From 7f3c4d0472f625c6587f8a49faf1a2695bdeb1ea Mon Sep 17 00:00:00 2001
From: horvist <horvist90@gmail.com>
Date: Sat, 5 Apr 2014 12:09:08 +0200
Subject: [PATCH] IP's are scanned reversly when the end IP address is lower
 than the start IP address.

---
 src/net/azib/ipscan/feeders/RangeFeeder.java  | 14 ++++++--
 .../azib/ipscan/util/InetAddressUtils.java    | 32 +++++++++++++++++--
 2 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/src/net/azib/ipscan/feeders/RangeFeeder.java b/src/net/azib/ipscan/feeders/RangeFeeder.java
index 4caf24ac..c3dbecf3 100644
--- a/src/net/azib/ipscan/feeders/RangeFeeder.java
+++ b/src/net/azib/ipscan/feeders/RangeFeeder.java
@@ -26,6 +26,7 @@ public class RangeFeeder extends AbstractFeeder {
 	private InetAddress endIP;
 	private InetAddress originalEndIP;
 	private InetAddress currentIP;
+	private boolean isReverse;
 	
 	double percentageComplete;
 	double percentageIncrement;
@@ -44,12 +45,15 @@ public class RangeFeeder extends AbstractFeeder {
 		try {
 			this.startIP = this.currentIP = InetAddress.getByName(startIP);
 			this.endIP = this.originalEndIP = InetAddress.getByName(endIP);
+			this.isReverse = false;
 		}
 		catch (UnknownHostException e) {
 			throw new FeederException("malformedIP");
 		}
 		if (InetAddressUtils.greaterThan(this.startIP, this.endIP)) {
-			throw new FeederException("range.greaterThan");
+			this.isReverse = true;
+			this.endIP = InetAddressUtils.decrement(InetAddressUtils
+					.decrement(this.endIP));
 		}
 		initPercentageIncrement();
 		this.endIP = InetAddressUtils.increment(this.endIP);
@@ -66,7 +70,7 @@ public class RangeFeeder extends AbstractFeeder {
 		rawEndIP = rawEndIP >= 0 ? rawEndIP : rawEndIP + Integer.MAX_VALUE;
 		rawStartIP = rawStartIP >= 0 ? rawStartIP : rawStartIP + Integer.MAX_VALUE;
 		// compute 1% of the whole range
-		percentageIncrement = 100.0/(rawEndIP - rawStartIP + 1);
+		percentageIncrement = Math.abs(100.0 / (rawEndIP - rawStartIP + 1));
 		percentageComplete = 0;
 	}
 	
@@ -78,7 +82,11 @@ public class RangeFeeder extends AbstractFeeder {
 	public ScanningSubject next() {
 		percentageComplete += percentageIncrement;
 		InetAddress prevIP = this.currentIP;
-		this.currentIP = InetAddressUtils.increment(prevIP);
+		if (this.isReverse) {
+			this.currentIP = InetAddressUtils.decrement(prevIP);
+		} else {
+			this.currentIP = InetAddressUtils.increment(prevIP);
+		}
 		return new ScanningSubject(prevIP);
 	}
 
diff --git a/src/net/azib/ipscan/util/InetAddressUtils.java b/src/net/azib/ipscan/util/InetAddressUtils.java
index 919e9c65..c8c451f0 100644
--- a/src/net/azib/ipscan/util/InetAddressUtils.java
+++ b/src/net/azib/ipscan/util/InetAddressUtils.java
@@ -82,11 +82,39 @@ public class InetAddressUtils {
 	 * Increments an IP address by 1.
 	 */
 	public static InetAddress increment(InetAddress address) {
+		return modifyInetAddress(address, true);
+	}
+
+	/**
+	 * Decrements an IP address by 1.
+	 */
+	public static InetAddress decrement(InetAddress address) {
+		return modifyInetAddress(address, false);
+	}
+
+	/**
+	 * Increments or decrements an IP address by 1.
+	 * 
+	 * @param address
+	 *            the IP address
+	 * @param isIncrement
+	 * @return incremented/decremented IP address
+	 */
+	private static InetAddress modifyInetAddress(InetAddress address,
+			boolean isIncrement) {
 		try {
 			byte[] newAddress = address.getAddress();
 			for (int i = newAddress.length-1; i >= 0; i--) {
-				if (++newAddress[i] != 0x00)
-					break;
+				if (isIncrement) {
+					if (++newAddress[i] != 0x00) {
+						break;
+					}
+				} else {
+					if (--newAddress[i] != 0x00) {
+						break;
+					}
+				}
+
 			}
 			return InetAddress.getByAddress(newAddress);
 		}