fix: close idle OTLP connections before the collector does (#184)

otel_test.go

@@ -0,0 +1,22 @@
+package otelsetup
+
+import (
+	"net/http"
+	"testing"
+	"time"
+)
+
+func TestOTLPHTTPClient_ClosesIdleConnectionsBeforeTheCollector(t *testing.T) {
+	c := otlpHTTPClient()
+	tr, ok := c.Transport.(*http.Transport)
+	if !ok {
+		t.Fatalf("transport is %T, want *http.Transport", c.Transport)
+	}
+	// Alloy's OTLP receiver closes connections idle for 1m; the client must close first.
+	if tr.IdleConnTimeout <= 0 || tr.IdleConnTimeout >= time.Minute {
+		t.Errorf("IdleConnTimeout = %v, want in (0, 1m)", tr.IdleConnTimeout)
+	}
+	if c.Timeout != 10*time.Second {
+		t.Errorf("Timeout = %v, want 10s (the exporters' default)", c.Timeout)
+	}
+}