Add MLST command in the form of a Get method (#269)

* Add MLST command in the form of a Get method

The `LIST` and `MLSD` commands are inefficient when the objective
is to retrieve one single `Entry` for a known path, because the only way
to get such an entry is to list the parent directory using a data
connection. The `MLST` fixes this by allowing one single `Entry` to be
returned using the control connection.

The name `Get` was chosen because it is often used in conjunction with
`List` as a mean to get one single entry.

Signed-off-by: Thomas Hallgren <thomas@datawire.io>

* Changes in response to code review:

- Rename `Get` to `GetEntry` (because it returns an `*Entry`)
- Add test-case for multiline response on the control connection
- Fix issues with parsing the multiline response.

Signed-off-by: Thomas Hallgren <thomas@datawire.io>

* Add sample output from MLST to GetEntry comment.

Signed-off-by: Thomas Hallgren <thomas@datawire.io>

* Changes in response to code review:

- Remove unused `time.Time` argument
- Add struct labels to make `govet` happy

Signed-off-by: Thomas Hallgren <thomas@datawire.io>

* Remove time arg when calling parseNextRFC3659ListLine

Signed-off-by: Thomas Hallgren <thomas@datawire.io>

Signed-off-by: Thomas Hallgren <thomas@datawire.io>

client_test.go

@@ -110,6 +110,40 @@ func testConn(t *testing.T, disableEPSV bool) {
 	_, err = c.FileSize("not-found")
 	assert.Error(err)
 
+	entry, err := c.GetEntry("magic-file")
+	if err != nil {
+		t.Error(err)
+	}
+	if entry == nil {
+		t.Fatal("expected entry, got nil")
+	}
+	if entry.Size != 42 {
+		t.Errorf("entry size %q, expected %q", entry.Size, 42)
+	}
+	if entry.Type != EntryTypeFile {
+		t.Errorf("entry type %q, expected %q", entry.Type, EntryTypeFile)
+	}
+	if entry.Name != "magic-file" {
+		t.Errorf("entry name %q, expected %q", entry.Name, "magic-file")
+	}
+
+	entry, err = c.GetEntry("multiline-dir")
+	if err != nil {
+		t.Error(err)
+	}
+	if entry == nil {
+		t.Fatal("expected entry, got nil")
+	}
+	if entry.Size != 0 {
+		t.Errorf("entry size %q, expected %q", entry.Size, 0)
+	}
+	if entry.Type != EntryTypeFolder {
+		t.Errorf("entry type %q, expected %q", entry.Type, EntryTypeFolder)
+	}
+	if entry.Name != "multiline-dir" {
+		t.Errorf("entry name %q, expected %q", entry.Name, "multiline-dir")
+	}
+
 	err = c.Delete("tset")
 	assert.NoError(err)
 
@@ -245,7 +279,7 @@ func TestMissingFolderDeleteDirRecur(t *testing.T) {
 }
 
 func TestListCurrentDir(t *testing.T) {
-	mock, c := openConn(t, "127.0.0.1")
+	mock, c := openConnExt(t, "127.0.0.1", "no-time", DialWithDisabledMLSD(true))
 
 	_, err := c.List("")
 	assert.NoError(t, err)

conn_test.go

@@ -90,7 +90,7 @@ func (mock *ftpMock) listen() {
 		// At least one command must have a multiline response
 		switch cmdParts[0] {
 		case "FEAT":
-			features := "211-Features:\r\n FEAT\r\n PASV\r\n EPSV\r\n UTF8\r\n SIZE\r\n"
+			features := "211-Features:\r\n FEAT\r\n PASV\r\n EPSV\r\n UTF8\r\n SIZE\r\n MLST\r\n"
 			switch mock.modtime {
 			case "std-time":
 				features += " MDTM\r\n MFMT\r\n"
@@ -178,6 +178,23 @@ func (mock *ftpMock) listen() {
 			mock.dataConn.write([]byte("-rw-r--r--   1 ftp      wheel           0 Jan 29 10:29 lo\r\ntotal 1"))
 			mock.printfLine("226 Transfer complete")
 			mock.closeDataConn()
+		case "MLSD":
+			if mock.dataConn == nil {
+				mock.printfLine("425 Unable to build data connection: Connection refused")
+				break
+			}
+
+			mock.dataConn.Wait()
+			mock.printfLine("150 Opening data connection for file list")
+			mock.dataConn.write([]byte("Type=file;Size=0;Modify=20201213202400; lo\r\n"))
+			mock.printfLine("226 Transfer complete")
+			mock.closeDataConn()
+		case "MLST":
+			if cmdParts[1] == "multiline-dir" {
+				mock.printfLine("250-File data\r\n Type=dir;Size=0; multiline-dir\r\n Modify=20201213202400; multiline-dir\r\n250 End")
+			} else {
+				mock.printfLine("250-File data\r\n Type=file;Size=42;Modify=20201213202400; magic-file\r\n250 End")
+			}
 		case "NLST":
 			if mock.dataConn == nil {
 				mock.printfLine("425 Unable to build data connection: Connection refused")

