xmpp XMPP Addresses aka. JIDs (Jabber Identifiers) Validating a JID (generic)

Example

Unlike emails, JIDs were defined with Internationalization (i18n) in mind using the Preparation, Enforcement, and Comparison of Internationalized Strings (PRECIS) framework. PRECIS (defined in RFC 7564), is a framework for comparing strings safely in a variety of contexts. For instance, imagine you have registered the nickname “Richard IV” (Latin capital letters I, Vee) in a group chat: Using PRECIS the chat application could ensure that no one else comes along and registers the nickname “Richard Ⅳ” (Unicode Roman Numeral 4) and uses it to impersonate you.

The algorithm for validating a JID that has already been split into its localpart, domainpart, and resourcepart (See: Splitting a JID (generic) for information on extracing the parts of a JID from a string) is as follows:

The Validations step should perform the following:

• Check that the localpart is less than 1024 bytes (bytes, not glyphs)
• Check that the localpart doesnot contain any of "&'/:<>@
• Check that the resourcepart is less than 1024 bytes
• Check that the domainpart is greater than zero bytes and less than 1024 bytes (and possibly validate that the individual parts of the domain fit into DNS requirements)
• If the domain is a valid IPv6 address, ensrue that it uses bracketed notation (eg. [::1] instead of ::1)