Fixed ImapFolder.Sort() to always return the UIDs in the correct order.

If the IMAP server did not support ESEARCH, the order of the returned
UniqueIds was always sorted in ascending order even if that is not
the order of the UIDs returned by the IMAP server in the untagged
`SORT` response.

Fixes issue #789

MailKit/Net/Imap/ImapFolder.cs

@@ -4508,7 +4508,7 @@ async Task<IList<int>> GetIndexesAsync (IList<UniqueId> uids, bool doAsync, Canc
 		{
 			var command = string.Format ("SEARCH UID {0}\r\n", UniqueIdSet.ToString (uids));
 			var ic = new ImapCommand (Engine, cancellationToken, this, command);
-			var results = new SearchResults ();
+			var results = new SearchResults (SortOrder.Ascending);
 
 			if ((Engine.Capabilities & ImapCapabilities.ESearch) != 0)
 				ic.RegisterUntaggedHandler ("ESEARCH", ESearchMatchesAsync);

MailKit/Net/Imap/ImapFolderSearch.cs

@@ -337,8 +337,8 @@ static string BuildSortOrder (IList<OrderBy> orderBy)
 
 		static async Task SearchMatchesAsync (ImapEngine engine, ImapCommand ic, int index, bool doAsync)
 		{
-			var uids = new UniqueIdSet (SortOrder.Ascending);
 			var results = (SearchResults) ic.UserData;
+			var uids = results.UniqueIds;
 			ImapToken token;
 			uint uid;
 
@@ -387,7 +387,6 @@ static async Task ESearchMatchesAsync (ImapEngine engine, ImapCommand ic, int in
 		{
 			var token = await engine.ReadTokenAsync (doAsync, ic.CancellationToken).ConfigureAwait (false);
 			var results = (SearchResults) ic.UserData;
-			UniqueIdSet uids = null;
 			int parenDepth = 0;
 			//bool uid = false;
 			string atom;
@@ -500,18 +499,17 @@ static async Task ESearchMatchesAsync (ImapEngine engine, ImapCommand ic, int in
 				case "ALL":
 					ImapEngine.AssertToken (token, ImapTokenType.Atom, ImapEngine.GenericUntaggedResponseSyntaxErrorFormat, "ESEARCH", token);
 
-					uids = ImapEngine.ParseUidSet (token, ic.Folder.UidValidity, ImapEngine.GenericItemSyntaxErrorFormat, atom, token);
+					var uids = ImapEngine.ParseUidSet (token, ic.Folder.UidValidity, ImapEngine.GenericItemSyntaxErrorFormat, atom, token);
 
 					results.Count = uids.Count;
+					results.UniqueIds = uids;
 					break;
 				default:
 					throw ImapEngine.UnexpectedToken (ImapEngine.GenericUntaggedResponseSyntaxErrorFormat, "ESEARCH", token);
 				}
 
 				token = await engine.ReadTokenAsync (doAsync, ic.CancellationToken).ConfigureAwait (false);
 			} while (true);
-
-			results.UniqueIds = uids ?? new UniqueIdSet ();
 		}
 
 		async Task<SearchResults> SearchAsync (string query, bool doAsync, CancellationToken cancellationToken)
@@ -531,7 +529,7 @@ async Task<SearchResults> SearchAsync (string query, bool doAsync, CancellationT
 			if ((Engine.Capabilities & ImapCapabilities.ESearch) != 0)
 				ic.RegisterUntaggedHandler ("ESEARCH", ESearchMatchesAsync);
 			ic.RegisterUntaggedHandler ("SEARCH", SearchMatchesAsync);
-			ic.UserData = new SearchResults ();
+			ic.UserData = new SearchResults (SortOrder.Ascending);
 
 			Engine.QueueCommand (ic);
 
@@ -669,7 +667,7 @@ async Task<IList<UniqueId>> SearchAsync (SearchQuery query, bool doAsync, Cancel
 			// respond with "* SEARCH ..." instead of "* ESEARCH ..." even when using the extended
 			// search syntax.
 			ic.RegisterUntaggedHandler ("SEARCH", SearchMatchesAsync);
-			ic.UserData = new SearchResults ();
+			ic.UserData = new SearchResults (SortOrder.Ascending);
 
 			Engine.QueueCommand (ic);
 

MailKit/Search/SearchResults.cs

@@ -41,9 +41,10 @@ public class SearchResults
 		/// <remarks>
 		/// Creates a new <see cref="SearchResults"/>.
 		/// </remarks>
-		public SearchResults ()
+		/// <param name="order">The expected sort-order of the results.</param>
+		public SearchResults (SortOrder order = SortOrder.None)
 		{
-			UniqueIds = new UniqueId[0];
+			UniqueIds = new UniqueIdSet (order);
 		}
 
 		/// <summary>

UnitTests/Net/Imap/ImapClientTests.cs

@@ -3008,8 +3008,9 @@ public void TestDovecot ()
 				Assert.IsFalse (matches.Min.HasValue, "MIN should not be set");
 				Assert.AreEqual (0, matches.Count, "COUNT should not be set");
 				Assert.AreEqual (14, matches.UniqueIds.Count);
+				var expectedSortByReverseArrivalResults = new uint[] { 7, 14, 6, 13, 5, 12, 4, 11, 3, 10, 2, 9, 1, 8 };
 				for (int i = 0; i < matches.UniqueIds.Count; i++)
-					Assert.AreEqual (i + 1, matches.UniqueIds[i].Id);
+					Assert.AreEqual (expectedSortByReverseArrivalResults[i], matches.UniqueIds[i].Id);
 
 				destination.GetStreams (UniqueIdRange.All, GetStreamsCallback);
 				destination.GetStreams (new int[] { 0, 1, 2 }, GetStreamsCallback);
@@ -3632,8 +3633,9 @@ public async void TestDovecotAsync ()
 				Assert.IsFalse (matches.Min.HasValue, "MIN should not be set");
 				Assert.AreEqual (0, matches.Count, "COUNT should not be set");
 				Assert.AreEqual (14, matches.UniqueIds.Count);
+				var expectedSortByReverseArrivalResults = new uint[] { 7, 14, 6, 13, 5, 12, 4, 11, 3, 10, 2, 9, 1, 8 };
 				for (int i = 0; i < matches.UniqueIds.Count; i++)
-					Assert.AreEqual (i + 1, matches.UniqueIds[i].Id);
+					Assert.AreEqual (expectedSortByReverseArrivalResults[i], matches.UniqueIds[i].Id);
 
 				await destination.GetStreamsAsync (UniqueIdRange.All, GetStreamsCallback);
 				await destination.GetStreamsAsync (new int[] { 0, 1, 2 }, GetStreamsCallback);