Add two utility methods for IPv4 netmasks.
1. Add a validating method to convert a netmask to a prefix length.
2. Add a function to get the implicit netmask of an IPv4 address.
3. Add a unit test.
Bug: 19704592
Change-Id: Icb9f58d3903ea01df9e3720383c9bd5db6dd8f26
diff --git a/core/java/android/net/NetworkUtils.java b/core/java/android/net/NetworkUtils.java
index 8003afb..4f35a22 100644
--- a/core/java/android/net/NetworkUtils.java
+++ b/core/java/android/net/NetworkUtils.java
@@ -230,6 +230,25 @@
}
/**
+ * Convert an IPv4 netmask to a prefix length, checking that the netmask is contiguous.
+ * @param netmask as a {@code Inet4Address}.
+ * @return the network prefix length
+ * @throws IllegalArgumentException the specified netmask was not contiguous.
+ * @hide
+ */
+ public static int netmaskToPrefixLength(Inet4Address netmask) {
+ // inetAddressToInt returns an int in *network* byte order.
+ int i = Integer.reverseBytes(inetAddressToInt(netmask));
+ int prefixLength = Integer.bitCount(i);
+ int trailingZeros = Integer.numberOfTrailingZeros(i);
+ if (trailingZeros != 32 - prefixLength) {
+ throw new IllegalArgumentException("Non-contiguous netmask: " + Integer.toHexString(i));
+ }
+ return prefixLength;
+ }
+
+
+ /**
* Create an InetAddress from a string where the string must be a standard
* representation of a V4 or V6 address. Avoids doing a DNS lookup on failure
* but it will throw an IllegalArgumentException in that case.
@@ -309,6 +328,22 @@
}
/**
+ * Returns the implicit netmask of an IPv4 address, as was the custom before 1993.
+ */
+ public static int getImplicitNetmask(Inet4Address address) {
+ int firstByte = address.getAddress()[0] & 0xff; // Convert to an unsigned value.
+ if (firstByte < 128) {
+ return 8;
+ } else if (firstByte < 192) {
+ return 16;
+ } else if (firstByte < 224) {
+ return 24;
+ } else {
+ return 32; // Will likely not end well for other reasons.
+ }
+ }
+
+ /**
* Utility method to parse strings such as "192.0.2.5/24" or "2001:db8::cafe:d00d/64".
* @hide
*/