ftp.go

@@ -678,6 +678,58 @@ func (c *ServerConn) List(path string) (entries []*Entry, err error) {
 	return entries, errs.ErrorOrNil()
 }
 
+// GetEntry issues a MLST FTP command which retrieves one single Entry using the
+// control connection. The returnedEntry will describe the current directory
+// when no path is given.
+func (c *ServerConn) GetEntry(path string) (entry *Entry, err error) {
+	if !c.mlstSupported {
+		return nil, &textproto.Error{Code: StatusNotImplemented, Msg: StatusText(StatusNotImplemented)}
+	}
+	space := " "
+	if path == "" {
+		space = ""
+	}
+	_, msg, err := c.cmd(StatusRequestedFileActionOK, "%s%s%s", "MLST", space, path)
+	if err != nil {
+		return nil, err
+	}
+
+	// The expected reply will look something like:
+	//
+	//    250-File details
+	//     Type=file;Size=1024;Modify=20220813133357; path
+	//    250 End
+	//
+	// Multiple lines are allowed though, so it can also be in the form:
+	//
+	//    250-File details
+	//     Type=file;Size=1024; path
+	//     Modify=20220813133357; path
+	//    250 End
+	lines := strings.Split(msg, "\n")
+	lc := len(lines)
+
+	// lines must be a multi-line message with a length of 3 or more, and we
+	// don't care about the first and last line
+	if lc < 3 {
+		return nil, errors.New("invalid response")
+	}
+
+	e := &Entry{}
+	for _, l := range lines[1 : lc-1] {
+		// According to RFC 3659, the entry lines must start with a space when passed over the
+		// control connection. Some servers don't seem to add that space though. Both forms are
+		// accepted here.
+		if len(l) > 0 && l[0] == ' ' {
+			l = l[1:]
+		}
+		if e, err = parseNextRFC3659ListLine(l, c.options.location, e); err != nil {
+			return nil, err
+		}
+	}
+	return e, nil
+}
+
 // IsTimePreciseInList returns true if client and server support the MLSD
 // command so List can return time with 1-second precision for all files.
 func (c *ServerConn) IsTimePreciseInList() bool {

parse.go

@@ -27,7 +27,11 @@ var dirTimeFormats = []string{
 }
 
 // parseRFC3659ListLine parses the style of directory line defined in RFC 3659.
-func parseRFC3659ListLine(line string, now time.Time, loc *time.Location) (*Entry, error) {
+func parseRFC3659ListLine(line string, _ time.Time, loc *time.Location) (*Entry, error) {
+	return parseNextRFC3659ListLine(line, loc, &Entry{})
+}
+
+func parseNextRFC3659ListLine(line string, loc *time.Location, e *Entry) (*Entry, error) {
 	iSemicolon := strings.Index(line, ";")
 	iWhitespace := strings.Index(line, " ")
 
@@ -35,8 +39,12 @@ func parseRFC3659ListLine(line string, now time.Time, loc *time.Location) (*Entr
 		return nil, errUnsupportedListLine
 	}
 
-	e := &Entry{
-		Name: line[iWhitespace+1:],
+	name := line[iWhitespace+1:]
+	if e.Name == "" {
+		e.Name = name
+	} else if e.Name != name {
+		// All lines must have the same name
+		return nil, errUnsupportedListLine
 	}
 
 	for _, field := range strings.Split(line[:iWhitespace-1], ";") {