1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 package org.apache.commons.fileupload.util.mime; 18 19 import java.io.IOException; 20 import java.io.OutputStream; 21 22 /** 23 * @since 1.3 24 */ 25 final class QuotedPrintableDecoder { 26 27 /** 28 * The shift value required to create the upper nibble 29 * from the first of 2 byte values converted from ascii hex. 30 */ 31 private static final int UPPER_NIBBLE_SHIFT = Byte.SIZE / 2; 32 33 /** 34 * Hidden constructor, this class must not be instantiated. 35 */ 36 private QuotedPrintableDecoder() { 37 // do nothing 38 } 39 40 /** 41 * Decode the encoded byte data writing it to the given output stream. 42 * 43 * @param data The array of byte data to decode. 44 * @param out The output stream used to return the decoded data. 45 * 46 * @return the number of bytes produced. 47 * @throws IOException 48 */ 49 public static int decode(byte[] data, OutputStream out) throws IOException { 50 int off = 0; 51 int length = data.length; 52 int endOffset = off + length; 53 int bytesWritten = 0; 54 55 while (off < endOffset) { 56 byte ch = data[off++]; 57 58 // space characters were translated to '_' on encode, so we need to translate them back. 59 if (ch == '_') { 60 out.write(' '); 61 } else if (ch == '=') { 62 // we found an encoded character. Reduce the 3 char sequence to one. 63 // but first, make sure we have two characters to work with. 64 if (off + 1 >= endOffset) { 65 throw new IOException("Invalid quoted printable encoding; truncated escape sequence"); 66 } 67 68 byte b1 = data[off++]; 69 byte b2 = data[off++]; 70 71 // we've found an encoded carriage return. The next char needs to be a newline 72 if (b1 == '\r') { 73 if (b2 != '\n') { 74 throw new IOException("Invalid quoted printable encoding; CR must be followed by LF"); 75 } 76 // this was a soft linebreak inserted by the encoding. We just toss this away 77 // on decode. 78 } else { 79 // this is a hex pair we need to convert back to a single byte. 80 int c1 = hexToBinary(b1); 81 int c2 = hexToBinary(b2); 82 out.write((c1 << UPPER_NIBBLE_SHIFT) | c2); 83 // 3 bytes in, one byte out 84 bytesWritten++; 85 } 86 } else { 87 // simple character, just write it out. 88 out.write(ch); 89 bytesWritten++; 90 } 91 } 92 93 return bytesWritten; 94 } 95 96 /** 97 * Convert a hex digit to the binary value it represents. 98 * 99 * @param b the ascii hex byte to convert (0-0, A-F, a-f) 100 * @return the int value of the hex byte, 0-15 101 * @throws IOException if the byte is not a valid hex digit. 102 */ 103 private static int hexToBinary(final byte b) throws IOException { 104 // CHECKSTYLE IGNORE MagicNumber FOR NEXT 1 LINE 105 final int i = Character.digit((char) b, 16); 106 if (i == -1) { 107 throw new IOException("Invalid quoted printable encoding: not a valid hex digit: " + b); 108 } 109 return i; 110 } 111 112 }