feat(loadtest): sync add real 500-session capacity harness

internal/loadharness/server_metrics_test.go

@@ -0,0 +1,33 @@
+package loadharness
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestServerMetricsScrapeSelectsBoundedCapacitySignals(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		fmt.Fprintln(w, `telesrv_mtproto_raw_connections 500`)
+		fmt.Fprintln(w, `telesrv_mtproto_sessions{state="active"} 499`)
+		fmt.Fprintln(w, `telesrv_mtproto_sessions{state="provisional"} 1`)
+		for i := 0; i < 256; i++ {
+			fmt.Fprintf(w, "telesrv_mtproto_rpc_result_wire_bytes_total{method=%q} 1\n", fmt.Sprintf("method-%d", i))
+		}
+		fmt.Fprintln(w, `unrelated_high_cardinality{user_id="secret"} 1`)
+	}))
+	defer server.Close()
+	client := newServerMetricsClient(server.URL)
+	values, err := client.scrape(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if values["telesrv_mtproto_raw_connections"] != 500 || values["telesrv_mtproto_sessions"] != 500 || values["telesrv_mtproto_rpc_result_wire_bytes_total"] != 256 {
+		t.Fatalf("values = %#v", values)
+	}
+	if len(values) != 3 || client.successes() != 1 || client.failures() != 0 {
+		t.Fatalf("bounded values/scrapes = %#v, %d/%d", values, client.successes(), client.failures())
+	}
+}