emsmdb: emit anti-SyncMessagePartial marker into messageChangePartial ICS elements

References: GXL-624, DESK-3529

Author: jengelh

exch/emsmdb/ftstream_producer.cpp

@@ -692,9 +692,30 @@ BOOL fxstream_producer::write_messagechangepartial(
 	for (size_t i = 0; i < pmsg->count; ++i) {
 		if (!write_uint32(MetaTagIncrementalSyncMessagePartial))
 			return FALSE;
+		/*
+		 * [Grep keyword: FAULTY-PARTIALS]. Earlier in
+		 * icsdownctx_object_get_changepartial(), ungrouped tags were
+		 * put into the special (struct MSGCHG_PARTIAL::pchanges)
+		 * pseudo-group with id UINT32_MAX/0xffffffff. pmsg->pgpinfo
+		 * does not have any group with id 0xffffffff, and OL would
+		 * rightfully deleted ungrouped properties from an .ost.
+		 *
+		 * OXCFXICS has terrible explanations, but it appears very much
+		 * like we are supposed to use a proptag terminator instead
+		 * (see below).
+		 */
 		if (!write_uint32(pmsg->pchanges[i].group))
 			return FALSE;	
 		for (const auto &ipv : pmsg->pchanges[i].proplist) {
+			/*
+			 * When we are in our special group (of ungrouped tags),
+			 * emit the marker for "terminating" SyncMessagePartial,
+			 * as per OXCFXICS v25 2.2.4.3.15.
+			 */
+			if (pmsg->pchanges[i].group == UINT32_MAX) {
+				if (!write_uint32(UINT32_MAX))
+					return FALSE;
+			}
 			switch (ipv.proptag) {
 			case PR_MESSAGE_RECIPIENTS:
 				if (pmsg->children.prcpts == nullptr)

exch/emsmdb/icsdownctx_object.cpp

@@ -680,6 +680,8 @@ static BOOL icsdownctx_object_get_changepartial(icsdownctx_object *pctx,
 	}
 	if (ugrp_tags.empty())
 		return TRUE;
+
+	/* Special "group" for write_messagechangepartial(). */
 	auto &pl = pmsg->pchanges[i].proplist;
 	pmsg->pchanges[i].group = UINT32_MAX;
 	pl.ppropval = cu_alloc<TAGGED_PROPVAL>(ugrp_tags.size());