Java tutorial
/* * Copyright (C) 2010 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.util; import android.annotation.UnsupportedAppUsage; import java.io.UnsupportedEncodingException; /** * Utilities for encoding and decoding the Base64 representation of * binary data. See RFCs <a * href="http://www.ietf.org/rfc/rfc2045.txt">2045</a> and <a * href="http://www.ietf.org/rfc/rfc3548.txt">3548</a>. */ public class Base64 { /** * Default values for encoder/decoder flags. */ public static final int DEFAULT = 0; /** * Encoder flag bit to omit the padding '=' characters at the end * of the output (if any). */ public static final int NO_PADDING = 1; /** * Encoder flag bit to omit all line terminators (i.e., the output * will be on one long line). */ public static final int NO_WRAP = 2; /** * Encoder flag bit to indicate lines should be terminated with a * CRLF pair instead of just an LF. Has no effect if {@code * NO_WRAP} is specified as well. */ public static final int CRLF = 4; /** * Encoder/decoder flag bit to indicate using the "URL and * filename safe" variant of Base64 (see RFC 3548 section 4) where * {@code -} and {@code _} are used in place of {@code +} and * {@code /}. */ public static final int URL_SAFE = 8; /** * Flag to pass to {@link Base64OutputStream} to indicate that it * should not close the output stream it is wrapping when it * itself is closed. */ public static final int NO_CLOSE = 16; // -------------------------------------------------------- // shared code // -------------------------------------------------------- /* package */ static abstract class Coder { public byte[] output; public int op; /** * Encode/decode another block of input data. this.output is * provided by the caller, and must be big enough to hold all * the coded data. On exit, this.opwill be set to the length * of the coded data. * * @param finish true if this is the final call to process for * this object. Will finalize the coder state and * include any final bytes in the output. * * @return true if the input so far is good; false if some * error has been detected in the input stream.. */ public abstract boolean process(byte[] input, int offset, int len, boolean finish); /** * @return the maximum number of bytes a call to process() * could produce for the given number of input bytes. This may * be an overestimate. */ public abstract int maxOutputSize(int len); } // -------------------------------------------------------- // decoding // -------------------------------------------------------- /** * Decode the Base64-encoded data in input and return the data in * a new byte array. * * <p>The padding '=' characters at the end are considered optional, but * if any are present, there must be the correct number of them. * * @param str the input String to decode, which is converted to * bytes using the default charset * @param flags controls certain features of the decoded output. * Pass {@code DEFAULT} to decode standard Base64. * * @throws IllegalArgumentException if the input contains * incorrect padding */ public static byte[] decode(String str, int flags) { return decode(str.getBytes(), flags); } /** * Decode the Base64-encoded data in input and return the data in * a new byte array. * * <p>The padding '=' characters at the end are considered optional, but * if any are present, there must be the correct number of them. * * @param input the input array to decode * @param flags controls certain features of the decoded output. * Pass {@code DEFAULT} to decode standard Base64. * * @throws IllegalArgumentException if the input contains * incorrect padding */ public static byte[] decode(byte[] input, int flags) { return decode(input, 0, input.length, flags); } /** * Decode the Base64-encoded data in input and return the data in * a new byte array. * * <p>The padding '=' characters at the end are considered optional, but * if any are present, there must be the correct number of them. * * @param input the data to decode * @param offset the position within the input array at which to start * @param len the number of bytes of input to decode * @param flags controls certain features of the decoded output. * Pass {@code DEFAULT} to decode standard Base64. * * @throws IllegalArgumentException if the input contains * incorrect padding */ public static byte[] decode(byte[] input, int offset, int len, int flags) { // Allocate space for the most data