diff --git a/cdn/supervisor/task/manager.go b/cdn/supervisor/task/manager.go
index caa2836c6..f55a0e6eb 100644
--- a/cdn/supervisor/task/manager.go
+++ b/cdn/supervisor/task/manager.go
@@ -202,14 +202,14 @@ func (tm *Manager) AddOrUpdate(registerTask *types.SeedTask) (seedTask *types.Se
 		synclock.UnLock(registerTask.TaskID, true)
 		return nil, errors.Wrapf(errTaskIDConflict, "register task %#v is conflict with exist task %#v", registerTask, seedTask)
 	}
-	if seedTask.SourceFileLength != source.UnKnownSourceFileLen {
+	if seedTask.SourceFileLength != source.UnknownSourceFileLen {
 		synclock.UnLock(registerTask.TaskID, true)
 		return seedTask, nil
 	}
 	synclock.UnLock(registerTask.TaskID, true)
 	synclock.Lock(registerTask.TaskID, false)
 	defer synclock.UnLock(registerTask.TaskID, false)
-	if seedTask.SourceFileLength != source.UnKnownSourceFileLen {
+	if seedTask.SourceFileLength != source.UnknownSourceFileLen {
 		return seedTask, nil
 	}
 	// get sourceContentLength with req.Header
diff --git a/cdn/types/seed_task_info.go b/cdn/types/seed_task_info.go
index 7718ef891..e6f20dd60 100644
--- a/cdn/types/seed_task_info.go
+++ b/cdn/types/seed_task_info.go
@@ -56,7 +56,7 @@ func NewSeedTask(taskID string, rawURL string, urlMeta *base.UrlMeta) *SeedTask
 		RequestDigest:    urlMeta.Digest,
 		URL:              rawURL,
 		TaskURL:          urlutils.FilterURLParam(rawURL, strings.Split(urlMeta.Filter, "&")),
-		SourceFileLength: source.UnKnownSourceFileLen,
+		SourceFileLength: source.UnknownSourceFileLen,
 		CdnFileLength:    0,
 		PieceSize:        0,
 		Range:            urlMeta.Range,
diff --git a/client/daemon/peer/piece_manager.go b/client/daemon/peer/piece_manager.go
index 2a823a292..4e5f41e30 100644
--- a/client/daemon/peer/piece_manager.go
+++ b/client/daemon/peer/piece_manager.go
@@ -355,7 +355,7 @@ func (pm *pieceManager) DownloadSource(ctx context.Context, pt Task, request *sc
 	if err != nil {
 		log.Warnf("get content length error: %s for %s", err, request.Url)
 	}
-	if contentLength == -1 {
+	if contentLength < 0 {
 		log.Warnf("can not get content length for %s", request.Url)
 	} else {
 		err = pm.storageManager.UpdateTask(ctx,
@@ -391,7 +391,7 @@ func (pm *pieceManager) DownloadSource(ctx context.Context, pt Task, request *sc
 	// 2. save to storage
 	pieceSize := pm.computePieceSize(contentLength)
 	// handle resource which content length is unknown
-	if contentLength == -1 {
+	if contentLength < 0 {
 		var n int64
 		for pieceNum := int32(0); ; pieceNum++ {
 			size := pieceSize
diff --git a/pkg/source/hdfsprotocol/hdfs_source_client.go b/pkg/source/hdfsprotocol/hdfs_source_client.go
index b0c0e1f39..71944a9b9 100644
--- a/pkg/source/hdfsprotocol/hdfs_source_client.go
+++ b/pkg/source/hdfsprotocol/hdfs_source_client.go
@@ -80,11 +80,11 @@ type HDFSSourceClientOption func(p *hdfsSourceClient)
 func (h *hdfsSourceClient) GetContentLength(request *source.Request) (int64, error) {
 	hdfsClient, path, err := h.getHDFSClientAndPath(request.URL)
 	if err != nil {
-		return source.UnKnownSourceFileLen, err
+		return source.UnknownSourceFileLen, err
 	}
 	info, err := hdfsClient.Stat(path)
 	if err != nil {
-		return source.UnKnownSourceFileLen, err
+		return source.UnknownSourceFileLen, err
 	}
 	return info.Size(), nil
 }
diff --git a/pkg/source/hdfsprotocol/hdfs_source_client_test.go b/pkg/source/hdfsprotocol/hdfs_source_client_test.go
index 8bfdc0620..e0b6bed4b 100644
--- a/pkg/source/hdfsprotocol/hdfs_source_client_test.go
+++ b/pkg/source/hdfsprotocol/hdfs_source_client_test.go
@@ -51,7 +51,7 @@ const (
 
