i3-msg hack to implement the "SUBSCRIBE" message type

i3-msg-subscribe.patch

diff --git a/i3-msg/main.c b/i3-msg/main.c
index 354e8af..a1af25c 100644
--- a/i3-msg/main.c
+++ b/i3-msg/main.c
@@ -124,16 +124,18 @@ int main(int argc, char *argv[]) {
     uint32_t message_type = I3_IPC_MESSAGE_TYPE_COMMAND;
     char *payload = NULL;
     bool quiet = false;
+    bool monitor = false;
 
     static struct option long_options[] = {
         {"socket", required_argument, 0, 's'},
         {"type", required_argument, 0, 't'},
         {"version", no_argument, 0, 'v'},
         {"quiet", no_argument, 0, 'q'},
+        {"monitor", no_argument, 0, 'm'},
         {"help", no_argument, 0, 'h'},
         {0, 0, 0, 0}};
 
-    char *options_string = "s:t:vhq";
+    char *options_string = "s:t:vhqm";
 
     while ((o = getopt_long(argc, argv, options_string, long_options, &option_index)) != -1) {
         if (o == 's') {
@@ -145,6 +147,8 @@ int main(int argc, char *argv[]) {
                 message_type = I3_IPC_MESSAGE_TYPE_COMMAND;
             else if (strcasecmp(optarg, "get_workspaces") == 0)
                 message_type = I3_IPC_MESSAGE_TYPE_GET_WORKSPACES;
+            else if (strcasecmp(optarg, "subscribe") == 0)
+                message_type = I3_IPC_MESSAGE_TYPE_SUBSCRIBE;
             else if (strcasecmp(optarg, "get_outputs") == 0)
                 message_type = I3_IPC_MESSAGE_TYPE_GET_OUTPUTS;
             else if (strcasecmp(optarg, "get_tree") == 0)
@@ -157,17 +161,19 @@ int main(int argc, char *argv[]) {
                 message_type = I3_IPC_MESSAGE_TYPE_GET_VERSION;
             else {
                 printf("Unknown message type\n");
-                printf("Known types: command, get_workspaces, get_outputs, get_tree, get_marks, get_bar_config, get_version\n");
+                printf("Known types: command, get_workspaces, subscribe, get_outputs, get_tree, get_marks, get_bar_config, get_version\n");
                 exit(EXIT_FAILURE);
             }
         } else if (o == 'q') {
             quiet = true;
+        } else if (o == 'm') {
+            monitor = true;
         } else if (o == 'v') {
             printf("i3-msg " I3_VERSION "\n");
             return 0;
         } else if (o == 'h') {
             printf("i3-msg " I3_VERSION "\n");
-            printf("i3-msg [-s <socket>] [-t <type>] <message>\n");
+            printf("i3-msg [-s <socket>] [-t <type>] [-m] <message>\n");
             return 0;
         }
     }
@@ -219,16 +225,19 @@ int main(int argc, char *argv[]) {
     uint32_t reply_type;
     uint8_t *reply;
     int ret;
+recv:
     if ((ret = ipc_recv_message(sockfd, &reply_type, &reply_length, &reply)) != 0) {
         if (ret == -1)
             err(EXIT_FAILURE, "IPC: read()");
         exit(1);
     }
-    if (reply_type != message_type)
+
+    /* For events, the highest bit of the message type is set to 1. */
+    if (reply_type != message_type && (message_type == I3_IPC_MESSAGE_TYPE_SUBSCRIBE && !(reply_type >> 31)))
         errx(EXIT_FAILURE, "IPC: Received reply of type %d but expected %d", reply_type, message_type);
-    /* For the reply of commands, have a look if that command was successful.
+    /* For the reply of commands or subscribes, have a look if that command was successful.
      * If not, nicely format the error message. */
-    if (reply_type == I3_IPC_MESSAGE_TYPE_COMMAND) {
+    if (reply_type == I3_IPC_MESSAGE_TYPE_COMMAND || reply_type == I3_IPC_MESSAGE_TYPE_SUBSCRIBE) {
         yajl_handle handle;
         handle = yajl_alloc(&reply_callbacks, NULL, NULL);
         yajl_status state = yajl_parse(handle, (const unsigned char *)reply, reply_length);
@@ -246,6 +255,9 @@ int main(int argc, char *argv[]) {
     printf("%.*s\n", reply_length, reply);
     free(reply);
 
+    if (reply_type == I3_IPC_MESSAGE_TYPE_SUBSCRIBE || monitor)
+        goto recv;
+
     close(sockfd);
 
     return 0;