the input could represent. // (It could contain less if it contains whitespace, etc.) Decoder decoder = new Decoder(flags, new byte[len * 3 / 4]); if (!decoder.process(input, offset, len, true)) { throw new IllegalArgumentException("bad base-64"); } // Maybe we got lucky and allocated exactly enough output space. if (decoder.op == decoder.output.length) { return decoder.output; } // Need to shorten the array, so allocate a new one of the // right size and copy. byte[] temp = new byte[decoder.op]; System.arraycopy(decoder.output, 0, temp, 0, decoder.op); return temp; } /* package */ static class Decoder extends Coder { /** * Lookup table for turning bytes into their position in the * Base64 alphabet. */ private static final int DECODE[] = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, }; /** * Decode lookup table for the "web safe" variant (RFC 3548 * sec. 4) where - and _ replace + and /. */ private static final int DECODE_WEBSAFE[] = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, 63, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, }; /** Non-data values in the DECODE arrays. */ private static final int SKIP = -1; private static final int EQUALS = -2; /** * States 0-3 are reading through the next input tuple. * State 4 is having read one '=' and expecting exactly * one more. * State 5 is expecting no more data or padding characters * in the input. * State 6 is the error state; an error has been detected * in the input and no future input can "fix" it. */ private int state; // state number (0 to 6) private int value; final private int[] alphabet; public Decoder(int flags, byte[] output) { this.output = output; alphabet = ((flags & URL_SAFE) == 0) ? DECODE : DECODE_WEBSAFE; state = 0; value = 0; } /** * @return an overestimate for the number of bytes {@code * len} bytes could decode to. */ public int maxOutputSize(int len) { return len * 3 / 4 + 10; } /** * Decode another block of input data. * * @return true if the state machine is still healthy. false if * bad base-64 data has been detected in the input stream. */ public boolean process(byte[] input, int offset, int len, boolean finish) { if (this.state == 6) return false; int p = offset; len += offset; // Using local variables makes the decoder about 12% // faster than if we manipulate the member variables in // the loop. (Even alphabet makes a measurable // difference, which is somewhat surprising to me since // the member variable is final.) int state = this.state; int value = this.value; int op = 0; final byte[] output = this.output; final int[] alphabet = this.alphabet; while (p < len) { // Try the fast path: we're starting a new tuple and the // next four bytes of the input stream are all data // bytes. This corresponds to going through states // 0-1-2-3-0. We expect to use this method for most of // the data. // // If any of the next four bytes of input are non-data // (whitespace, etc.), value will end up negative. (All // the non-data values in decode are small negative // numbers, so shifting any of them up and or'ing them // together will result in a value with its top bit set.) // // You can remove this whole block and the output should // be the same, just slower. if (state == 0) { while (p + 4 <= len && (value = ((alphabet[input[p] & 0xff] << 18) | (alphabet[input[p + 1] & 0xff] << 12) | (alphabet[input[p + 2] & 0xff] << 6) | (alphabet[input[p + 3] & 0xff]))) >= 0) { output[op + 2] = (byte) value; output[op + 1] = (byte) (value >> 8); output[op] = (byte) (value >> 16); op += 3; p += 4; } if (p >= len) break; } // The fast path isn't available -- either we've read a // partial tuple, or the next four input bytes aren't all // data, or whatever. Fall back to the slower state // machine implementation. int d = alphabet[input[p++] & 0xff]; switch (state) { case 0: if (d >= 0) { value = d; ++state; } else if (d != SKIP) { this.state = 6; return false; } break; case 1: if (d >= 0) { value = (value << 6) | d; ++state; } else if (d != SKIP) { this.state = 6; return false; } break; case 2: if (d >= 0) { value = (value << 6) | d; ++state; } else if (d == EQUALS) { // Emit the last (partial) output tuple; // expect exactly one more padding character. output[op++] = (byte) (value >> 4); state = 4; } else if (d != SKIP) { this.state = 6; return false; } break; case 3: if (d >= 0) { // Emit the output triple and return to state 0. value = (value << 