In a simple @EnableZuulProxy application, requests with Content-Type application/x-www-form-urlencoded or multipart/form-data gets wrapped in a FormBodyRequestWrapper by FormBodyWrapperFilter. This decodes the content and reencode it for the backend.
However, from what I can see, requests of other content types (let's say application/json) in a service discovery enabled route will get their InputStream directly proxied to the client used through the RibbonCommandContext.
In Apache HttpClient for example, the input stream will be wrapped in a BasicHttpEntity in the RibbonApacheHttpRequest.
Why is this necessary? Couldn't we just handle all requests the same way?
See https://github.com/spring-cloud/spring-cloud-netflix/issues/109 for the original issue.
The zuul request wrapper buffers the request and it needed to be added back for the proxy. This is one of the reasons spring cloud gateway was built, since it doesn't have these problems.