cockpit: Implement PCP metrics channel in the Python bridge

The Python bridge still used the separate `cockpit-pcp` bridge for
metrics gathering. For us to remove the full C bridge implementation the
separate PCP bridge also has to be rewritten.

This rewrite is a more or less Python copy of the C implementation using
the Python PCP module. Even though the Python PCP module offers a
"higher level" fetchGroup API but preliminary testing has found this has
some issues with changing multi instance values and instances can not be
omitted with a fetch group (but this can be done in our own code)

Co-Authored-By: Allison Karlitskaya <[email protected]>
Co-Authored-By: Tomas Matus <[email protected]>

pkg/pcp/manifest.json

@@ -1,11 +1,5 @@
 {
     "requires": {
         "cockpit": "239"
-    },
-    "bridges": [
-        {
-            "match": { "payload": "metrics1" },
-            "spawn": [ "${libexecdir}/cockpit-pcp" ]
-        }
-    ]
+    }
 }

pyproject.toml

@@ -31,6 +31,10 @@ module = [
     "libvirt_qemu",
     "pika",
 
+    # run without pcp module types
+    "pcp",
+    "cpmapi",
+
     # run without gobject-introspection (used from cockpit-client for Gtk)
     "gi.*",
 
@@ -158,6 +162,7 @@ ignore_names = [
    "do_*",
    "pytest_*",
    "test[A-Z0-9]*",
+   "pytestmark",
 ]
 ignore_decorators = [
    "@*.getter",
@@ -200,6 +205,8 @@ wheel_build_env = pkg
 # All other environments (names like py311-lint, py36-pytest, etc) are isolated
 # from the system and get their packages from PyPI, according to the specific
 # test environment being requested.  We build the wheel in a common environment.
+# These tests will not run the PCP tests as there is no wheel available.
+# https://github.com/performancecopilot/pcp/issues/2076
 [testenv]
 package = wheel
 wheel_build_env = venv-pkg

src/cockpit/channels/__init__.py

@@ -20,6 +20,7 @@
 from .http import HttpChannel
 from .metrics import InternalMetricsChannel
 from .packages import PackagesChannel
+from .pcp import PcpMetricsChannel
 from .stream import SocketStreamChannel, SubprocessStreamChannel
 from .trivial import EchoChannel, NullChannel
 
@@ -35,6 +36,7 @@
     InternalMetricsChannel,
     NullChannel,
     PackagesChannel,
+    PcpMetricsChannel,
     SubprocessStreamChannel,
     SocketStreamChannel,
 ]