NIP-91

Protocol Negotiation

draft optional

This NIP defines a method for clients to negotiate extension protocols with relays.

Protocol Names

Each protocol has a protocol name that can uniquely identify the protocol. Currently the following formats are recommended:

nip-XX-<description>: For protocols standardized in NIPs. Experimental protocols are recommended to have a unique description to not conflict.
<namespace>/<protocol>: For custom protocols. The namespace should uniquely identify the standardizing body for this protocol with a DNS name. (example: example.com/example-protocol)
x/<protocol>: For custom protocols without a namespace.

Any protocol name outside this list MUST NOT be used.

Protocol Offers

The relay may send a protocol offer as a PN-OFFER message:

[
  "PN-OFFER",
  {
    "example.com/example-protocol": {...},
    "nip-XX-example-protocol": {...}
  }
]

The first entry MUST be an object, with the keys being protocol names, and the values being objects. The format of the object is up to the protocol to define.

A protocol offer can be sent multiple times in a connection, such as to update availability based off of their NIP-42 authentication status.

Clients SHOULD be able to handle protocol offers being able to be withdrawn. The removal of a protocol from a PN-OFFER does not affect existing active protocols, a PN-SHUTDOWN must be sent if that is required.

Protocol Requests

A client may request a protocol offered by the relay be enabled with the PN-REQUEST message:

[
  "PN-REQUEST",
  "example.com/example-protocol",
  {...}
]

The first entry MUST be the protocol name, and the second entry MUST be a protocol-dependent object for the protocol enable request.

The relay SHOULD respond with a PN-OK or PN-ERROR message:

[
  "PN-OK",
  "example.com/example-protocol",
  {...}
]

[
  "PN-ERROR",
  "example.com/example-protocol",
  "improper protocol request data"
]

In both messages, the first entry MUST be the protocol name. The second entry depends on the type:

PN-OK: Response data for the protocol negotiation. After this message, the protocol can be used.
PN-ERROR: An error message.

An error message SHOULD start with a single-word prefix, followed by a colon (:) and space character, and a human readable message. The following types are defined:

error: An internal error has occurred in the relay.
not-offered: The protocol was not offered. This may happen due to a PN-REQUEST being sent at the same time as a new PN-OFFER.
bad-data: The client has sent improper protocol negotiation data.

Protocol Shutdown

The relay or client may shut down the usage of the protocol any time with a PN-SHUTDOWN message:

[
  "PN-SHUTDOWN",
  "example.com/example-protocol"
]

After this message, the sending party will no longer accept and send new protocol messages, and the receiver should not continue attempting to use the protocol functionality.

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