nixos/tests/loki: use curl instead of promtail for log injection

This is in preparation of the promtail removal because promtail reached
its end of life.

nixos/tests/loki.nix

@@ -1,4 +1,4 @@
-{ lib, pkgs, ... }:
+{ pkgs, ... }:
 
 {
   name = "loki";
@@ -12,45 +12,26 @@
         enable = true;
         configFile = "${pkgs.grafana-loki.src}/cmd/loki/loki-local-config.yaml";
       };
-      services.promtail = {
-        enable = true;
-        configuration = {
-          server = {
-            http_listen_port = 9080;
-            grpc_listen_port = 0;
-          };
-          clients = [ { url = "http://localhost:3100/loki/api/v1/push"; } ];
-          scrape_configs = [
-            {
-              job_name = "system";
-              static_configs = [
-                {
-                  targets = [ "localhost" ];
-                  labels = {
-                    job = "varlogs";
-                    __path__ = "/var/log/*log";
-                  };
-                }
-              ];
-            }
-          ];
-        };
-      };
     };
 
   testScript = ''
+    import json
+    import time
+
     machine.start
     machine.wait_for_unit("loki.service")
-    machine.wait_for_unit("promtail.service")
     machine.wait_for_open_port(3100)
-    machine.wait_for_open_port(9080)
-    machine.succeed("echo 'Loki Ingestion Test' > /var/log/testlog")
-    # should not have access to journal unless specified
-    machine.fail(
-        "systemctl show --property=SupplementaryGroups promtail | grep -q systemd-journal"
-    )
-    machine.wait_until_succeeds(
-        "${pkgs.grafana-loki}/bin/logcli --addr='http://localhost:3100' query --no-labels '{job=\"varlogs\",filename=\"/var/log/testlog\"}' | grep -q 'Loki Ingestion Test'"
-    )
+
+    payload = json.dumps({
+        "streams": [{
+            "stream": {"job": "test"},
+            "values": [
+                [str(time.time_ns()), "Loki Ingestion Test"],
+            ],
+        }],
+    })
+    machine.succeed(f"curl --json '{payload}' http://localhost:3100/loki/api/v1/push")
+
+    machine.wait_until_succeeds("logcli query --no-labels '{job=\"test\"}' | grep -q 'Loki Ingestion Test'")
   '';
 }