Delete unnecessary FingerprintUpdatingReader (#202)

* Merged FingerprintUpdatingReader into Reader

* Add a robust test for fingerprint updating

* lint

* Don't save fingerprintSize on reader

Author: djaglowski

operator/builtin/input/file/file_test.go

@@ -635,6 +635,65 @@ func TestFileReader_FingerprintUpdated(t *testing.T) {
 	require.Equal(t, []byte("testlog1\n"), reader.Fingerprint.FirstBytes)
 }
 
+// Test that a fingerprint:
+// - Starts empty
+// - Updates as a file is read
+// - Stops updating when the max fingerprint size is reached
+// - Stops exactly at max fingerprint size, regardless of content
+func TestFingerprintGrowsAndStops(t *testing.T) {
+	t.Parallel()
+
+	// Use a number with many factors.
+	// Sometimes fingerprint length will align with
+	// the end of a line, sometimes not. Test both.
+	maxFP := 360
+
+	// Use prime numbers to ensure variation in
+	// whether or not they are factors of maxFP
+	lineLens := []int{3, 5, 7, 11, 13, 17, 19, 23, 27}
+
+	for _, lineLen := range lineLens {
+		t.Run(fmt.Sprintf("%d", lineLen), func(t *testing.T) {
+			t.Parallel()
+			operator, _, tempDir := newTestFileOperator(t, func(cfg *InputConfig) {
+				cfg.FingerprintSize = helper.ByteSize(maxFP)
+			}, nil)
+			defer operator.Stop()
+
+			temp := openTemp(t, tempDir)
+			tempCopy := openFile(t, temp.Name())
+			fp, err := operator.NewFingerprint(temp)
+			require.NoError(t, err)
+			require.Equal(t, []byte(""), fp.FirstBytes)
+
+			reader, err := operator.NewReader(temp.Name(), tempCopy, fp)
+			require.NoError(t, err)
+			defer reader.Close()
+
+			// keep track of what has been written to the file
+			fileContent := []byte{}
+
+			// keep track of expected fingerprint size
+			expectedFP := 0
+
+			// Write lines until file is much larger than the length of the fingerprint
+			for len(fileContent) < 2*maxFP {
+				expectedFP += lineLen
+				if expectedFP > maxFP {
+					expectedFP = maxFP
+				}
+
+				line := stringWithLength(lineLen-1) + "\n"
+				fileContent = append(fileContent, []byte(line)...)
+
+				writeString(t, temp, line)
+				reader.ReadToEnd(context.Background())
+				require.Equal(t, fileContent[:expectedFP], reader.Fingerprint.FirstBytes)
+			}
+		})
+	}
+}
+
 func TestEncodings(t *testing.T) {
 	t.Parallel()
 	cases := []struct {

operator/builtin/input/file/reader.go

@@ -18,7 +18,6 @@ import (
 	"bufio"
 	"context"
 	"fmt"
-	"io"
 	"os"
 	"path/filepath"
 
@@ -107,7 +106,6 @@ func (f *Reader) InitializeOffset(startAtBeginning bool) error {
 		}
 		f.Offset = info.Size()
 	}
-
 	return nil
 }
 
@@ -118,8 +116,7 @@ func (f *Reader) ReadToEnd(ctx context.Context) {
 		return
 	}
 
-	fr := NewFingerprintUpdatingReader(f.file, f.Offset, f.Fingerprint, f.fileInput.fingerprintSize)
-	scanner := NewPositionalScanner(fr, f.fileInput.MaxLogSize, f.Offset, f.fileInput.SplitFunc)
+	scanner := NewPositionalScanner(f, f.fileInput.MaxLogSize, f.Offset, f.fileInput.SplitFunc)
 
 	// Iterate over the tokenized file, emitting entries as we go
 	for {
@@ -215,34 +212,14 @@ func getScannerError(scanner *PositionalScanner) error {
 	return nil
 }
 
-// NewFingerprintUpdatingReader creates a new FingerprintUpdatingReader starting starting at the given offset
-func NewFingerprintUpdatingReader(r io.Reader, offset int64, f *Fingerprint, fingerprintSize int) *FingerprintUpdatingReader {
-	return &FingerprintUpdatingReader{
-		fingerprint:     f,
-		fingerprintSize: fingerprintSize,
-		reader:          r,
-		offset:          offset,
-	}
-}
-
-// FingerprintUpdatingReader wraps another reader, and updates the fingerprint
-// with each read in the first fingerPrintSize bytes
-type FingerprintUpdatingReader struct {
-	fingerprint     *Fingerprint
-	fingerprintSize int
-	reader          io.Reader
-	offset          int64
-}
-
-// Read reads from the wrapped reader, saving the read bytes to the fingerprint
-func (f *FingerprintUpdatingReader) Read(dst []byte) (int, error) {
-	if len(f.fingerprint.FirstBytes) == f.fingerprintSize {
-		return f.reader.Read(dst)
+// Read from the file and update the fingerprint if necessary
+func (f *Reader) Read(dst []byte) (int, error) {
+	if len(f.Fingerprint.FirstBytes) == f.fileInput.fingerprintSize {
+		return f.file.Read(dst)
 	}
-	n, err := f.reader.Read(dst)
-	appendCount := min0(n, f.fingerprintSize-int(f.offset))
-	f.fingerprint.FirstBytes = append(f.fingerprint.FirstBytes[:f.offset], dst[:appendCount]...)
-	f.offset += int64(n)
+	n, err := f.file.Read(dst)
+	appendCount := min0(n, f.fileInput.fingerprintSize-int(f.Offset))
+	f.Fingerprint.FirstBytes = append(f.Fingerprint.FirstBytes[:f.Offset], dst[:appendCount]...)
 	return n, err
 }