 const (
 	hdfsNotExistFileURL                 = "hdfs://127.0.0.1:9000/user/root/input/f3.txt"
-	hdfsNotExistFileContentLength int64 = source.UnKnownSourceFileLen
+	hdfsNotExistFileContentLength int64 = source.UnknownSourceFileLen
 )
 
 var fakeHDFSClient = &hdfs.Client{}
diff --git a/pkg/source/httpprotocol/http_source_client.go b/pkg/source/httpprotocol/http_source_client.go
index 0b6d477ca..7f691d548 100644
--- a/pkg/source/httpprotocol/http_source_client.go
+++ b/pkg/source/httpprotocol/http_source_client.go
@@ -127,12 +127,12 @@ func WithHTTPClient(client *http.Client) HTTPSourceClientOption {
 func (client *httpSourceClient) GetContentLength(request *source.Request) (int64, error) {
 	resp, err := client.doRequest(http.MethodGet, request)
 	if err != nil {
-		return source.UnKnownSourceFileLen, err
+		return source.UnknownSourceFileLen, err
 	}
 	defer resp.Body.Close()
 	err = source.CheckResponseCode(resp.StatusCode, []int{http.StatusOK, http.StatusPartialContent})
 	if err != nil {
-		return source.UnKnownSourceFileLen, err
+		return source.UnknownSourceFileLen, err
 	}
 	return resp.ContentLength, nil
 }
diff --git a/pkg/source/ossprotocol/oss_source_client.go b/pkg/source/ossprotocol/oss_source_client.go
index 8a1725215..c56ba1e0a 100644
--- a/pkg/source/ossprotocol/oss_source_client.go
+++ b/pkg/source/ossprotocol/oss_source_client.go
@@ -92,19 +92,19 @@ type ossSourceClient struct {
 func (osc *ossSourceClient) GetContentLength(request *source.Request) (int64, error) {
 	client, err := osc.getClient(request.Header)
 	if err != nil {
-		return source.UnKnownSourceFileLen, err
+		return source.UnknownSourceFileLen, err
 	}
 	bucket, err := client.Bucket(request.URL.Host)
 	if err != nil {
-		return source.UnKnownSourceFileLen, errors.Wrapf(err, "get oss bucket: %s", request.URL.Host)
+		return source.UnknownSourceFileLen, errors.Wrapf(err, "get oss bucket: %s", request.URL.Host)
 	}
 	header, err := bucket.GetObjectMeta(request.URL.Path, getOptions(request.Header)...)
 	if err != nil {
-		return source.UnKnownSourceFileLen, errors.Wrapf(err, "get oss object %s meta", request.URL.Path)
+		return source.UnknownSourceFileLen, errors.Wrapf(err, "get oss object %s meta", request.URL.Path)
 	}
 	contentLen, err := strconv.ParseInt(header.Get(oss.HTTPHeaderContentLength), 10, 64)
 	if err != nil {
-		return source.UnKnownSourceFileLen, errors.Wrapf(err, "parse content-length str to int64")
+		return source.UnknownSourceFileLen, errors.Wrapf(err, "parse content-length str to int64")
 	}
 	return contentLen, nil
 }
diff --git a/pkg/source/source_client.go b/pkg/source/source_client.go
index 03af6817c..b595fdce1 100644
--- a/pkg/source/source_client.go
+++ b/pkg/source/source_client.go
@@ -82,14 +82,14 @@ func IsNoClientFoundError(err error) bool {
 }
 
 const (
-	UnKnownSourceFileLen = -2
+	UnknownSourceFileLen = -2
 )
 
 // ResourceClient defines the API interface to interact with source.
 type ResourceClient interface {
 
 	// GetContentLength get length of resource content
-	// return source.UnKnownSourceFileLen if response status is not StatusOK and StatusPartialContent
+	// return source.UnknownSourceFileLen if response status is not StatusOK and StatusPartialContent
 	GetContentLength(request *Request) (int64, error)
 
 	// IsSupportRange checks if resource supports breakpoint continuation
@@ -218,7 +218,7 @@ func (c *clientWrapper) GetLastModified(request *Request) (int64, error) {
 func GetContentLength(request *Request) (int64, error) {
 	client, ok := _defaultManager.GetClient(request.URL.Scheme)
 	if !ok {
-		return UnKnownSourceFileLen, errors.Wrapf(ErrNoClientFound, "scheme: %s", request.URL.Scheme)
+		return UnknownSourceFileLen, errors.Wrapf(ErrNoClientFound, "scheme: %s", request.URL.Scheme)
 	}
 	if _, ok := request.Context().Deadline(); !ok {
 		ctx, cancel := context.WithTimeout(context.Background(), 4*time.Second)