. This inconsistency with common conventions, like those used by Java Spring, can lead to unexpected behavior when interacting with other systems.

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I think this is working as intended.
URIs are textual, they cannot represent "key with no value". Well, they could, but they don't.

As your example http://google.com?test2&test3=&test4=null shows, that URI has the keys test2, test3 and test4.
Their values are the strings "", "" and "null".
There is no support in a Uri for having a key with no string value, so if the key is there, the value is at least the empty string.

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That said, while this is intentional, it doesn't mean we can't change it. (It's harder, because it may break existing code).
So labeleing as enhancement request.

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Thanks for your reply, Lasse. Your explanation made me realize an error in my reasoning (of course the String "null" cannot always be taken to mean null), but the main point is still valid:

To me it would seem reasonable if the following test passed, which currently it does not do.

import 'package:flutter_test/flutter_test.dart';

void main() {
  test(
    "URI encoding should not change value assigned to a parameter",
    () {
      final queryParameters = {"test": null};
      final uri = Uri(queryParameters: queryParameters);
      final uriString = uri.toString();
      final parsedUri = Uri.parse(uriString);
      final parsedParameters = parsedUri.queryParameters;
      expect(queryParameters["test"], parsedParameters["test"]);
    },
  );
}

This could be reached by removing all key-value-pairs with a null value when creating the query string. But yes, this might break existing code.

If you're happy to say the current behaviour is as intended, we can close this.

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