handle files: does not send an error if the transfer could not be open

if TransferOpen fails we already sent an error to the client, even
before the previous commit.

In handle dirs we don't send an error if TransferOpen fails, in handle
files we could send an error instead, so check the error type.

Author: drakkan

client_handler.go

@@ -3,7 +3,6 @@ package ftpserver
 
 import (
 	"bufio"
-	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -13,6 +12,14 @@ import (
 	"github.com/fclairamb/ftpserverlib/log"
 )
 
+type openTransferError struct {
+	err string
+}
+
+func (e *openTransferError) Error() string {
+	return fmt.Sprintf("Unable to open transfer: %s", e.err)
+}
+
 // nolint: maligned
 type clientHandler struct {
 	id          uint32          // ID of the client
@@ -254,16 +261,20 @@ func (c *clientHandler) writeMessage(code int, message string) {
 
 func (c *clientHandler) TransferOpen() (net.Conn, error) {
 	if c.transfer == nil {
-		c.writeMessage(StatusActionNotTaken, "No passive connection declared")
-		return nil, errors.New("no passive connection declared")
+		err := &openTransferError{err: "No passive connection declared"}
+		c.writeMessage(StatusActionNotTaken, err.Error())
+
+		return nil, err
 	}
 
 	conn, err := c.transfer.Open()
 	if err != nil {
 		c.logger.Warn(
 			"Unable to open transfer",
 			"error", err)
-		c.writeMessage(StatusCannotOpenDataConnection, fmt.Sprintf("Unable to open transfer: %v", err))
+
+		err = &openTransferError{err: err.Error()}
+		c.writeMessage(StatusCannotOpenDataConnection, err.Error())
 
 		return conn, err
 	}

handle_files.go

@@ -32,7 +32,6 @@ func (c *clientHandler) handleRETR() error {
 // To make sure we don't miss any step, we execute everything in order
 func (c *clientHandler) transferFile(write bool, append bool) {
 	var file afero.File
-
 	var err error
 
 	path := c.absPath(c.param)
@@ -77,9 +76,7 @@ func (c *clientHandler) transferFile(write bool, append bool) {
 			defer c.TransferClose()
 
 			// Copy the data
-
 			var in io.Reader
-
 			var out io.Writer
 
 			if write { // ... from the connection to the file
@@ -107,8 +104,11 @@ func (c *clientHandler) transferFile(write bool, append bool) {
 	}
 
 	if err != nil {
-		c.writeMessage(StatusActionNotTaken, "Could not transfer file: "+err.Error())
-		return
+		// if the transfer could not be open we already sent an error
+		if _, isOpenTransferErr := err.(*openTransferError); !isOpenTransferErr {
+			c.writeMessage(StatusActionNotTaken, "Could not transfer file: "+err.Error())
+			return
+		}
 	}
 }