server.go
func (ctx *RequestCtx) SetContentTypeBytes(contentType []byte) {
	ctx.Response.Header.SetContentTypeBytes(contentType)
}
func (ctx *RequestCtx) SetContentTypeBytes(contentType []byte) {
	ctx.Response.Header.SetContentTypeBytes(contentType)
}
// SetContentTypeBytes sets response Content-Type.
//
// It is safe modifying contentType buffer after function return.