app/vminsert: really fix #60

ReadLinesBlock may accept dstBuf with non-zero length. In this case the last line without trailing newline isn't read.
Fix this by comparing len(dstBuf) to 0 instead of its original length.

app/vminsert/common/lines_reader.go

@@ -20,7 +20,6 @@ const defaultBlockSize = 64 * 1024
 //
 // Returns (dstBuf, tailBuf).
 func ReadLinesBlock(r io.Reader, dstBuf, tailBuf []byte) ([]byte, []byte, error) {
-	origDstBufLen := len(dstBuf)
 	if cap(dstBuf) < defaultBlockSize {
 		dstBuf = bytesutil.Resize(dstBuf, defaultBlockSize)
 	}
@@ -33,7 +32,7 @@ again:
 		if err == nil {
 			return dstBuf, tailBuf, fmt.Errorf("no forward progress made")
 		}
-		if err == io.EOF && len(dstBuf) > origDstBufLen {
+		if err == io.EOF && len(dstBuf) > 0 {
 			// Missing newline in the end of stream. This is OK,
 			/// so suppress io.EOF for now. It will be returned during the next
 			// call to ReadLinesBlock.

app/vminsert/common/lines_reader_test.go

@@ -79,6 +79,7 @@ func TestReadLineBlockSuccessSingleByteReader(t *testing.T) {
 	f("\nfoo", "", "")
 	f("foo\nbar", "foo", "")
 	f("foo\nbar\nbaz", "foo", "")
+	f("foo", "foo", "")
 
 	// The maximum line size
 	b := make([]byte, maxLineSize+10)