1 /* 2 * Copyright (C) 2011 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.android.settings.bluetooth; 18 19 import android.text.InputFilter; 20 import android.text.Spanned; 21 22 /** 23 * This filter will constrain edits so that the text length is not 24 * greater than the specified number of bytes using UTF-8 encoding. 25 * <p>The JNI method used by {@link android.server.BluetoothService} 26 * to convert UTF-16 to UTF-8 doesn't support surrogate pairs, 27 * therefore code points outside of the basic multilingual plane 28 * (0000-FFFF) will be encoded as a pair of 3-byte UTF-8 characters, 29 * rather than a single 4-byte UTF-8 encoding. Dalvik implements this 30 * conversion in {@code convertUtf16ToUtf8()} in 31 * {@code dalvik/vm/UtfString.c}. 32 * <p>This JNI method is unlikely to change in the future due to 33 * backwards compatibility requirements. It's also unclear whether 34 * the installed base of Bluetooth devices would correctly handle the 35 * encoding of surrogate pairs in UTF-8 as 4 bytes rather than 6. 36 * However, this filter will still work in scenarios where surrogate 37 * pairs are encoded as 4 bytes, with the caveat that the maximum 38 * length will be constrained more conservatively than necessary. 39 */ 40 public class Utf8ByteLengthFilter implements InputFilter { 41 private final int mMaxBytes; 42 43 Utf8ByteLengthFilter(int maxBytes) { 44 mMaxBytes = maxBytes; 45 } 46 47 public CharSequence filter(CharSequence source, int start, int end, 48 Spanned dest, int dstart, int dend) { 49 int srcByteCount = 0; 50 // count UTF-8 bytes in source substring 51 for (int i = start; i < end; i++) { 52 char c = source.charAt(i); 53 srcByteCount += (c < (char) 0x0080) ? 1 : (c < (char) 0x0800 ? 2 : 3); 54 } 55 int destLen = dest.length(); 56 int destByteCount = 0; 57 // count UTF-8 bytes in destination excluding replaced section 58 for (int i = 0; i < destLen; i++) { 59 if (i < dstart || i >= dend) { 60 char c = dest.charAt(i); 61 destByteCount += (c < (char) 0x0080) ? 1 : (c < (char) 0x0800 ? 2 : 3); 62 } 63 } 64 int keepBytes = mMaxBytes - destByteCount; 65 if (keepBytes <= 0) { 66 return ""; 67 } else if (keepBytes >= srcByteCount) { 68 return null; // use original dest string 69 } else { 70 // find end position of largest sequence that fits in keepBytes 71 for (int i = start; i < end; i++) { 72 char c = source.charAt(i); 73 keepBytes -= (c < (char) 0x0080) ? 1 : (c < (char) 0x0800 ? 2 : 3); 74 if (keepBytes < 0) { 75 return source.subSequence(start, i); 76 } 77 } 78 // If the entire substring fits, we should have returned null 79 // above, so this line should not be reached. If for some 80 // reason it is, return null to use the original dest string. 81 return null; 82 } 83 } 84 } 85
