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| 1 | +package com.thealgorithms.conversions; |
| 2 | + |
| 3 | +import java.nio.charset.StandardCharsets; |
| 4 | +import java.util.ArrayList; |
| 5 | +import java.util.List; |
| 6 | + |
| 7 | +/** |
| 8 | + * Base64 is a group of binary-to-text encoding schemes that represent binary data |
| 9 | + * in an ASCII string format by translating it into a radix-64 representation. |
| 10 | + * Each base64 digit represents exactly 6 bits of data. |
| 11 | + * |
| 12 | + * Base64 encoding is commonly used when there is a need to encode binary data |
| 13 | + * that needs to be stored and transferred over media that are designed to deal |
| 14 | + * with textual data. |
| 15 | + * |
| 16 | + * Wikipedia Reference: https://en.wikipedia.org/wiki/Base64 |
| 17 | + * Author: Nithin U. |
| 18 | + * Github: https://github.com/NithinU2802 |
| 19 | + */ |
| 20 | + |
| 21 | +public final class Base64 { |
| 22 | + |
| 23 | + // Base64 character set |
| 24 | + private static final String BASE64_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; |
| 25 | + private static final char PADDING_CHAR = '='; |
| 26 | + |
| 27 | + private Base64() { |
| 28 | + } |
| 29 | + |
| 30 | + /** |
| 31 | + * Encodes the given byte array to a Base64 encoded string. |
| 32 | + * |
| 33 | + * @param input the byte array to encode |
| 34 | + * @return the Base64 encoded string |
| 35 | + * @throws IllegalArgumentException if input is null |
| 36 | + */ |
| 37 | + public static String encode(byte[] input) { |
| 38 | + if (input == null) { |
| 39 | + throw new IllegalArgumentException("Input cannot be null"); |
| 40 | + } |
| 41 | + |
| 42 | + if (input.length == 0) { |
| 43 | + return ""; |
| 44 | + } |
| 45 | + |
| 46 | + StringBuilder result = new StringBuilder(); |
| 47 | + int padding = 0; |
| 48 | + |
| 49 | + // Process input in groups of 3 bytes |
| 50 | + for (int i = 0; i < input.length; i += 3) { |
| 51 | + // Get up to 3 bytes |
| 52 | + int byte1 = input[i] & 0xFF; |
| 53 | + int byte2 = (i + 1 < input.length) ? (input[i + 1] & 0xFF) : 0; |
| 54 | + int byte3 = (i + 2 < input.length) ? (input[i + 2] & 0xFF) : 0; |
| 55 | + |
| 56 | + // Calculate padding needed |
| 57 | + if (i + 1 >= input.length) { |
| 58 | + padding = 2; |
| 59 | + } else if (i + 2 >= input.length) { |
| 60 | + padding = 1; |
| 61 | + } |
| 62 | + |
| 63 | + // Combine 3 bytes into a 24-bit number |
| 64 | + int combined = (byte1 << 16) | (byte2 << 8) | byte3; |
| 65 | + |
| 66 | + // Extract four 6-bit groups |
| 67 | + result.append(BASE64_CHARS.charAt((combined >> 18) & 0x3F)); |
| 68 | + result.append(BASE64_CHARS.charAt((combined >> 12) & 0x3F)); |
| 69 | + result.append(BASE64_CHARS.charAt((combined >> 6) & 0x3F)); |
| 70 | + result.append(BASE64_CHARS.charAt(combined & 0x3F)); |
| 71 | + } |
| 72 | + |
| 73 | + // Replace padding characters |
| 74 | + if (padding > 0) { |
| 75 | + result.setLength(result.length() - padding); |
| 76 | + for (int i = 0; i < padding; i++) { |
| 77 | + result.append(PADDING_CHAR); |
| 78 | + } |
| 79 | + } |
| 80 | + |
| 81 | + return result.toString(); |
| 82 | + } |
| 83 | + |
| 84 | + /** |
| 85 | + * Encodes the given string to a Base64 encoded string using UTF-8 encoding. |
| 86 | + * |
| 87 | + * @param input the string to encode |
| 88 | + * @return the Base64 encoded string |
| 89 | + * @throws IllegalArgumentException if input is null |
| 90 | + */ |
| 91 | + public static String encode(String input) { |
| 92 | + if (input == null) { |
| 93 | + throw new IllegalArgumentException("Input cannot be null"); |
| 94 | + } |
| 95 | + |
| 96 | + return encode(input.getBytes(StandardCharsets.UTF_8)); |
| 97 | + } |
| 98 | + |
| 99 | + /** |
| 100 | + * Decodes the given Base64 encoded string to a byte array. |
| 101 | + * |
| 102 | + * @param input the Base64 encoded string to decode |
