Function HeadObject

api/object.go:142–194

object-level API HeadObject returns the object properties; can be conventionally used to establish local (in cluster) presence.

(baseParams BaseParams, bck cmn.Bck, object string, checkExists ...bool)

// HeadObject returns the object properties; can be conventionally used to establish
// local (in cluster) presence.
func HeadObject(baseParams BaseParams, bck cmn.Bck, object string, checkExists ...bool) (*cmn.ObjectProps, error) {
	var (
		q             url.Values
		checkIsCached bool
	)
	if len(checkExists) > 0 {
		checkIsCached = checkExists[0]
	}
	baseParams.Method = http.MethodHead

	if checkIsCached {
		q = make(url.Values, 4)
		q = bck.AddToQuery(q)
		q.Set(apc.QparamHeadObj, strconv.Itoa(apc.HeadObjAvoidRemote)) // TODO: support the entire enum
		q.Set(apc.QparamSilent, "true")
	} else {
		q = bck.AddToQuery(nil)
	}

	reqParams := AllocRp()
	defer FreeRp(reqParams)
	{
		reqParams.BaseParams = baseParams
		reqParams.Path = apc.URLPathObjects.Join(bck.Name, object)
		reqParams.Query = q
	}
	resp, err := reqParams.doResp(nil)
	if err != nil {
		return nil, err
	}
	if checkIsCached {
		return nil, err
	}

	// NOTE: compare with `headObject()` in target.go
	// first, cnm.ObjAttrs
	op := &cmn.ObjectProps{}
	op.Cksum = op.ObjAttrs.FromHeader(resp.Header)
	// second, all the rest
	err = cmn.IterFields(op, func(tag string, field cmn.IterField) (error, bool) {
		headerName := cmn.PropToHeader(tag)
		// skip the missing ones
		if _, ok := resp.Header[textproto.CanonicalMIMEHeaderKey(headerName)]; !ok {
			return nil, false
		}
		// single-value
		return field.SetValue(resp.Header.Get(headerName), true /*force*/), false
	}, cmn.IterOpts{OnlyRead: false})
	if err != nil {
		return nil, err
	}
	return op, nil
}

// Given cos.SimpleKVs (map[string]string) keys and values, sets object's custom properties.
// By default, adds new or updates existing custom keys.