Fix tail following on EOF

plugins/common/encoding/decoder.go

@@ -7,8 +7,6 @@ import (
 	"golang.org/x/text/encoding/unicode"
 )
 
-type Decoder = encoding.Decoder
-
 // NewDecoder returns a x/text Decoder for the specified text encoding.  The
 // Decoder converts a character encoding into utf-8 bytes.  If a BOM is found
 // it will be converted into a utf-8 BOM, you can use
@@ -24,13 +22,13 @@ type Decoder = encoding.Decoder
 func NewDecoder(enc string) (*Decoder, error) {
 	switch enc {
 	case "utf-8":
-		return unicode.UTF8.NewDecoder(), nil
+		return &Decoder{Transformer: unicode.UTF8.NewDecoder()}, nil
 	case "utf-16le":
-		return unicode.UTF16(unicode.LittleEndian, unicode.IgnoreBOM).NewDecoder(), nil
+		return newDecoder(unicode.UTF16(unicode.LittleEndian, unicode.IgnoreBOM).NewDecoder()), nil
 	case "utf-16be":
-		return unicode.UTF16(unicode.BigEndian, unicode.IgnoreBOM).NewDecoder(), nil
+		return newDecoder(unicode.UTF16(unicode.BigEndian, unicode.IgnoreBOM).NewDecoder()), nil
 	case "none", "":
-		return encoding.Nop.NewDecoder(), nil
+		return newDecoder(encoding.Nop.NewDecoder()), nil
 	}
 	return nil, errors.New("unknown character encoding")
 }

plugins/common/encoding/decoder_reader.go

@@ -0,0 +1,171 @@
+package encoding
+
+import (
+	"errors"
+	"io"
+
+	"golang.org/x/text/transform"
+)
+
+// Other than resetting r.err and r.transformComplete in Read() this
+// was copied from x/text
+
+func newDecoder(t transform.Transformer) *Decoder {
+	return &Decoder{Transformer: t}
+}
+
+// A Decoder converts bytes to UTF-8. It implements transform.Transformer.
+//
+// Transforming source bytes that are not of that encoding will not result in an
+// error per se. Each byte that cannot be transcoded will be represented in the
+// output by the UTF-8 encoding of '\uFFFD', the replacement rune.
+type Decoder struct {
+	transform.Transformer
+
+	// This forces external creators of Decoders to use names in struct
+	// initializers, allowing for future extendibility without having to break
+	// code.
+	_ struct{}
+}
+
+// Bytes converts the given encoded bytes to UTF-8. It returns the converted
+// bytes or nil, err if any error occurred.
+func (d *Decoder) Bytes(b []byte) ([]byte, error) {
+	b, _, err := transform.Bytes(d, b)
+	if err != nil {
+		return nil, err
+	}
+	return b, nil
+}
+
+// String converts the given encoded string to UTF-8. It returns the converted
+// string or "", err if any error occurred.
+func (d *Decoder) String(s string) (string, error) {
+	s, _, err := transform.String(d, s)
+	if err != nil {
+		return "", err
+	}
+	return s, nil
+}
+
+// Reader wraps another Reader to decode its bytes.
+//
+// The Decoder may not be used for any other operation as long as the returned
+// Reader is in use.
+func (d *Decoder) Reader(r io.Reader) io.Reader {
+	return NewReader(r, d)
+}
+
+// Reader wraps another io.Reader by transforming the bytes read.
+type Reader struct {
+	r   io.Reader
+	t   transform.Transformer
+	err error
+
+	// dst[dst0:dst1] contains bytes that have been transformed by t but
+	// not yet copied out via Read.
+	dst        []byte
+	dst0, dst1 int
+
+	// src[src0:src1] contains bytes that have been read from r but not
+	// yet transformed through t.
+	src        []byte
+	src0, src1 int
+
+	// transformComplete is whether the transformation is complete,
+	// regardless of whether or not it was successful.
+	transformComplete bool
+}
+
+var (
+	// ErrShortDst means that the destination buffer was too short to
+	// receive all of the transformed bytes.
+	ErrShortDst = errors.New("transform: short destination buffer")
+
+	// ErrShortSrc means that the source buffer has insufficient data to
+	// complete the transformation.
+	ErrShortSrc = errors.New("transform: short source buffer")
+
+	// errInconsistentByteCount means that Transform returned success (nil
+	// error) but also returned nSrc inconsistent with the src argument.
+	errInconsistentByteCount = errors.New("transform: inconsistent byte count returned")
+)
+
+const defaultBufSize = 4096
+
+// NewReader returns a new Reader that wraps r by transforming the bytes read
+// via t. It calls Reset on t.
+func NewReader(r io.Reader, t transform.Transformer) *Reader {
+	t.Reset()
+	return &Reader{
+		r:   r,
+		t:   t,
+		dst: make([]byte, defaultBufSize),
+		src: make([]byte, defaultBufSize),
+	}
+}
+
+// Read implements the io.Reader interface.
+func (r *Reader) Read(p []byte) (int, error) {
+	// Clear previous errors so a Read can be performed even if the last call
+	// returned EOF.
+	r.err = nil
+	r.transformComplete = false
+
+	n, err := 0, error(nil)
+	for {
+		// Copy out any transformed bytes and return the final error if we are done.
+		if r.dst0 != r.dst1 {
+			n = copy(p, r.dst[r.dst0:r.dst1])
+			r.dst0 += n
+			if r.dst0 == r.dst1 && r.transformComplete {
+				return n, r.err
+			}
+			return n, nil
+		} else if r.transformComplete {
+			return 0, r.err
+		}
+
+		// Try to transform some source bytes, or to flush the transformer if we
+		// are out of source bytes. We do this even if r.r.Read returned an error.
+		// As the io.Reader documentation says, "process the n > 0 bytes returned
+		// before considering the error".
+		if r.src0 != r.src1 || r.err != nil {
+			r.dst0 = 0
+			r.dst1, n, err = r.t.Transform(r.dst, r.src[r.src0:r.src1], r.err == io.EOF)
+			r.src0 += n
+
+			switch {
+			case err == nil:
+				if r.src0 != r.src1 {
+					r.err = errInconsistentByteCount
+				}
+				// The Transform call was successful; we are complete if we
+				// cannot read more bytes into src.
+				r.transformComplete = r.err != nil
+				continue
+			case err == ErrShortDst && (r.dst1 != 0 || n != 0):
+				// Make room in dst by copying out, and try again.
+				continue
+			case err == ErrShortSrc && r.src1-r.src0 != len(r.src) && r.err == nil:
+				// Read more bytes into src via the code below, and try again.
+			default:
+				r.transformComplete = true
+				// The reader error (r.err) takes precedence over the
+				// transformer error (err) unless r.err is nil or io.EOF.
+				if r.err == nil || r.err == io.EOF {
+					r.err = err
+				}
+				continue
+			}
+		}
+
+		// Move any untransformed source bytes to the start of the buffer
+		// and read more bytes.
+		if r.src0 != 0 {
+			r.src0, r.src1 = 0, copy(r.src, r.src[r.src0:r.src1])
+		}
+		n, r.err = r.r.Read(r.src[r.src1:])
+		r.src1 += n
+	}
+}

