Fix for hexdumpc with --length

Author: fileformat

cmd/hexdumpc/hexdumpc.go

@@ -28,19 +28,24 @@ func hexdump(fileName string, offset, length int64, w io.Writer) error {
 		return err
 	}
 	defer file.Close()
-	// Seek to the offset
+
+	reader := bufio.NewReaderSize(file, 1024*1024)
+
 	if offset > 0 {
-		if _, err := file.Seek(offset, io.SeekStart); err != nil {
+		skip := make([]byte, offset)
+		skipCount, err := io.ReadFull(reader, skip)
+		if err != nil {
 			return err
 		}
+		if int64(skipCount) != offset {
+			return fmt.Errorf("failed to skip the requested number of bytes (actual: %d, expected: %d)", skipCount, offset)
+		}
 	}
 
-	reader := bufio.NewReaderSize(file, 1024*1024)
-
 	var count int64 = 0
+	var buf = make([]byte, 16)
 	for {
 		// Read a chunk of data
-		buf := make([]byte, 16)
 		n, err := reader.Read(buf)
 		if err != nil {
 			if err == io.EOF {
@@ -133,8 +138,12 @@ func main() {
 			arg = "/dev/stdin"
 		}
 
-		if err := hexdump(arg, *offset, *length, bufio.NewWriter(os.Stdout)); err != nil {
-			panic(err)
+		w := bufio.NewWriter(os.Stdout)
+		if err := hexdump(arg, *offset, *length, w); err != nil {
+			w.Flush()
+			fmt.Printf("ERROR: %v\n", err)
+			os.Exit(1)
 		}
+		w.Flush()
 	}
 }