Implement HeadObject handler

Signed-off-by: Evgeniy Kulikov <kim@nspcc.ru>

api/handler/head.go

@@ -0,0 +1,47 @@
+package handler
+
+import (
+	"net/http"
+	"strconv"
+
+	"github.com/gorilla/mux"
+	"github.com/nspcc-dev/neofs-s3-gate/api"
+	"github.com/nspcc-dev/neofs-s3-gate/api/layer"
+	"go.uber.org/zap"
+)
+
+func (h *handler) HeadObjectHandler(w http.ResponseWriter, r *http.Request) {
+	var (
+		err error
+		inf *layer.ObjectInfo
+
+		req = mux.Vars(r)
+		bkt = req["bucket"]
+		obj = req["object"]
+		rid = api.GetRequestID(r.Context())
+	)
+
+	if inf, err = h.obj.GetObjectInfo(r.Context(), bkt, obj); err != nil {
+		h.log.Error("could not fetch object info",
+			zap.String("request_id", rid),
+			zap.String("bucket_name", bkt),
+			zap.String("object_name", obj),
+			zap.Error(err))
+
+		api.WriteErrorResponse(r.Context(), w, api.Error{
+			Code:           api.GetAPIError(api.ErrInternalError).Code,
+			Description:    err.Error(),
+			HTTPStatusCode: http.StatusInternalServerError,
+		}, r.URL)
+
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
+
+	w.Header().Set("Content-Type", inf.ContentType)
+	w.Header().Set("Content-Length", strconv.FormatInt(inf.Size, 10))
+
+	w.Header().Set("Last-Modified", inf.Created.Format(http.TimeFormat))
+
+}