From b19c1fd7f935d829c24d8ecc97a0ed82378a206d Mon Sep 17 00:00:00 2001
From: Peter Saint-Andre
Whether or not the roster has been modified since the version ID enumerated by the client, the server MUST either return the complete roster as described in RFC 3921 or return an empty IQ-result (thus indicating that any roster modifications will be sent via roster pushes, as described below). In general, unless returning the complete roster would use less bandwidth than sending individual roster pushes to the client (e.g., if the roster contains only a few items), the server SHOULD send an empty IQ-result and then send the modifications (if any) via roster pushes. In addition, if the client signals a version ID that is different from the version currently on file at the server for that JID, the server MUST return the whole current roster as if client announced its version to be the empty string, thus bootstrapping the client's local cache.
+Whether or not the roster has been modified since the version ID enumerated by the client, the server MUST either return the complete roster as described in RFC 3921 or return an empty IQ-result (thus indicating that any roster modifications will be sent via roster pushes, as described below). In general, unless returning the complete roster would (1) use less bandwidth than sending individual roster pushes to the client (e.g., if the roster contains only a few items) or (2) the server cannot associate the version ID with any previous version it has on file, the server SHOULD send an empty IQ-result and then send the modifications (if any) via roster pushes.
The client MUST handle an "interim roster push" in the same way it handles any roster push (indeed, from the client's perspective it cannot tell the difference between an "interim" roster push and a "live" roster push). If the client's session ends before it receives all of the interim roster pushes, when requesting the roster after reconnection it SHOULD request the version associated with the last roster push it received during the session that was disconnected, not the version associated with the roster result it received at the start of the session that was disconnected.