[Cronet] Public key pinning for Java API

components/cronet/android/api/src/org/chromium/net/CronetUtil.java

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+package org.chromium.net;
+
+import java.net.IDN;
+import java.util.regex.Pattern;
+
+/**
+ * A set of generic utility methods.
+ */
+class CronetUtil {
+    // Expression that defines a valid IPv4 decimal number in range [0, 255].
+    private static final String VALID_IP_NUMBER =
+            "([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])";
+    // Expression that defines a valid IPv4 address, which is the sequence of four
+    // |VALID_IP_NUMBER| numbers separated by '.'.
+    private static final String VALID_IP_EXPR =
+            "^(" + VALID_IP_NUMBER + "\\.){3}" + VALID_IP_NUMBER + "$";
+    private static final Pattern VALID_IP_PATTERN = Pattern.compile(VALID_IP_EXPR);
+
+    private CronetUtil() {}
+
+    /**
+     * Checks whether a given string that represents a host name is valid. The method
+     * verifies the length of the host name labels (max 63 characters) and the total length of
+     * the host name (max 255 characters). The method does not verify the validity of the top
+     * level domain.
+     *
+     * Note: Currently Cronet doesn't have native implementation of host name validation that can
+     *       be used. There is code that parses a provided URL but doesn't ensure its correctness.
+     *       The implementation relies on {@code getaddrinfo} function.
+     *
+     * @param hostName host name to check.
+     * @return true if the string is a valid host name.
+     */
+    static boolean isValidHostName(String hostName) {
+        try {
+            IDN.toASCII(hostName, IDN.USE_STD3_ASCII_RULES);
+        } catch (IllegalArgumentException ex) {
+            // The hostname is illegal according to RFC 1122 and RFC 1123.
+            return false;
+        }
+        return true;
+    }
+
+    /**
+     * Checks whether a given string that represents an IPv4 address is valid.
+     * The format of the string should be in the decimal xxx.xxx.xxx.xxx format
+     * with no leading zeroes.
+     *
+     * @param addr IPv4 address to check.
+     * @return true if the string is a valid IPv4 address.
+     */
+    static boolean isValidIPv4(String addr) {
+        return VALID_IP_PATTERN.matcher(addr).matches();
+    }
+}