Added new extension "sync"

Periodically poll registries and pull images according to sync's config
Added sync on demand, syncing when clients asks for an image which
zot doesn't have.

Signed-off-by: Petu Eusebiu <peusebiu@cisco.com>

pkg/extensions/sync/http_handler.go

@@ -0,0 +1,60 @@
+package sync
+
+import (
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/anuvu/zot/pkg/log"
+)
+
+type PostHandler struct {
+	Address    string
+	Port       string
+	ServerCert string
+	ServerKey  string
+	CACert     string
+	Cfg        Config
+	Log        log.Logger
+}
+
+func (h *PostHandler) Handler(w http.ResponseWriter, r *http.Request) {
+	upstreamCtx, policyCtx, err := getLocalContexts(h.ServerCert, h.ServerKey, h.CACert, h.Log)
+	if err != nil {
+		WriteData(w, http.StatusInternalServerError, err.Error())
+
+		return
+	}
+
+	defer policyCtx.Destroy() //nolint: errcheck
+
+	var credentialsFile CredentialsFile
+
+	if h.Cfg.CredentialsFile != "" {
+		credentialsFile, err = getFileCredentials(h.Cfg.CredentialsFile)
+		if err != nil {
+			h.Log.Error().Err(err).Msgf("couldn't get registry credentials from %s", h.Cfg.CredentialsFile)
+			WriteData(w, http.StatusInternalServerError, err.Error())
+		}
+	}
+
+	localRegistryName := strings.Replace(fmt.Sprintf("%s:%s", h.Address, h.Port), "0.0.0.0", "127.0.0.1", 1)
+
+	for _, regCfg := range h.Cfg.Registries {
+		upstreamRegistryName := strings.Replace(strings.Replace(regCfg.URL, "http://", "", 1), "https://", "", 1)
+
+		if err := syncRegistry(regCfg, h.Log, localRegistryName, upstreamCtx, policyCtx,
+			credentialsFile[upstreamRegistryName]); err != nil {
+			h.Log.Err(err).Msg("error while syncing")
+			WriteData(w, http.StatusInternalServerError, err.Error())
+		}
+	}
+
+	WriteData(w, http.StatusOK, "")
+}
+
+func WriteData(w http.ResponseWriter, status int, msg string) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	_, _ = w.Write([]byte(msg))
+}