admin: allow disabling display of metrics

This is useful in situations where the admins of the Snikket
server (i.e. those who care for the docker containers) are not the
same people as the people who are admins of the Snikket service
(i.e. those who care for the users).

snikket_web/admin.py

@@ -20,6 +20,7 @@ from quart import (
     request,
     abort,
     flash,
+    current_app,
 )
 
 from flask_babel import lazy_gettext as _l, _
@@ -33,7 +34,11 @@ bp = Blueprint("admin", __name__, url_prefix="/admin")
 @bp.route("/")
 @client.require_admin_session()
 async def index() -> str:
-    return await render_template("admin_home.html")
+    show_metrics = current_app.config["SHOW_METRICS"]
+    return await render_template(
+        "admin_home.html",
+        show_metrics=show_metrics,
+    )
 
 
 class PasswordResetLinkPost(BaseForm):
@@ -575,7 +580,9 @@ def get_system_stats() -> typing.MutableMapping[
         (time.monotonic() - _MONOTONIC_EPOCH)
     )
 
+    mem_total, mem_available = None, None
     load5: typing.Optional[float] = None
+
     try:
         with open("/proc/loadavg") as f:
             stats = f.read().split()
@@ -583,7 +590,6 @@ def get_system_stats() -> typing.MutableMapping[
     except (ValueError, IndexError, TypeError, OSError):
         pass
 
-    mem_total, mem_available = None, None
     try:
         with open("/proc/meminfo") as f:
             for line in f:
@@ -650,37 +656,43 @@ async def system() -> typing.Union[str, quart.Response]:
             # redirect only if not previewing
             return redirect(url_for(".system"))
 
-    version = await client.get_server_version()
-    now = time.time()
-    try:
-        prosody_metrics = await client.get_system_metrics()
-    except quart.exceptions.NotFound:
-        # server does not offer the endpoint for whatever reason -- ignore
-        prosody_metrics = {}
+    version = None
+    now = None
+    show_metrics = current_app.config["SHOW_METRICS"]
+    if show_metrics:
+        version = await client.get_server_version()
+        now = time.time()
+        try:
+            prosody_metrics = await client.get_system_metrics()
+        except quart.exceptions.NotFound:
+            # server does not offer the endpoint for whatever reason -- ignore
+            prosody_metrics = {}
 
-    metrics = get_system_stats()
-    try:
-        prosody_cpu_metrics = prosody_metrics["cpu"]
-    except KeyError:
-        pass
+        metrics = get_system_stats()
+        try:
+            prosody_cpu_metrics = prosody_metrics["cpu"]
+        except KeyError:
+            pass
+        else:
+            metrics["prosody_cpu"] = (prosody_cpu_metrics["value"] /
+                                      (now - prosody_cpu_metrics["since"]))
+
+        try:
+            metrics["prosody_rss"] = prosody_metrics["memory"]
+        except KeyError:
+            pass
+
+        try:
+            metrics["prosody_devices"] = prosody_metrics["c2s"]
+        except KeyError:
+            pass
+
+        for k in list(metrics.keys()):
+            if metrics[k] is None:
+                # so that defaulting in jinja works
+                del metrics[k]
     else:
-        metrics["prosody_cpu"] = (prosody_cpu_metrics["value"] /
-                                  (now - prosody_cpu_metrics["since"]))
-
-    try:
-        metrics["prosody_rss"] = prosody_metrics["memory"]
-    except KeyError:
-        pass
-
-    try:
-        metrics["prosody_devices"] = prosody_metrics["c2s"]
-    except KeyError:
-        pass
-
-    for k in list(metrics.keys()):
-        if metrics[k] is None:
-            # so that defaulting in jinja works
-            del metrics[k]
+        metrics = {}
 
     return await render_template(
         "admin_system.html",
@@ -688,4 +700,5 @@ async def system() -> typing.Union[str, quart.Response]:
         version=_version.version,
         prosody_version=version,
         form=form,
+        show_metrics=show_metrics,
     )