1 files changed, 50 insertions, 22 deletions

diff --git a/app.py b/app.py
index 1ae9760..dd3edfc 100755
--- a/app.py
+++ b/app.py
@@ -70,18 +70,23 @@ def hostname():
 
 
 class Response:
-    def __init__(self, data):
-        self.data = data
+    DEFAULT_STATUS = http.server.HTTPStatus.OK
+
+    @staticmethod
+    def body_from_json(body):
+        return json.dumps(body, ensure_ascii=False, indent=4)
+
+    def __init__(self, body, status=None):
+        if status is None:
+            status = Response.DEFAULT_STATUS
+        self.status = status
+        self.body = body
 
     def headers(self):
         yield 'Content-Type', 'text/html; charset=utf-8'
 
-    @staticmethod
-    def dump_json(data):
-        return json.dumps(data, ensure_ascii=False, indent=4)
-
-    def body(self):
-        return self.dump_json(self.data)
+    def encode_body(self):
+        return self.body.encode(errors='replace')
 
     def write_as_cgi_script(self):
         self.write_headers_as_cgi_script()
@@ -93,26 +98,31 @@ class Response:
         print()
 
     def write_body_as_cgi_script(self):
-        if self.data is not None:
-            print(self.body())
+        if self.body is not None:
+            print(self.body)
 
-    def write_as_request_handler(self, handler):
-        handler.send_response(http.server.HTTPStatus.OK)
-        self.write_headers_as_request_handler(handler)
-        self.write_body_as_request_handler(handler)
+    def write_to_request_handler(self, handler):
+        handler.send_response(self.status)
+        self.write_headers_to_request_handler(handler)
+        self.write_body_to_request_handler(handler)
 
-    def write_headers_as_request_handler(self, handler):
+    def write_headers_to_request_handler(self, handler):
         for name, val in self.headers():
             handler.send_header(name, val)
         handler.end_headers()
 
-    def write_body_as_request_handler(self, handler):
-        if self.data is not None:
-            handler.wfile.write(self.body().encode(errors='replace'))
+    def write_body_to_request_handler(self, handler):
+        if self.body is not None:
+            handler.wfile.write(self.encode_body())
 
 
 def run_do(*args, **kwargs):
     output = subprocess.run(args, stdin=DEVNULL, stdout=PIPE, stderr=STDOUT, universal_newlines=True, **kwargs)
+    # Include the output in the exception's message:
+    try:
+        output.check_returncode()
+    except Exception as e:
+        raise RuntimeError("Command's output was this:\n" + output.stdout) from e
     return output.stdout
 
 
@@ -195,7 +205,7 @@ class Loginctl(Systemd):
 class Task(abc.ABC):
     def complete(self):
         self.run()
-        return Response(self.result())
+        return Response(Response.body_from_json(self.result()))
 
     @abc.abstractmethod
     def run(self):
@@ -301,7 +311,10 @@ class UserInstanceStatusTaskList(Task):
             self.tasks = {user.name: UserInstanceStatusTask.su(user) for user in systemd_users()}
         else:
             # As a regular user, we can only query ourselves.
-            self.tasks = {get_current_user().name: UserInstanceStatusTask()}
+            self.tasks = {}
+            user = get_current_user()
+            if user_instance_active(user):
+                self.tasks[user.name] = UserInstanceStatusTask()
 
     def run(self):
         for task in self.tasks.values():
@@ -353,6 +366,19 @@ def get_current_user():
     return User(entry.pw_uid, entry.pw_name)
 
 
+def user_instance_active(user):
+    # I'm pretty sure this is the way to determine if the user instance is
+    # running?
+    # Source: https://www.freedesktop.org/software/systemd/man/user@.service.html
+    unit_name = f'user@{user.uid}.service'
+    cmd = Systemctl.system('is-active', unit_name, '--quiet')
+    try:
+        cmd.run().result()
+        return True
+    except Exception:
+        return False
+
+
 # A pitiful attempt to find a list of possibly-systemd-enabled users follows
 # (i.e. users that might be running a per-user systemd instance).
 # I don't know of a better way than probing /run/user/UID.
@@ -394,16 +420,18 @@ def systemd_users():
         for line in lines:
             # This assumes user names cannot contain spaces.
             # loginctl list-users output must be in the UID NAME format.
-            info = line.split(' ', 2)
+            info = line.lstrip().split(' ', 2)
             if len(info) < 2:
                 raise RuntimeError(f'invalid `loginctl list-users` output:\n{output}')
             uid, user = info[0], info[1]
             yield User(uid, user)
 
     def show_users(users):
+        user_args = [user.name for user in users]
+        if not user_args:
+            return None
         properties = 'UID', 'Name', 'RuntimePath'
         prop_args = (arg for prop in properties for arg in ('-p', prop))
-        user_args = (user.name for user in users)
         output = Loginctl('show-user', *prop_args, '--value', *user_args).run().result()
         lines = output.splitlines()
         # Assuming that for muptiple users, the properties will be separated by