// JoinLoaders - joins multiple loaders into a single loader. The returned
// loader will call each of the given loaders in order. If any of the loaders
// return an error, the returned loader will return that error.
func JoinLoaders(loaders ...MetricsLoaderFn) MetricsLoaderFn {
	return func(ctx context.Context, m MetricValues, c *metricsCache) error {
		for _, loader := range loaders {
			if err := loader(ctx, m, c); err != nil {

	// ErrIncompatibleEncryptionMethod indicates that both SSE-C headers and SSE-S3 headers were specified, and are incompatible
	// The client needs to remove the SSE-S3 header or the SSE-C headers
	ErrIncompatibleEncryptionMethod = Errorf("Server side encryption specified with both SSE-C and SSE-S3 headers")

	Type() types.TargetType
}

var (

	// systemTargets is the set of enabled loggers.
	// Must be immutable at all times.
	// Can be swapped to another while holding swapMu
	systemTargets  = []Target{}
	swapSystemMuRW sync.RWMutex

	// auditTargets is the list of enabled audit loggers
	// Must be immutable at all times.
	// Can be swapped to another while holding swapMu
	auditTargets  = []Target{}

	objInfo, err := getObjectInfo(ctx, bucket, object, gopts)
	if err != nil {
		// Versioning enabled quite possibly object is deleted might be delete-marker
		// if present set the headers, no idea why AWS S3 sets these headers.
		if objInfo.VersionID != "" && objInfo.DeleteMarker {
			w.Header()[xhttp.AmzVersionID] = []string{objInfo.VersionID}
			w.Header()[xhttp.AmzDeleteMarker] = []string{strconv.FormatBool(objInfo.DeleteMarker)}

			return
		}
		if globalBucketVersioningSys.PrefixEnabled(srcBucket, srcObject) && gr != nil {
			// Versioning enabled quite possibly object is deleted might be delete-marker
			// if present set the headers, no idea why AWS S3 sets these headers.
			if gr.ObjInfo.VersionID != "" && gr.ObjInfo.DeleteMarker {
				w.Header()[xhttp.AmzVersionID] = []string{gr.ObjInfo.VersionID}

	doneCh := make(chan error, 1)
	defer xioutil.SafeClose(doneCh)

	// Save rebalance.bin periodically.
	go func() {
		// Update rebalance.bin periodically once every 5-10s, chosen randomly
		// to avoid multiple pool leaders herding to update around the same
		// time.
		r := rand.New(rand.NewSource(time.Now().UnixNano()))
		randSleepFor := func() time.Duration {
			return 5*time.Second + time.Duration(float64(5*time.Second)*r.Float64())
		}

	// handler for validating incoming authorization headers.
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		tc, ok := r.Context().Value(mcontext.ContextTraceKey).(*mcontext.TraceCtxt)

		aType := getRequestAuthType(r)
		switch aType {
		case authTypeSigned, authTypeSignedV2, authTypeStreamingSigned, authTypeStreamingSignedTrailer:
			// Verify if date headers are set, if not reject the request

			readers[index] = newBitrotReader(disk, metaArr[index].Data, bucket, partPath, tillOffset,
				checksumInfo.Algorithm, checksumInfo.Hash, erasure.ShardSize())

			// Prefer local disks
			prefer[index] = disk.Hostname() == ""
		}

		written, err := erasure.Decode(ctx, writer, readers, partOffset, partLength, partSize, prefer)

		Code:           "KeyTooLongError",
		Description:    "Your key is too long",
		HTTPStatusCode: http.StatusBadRequest,
	},
	ErrUnsignedHeaders: {
		Code:           "AccessDenied",
		Description:    "There were headers present in the request which were not signed",
		HTTPStatusCode: http.StatusBadRequest,
	},
	ErrInvalidQueryParams: {
		Code:           "AuthorizationQueryParametersError",

	got, err := scanDataFolder(context.Background(), nil, base, dataUsageCache{Info: dataUsageCacheInfo{Name: "bucket"}}, getSize, 0, weSleep)
	if err != nil {
		t.Fatal(err)
	}
	if got.root() == nil {
		t.Log("cached folders:")
		for folder := range got.Cache {
			t.Log("folder:", folder)
		}
		t.Fatal("got nil root.")
	}

	// Test dirs
	want := []struct {
		path       string
		isNil      bool
		size, objs int