CRI: Add host networking helper

We do a ton of host networking checks around the CRI plugin, all mainly
doing the same thing of checking the different quirks on various platforms
(for windows are we a HostProcess pod, for linux is namespace mode the
right thing, darwin doesn't have CNI support etc.) which could all be
bundled up into a small helper that can be re-used.

Signed-off-by: Danny Canter <danny@dcantah.dev>

pkg/cri/server/helpers.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"path"
 	"path/filepath"
+	goruntime "runtime"
 	"strconv"
 	"strings"
 	"time"
@@ -582,3 +583,22 @@ func (c *criService) getContainerStatuses(ctx context.Context, podSandboxID stri
 	}
 	return containerStatuses, nil
 }
+
+// hostNetwork handles checking if host networking was requested.
+func hostNetwork(config *runtime.PodSandboxConfig) bool {
+	var hostNet bool
+	switch goruntime.GOOS {
+	case "windows":
+		// Windows HostProcess pods can only run on the host network
+		hostNet = config.GetWindows().GetSecurityContext().GetHostProcess()
+	case "darwin":
+		// No CNI on Darwin yet.
+		hostNet = true
+	default:
+		// Even on other platforms, the logic containerd uses is to check if NamespaceMode == NODE.
+		// So this handles Linux, as well as any other platforms not governed by the cases above
+		// that have special quirks.
+		hostNet = config.GetLinux().GetSecurityContext().GetNamespaceOptions().GetNetwork() == runtime.NamespaceMode_NODE
+	}
+	return hostNet
+}