[WIP] API middleware handler to update network list

API middleware handler to update memory list of networks if
Config.Network.NetworkConfigDir is newer.

Fixes containers#11828

Signed-off-by: Jhon Honce <[email protected]>

pkg/api/server/handler_cache_networks.go

@@ -0,0 +1,55 @@
+package server
+
+import (
+	"net/http"
+	"os"
+	"sync"
+
+	"github.com/containers/podman/v3/libpod"
+	api "github.com/containers/podman/v3/pkg/api/types"
+	"github.com/gorilla/mux"
+	"github.com/sirupsen/logrus"
+)
+
+var (
+	previousNetworkUpdate os.FileInfo
+	networkUpdateSync     sync.Once
+)
+
+// cacheNetworksHandler refreshes the in-memory network cache if the
+// network configuration directory has been changed
+func cacheNetworksHandler() mux.MiddlewareFunc {
+	return func(h http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			runtime := r.Context().Value(api.RuntimeKey).(*libpod.Runtime)
+			cfg, err := runtime.GetConfig()
+			if err != nil {
+				logrus.Infof("Failed to retrieve podman configuration: %v", err)
+			} else {
+				netCfg := cfg.Network.NetworkConfigDir
+
+				// First pass of this handler is for initialization.
+				// 1+ passes will update memory network cache/configuration if the modification
+				// time of the network configuration directory changes.
+				networkUpdateSync.Do(func() {
+					var err error
+					previousNetworkUpdate, err = os.Stat(netCfg)
+					logrus.Infof("Failed to access %q: %v", netCfg, err)
+				})
+
+				if now, err := os.Stat(netCfg); err != nil {
+					logrus.Infof("Failed to access %q: %v", netCfg, err)
+				} else {
+					if now.ModTime().After(previousNetworkUpdate.ModTime()) {
+						//
+						// Reload network cache/configuration
+						//
+						previousNetworkUpdate = now
+					}
+				}
+			}
+
+			h.ServeHTTP(w, r)
+		})
+	}
+}