GeezerVison

BindBody compares the request media type against the lowercase MIME constants as-is, so a client that sends a supported type in a different case gets a 415. Media type and subtype names are case-insensitive (RFC 9110 section 8.3.1).

e.POST("/", func(c *echo.Context) error {
	var v struct{ ID int `json:"id"` }
	return c.Bind(&v)
})
// POST / with Content-Type: Application/JSON and body {"id": 1}
// got: 415 Unsupported Media Type, expected: bound with ID=1

The same happens for Application/XML, Text/XML, Application/X-WWW-Form-Urlencoded and Multipart/Form-Data.

The fix lowercases the media type before the switch. Parameters are left untouched, and the form and multipart branches already go through net/http, which parses the type with mime.ParseMediaType. #3095 had the same change and was labelled bug/v5 before its author closed it.

TestDefaultBinder_BindBody_MediaTypeIsCaseInsensitive covers all five types. On master every case fails with code=415, message=Unsupported Media Type. With the fix, go test -race ./..., go vet, staticcheck and golint all pass.