Why doesn’t ProducesAttribute implement IActionConstraint?

[voroninp]

It seems reasonable to consider [Produces] attribute and the value of Accept header when selecting acton, but it does not participate in routing.

[engineering87]

Hello @voroninp,
[Produces] doesn’t implement IActionConstraint because it influences response formatting after the action is chosen, unlike [Consumes] which can affect selection. So, by default the framework doesn’t route on the Accept header but it returns 406 if unsupported, so if you need that behavior you’d have to add a custom constraint or define separate endpoints.

[voroninp]

Yes, did that.

How does [Produces] interact with output formatters? Does it mean you're specified in producer should be the one supported by the formatter? Unless action method directly writes to the response)?

[engineering87]

Yes, did that.

How does [Produces] interact with output formatters? Does it mean you're specified in producer should be the one supported by the formatter? Unless action method directly writes to the response)?

[Produces] limits the set of content types an action can return. The output formatter must support at least one of these types, otherwise you’ll get a 406. It doesn’t add new formatters but just constrains negotiation. If the action writes directly to the response, [Produces] has no effect.

[voroninp]

The fun fact, the action gets executed, even, if Accept and Produces mismatch.