sftpd: add support for upload resume

we support resume only if the client sets the correct offset while resuming
the upload.
Based on the specs the offset is optional for resume, but all the tested
clients sets a right offset.
If an invalid offset is given we interrupt the transfer with the error
"Invalid write offset ..."

See https://github.com/pkg/sftp/issues/295

This commit add a new upload mode: "atomic with resume support", this acts
as atomic but if there is an upload error the temporary file is renamed
to the requested path and not deleted, this way a client can reconnect
and resume the upload

sftpd/handler.go

@@ -75,19 +75,20 @@ func (c Connection) Fileread(request *sftp.Request) (io.ReaderAt, error) {
 	c.Log(logger.LevelDebug, logSender, "fileread requested for path: %#v", p)
 
 	transfer := Transfer{
-		file:          file,
-		path:          p,
-		start:         time.Now(),
-		bytesSent:     0,
-		bytesReceived: 0,
-		user:          c.User,
-		connectionID:  c.ID,
-		transferType:  transferDownload,
-		lastActivity:  time.Now(),
-		isNewFile:     false,
-		protocol:      c.protocol,
-		transferError: nil,
-		isFinished:    false,
+		file:           file,
+		path:           p,
+		start:          time.Now(),
+		bytesSent:      0,
+		bytesReceived:  0,
+		user:           c.User,
+		connectionID:   c.ID,
+		transferType:   transferDownload,
+		lastActivity:   time.Now(),
+		isNewFile:      false,
+		protocol:       c.protocol,
+		transferError:  nil,
+		isFinished:     false,
+		minWriteOffset: 0,
 	}
 	addTransfer(&transfer)
 	return &transfer, nil
@@ -106,7 +107,7 @@ func (c Connection) Filewrite(request *sftp.Request) (io.WriterAt, error) {
 	}
 
 	filePath := p
-	if uploadMode == uploadModeAtomic {
+	if isAtomicUploadEnabled() {
 		filePath = getUploadTempFilePath(p)
 	}
 
@@ -376,19 +377,20 @@ func (c Connection) handleSFTPUploadToNewFile(requestPath, filePath string) (io.
 	utils.SetPathPermissions(filePath, c.User.GetUID(), c.User.GetGID())
 
 	transfer := Transfer{
-		file:          file,
-		path:          requestPath,
-		start:         time.Now(),
-		bytesSent:     0,
-		bytesReceived: 0,
-		user:          c.User,
-		connectionID:  c.ID,
-		transferType:  transferUpload,
-		lastActivity:  time.Now(),
-		isNewFile:     true,
-		protocol:      c.protocol,
-		transferError: nil,
-		isFinished:    false,
+		file:           file,
+		path:           requestPath,
+		start:          time.Now(),
+		bytesSent:      0,
+		bytesReceived:  0,
+		user:           c.User,
+		connectionID:   c.ID,
+		transferType:   transferUpload,
+		lastActivity:   time.Now(),
+		isNewFile:      true,
+		protocol:       c.protocol,
+		transferError:  nil,
+		isFinished:     false,
+		minWriteOffset: 0,
 	}
 	addTransfer(&transfer)
 	return &transfer, nil
@@ -402,15 +404,10 @@ func (c Connection) handleSFTPUploadToExistingFile(pflags sftp.FileOpenFlags, re
 		return nil, sftp.ErrSshFxFailure
 	}
 
+	minWriteOffset := int64(0)
 	osFlags := getOSOpenFlags(pflags)
 
-	if osFlags&os.O_TRUNC == 0 {
-		// see https://github.com/pkg/sftp/issues/295
-		c.Log(logger.LevelInfo, logSender, "upload resume is not supported, returning error for file: %#v", requestPath)
-		return nil, sftp.ErrSshFxOpUnsupported
-	}
-
-	if uploadMode == uploadModeAtomic {
+	if isAtomicUploadEnabled() {
 		err = os.Rename(requestPath, filePath)
 		if err != nil {
 			c.Log(logger.LevelError, logSender, "error renaming existing file for atomic upload, source: %#v, dest: %#v, err: %v",
@@ -425,26 +422,30 @@ func (c Connection) handleSFTPUploadToExistingFile(pflags sftp.FileOpenFlags, re
 		return nil, sftp.ErrSshFxFailure
 	}
 
-	// FIXME: this need to be changed when we add upload resume support
-	// the file is truncated so we need to decrease quota size but not quota files
-	dataprovider.UpdateUserQuota(dataProvider, c.User, 0, -fileSize, false)
+	if pflags.Append && osFlags&os.O_TRUNC == 0 {
+		c.Log(logger.LevelDebug, logSender, "upload resume requested, file path: %#v initial size: %v", filePath, fileSize)
+		minWriteOffset = fileSize
+	} else {
+		dataprovider.UpdateUserQuota(dataProvider, c.User, 0, -fileSize, false)
+	}
 
 	utils.SetPathPermissions(filePath, c.User.GetUID(), c.User.GetGID())
 
 	transfer := Transfer{
-		file:          file,
-		path:          requestPath,
-		start:         time.Now(),
-		bytesSent:     0,
-		bytesReceived: 0,
-		user:          c.User,
-		connectionID:  c.ID,
-		transferType:  transferUpload,
-		lastActivity:  time.Now(),
-		isNewFile:     false,
-		protocol:      c.protocol,
-		transferError: nil,
-		isFinished:    false,
+		file:           file,
+		path:           requestPath,
+		start:          time.Now(),
+		bytesSent:      0,
+		bytesReceived:  0,
+		user:           c.User,
+		connectionID:   c.ID,
+		transferType:   transferUpload,
+		lastActivity:   time.Now(),
+		isNewFile:      false,
+		protocol:       c.protocol,
+		transferError:  nil,
+		isFinished:     false,
+		minWriteOffset: minWriteOffset,
 	}
 	addTransfer(&transfer)
 	return &transfer, nil
@@ -600,9 +601,10 @@ func getOSOpenFlags(requestFlags sftp.FileOpenFlags) (flags int) {
 	} else if requestFlags.Write {
 		osFlags |= os.O_WRONLY
 	}
-	if requestFlags.Append {
+	// we ignore Append flag since pkg/sftp use WriteAt that cannot work with os.O_APPEND
+	/*if requestFlags.Append {
 		osFlags |= os.O_APPEND
-	}
+	}*/
 	if requestFlags.Creat {
 		osFlags |= os.O_CREATE
 	}