Implement support for swaymsg -t SUBSCRIBE [-m]

In `i3 4.16`, `i3-msg` can be used with the message type `subscribe`
and has the ability to monitor for responses until killed. This adds
support for both to swaymsg.

If the JSON array of event types is malformed or contains an invalid
event, sway will send a response with `success` set to `false`. If
swaymsg sees this, it will not display the failure and exit.

If the `subscribe` event is successful, swaymsg will wait for the first
response and display that instead of the success message. If
`-m/--monitor` is given, swaymsg will continue monitor for responses
until killed or a malformed response is received.

For the `subscribe` event, the responses will always be printed as JSON.
If `-r/--raw` is given, the JSON will not be pretty printed, which may
be preferred when monitoring due to there being multiple responses.

Example: `swaymsg -t SUBSCRIBE -m "['window']"`

1 files changed, 11 insertions, 0 deletions

diff --git a/swaymsg/swaymsg.1.scd b/swaymsg/swaymsg.1.scd
index eaac8105..f55f86a9 100644
--- a/swaymsg/swaymsg.1.scd
+++ b/swaymsg/swaymsg.1.scd
@@ -13,6 +13,12 @@ _swaymsg_ [options...] [message]
 *-h, --help*
         Show help message and quit.
 
+*-m, --monitor*
+        Monitor for responses until killed instead of exiting after the first
+        response. This can only be used with the IPC message type _subscribe_. If
+        there is a malformed response or an invalid event type was requested,
+        swaymsg will stop monitoring and exit.
+
 *-q, --quiet*
         Sends the IPC message but does not print the response from sway.
 
@@ -71,3 +77,8 @@ _swaymsg_ [options...] [message]
 
 *send\_tick*
         Sends a tick event to all subscribed clients.
+
+*subscribe*
+        Subscribe to a list of event types. The argument for this type should be
+        provided in the form of a valid JSON array. If any of the types are invalid
+        or if an valid JSON array is not provided, this will result in an failure.