Added workspace ID in GET_WORKSPACES response.

docs/ipc

@@ -164,6 +164,10 @@ sending a reply. Expect the socket to be shut down.
 The reply consists of a serialized list of workspaces. Each workspace has the
 following properties:
 
+id (integer)::
+	The internal ID (actually a C pointer value) of this container. Do not
+	make any assumptions about it. You can use it to (re-)identify and
+	address containers when talking to i3.
 num (integer)::
 	The logical number of the workspace. Corresponds to the command
 	to switch to this workspace. For named workspaces, this will be -1.

i3bar/include/workspaces.h

@@ -30,6 +30,7 @@ void parse_workspaces_json(char *json);
 void free_workspaces(void);
 
 struct i3_ws {
+    uintptr_t id;             /* Workspace ID - C pointer to a workspace container */
     int num;                  /* The internal number of the ws */
     char *canonical_name;     /* The true name of the ws according to the ipc */
     i3String *name;           /* The name of the ws that is displayed on the bar */

i3bar/src/workspaces.c

@@ -61,6 +61,12 @@ static int workspaces_boolean_cb(void *params_, int val) {
 static int workspaces_integer_cb(void *params_, long long val) {
     struct workspaces_json_params *params = (struct workspaces_json_params *)params_;
 
+    if (!strcmp(params->cur_key, "id")) {
+        params->workspaces_walk->id = val;
+        FREE(params->cur_key);
+        return 1;
+    }
+
     if (!strcmp(params->cur_key, "num")) {
         params->workspaces_walk->num = (int)val;
         FREE(params->cur_key);

src/ipc.c

@@ -906,6 +906,9 @@ IPC_HANDLER(get_workspaces) {
             assert(ws->type == CT_WORKSPACE);
             y(map_open);
 
+            ystr("id");
+            y(integer, (uintptr_t)ws);
+
             ystr("num");
             y(integer, ws->num);