tests: Unit tests and fixes for copyBuffer. (#2333)

- Unit tests for copyBuffer.
- Shadowing fix for copyBuffer.

erasure-utils.go

@@ -163,10 +163,9 @@ func copyBuffer(writer io.Writer, disk StorageAPI, volume string, path string, b
 	for {
 		n, err := disk.ReadFile(volume, path, startOffset, buf)
 		if n > 0 {
-			var m int
+			m, wErr := writer.Write(buf[:n])
-			m, err = writer.Write(buf[:n])
+			if wErr != nil {
-			if err != nil {
+				return wErr
-				return err
 			}
 			if int64(m) != n {
 				return io.ErrShortWrite

erasure-utils_test.go

@@ -17,6 +17,9 @@
 package main
 
 import (
+	"bytes"
+	"errors"
+	"io"
 	"testing"
 )
 
@@ -63,3 +66,92 @@ func TestGetChunkSize(t *testing.T) {
 		}
 	}
 }
+
+// TestCopyBuffer - Tests validate the result and errors produced when `copyBuffer` is called with sample inputs.
+func TestCopyBuffer(t *testing.T) {
+	// create posix test setup
+	disk, diskPath, err := newPosixTestSetup()
+	if err != nil {
+		t.Fatalf("Unable to create posix test setup, %s", err)
+	}
+	defer removeAll(diskPath)
+
+	volume := "success-vol"
+	// Setup test environment.
+	if err = disk.MakeVol(volume); err != nil {
+		t.Fatalf("Unable to create volume, %s", err)
+	}
+
+	// creating io.Writer for the input to copyBuffer.
+	buffers := []*bytes.Buffer{
+		new(bytes.Buffer),
+		new(bytes.Buffer),
+		new(bytes.Buffer),
+	}
+
+	testFile := "testFile"
+	testContent := []byte("hello, world")
+	err = disk.AppendFile(volume, testFile, testContent)
+
+	testCases := []struct {
+		writer io.Writer
+		disk   StorageAPI
+		volume string
+		path   string
+		buf    []byte
+
+		expectedResult []byte
+		// flag to indicate whether test case should pass.
+		shouldPass  bool
+		expectedErr error
+	}{
+		// Test case - 1.
+		// case with empty buffer.
+		{nil, nil, "", "", []byte{}, nil, false, errors.New("empty buffer in readBuffer")},
+		// Test case - 2.
+		// Test case with empty volume.
+		{buffers[0], disk, "", "", make([]byte, 5), nil, false, errInvalidArgument},
+		// Test case - 3.
+		// Test case with non existent volume.
+		{buffers[0], disk, "abc", "", make([]byte, 5), nil, false, errVolumeNotFound},
+		// Test case - 4.
+		// Test case with empty filename/path.
+		{buffers[0], disk, volume, "", make([]byte, 5), nil, false, errIsNotRegular},
+		// Test case - 5.
+		// Test case with non existent file name.
+		{buffers[0], disk, volume, "abcd", make([]byte, 5), nil, false, errFileNotFound},
+		// Test case - 6.
+		// Test case where the writer returns EOF.
+		{NewEOFWriter(buffers[0], 3), disk, volume, testFile, make([]byte, 5), nil, false, io.EOF},
+		// Test case - 7.
+		// Test case to produce io.ErrShortWrite, the TruncateWriter returns after writing 3 bytes.
+		{TruncateWriter(buffers[1], 3), disk, volume, testFile, make([]byte, 5), nil, false, io.ErrShortWrite},
+		// Teset case - 8.
+		// Valid case, expected to read till EOF and write the contents into the writer.
+		{buffers[2], disk, volume, testFile, make([]byte, 5), testContent, true, nil},
+	}
+	// iterate over the test cases and call copy Buffer with data.
+	for i, testCase := range testCases {
+		actualErr := copyBuffer(testCase.writer, testCase.disk, testCase.volume, testCase.path, testCase.buf)
+
+		if actualErr != nil && testCase.shouldPass {
+			t.Errorf("Test %d: Expected to pass but failed instead with \"%s\"", i+1, actualErr)
+		}
+
+		if actualErr == nil && !testCase.shouldPass {
+			t.Errorf("Test %d: Expected to fail with error <Error> \"%v\", but instead passed", i+1, testCase.expectedErr)
+		}
+		// Failed as expected, but does it fail for the expected reason.
+		if actualErr != nil && !testCase.shouldPass {
+			if testCase.expectedErr.Error() != actualErr.Error() {
+				t.Errorf("Test %d: Expected Error to be \"%v\", but instead found \"%v\" ", i+1, testCase.expectedErr, actualErr)
+			}
+		}
+		// test passed as expected, asserting the result.
+		if actualErr == nil && testCase.shouldPass {
+			if !bytes.Equal(testCase.expectedResult, buffers[2].Bytes()) {
+				t.Errorf("Test %d: copied buffer differs from the expected one.", i+1)
+			}
+		}
+	}
+}

test-utils_test.go

@@ -400,6 +400,36 @@ func getRandomBucketName() string {
 
 }
 
+// TruncateWriter - Writes `n` bytes, then returns with number of bytes written.
+// differs from iotest.TruncateWriter, the difference is commented in the Write method.
+func TruncateWriter(w io.Writer, n int64) io.Writer {
+	return &truncateWriter{w, n}
+}
+
+type truncateWriter struct {
+	w io.Writer
+	n int64
+}
+
+func (t *truncateWriter) Write(p []byte) (n int, err error) {
+	if t.n <= 0 {
+		return len(p), nil
+	}
+	// real write
+	n = len(p)
+	if int64(n) > t.n {
+		n = int(t.n)
+	}
+	n, err = t.w.Write(p[0:n])
+	t.n -= int64(n)
+	// Removed from iotest.TruncateWriter.
+	// Need the Write method to return truncated number of bytes written, not the size of the buffer requested to be written.
+	// if err == nil {
+	// 	n = len(p)
+	// }
+	return
+}
+
 // NewEOFWriter returns a Writer that writes to w,
 // but returns EOF error after writing n bytes.
 func NewEOFWriter(w io.Writer, n int64) io.Writer {