Message Type and Protocol Identifier URIs

Message types and protocols are identified with URIs that match certain conventions.

MTURI

A message type URI (MTURI) identifies message types unambiguously. Standardizing its format is important because it is parsed by agents that will map messages to handlers--basically, code will look at this string and say, "Do I have something that can handle this message type inside protocol X version Y?" When that analysis happens, it must do more than compare the string for exact equality; it may need to check for semver compatibility, and it has to compare the protocol name and message type name ignoring case and punctuation.

The URI MUST be composed as follows:

message-type-uri  = doc-uri delim protocol-name 
    "/" protocol-version "/" message-type-name
delim             = "?" / "/" / "&" / ":" / ";" / "="
protocol-name     = identifier
protocol-version  = semver
message-type-name = identifier
identifier        = alpha *(*(alphanum / "_" / "-" / ".") alphanum)

It can be loosely matched and parsed with the following regex:

(.*?)([a-z0-9._-]+)/(\d[^/]*)/([a-z0-9._-]+)$

A match will have captures groups of (1) = doc-uri, (2) = protocol-name, (3) = protocol-version, and (4) = message-type-name.

The goals of this URI are, in descending priority:

• Code can use the URI to route messages to protocol handlers using semver rules.

• The definition of a protocol should be tied to the URI such that it is semantically stable. This means that once version 1.0 of a protocol is defined, its definition should not change in ways that would break implementations.

• Developers can discover information about novel protocols, using the URI to browse or search the web.

The doc-uri portion is any URI that exposes documentation about protocols. A developer should be able to browse to that URI and use human intelligence to look up the named and versioned protocol. Optionally and preferably, the full URI may produce a page of documentation about the specific message type, with no human mediation involved.

PIURI

A shorter URI that follows the same conventions but lacks the message-type-name portion is called a protocol identifier URI (PIURI).

protocol-identifier-uri  = doc-uri delim protocol-name 
    "/" semver

Its loose matcher regex is:

(.*?)([a-z0-9._-]+)/(\d[^/]*)/?$

Some examples of valid MTURIs and PIURIs include:

• http://example.com/protocols?which=lets_do_lunch/1.0/ (PIURI with fully automated lookup of protocol docs)
• http://example.com/message_types?which=lets_do_lunch/1.0/proposal (MTURI)
• https://github.com/hyperledger/indy-hipe/tree/d7879f5e/text:trust_ping/1.0/ping (MTURI). Note that this URI returns a 404 error if followed directly--but per rules described above, the developer should browse to the doc root (https://github.com/hyperledger/indy-hipe/tree/d7879f5e/text) and look for documentation on the trust_ping/1.0 protocol.
• did:sov:BzCbsNYhMrjHiqZDTUASHg;spec/trust_ping/1.0/ping (MTURI) This uses a DID reference to look up an endpoint named spec that serves information about protocols. (The exact syntax of DID references--URIs where the DID functions like a domain name, and additional info is fetched from a DID Doc in much the same way IP address and hostname definitions are fetched from a DNS record--is still being finalized. See the latest DID Spec for details.)