| 103 | + * @return the decoded byte array |
| 104 | + * @throws IllegalArgumentException if input is null or contains invalid Base64 characters |
| 105 | + */ |
| 106 | + public static byte[] decode(String input) { |
| 107 | + if (input == null) { |
| 108 | + throw new IllegalArgumentException("Input cannot be null"); |
| 109 | + } |
| 110 | + |
| 111 | + if (input.isEmpty()) { |
| 112 | + return new byte[0]; |
| 113 | + } |
| 114 | + |
| 115 | + // Strict RFC 4648 compliance: length must be a multiple of 4 |
| 116 | + if (input.length() % 4 != 0) { |
| 117 | + throw new IllegalArgumentException("Invalid Base64 input length; must be multiple of 4"); |
| 118 | + } |
| 119 | + |
| 120 | + // Validate padding: '=' can only appear at the end (last 1 or 2 chars) |
| 121 | + int firstPadding = input.indexOf('='); |
| 122 | + if (firstPadding != -1 && firstPadding < input.length() - 2) { |
| 123 | + throw new IllegalArgumentException("Padding '=' can only appear at the end (last 1 or 2 characters)"); |
| 124 | + } |
| 125 | + |
| 126 | + List<Byte> result = new ArrayList<>(); |
| 127 | + |
| 128 | + // Process input in groups of 4 characters |
| 129 | + for (int i = 0; i < input.length(); i += 4) { |
| 130 | + // Get up to 4 characters |
| 131 | + int char1 = getBase64Value(input.charAt(i)); |
| 132 | + int char2 = getBase64Value(input.charAt(i + 1)); |
| 133 | + int char3 = input.charAt(i + 2) == '=' ? 0 : getBase64Value(input.charAt(i + 2)); |
| 134 | + int char4 = input.charAt(i + 3) == '=' ? 0 : getBase64Value(input.charAt(i + 3)); |
| 135 | + |
| 136 | + // Combine four 6-bit groups into a 24-bit number |
| 137 | + int combined = (char1 << 18) | (char2 << 12) | (char3 << 6) | char4; |
| 138 | + |
| 139 | + // Extract three 8-bit bytes |
| 140 | + result.add((byte) ((combined >> 16) & 0xFF)); |
| 141 | + if (input.charAt(i + 2) != '=') { |
| 142 | + result.add((byte) ((combined >> 8) & 0xFF)); |
| 143 | + } |
| 144 | + if (input.charAt(i + 3) != '=') { |
| 145 | + result.add((byte) (combined & 0xFF)); |
| 146 | + } |
| 147 | + } |
| 148 | + |
| 149 | + // Convert List<Byte> to byte[] |
| 150 | + byte[] resultArray = new byte[result.size()]; |
| 151 | + for (int i = 0; i < result.size(); i++) { |
| 152 | + resultArray[i] = result.get(i); |
| 153 | + } |
| 154 | + |
| 155 | + return resultArray; |
| 156 | + } |
| 157 | + |
| 158 | + /** |
| 159 | + * Decodes the given Base64 encoded string to a string using UTF-8 encoding. |
| 160 | + * |
| 161 | + * @param input the Base64 encoded string to decode |
| 162 | + * @return the decoded string |
| 163 | + * @throws IllegalArgumentException if input is null or contains invalid Base64 characters |
| 164 | + */ |
| 165 | + public static String decodeToString(String input) { |
| 166 | + if (input == null) { |
| 167 | + throw new IllegalArgumentException("Input cannot be null"); |
| 168 | + } |
| 169 | + |
| 170 | + byte[] decodedBytes = decode(input); |
| 171 | + return new String(decodedBytes, StandardCharsets.UTF_8); |
| 172 | + } |
| 173 | + |
| 174 | + /** |
| 175 | + * Gets the numeric value of a Base64 character. |
| 176 | + * |
| 177 | + * @param c the Base64 character |
| 178 | + * @return the numeric value (0-63) |
| 179 | + * @throws IllegalArgumentException if character is not a valid Base64 character |
| 180 | + */ |
| 181 | + private static int getBase64Value(char c) { |
| 182 | + if (c >= 'A' && c <= 'Z') { |
| 183 | + return c - 'A'; |
| 184 | + } else if (c >= 'a' && c <= 'z') { |
| 185 | + return c - 'a' + 26; |
| 186 | + } else if (c >= '0' && c <= '9') { |
| 187 | + return c - '0' + 52; |
| 188 | + } else if (c == '+') { |
| 189 | + return 62; |
| 190 | + } else if (c == '/') { |
| 191 | + return 63; |
| 192 | + } else { |
| 193 | + throw new IllegalArgumentException("Invalid Base64 character: " + c); |
| 194 | + } |
| 195 | + } |
| 196 | +} |
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