plugins/inputs/tail/tail_test.go

@@ -346,3 +346,47 @@ func TestCharacterEncoding(t *testing.T) {
 		})
 	}
 }
+
+func TestTailEOF(t *testing.T) {
+	tmpfile, err := ioutil.TempFile("", "")
+	require.NoError(t, err)
+	defer os.Remove(tmpfile.Name())
+	_, err = tmpfile.WriteString("cpu usage_idle=100\r\n")
+	require.NoError(t, err)
+	err = tmpfile.Sync()
+	require.NoError(t, err)
+
+	tt := NewTail()
+	tt.Log = testutil.Logger{}
+	tt.FromBeginning = true
+	tt.Files = []string{tmpfile.Name()}
+	tt.SetParserFunc(parsers.NewInfluxParser)
+
+	err = tt.Init()
+	require.NoError(t, err)
+
+	acc := testutil.Accumulator{}
+	require.NoError(t, tt.Start(&acc))
+	defer tt.Stop()
+	require.NoError(t, acc.GatherError(tt.Gather))
+	acc.Wait(1) // input hits eof
+
+	_, err = tmpfile.WriteString("cpu2 usage_idle=200\r\n")
+	require.NoError(t, err)
+	err = tmpfile.Sync()
+	require.NoError(t, err)
+
+	acc.Wait(2)
+	require.NoError(t, acc.GatherError(tt.Gather))
+	acc.AssertContainsFields(t, "cpu",
+		map[string]interface{}{
+			"usage_idle": float64(100),
+		})
+	acc.AssertContainsFields(t, "cpu2",
+		map[string]interface{}{
+			"usage_idle": float64(200),
+		})
+
+	err = tmpfile.Close()
+	require.NoError(t, err)
+}