add fallbacks for determining UIDNEXT

if the server sends no UIDNEXT, do an initial FETCH to query the UID of
the last message.

same if the server sends no APPENDUID.

this allows us to remove the arbitrary limitation of the UID range to
INT_MAX, at the cost of additional round-trips.

src/drv_imap.c

@@ -151,6 +151,7 @@ struct imap_cmd {
 		char to_trash; /* we are storing to trash, not current. */
 		char create; /* create the mailbox if we get an error which suggests so. */
 		char failok; /* Don't complain about NO response. */
+		char lastuid; /* querying the last UID in the mailbox. */
 	} param;
 };
 
@@ -1051,7 +1052,15 @@ parse_fetch_rsp( imap_store_t *ctx, list_t *list, char *s ATTR_UNUSED )
 		}
 	}
 
-	if (body) {
+	if (!uid) {
+		assert( !body && !tuid && !msgid );
+		// Ignore async flag updates for now.
+	} else if ((cmdp = ctx->in_progress) && cmdp->param.lastuid) {
+		assert( !body && !tuid && !msgid );
+		// Workaround for server not sending UIDNEXT and/or APPENDUID.
+		ctx->gen.uidnext = uid + 1;
+	} else if (body) {
+		assert( !tuid && !msgid );
 		for (cmdp = ctx->in_progress; cmdp; cmdp = cmdp->next)
 			if (cmdp->param.uid == uid)
 				goto gotuid;
@@ -1065,7 +1074,7 @@ parse_fetch_rsp( imap_store_t *ctx, list_t *list, char *s ATTR_UNUSED )
 		msgdata->date = date;
 		if (status & M_FLAGS)
 			msgdata->flags = mask;
-	} else if (uid) { /* ignore async flag updates for now */
+	} else {
 		/* XXX this will need sorting for out-of-order (multiple queries) */
 		cur = nfcalloc( sizeof(*cur) );
 		*ctx->msgapp = &cur->gen;
@@ -1081,8 +1090,6 @@ parse_fetch_rsp( imap_store_t *ctx, list_t *list, char *s ATTR_UNUSED )
 			memcpy( cur->gen.tuid, tuid, TUIDL );
 		else
 			cur->gen.tuid[0] = 0;
-		if (ctx->gen.uidnext <= uid) /* in case the server sends no UIDNEXT */
-			ctx->gen.uidnext = uid + 1;
 	}
 
 	free_list( list );
@@ -2287,6 +2294,9 @@ imap_select_box( store_t *gctx, const char *name )
 	return DRV_OK;
 }
 
+static void imap_open_box_p2( imap_store_t *, imap_cmd_t *, int );
+static void imap_open_box_p3( imap_store_t *, imap_cmd_t *, int );
+
 static void
 imap_open_box( store_t *gctx,
                void (*cb)( int sts, void *aux ), void *aux )
@@ -2304,11 +2314,38 @@ imap_open_box( store_t *gctx,
 
 	INIT_IMAP_CMD(imap_cmd_simple_t, cmd, cb, aux)
 	cmd->gen.param.failok = 1;
-	imap_exec( ctx, &cmd->gen, imap_done_simple_box,
+	imap_exec( ctx, &cmd->gen, imap_open_box_p2,
 	           "SELECT \"%\\s\"", buf );
 	free( buf );
 }
 
+static void
+imap_open_box_p2( imap_store_t *ctx, imap_cmd_t *gcmd, int response )
+{
+	imap_cmd_simple_t *cmdp = (imap_cmd_simple_t *)gcmd;
+	imap_cmd_simple_t *cmd;
+
+	if (response != RESP_OK || ctx->gen.uidnext) {
+		imap_done_simple_box( ctx, &cmdp->gen, response );
+		return;
+	}
+
+	INIT_IMAP_CMD(imap_cmd_simple_t, cmd, cmdp->callback, cmdp->callback_aux)
+	cmd->gen.param.lastuid = 1;
+	imap_exec( ctx, &cmd->gen, imap_open_box_p3,
+	           "UID FETCH *:* (UID)" );
+}
+
+static void
+imap_open_box_p3( imap_store_t *ctx, imap_cmd_t *gcmd, int response )
+{
+	// This will happen if the box is empty.
+	if (!ctx->gen.uidnext)
+		ctx->gen.uidnext = 1;
+
+	imap_done_simple_box( ctx, gcmd, response );
+}
+
 /******************* imap_create_box *******************/
 
 static void
@@ -2443,7 +2480,7 @@ imap_load_box( store_t *gctx, int minuid, int maxuid, int newuid, int seenuid, i
 			imap_submit_load( ctx, buf, shifted_bit( ctx->gen.opts, OPEN_OLD_IDS, WantMsgids ), sts );
 		}
 		if (maxuid == INT_MAX)
-			maxuid = ctx->gen.uidnext ? ctx->gen.uidnext - 1 : 0x7fffffff;
+			maxuid = ctx->gen.uidnext - 1;
 		if (maxuid >= minuid) {
 			imap_range_t ranges[3];
 			ranges[0].first = minuid;
@@ -2720,6 +2757,7 @@ imap_store_msg_p2( imap_store_t *ctx ATTR_UNUSED, imap_cmd_t *cmd, int response
 /******************* imap_find_new_msgs *******************/
 
 static void imap_find_new_msgs_p2( imap_store_t *, imap_cmd_t *, int );
+static void imap_find_new_msgs_p3( imap_store_t *, imap_cmd_t *, int );
 
 static void
 imap_find_new_msgs( store_t *gctx, int newuid,
@@ -2738,15 +2776,35 @@ static void
 imap_find_new_msgs_p2( imap_store_t *ctx, imap_cmd_t *gcmd, int response )
 {
 	imap_cmd_find_new_t *cmdp = (imap_cmd_find_new_t *)gcmd;
-	imap_cmd_simple_t *cmd;
+	imap_cmd_find_new_t *cmd;
 
 	if (response != RESP_OK) {
 		imap_done_simple_box( ctx, gcmd, response );
 		return;
 	}
+
+	ctx->gen.uidnext = 0;
+
+	INIT_IMAP_CMD_X(imap_cmd_find_new_t, cmd, cmdp->gen.callback, cmdp->gen.callback_aux)
+	cmd->uid = cmdp->uid;
+	cmd->gen.gen.param.lastuid = 1;
+	imap_exec( ctx, &cmd->gen.gen, imap_find_new_msgs_p3,
+	           "UID FETCH *:* (UID)" );
+}
+
+static void
+imap_find_new_msgs_p3( imap_store_t *ctx, imap_cmd_t *gcmd, int response )
+{
+	imap_cmd_find_new_t *cmdp = (imap_cmd_find_new_t *)gcmd;
+	imap_cmd_simple_t *cmd;
+
+	if (response != RESP_OK || ctx->gen.uidnext <= cmdp->uid) {
+		imap_done_simple_box( ctx, gcmd, response );
+		return;
+	}
 	INIT_IMAP_CMD(imap_cmd_simple_t, cmd, cmdp->gen.callback, cmdp->gen.callback_aux)
 	imap_exec( (imap_store_t *)ctx, &cmd->gen, imap_done_simple_box,
-	           "UID FETCH %d:" stringify(INT_MAX) " (UID BODY.PEEK[HEADER.FIELDS (X-TUID)])", cmdp->uid );
+	           "UID FETCH %d:%d (UID BODY.PEEK[HEADER.FIELDS (X-TUID)])", cmdp->uid, ctx->gen.uidnext - 1 );
 }
 
 /******************* imap_list_store *******************/