http.go
func (req *Request) ReleaseBody(size int) {
	if cap(req.body.B) > size {
		req.closeBodyStream()
		req.body = nil
	}
}
func (req *Request) ReleaseBody(size int) {
	if cap(req.body.B) > size {
		req.closeBodyStream()
		req.body = nil
	}
}
// ReleaseBody retires the request body if it is greater than "size" bytes.
//
// This permits GC to reclaim the large buffer.  If used, must be before
// ReleaseRequest.
//
// Use this method only if you really understand how it works.
// The majority of workloads don't need this method.