6) | d; output[op + 2] = (byte) value; output[op + 1] = (byte) (value >> 8); output[op] = (byte) (value >> 16); op += 3; state = 0; } else if (d == EQUALS) { // Emit the last (partial) output tuple; // expect no further data or padding characters. output[op + 1] = (byte) (value >> 2); output[op] = (byte) (value >> 10); op += 2; state = 5; } else if (d != SKIP) { this.state = 6; return false; } break; case 4: if (d == EQUALS) { ++state; } else if (d != SKIP) { this.state = 6; return false; } break; case 5: if (d != SKIP) { this.state = 6; return false; } break; } } if (!finish) { // We're out of input, but a future call could provide // more. this.state = state; this.value = value; this.op = op; return true; } // Done reading input. Now figure out where we are left in // the state machine and finish up. switch (state) { case 0: // Output length is a multiple of three. Fine. break; case 1: // Read one extra input byte, which isn't enough to // make another output byte. Illegal. this.state = 6; return false; case 2: // Read two extra input bytes, enough to emit 1 more // output byte. Fine. output[op++] = (byte) (value >> 4); break; case 3: // Read three extra input bytes, enough to emit 2 more // output bytes. Fine. output[op++] = (byte) (value >> 10); output[op++] = (byte) (value >> 2); break; case 4: // Read one padding '=' when we expected 2. Illegal. this.state = 6; return false; case 5: // Read all the padding '='s we expected and no more. // Fine. break; } this.state = state; this.op = op; return true; } } // -------------------------------------------------------- // encoding // -------------------------------------------------------- /** * Base64-encode the given data and return a newly allocated * String with the result. * * @param input the data to encode * @param flags controls certain features of the encoded output. * Passing {@code DEFAULT} results in output that * adheres to RFC 2045. */ public static String encodeToString(byte[] input, int flags) { try { return new String(encode(input, flags), "US-ASCII"); } catch (UnsupportedEncodingException e) { // US-ASCII is guaranteed to be available. throw new AssertionError(e); } } /** * Base64-encode the given data and return a newly allocated * String with the result. * * @param input the data to encode * @param offset the position within the input array at which to * start * @param len the number of bytes of input to encode * @param flags controls certain features of the encoded output. * Passing {@code DEFAULT} results in output that * adheres to RFC 2045. */ public static String encodeToString(byte[] input, int offset, int len, int flags) { try { return new String(encode(input, offset, len, flags), "US-ASCII"); } catch (UnsupportedEncodingException e) { // US-ASCII is guaranteed to be available. throw new AssertionError(e); } } /** * Base64-encode the given data and return a newly allocated * byte[] with the result. * * @param input the data to encode * @param flags controls certain features of the encoded output. * Passing {@code DEFAULT} results in output that * adheres to RFC 2045. */ public static byte[] encode(byte[] input, int flags) { return encode(input, 0, input.length, flags); } /** * Base64-encode the given data and return a newly allocated * byte[] with the result. * * @param input the data to encode * @param offset the position within the input array at which to * start * @param len the number of bytes of input to encode * @param flags controls certain features of the encoded output. * Passing {@code DEFAULT} results in output that * adheres to RFC 2045. */ public static byte[] encode(byte[] input, int offset, int len, int flags) { Encoder encoder = new Encoder(flags, null); // Compute the exact length of the array we will produce. int output_len = len / 3 * 4; // Account for the tail of the data and the padding bytes, if any. if (encoder.do_padding) { if (len % 3 > 0) { output_len += 4; } } else { switch (len % 3) { case 0: break; case 1: output_len += 2; break; case 2: output_len += 3; break; } } // Account for the newlines, if any. if (encoder.do_newline && len > 0) { output_len += (((len - 1) / (3 * Encoder.LINE_GROUPS)) + 1) * (encoder.do_cr ? 