Comment by Animats | Hacker News Reader

Comment by Animats | Hacker News Reader

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There have been lots of RPC protocols. Here are some still in use.

Transport level:

* Sun RPC [1]. QNX still uses this. It can run over UDP or over raw Ethernet. It just transfers an array of bytes and gets an array of bytes back - marshalling is a higher level problem. It handles messages bigger than one packet, and retransmission. It's simple and performance is good, but there is no security.

* Stream Control Transmission Protocol. Telcos still use this. It's how Signalling System 7 is sent over IP.

Although many implementations exist for both, they've never been popular outside their niches.

Marshalling level:

* CORBA - you define interfaces in a special language and compile them. Data is not self-describing.

* SOAP, from the XML era.

* Google Protocol Buffers - another system where you compile definitions.

* HTTP/JSON - where we are now.

Plus a lot of Microsoft-specific stuff.

Either you have a system where both ends have to exactly agree on format, you have a verbose format with unneeded description data in every message, or you have a very complicated negotiation at connection time. This leads to much disagreement.

[1] https://en.wikipedia.org/wiki/Sun_RPC

> CORBA - you define interfaces in a special language and compile them. Data is not self-describing.

OMG the Common Object Request Broker Architecture (which coincidentally was created by OMG). I never thought I'd see that acronym again, and all these years later, I still don't understand what it is.

But is it not obvious? It’s the architecture for brokering requests of objects most common.

No no no, it's a Common broker architecture for object requests

Yeah, but the question at hand is why layer it over TCP.

SunRPC over UDP is close, but then you push reliability and congestion management into every application.

SCTP, from the parent's list, is a "over IP" protocol, not over TCP.

(Though it can be tunneled through UDP, to get around Internet ossification.)

> HTTP/JSON - where we are now.

That’s not a protocol either, you can use HTTP as an RPC (with a JSON payload), but you can also define a transport-independent JSON RPC protocol (e.g. JSON-RPC2, which can be used over HTTP but can also be used over simpler sockets, for instance chrome’s dev tools protocol is JSON-RPC2 over websocket or a pipe)

> Stream Control Transmission Protocol. Telcos still use this. It's how Signalling System 7 is sent over IP.

WebRTC is also a relatively thin wrapper over SCTP.

Yep, WebRTC data channels use SCTP (tunneled in UDP and DTLS), audio/video stuff is just SRTP (in DTLS) I think.

> SOAP, from the XML era.

Don't forget XML-RPC :-)

Remembered and now intentionally forgotten :-)

Ah, yes. I had to do XML-RPC from Rust recently. The login handshake for Second Life is XML-RPC. No other part of the system is.

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