simplify countLines, more informative errors

storage/fileStorage.go

@@ -2,8 +2,8 @@ package storage
 
 import (
 	"bufio"
-	"bytes"
 	"encoding/json"
+	"fmt"
 	"github.com/google/uuid"
 	"github.com/juju/fslock"
 	"io"
@@ -24,30 +24,15 @@ const (
 	defaultLockFile = "/tmp/dc4bc_storage_lock"
 )
 
-func countLines(r io.Reader) (uint64, error) {
+func countLines(r io.Reader) uint64 {
 	var count uint64
-	buf := make([]byte, bufio.MaxScanTokenSize)
-	for {
-		bufferSize, err := r.Read(buf)
-		if err != nil && err != io.EOF {
-			return 0, err
-		}
+	fileScanner := bufio.NewScanner(r)
 
-		var buffPosition int
-		for {
-			i := bytes.IndexByte(buf[buffPosition:], EOL)
-			if i == -1 || bufferSize == buffPosition {
-				break
-			}
-			buffPosition += i + 1
-			count++
-		}
-		if err == io.EOF {
-			break
-		}
+	for fileScanner.Scan() {
+		count++
 	}
 
-	return count, nil
+	return count
 }
 
 // InitFileStorage inits append-only file storage
@@ -64,7 +49,7 @@ func InitFileStorage(filename string, lockFilename ...string) (Storage, error) {
 	}
 
 	if fs.dataFile, err = os.OpenFile(filename, os.O_APPEND|os.O_CREATE|os.O_RDWR, 0644); err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to open a data file: %v", err)
 	}
 	fs.reader = bufio.NewReader(fs.dataFile)
 	return &fs, nil
@@ -73,27 +58,28 @@ func InitFileStorage(filename string, lockFilename ...string) (Storage, error) {
 // Send sends a message to an append-only data file, returns a message with offset and id
 func (fs *FileStorage) Send(m Message) (Message, error) {
 	var (
-		err error
+		data []byte
+		err  error
 	)
 	if err = fs.lockFile.Lock(); err != nil {
-		return m, err
+		return m, fmt.Errorf("failed to lock a file: %v", err)
 	}
 	defer fs.lockFile.Unlock()
 
 	m.ID = uuid.New().String()
 
 	if _, err = fs.dataFile.Seek(0, 0); err != nil { // otherwise countLines will return zero
-		return m, err
+		return m, fmt.Errorf("failed to seek a offset to the start of a data file: %v", err)
 	}
-	if m.Offset, err = countLines(fs.dataFile); err != nil {
-		return m, err
+	m.Offset = countLines(fs.dataFile)
+
+	if data, err = json.Marshal(m); err != nil {
+		return m, fmt.Errorf("failed to marshal a message %v: %v", m, err)
 	}
-	data, err := json.Marshal(m)
-	if err != nil {
-		return m, err
+
+	if _, err = fmt.Fprintln(fs.dataFile, string(data)); err != nil {
+		return m, fmt.Errorf("failed to write a message to a data file: %v", err)
 	}
-	data = append(data, EOL)
-	_, err = fs.dataFile.Write(data)
 	return m, err
 }
 
@@ -106,7 +92,7 @@ func (fs *FileStorage) GetMessages(offset int) ([]Message, error) {
 		data Message
 	)
 	if _, err = fs.dataFile.Seek(0, 0); err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to seek a offset to the start of a data file: %v", err)
 	}
 	for {
 		row, err = fs.reader.ReadBytes(EOL)
@@ -125,7 +111,7 @@ func (fs *FileStorage) GetMessages(offset int) ([]Message, error) {
 		msgs = append(msgs, data)
 	}
 	if err != io.EOF {
-		return nil, err
+		return nil, fmt.Errorf("error while reading data file: %v", err)
 	}
 	return msgs, nil
 }