1 files changed, 103 insertions, 0 deletions
diff --git a/src/android/net/util/HostnameTransliterator.java b/src/android/net/util/HostnameTransliterator.java
new file mode 100644
index 0000000..cf126d1
--- /dev/null
+++ b/src/android/net/util/HostnameTransliterator.java
@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.util;
+
+import android.icu.text.Transliterator;
+import android.text.TextUtils;
+import android.util.Log;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.VisibleForTesting;
+
+import java.util.Collections;
+import java.util.Enumeration;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Transliterator to display a human-readable DHCP client hostname.
+ */
+public class HostnameTransliterator {
+    private static final String TAG = "HostnameTransliterator";
+
+    // Maximum length of hostname to be encoded in the DHCP message. Following RFC1035#2.3.4
+    // and this transliterator converts the device name to a single label, so the label length
+    // limit applies to the whole hostname.
+    private static final int MAX_DNS_LABEL_LENGTH = 63;
+
+    @Nullable
+    private final Transliterator mTransliterator;
+
+    public HostnameTransliterator() {
+        final Enumeration<String> availableIDs = Transliterator.getAvailableIDs();
+        final Set<String> actualIds = new HashSet<>(Collections.list(availableIDs));
+        final StringBuilder rules = new StringBuilder();
+        if (actualIds.contains("Any-ASCII")) {
+            rules.append(":: Any-ASCII; ");
+        } else if (actualIds.contains("Any-Latin") && actualIds.contains("Latin-ASCII")) {
+            rules.append(":: Any-Latin; :: Latin-ASCII; ");
+        } else {
+            Log.e(TAG, "ICU Transliterator doesn't include supported ID");
+            mTransliterator = null;
+            return;
+        }
+        mTransliterator = Transliterator.createFromRules("", rules.toString(),
+                Transliterator.FORWARD);
+    }
+
+    @VisibleForTesting
+    public HostnameTransliterator(Transliterator transliterator) {
+        mTransliterator = transliterator;
+    }
+
+    // RFC952 and RFC1123 stipulates an valid hostname should be:
+    // 1. Only contain the alphabet (A-Z, a-z), digits (0-9), minus sign (-).
+    // 2. No blank or space characters are permitted as part of a name.
+    // 3. The first character must be an alpha character or digit.
+    // 4. The last character must not be a minus sign (-).
+    private String maybeRemoveRedundantSymbols(@NonNull String string) {
+        String result = string.replaceAll("[^a-zA-Z0-9-]", "-");
+        result = result.replaceAll("-+", "-");
+        if (result.startsWith("-")) {
+            result = result.replaceFirst("-", "");
+        }
+        if (result.endsWith("-")) {
+            result = result.substring(0, result.length() - 1);
+        }
+        return result;
+    }
+
+    /**
+     *  Transliterate the device name to valid hostname that could be human-readable string.
+     */
+    public String transliterate(@NonNull String deviceName) {
+        if (deviceName == null) return null;
+        if (mTransliterator == null) {
+            if (!deviceName.matches("\\p{ASCII}*")) return null;
+            deviceName = maybeRemoveRedundantSymbols(deviceName);
+            if (TextUtils.isEmpty(deviceName)) return null;
+            return deviceName.length() > MAX_DNS_LABEL_LENGTH
+                    ? deviceName.substring(0, MAX_DNS_LABEL_LENGTH) : deviceName;
+        }
+
+        String hostname = maybeRemoveRedundantSymbols(mTransliterator.transliterate(deviceName));
+        if (TextUtils.isEmpty(hostname)) return null;
+        return hostname.length() > MAX_DNS_LABEL_LENGTH
+                ? hostname.substring(0, MAX_DNS_LABEL_LENGTH) : hostname;
+    }
+}