Merge pull request #386 from walles/johan/open-dev-fds

Handle paging non-seekable files in `/dev`

Author: walles

internal/reader/reader.go

@@ -259,7 +259,7 @@ func (reader *ReaderImpl) consumeLinesFromStream(stream io.Reader) {
 	// Preallocating the line pool and the lines slice improves large file
 	// reading performance by 10%.
 	linePool := linePool{}
-	if reader.FileName != nil && reader.GetLineCount() == 0 {
+	if reader.FileName != nil && reader.GetLineCount() == 0 && isSeekableFile(reader.FileName) {
 		lineCount, err := countLines(*reader.FileName)
 		if err != nil {
 			log.Warn("Failed to count lines in file: ", err)
@@ -378,6 +378,11 @@ func (reader *ReaderImpl) tailFile() error {
 		return nil
 	}
 
+	if !isSeekableFile(fileName) {
+		log.Debugf("Giving up on tailing, %s is not seekable", *fileName)
+		return nil
+	}
+
 	log.Debugf("Tailing file %s", *fileName)
 
 	for {
@@ -446,6 +451,28 @@ func (reader *ReaderImpl) tailFile() error {
 	}
 }
 
+func isSeekableFile(fileName *string) bool {
+	if fileName == nil {
+		return false
+	}
+
+	file, err := os.Open(*fileName)
+	if err != nil {
+		return false
+	}
+
+	defer func() {
+		err := file.Close()
+		if err != nil {
+			log.Debugf("Failed to close %s while checking seekability: %s", *fileName, err)
+		}
+	}()
+
+	_, err = file.Seek(0, io.SeekCurrent)
+
+	return err == nil
+}
+
 // NewFromStream creates a new stream reader
 //
 // The display name can be an empty string ("").
@@ -568,30 +595,39 @@ func NewFromTextForTesting(name string, text string) *ReaderImpl {
 	return returnMe
 }
 
-// Duplicate of moor/moor.go:TryOpen
 func TryOpen(filename string) error {
 	// Try opening the file
 	tryMe, err := os.Open(filename)
 	if err != nil {
 		return err
 	}
 
-	// Try reading a byte
-	buffer := make([]byte, 1)
-	_, err = tryMe.Read(buffer)
+	fileInfo, err := tryMe.Stat()
+	if err != nil {
+		closeErr := tryMe.Close()
+		if closeErr != nil {
+			return fmt.Errorf("failed to close %s after stat error: %w", filename, closeErr)
+		}
+
+		return err
+	}
+
+	if fileInfo.IsDir() {
+		closeErr := tryMe.Close()
+		if closeErr != nil {
+			return fmt.Errorf("failed to close directory %s: %w", filename, closeErr)
+		}
 
-	if err != nil && err.Error() == "EOF" {
-		// Empty file, this is fine
-		err = nil
+		return fmt.Errorf("%s is a directory", filename)
 	}
 
 	closeErr := tryMe.Close()
-	if err == nil && closeErr != nil {
+	if closeErr != nil {
 		// Everything worked up until Close(), report the Close() error
 		return closeErr
 	}
 
-	return err
+	return nil
 }
 
 // From: https://stackoverflow.com/a/52153000/473672

internal/reader/reader_test.go

@@ -311,6 +311,38 @@ func TestReadStreamDoneYesHighlighting(t *testing.T) {
 	assert.NilError(t, testMe.Wait())
 }
 
+func TestReadFromDevFd(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("/dev/fd is not available on Windows")
+
+		return
+	}
+
+	readPipe, writePipe, err := os.Pipe()
+	assert.NilError(t, err)
+	defer readPipe.Close() //nolint:errcheck
+
+	_, err = writePipe.WriteString("test\n")
+	assert.NilError(t, err)
+	assert.NilError(t, writePipe.Close())
+
+	fileName := "/dev/fd/" + strconv.Itoa(int(readPipe.Fd()))
+	testMe, err := NewFromFilename(fileName, formatters.TTY, ReaderOptions{Style: styles.Get("native")})
+	assert.NilError(t, err)
+	assert.NilError(t, testMe.Wait())
+
+	lines := testMe.GetLines(linemetadata.Index{}, 10)
+	assert.Equal(t, len(lines.Lines), 1)
+	assert.Equal(t, lines.Lines[0].Plain(), "test")
+}
+
+func TestTryOpenDirectory(t *testing.T) {
+	tempDir := t.TempDir()
+
+	err := TryOpen(tempDir)
+	assert.Assert(t, err != nil, "TryOpen should fail on directories")
+}
+
 func TestReadTextDone(t *testing.T) {
 	testMe := NewFromTextForTesting("", "Johan")
 

internal/reader/zopen.go

@@ -26,6 +26,13 @@ func ZOpen(filename string) (io.ReadCloser, string, error) {
 		return nil, "", err
 	}
 
+	_, err = file.Seek(0, 0)
+	if err != nil {
+		// File is not seekable, so we can't probe its contents.
+		// https://github.com/walles/moor/issues/385
+		return file, filename, nil
+	}
+
 	// Read the first 6 bytes to determine the compression type
 	firstBytes := make([]byte, 6)
 	_, err = file.Read(firstBytes)
@@ -54,8 +61,8 @@ func ZOpen(filename string) (io.ReadCloser, string, error) {
 		newName := strings.TrimSuffix(filename, ".gz")
 
 		// Ref: https://github.com/walles/moor/issues/194
-		if strings.HasSuffix(newName, ".tgz") {
-			newName = strings.TrimSuffix(newName, ".tgz") + ".tar"
+		if before, ok := strings.CutSuffix(newName, ".tgz"); ok {
+			newName = before + ".tar"
 		}
 
 		return reader, newName, err