awful.spawn: Use LGI's Async facilities

Normally, writing asynchronous code with Gio results in an awful mess of
spaghetti code, because every operation needs a callback that is called when
this operation is done. To improve upon this, LGI provides some magic with
coroutines that hide the asyncronous nature of things and you end up with
"normal looking" code.

Use this Gio.Async facility in awful.spawn to make the code easier to follow.

Signed-off-by: Uli Schlachter <uli.schlachter@informatik.uni-oldenburg.de>

lib/awful/spawn.lua

@@ -161,7 +161,6 @@ local capi =
 }
 local lgi = require("lgi")
 local Gio = lgi.Gio
-local GLib = lgi.GLib
 local util   = require("awful.util")
 local protected_call = require("gears.protected_call")
 
@@ -370,6 +369,33 @@ function spawn.easy_async(cmd, callback)
     })
 end
 
+local function read_stream(stream, line_callback, done_callback, close)
+    while true do
+        local line, length = stream:async_read_line()
+
+        if type(length) ~= "number" then
+            -- Error
+            print("Error in awful.spawn.read_lines:", tostring(length))
+            break
+        elseif end_of_file(line, length) then
+            -- End of file
+            break
+        else
+            -- Read a line
+            -- This needs tostring() for older lgi versions which returned
+            -- "GLib.Bytes" instead of Lua strings (I guess)
+            protected_call(line_callback, tostring(line))
+        end
+    end
+
+    if close then
+        stream:async_close()
+    end
+    if done_callback then
+        protected_call(done_callback)
+    end
+end
+
 --- Read lines from a Gio input stream
 -- @tparam Gio.InputStream input_stream The input stream to read from.
 -- @tparam function line_callback Function that is called with each line
@@ -379,38 +405,7 @@ end
 -- @tparam[opt=false] boolean close Should the stream be closed after end-of-file?
 function spawn.read_lines(input_stream, line_callback, done_callback, close)
     local stream = Gio.DataInputStream.new(input_stream)
-    local function done()
+    Gio.Async.start(read_stream)(stream, line_callback, done_callback, close)
-        if close then
-            stream:close()
-        end
-        if done_callback then
-            protected_call(done_callback)
-        end
-    end
-    local start_read, finish_read
-    start_read = function()
-        stream:read_line_async(GLib.PRIORITY_DEFAULT, nil, finish_read)
-    end
-    finish_read = function(obj, res)
-        local line, length = obj:read_line_finish(res)
-        if type(length) ~= "number" then
-            -- Error
-            print("Error in awful.spawn.read_lines:", tostring(length))
-            done()
-        elseif end_of_file(line, length) then
-            -- End of file
-            done()
-        else
-            -- Read a line
-            -- This needs tostring() for older lgi versions which returned
-            -- "GLib.Bytes" instead of Lua strings (I guess)
-            protected_call(line_callback, tostring(line))
-
-            -- Read the next line
-            start_read()
-        end
-    end
-    start_read()
 end
 
 capi.awesome.connect_signal("spawn::canceled" , spawn.on_snid_cancel   )