To accurately compare and match JIDs, a normalization step is required by RFC 7622 . This normalization is split into two steps called 'Preparation' and 'Enforcement' by RFC 8264  and maybe resource-intensive. The protocol defined herein, called "JID Prep" can be used to ask XMPP entities to perform such a normalization. Amongst other use-cases, this protocol can be used for testing purposes, where a test suite checks the conformance of an normalization implementation of, e.g., an XMPP server implementation.
Furthermore, in some environments, especially ones like IoT where devices with constraint resources are used, a client may not have access to the various Unicode and internationalization libraries necessary to properly normalize a JID. For those situations, this protocol can be used by a client to ask a server to normalize a JID on its behalf.
If a server supports JID Prep queries, it MUST specify the 'urn:xmpp:jidprep:1' feature in its service discovery information features as specified in Service Discovery (XEP-0030) .
To request preparation and enforcement, and thus normalization and validation, of a string to a JID, the client sends a JID Prep request to the service. This request is an <iq/> of type 'get', containing a <jid-validate-request/> element qualified by the 'urn:xmpp:jidprep:1' namespace. This element contains a <maybe-jid/> child element whose textual content is the string to normalize to and validate as JID.
If the given string can be enforced to a valid JID, then a <jid-validate-result/> with a <valid-jid/> child element is returned. This child element contains the normalized JID parts. The valid-jid element MUST contain <domainpart/> and may contain <localpart/> and/or <resourcepart/> elements. If the JID does not contain a local- or resourcepart, then the corresponding element is omitted. Those elements contain the normalized, i.e., PRECIS enforced, strings of the own JID parts.
If the service is given an invalid JID, a <jid-validate-result/> IQ result response with an <invalid-jid/> elmeent is returned.
To be able to feed arbitrary strings into the validator, not being limited by XML 1.0, the protocol supports an optional Base64 encoding of the string to validate. The requestor first encodes the string to UTF-8, then encodes the UTF-8 byte-sequence using Base64 (RFC 4648  § 4) and places the result into an <base64-maybe-jid/> element. This element is a put under the <jid-validate-base64-request/> IQ child element qualified by the 'urn:xmpp:jidprep:1' namespace.
The IQ respones of the service are identical to the ones of the non-Base64 case.
If supported, service announces 'urn:xmpp:jidprep:base64:1' feature.
If a client has the ability to perform the normalization process itself, it SHOULD NOT make use of the protocol defined herein.
Upon a successful response, it is RECOMMENDED that the client caches the result, mapping the original JID to the normalized version.
As the process for normalizing and validating a JID can be resource intensive, there is a possibility for denial of service attacks. A server MAY rate limit the number of requests to prevent such attacks. Likewise, the server MAY restrict access to the service torequests from users that are local to the server or otherwhise trusted.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.
TODO: Add once the XEP leaves the experimental state.
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