diff --git a/src/protocolP2P/FileList.java b/src/protocolP2P/FileList.java
index bc2ca69..103dec3 100644
--- a/src/protocolP2P/FileList.java
+++ b/src/protocolP2P/FileList.java
@@ -7,6 +7,7 @@ import exception.ProtocolError;
 import exception.InternalError;
 import exception.SizeError;
 import java.io.UnsupportedEncodingException;
+import tools.BytesArrayTools;
 
 /** Representation of payload for list response.
  * @author	Louis Royer
@@ -63,40 +64,14 @@ public class FileList extends Payload {
 	 */
 	protected byte[] toPacket() throws InternalError {
 		// compute size
-		int size = PAYLOAD_START_POSITION;
-		for (String s : fileList) {
-			size += s.length();
-			size += 1; // size for '\n'
-		}
-		size -=1; // remove trailing '\n'
+		int size = PAYLOAD_START_POSITION + BytesArrayTools.computeStringArraySize(fileList, "\n");
 		byte[] packet = new byte[size]; // java initialize all to zero
 		// set request/response code
 		packet[RequestResponseCode.RRCODE_POSITION] = requestResponseCode.codeValue;
 		// set payload size
 		setPayloadSize(size - PAYLOAD_START_POSITION, packet);
 		// Write fileList
-		int bCount = PAYLOAD_START_POSITION;
-		for(String s : fileList) {
-			if (bCount != PAYLOAD_START_POSITION) { // not on first iteration
-				try {
-					packet[bCount] = "\n".getBytes("UTF-8")[0]; // separator
-				} catch (UnsupportedEncodingException e) {
-					throw new InternalError();
-				}
-				bCount += 1;
-			}
-			// Copy filename
-			try {
-				byte[] sb = s.getBytes("UTF-8");
-				for(byte b : sb) {
-					packet[bCount] = b;
-					bCount += 1;
-				}
-			} catch (UnsupportedEncodingException e) {
-				throw new InternalError();
-			}
-			
-		}
+		BytesArrayTools.writeStringArray(packet, fileList, PAYLOAD_START_POSITION, "\n");
 		return packet;
 	}
 
diff --git a/src/tools/BytesArrayTools.java b/src/tools/BytesArrayTools.java
index 924f4fc..e09d9a8 100644
--- a/src/tools/BytesArrayTools.java
+++ b/src/tools/BytesArrayTools.java
@@ -1,5 +1,8 @@
 package tools;
 import exception.SizeError;
+import java.io.UnsupportedEncodingException;
+
+
 /** Helper to manipulate byte[].
  * @author	Louis Royer
  * @author	Flavien Haas
@@ -116,4 +119,46 @@ public class BytesArrayTools {
 		}
 		return new String(bArray, 0, cpt + 1);
 	}
+
+	/** Write a list of string to a byte array. String are separated by a separator.
+	 * @param byteArray	array to write
+	 * @param strArray	string array to read
+	 * @param start	start position to write in byteArray
+	 * @param separator	separator to use
+	 * @throws	InternalError
+	 */
+	public static void writeStringArray(byte[] byteArray, String[] strArray, int start, String separator) throws InternalError {
+		int bCount = start;
+		try {
+			byte[] sepb = separator.getBytes("UTF-8");
+			for(String s : strArray) {
+				// write separator
+				if (bCount != start) { // not on first iteration
+					for (byte b : sepb) {
+						byteArray[bCount] = b;
+						bCount += 1;
+					}
+				}
+				// Copy string
+				byte[] sb = s.getBytes("UTF-8");
+				for(byte b : sb) {
+					byteArray[bCount] = b;
+					bCount += 1;
+				}
+			}
+		} catch (UnsupportedEncodingException e) {
+			throw new InternalError();
+		}
+	}
+
+	public static int computeStringArraySize(String[] strArray, String separator) {
+		int size = 0;
+		for (String s: strArray) {
+			if (size != 0) {
+				size += separator.length();
+			}
+			size += s.length();
+		}
+		return size;
+	}
 }