Make Exists Mode for QueryParameters support empty parameters

[ppv-milestone]

Discussed in #2553

^{Originally posted by ppv-milestone July 17, 2024}
We need to match queries to an interface that accepts a request like this:
http://path/component?hello
But according to documentation the "Exists" Mode in QueryParameters will only match against non-empty parameters and our tests show that Prefix, Exact and Contains seem to be following the same (providing "" as a value to match for causes the service to fail).
Also tried with regular expressions in Path, but those does not seem to match on parameters.
Anyone has a workaround for this? Or maybe supporting empty parameters for Exists could be supported in next version?
Thanks a lot in advance!
Br,
Peter

[MihaZupan]

FWIW the query parameters here is matching what we do for headers:

reverse-proxy/src/ReverseProxy/Routing/HeaderMatcherPolicy.cs

Lines 78 to 83 in b1a1d8b

	HeaderMatchMode.Exists => !valueIsEmpty,
	HeaderMatchMode.NotExists => valueIsEmpty,
	HeaderMatchMode.ExactHeader => !valueIsEmpty && TryMatchExactOrPrefix(matcher, requestHeaderValues),
	HeaderMatchMode.HeaderPrefix => !valueIsEmpty && TryMatchExactOrPrefix(matcher, requestHeaderValues),
	HeaderMatchMode.Contains => !valueIsEmpty && TryMatchContainsOrNotContains(matcher, requestHeaderValues),
	HeaderMatchMode.NotContains => valueIsEmpty || TryMatchContainsOrNotContains(matcher, requestHeaderValues),

reverse-proxy/src/ReverseProxy/Routing/QueryParameterMatcherPolicy.cs

Lines 77 to 81 in b1a1d8b

	QueryParameterMatchMode.Exists => !valueIsEmpty,
	QueryParameterMatchMode.Exact => !valueIsEmpty && TryMatch(matcher, requestQueryParameterValues),
	QueryParameterMatchMode.Prefix => !valueIsEmpty && TryMatch(matcher, requestQueryParameterValues),
	QueryParameterMatchMode.Contains => !valueIsEmpty && TryMatch(matcher, requestQueryParameterValues),
	QueryParameterMatchMode.NotContains => valueIsEmpty || TryMatch(matcher, requestQueryParameterValues),

and the behavior was intentional for headers at least.
I'd find it surprising if the two were inconsistent.

[ppv-milestone]

FWIW the query parameters here is matching what we do for headers:

reverse-proxy/src/ReverseProxy/Routing/HeaderMatcherPolicy.cs

Lines 78 to 83 in b1a1d8b

	HeaderMatchMode.Exists => !valueIsEmpty,
	HeaderMatchMode.NotExists => valueIsEmpty,
	HeaderMatchMode.ExactHeader => !valueIsEmpty && TryMatchExactOrPrefix(matcher, requestHeaderValues),
	HeaderMatchMode.HeaderPrefix => !valueIsEmpty && TryMatchExactOrPrefix(matcher, requestHeaderValues),
	HeaderMatchMode.Contains => !valueIsEmpty && TryMatchContainsOrNotContains(matcher, requestHeaderValues),
	HeaderMatchMode.NotContains => valueIsEmpty || TryMatchContainsOrNotContains(matcher, requestHeaderValues),

reverse-proxy/src/ReverseProxy/Routing/QueryParameterMatcherPolicy.cs

Lines 77 to 81 in b1a1d8b

	QueryParameterMatchMode.Exists => !valueIsEmpty,
	QueryParameterMatchMode.Exact => !valueIsEmpty && TryMatch(matcher, requestQueryParameterValues),
	QueryParameterMatchMode.Prefix => !valueIsEmpty && TryMatch(matcher, requestQueryParameterValues),
	QueryParameterMatchMode.Contains => !valueIsEmpty && TryMatch(matcher, requestQueryParameterValues),
	QueryParameterMatchMode.NotContains => valueIsEmpty || TryMatch(matcher, requestQueryParameterValues),

and the behavior was intentional for headers at least. I'd find it surprising if the two were inconsistent.

Why do you assume the behavior was intentional for headers and not just the easiest approach? To me it sounds a bit counter-intuitive that Exists goes on whether it has a value instead of whether it actually is present or not - both for headers and query parameters.

[Tratcher]

It was intentional for headers. Empty headers have no semantic meaning and may be dropped by intermediaries.

The query situation is a bit different. We assume key-value pairs (?key1=a&key2=b), but having a single key without an equals sign is still meaningful (?key1&key2). AspNetCore isn't great at representing this case, it doesn't distinguish between key1= and key1.