2 : 1); } encoder.output = new byte[output_len]; encoder.process(input, offset, len, true); assert encoder.op == output_len; return encoder.output; } /* package */ static class Encoder extends Coder { /** * Emit a new line every this many output tuples. Corresponds to * a 76-character line length (the maximum allowable according to * <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>). */ public static final int LINE_GROUPS = 19; /** * Lookup table for turning Base64 alphabet positions (6 bits) * into output bytes. */ private static final byte ENCODE[] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/', }; /** * Lookup table for turning Base64 alphabet positions (6 bits) * into output bytes. */ private static final byte ENCODE_WEBSAFE[] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_', }; final private byte[] tail; /* package */ int tailLen; private int count; final public boolean do_padding; final public boolean do_newline; final public boolean do_cr; final private byte[] alphabet; public Encoder(int flags, byte[] output) { this.output = output; do_padding = (flags & NO_PADDING) == 0; do_newline = (flags & NO_WRAP) == 0; do_cr = (flags & CRLF) != 0; alphabet = ((flags & URL_SAFE) == 0) ? ENCODE : ENCODE_WEBSAFE; tail = new byte[2]; tailLen = 0; count = do_newline ? LINE_GROUPS : -1; } /** * @return an overestimate for the number of bytes {@code * len} bytes could encode to. */ public int maxOutputSize(int len) { return len * 8 / 5 + 10; } public boolean process(byte[] input, int offset, int len, boolean finish) { // Using local variables makes the encoder about 9% faster. final byte[] alphabet = this.alphabet; final byte[] output = this.output; int op = 0; int count = this.count; int p = offset; len += offset; int v = -1; // First we need to concatenate the tail of the previous call // with any input bytes available now and see if we can empty // the tail. switch (tailLen) { case 0: // There was no tail. break; case 1: if (p + 2 <= len) { // A 1-byte tail with at least 2 bytes of // input available now. v = ((tail[0] & 0xff) << 16) | ((input[p++] & 0xff) << 8) | (input[p++] & 0xff); tailLen = 0; } ; break; case 2: if (p + 1 <= len) { // A 2-byte tail with at least 1 byte of input. v = ((tail[0] & 0xff) << 16) | ((tail[1] & 0xff) << 8) | (input[p++] & 0xff); tailLen = 0; } break; } if (v != -1) { output[op++] = alphabet[(v >> 18) & 0x3f]; output[op++] = alphabet[(v >> 12) & 0x3f]; output[op++] = alphabet[(v >> 6) & 0x3f]; output[op++] = alphabet[v & 0x3f]; if (--count == 0) { if (do_cr) output[op++] = '\r'; output[op++] = '\n'; count = LINE_GROUPS; } } // At this point either there is no tail, or there are fewer // than 3 bytes of input available. // The main loop, turning 3 input bytes into 4 output bytes on // each iteration. while (p + 3 <= len) { v = ((input[p] & 0xff) << 16) | ((input[p + 1] & 0xff) << 8) | (input[p + 2] & 0xff); output[op] = alphabet[(v >> 18) & 0x3f]; output[op + 1] = alphabet[(v >> 12) & 0x3f]; output[op + 2] = alphabet[(v >> 6) & 0x3f]; output[op + 3] = alphabet[v & 0x3f]; p += 3; op += 4; if (--count == 0) { if (do_cr) output[op++] = '\r'; output[op++] = '\n'; count = LINE_GROUPS; } } if (finish) { // Finish up the tail of the input. Note that we need to // consume any bytes in tail before any bytes // remaining in input; there should be at most two bytes // total. if (p - tailLen == len - 1) { int t = 0; v = ((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 4; tailLen -= t; output[op++] = alphabet[(v >> 6) & 0x3f]; output[op++] = alphabet[v & 0x3f]; if (do_padding) { output[op++] = '='; output[op++] = '='; } if (do_newline) { if (do_cr) output[op++] = '\r'; output[op++] = '\n'; } } else if (p - tailLen == len - 2) { int t = 0; v = (((tailLen > 1 ? tail[t++] : input[p++]) & 0xff) << 10) | (((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 2); tailLen -= t; output[op++] = alphabet[(v >> 12) & 0x3f]; output[op++] = alphabet[(v >> 6) & 0x3f]; output[op++] = alphabet[v & 0x3f]; if (do_padding) { output[op++] = '='; } if (do_newline) { if (do_cr) output[op++] = '\r'; output[op++] = '\n'; } } else if (do_newline && op > 0 && count != LINE_GROUPS) { if (do_cr) output[op++] = '\r'; output[op++] = '\n'; } assert tailLen == 0; assert p == len; } else { // Save the leftovers in tail to be consumed on the next // call to encodeInternal. if (p == len - 1) { tail[tailLen++] = input[p]; } else if (p == len - 2) { tail[tailLen++] = input[p]; tail[tailLen++] = input[p + 1]; } } this.op = op; this.count = count; return true; } } @UnsupportedAppUsage private Base64() { } // don't instantiate }