JSON: avoid integer underflow in dir in orders.

Reported by Lexxie

See osdn #42595

freeciv/apply_patches.sh

@@ -5,6 +5,7 @@
 
 # Not in the upstream Freeciv server
 # ----------------------------------
+# 0001-JSON-avoid-integer-underflow-on-orders is osdn #42595
 # freeciv_segfauls_fix is a workaround some segfaults in the Freeciv server. Freeciv bug #23884.
 # message_escape is a patch for protecting against script injection in the message texts.
 # tutorial_ruleset changes the ruleset of the tutorial to one supported by Freeciv-web.
@@ -24,6 +25,7 @@
 # endgame-mapimg is used to generate a mapimg at endgame for hall of fame.
 
 declare -a PATCHLIST=(
+  "0001-JSON-avoid-integer-underflow-on-orders"
   "city_impr_fix2"
   "city-naming-change"
   "metachange"

freeciv/patches/0001-JSON-avoid-integer-underflow-on-orders.patch

@@ -0,0 +1,33 @@
+From 0e7309cd1645feb250df3fb211dacb1a23006b61 Mon Sep 17 00:00:00 2001
+From: Sveinung Kvilhaugsvik <[email protected]>
+Date: Fri, 2 Jul 2021 10:02:30 +0200
+Subject: [PATCH] JSON: avoid integer underflow in dir in orders.
+
+Reported by Lexxie
+
+See osdn #42595
+---
+ common/networking/dataio_json.c | 7 ++++++-
+ 1 file changed, 6 insertions(+), 1 deletion(-)
+
+diff --git a/common/networking/dataio_json.c b/common/networking/dataio_json.c
+index 90eb2a2996..8f8d67a853 100644
+--- a/common/networking/dataio_json.c
++++ b/common/networking/dataio_json.c
+@@ -289,7 +289,12 @@ void dio_put_unit_order_json(struct json_data_out *dout,
+     json_object_set_new(obj, "target", json_integer(order->target));
+     json_object_set_new(obj, "sub_target", json_integer(order->sub_target));
+     json_object_set_new(obj, "action", json_integer(order->action));
+-    json_object_set_new(obj, "dir", json_integer(order->dir));
++    if (order->dir == -1) {
++      /* Avoid integer underflow */
++      json_object_set_new(obj, "dir", json_integer(-1));
++    } else {
++      json_object_set_new(obj, "dir", json_integer(order->dir));
++    }
+     plocation_write_data(dout->json, location, obj);
+   } else {
+     dio_put_unit_order_raw(&dout->raw, order);
+-- 
+2.30.2
+