restructure check handlers

Signed-off-by: Christian Richter <crichter@owncloud.com>

ocis-pkg/handlers/checker.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"io"
 	"maps"
-	"net"
 	"net/http"
 
 	"golang.org/x/sync/errgroup"
@@ -92,7 +91,7 @@ func (h *CheckHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	g.SetLimit(h.conf.limit)
 
 	for name, check := range h.conf.checks {
-		g.Go(func() error {
+		g.Go(func() error { // https://go.dev/blog/loopvar-preview per iteration scope since go 1.22
 			if err := check(ctx); err != nil { // since go 1.22 for loops have a per-iteration scope instead of per-loop scope, no need to pin the check...
 				return fmt.Errorf("'%s': %w", name, err)
 			}
@@ -114,16 +113,3 @@ func (h *CheckHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		h.conf.logger.Panic().Err(err).Msg("failed to write response")
 	}
 }
-
-// NewTCPCheck returns a check that connects to a given tcp endpoint.
-func NewTCPCheck(address string) func(ctx context.Context) error {
-	return func(ctx context.Context) error {
-		conn, err := net.Dial("tcp", address)
-		if err != nil {
-			return err
-		}
-		defer conn.Close()
-
-		return nil
-	}
-}

ocis-pkg/handlers/checknats.go

@@ -0,0 +1,23 @@
+package handlers
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/nats-io/nats.go"
+)
+
+// NewNatsCheck checks the reachability of a nats server.
+func NewNatsCheck(natsCluster string, options ...nats.Option) func(context.Context) error {
+	return func(ctx context.Context) error {
+		n, err := nats.Connect(natsCluster, options...)
+		if err != nil {
+			return fmt.Errorf("could not connect to nats server: %v", err)
+		}
+		defer n.Close()
+		if n.Status() != nats.CONNECTED {
+			return fmt.Errorf("nats server not connected")
+		}
+		return nil
+	}
+}

ocis-pkg/handlers/checktcp.go

@@ -0,0 +1,23 @@
+package handlers
+
+import (
+	"context"
+	"net"
+)
+
+// NewTCPCheck returns a check that connects to a given tcp endpoint.
+func NewTCPCheck(address string) func(ctx context.Context) error {
+	return func(ctx context.Context) error {
+		conn, err := net.Dial("tcp", address)
+		if err != nil {
+			return err
+		}
+
+		err = conn.Close()
+		if err != nil {
+			return err
+		}
+		
+		return nil
+	}
+}