I don’t think this matters at all. People usually are not writing their own http libraries. They use existing ones, and those already take care of reading the h

I don’t think this matters at all. People usually are not writing their own http libraries. They use existing ones, and those already take care of reading the http headers and the body separately. One should avoid handwriting a http server for avoiding security issues and to benefit from performance gains - eg using http/2. Once one had the body - which will typically be read in one go for usual RPC use cases - it’s as easy to deserialize json as anything else that could be transferred there.