Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you 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. */ /* * This package is based on the work done by Keiron Liddle, Aftex Software * <keiron@aftexsw.com> to whom the Ant project is very grateful for his * great code. */ package org.apache.commons.compress.compressors.bzip2; import java.io.IOException; import java.io.InputStream; import org.apache.commons.compress.compressors.CompressorInputStream; /** * An input stream that decompresses from the BZip2 format to be read as any other stream. * * @NotThreadSafe */ public class BZip2CompressorInputStream extends CompressorInputStream implements BZip2Constants { /** * Index of the last char in the block, so the block size == last + 1. */ private int last; /** * Index in zptr[] of original string after sorting. */ private int origPtr; /** * always: in the range 0 .. 9. The current block size is 100000 * this * number. */ private int blockSize100k; private boolean blockRandomised; private int bsBuff; private int bsLive; private final CRC crc = new CRC(); private int nInUse; private InputStream in; private int currentChar = -1; private static final int EOF = 0; private static final int START_BLOCK_STATE = 1; private static final int RAND_PART_A_STATE = 2; private static final int RAND_PART_B_STATE = 3; private static final int RAND_PART_C_STATE = 4; private static final int NO_RAND_PART_A_STATE = 5; private static final int NO_RAND_PART_B_STATE = 6; private static final int NO_RAND_PART_C_STATE = 7; private int currentState = START_BLOCK_STATE; private int storedBlockCRC, storedCombinedCRC; private int computedBlockCRC, computedCombinedCRC; // Variables used by setup* methods exclusively private int su_count; private int su_ch2; private int su_chPrev; private int su_i2; private int su_j2; private int su_rNToGo; private int su_rTPos; private int su_tPos; private char su_z; /** * All memory intensive stuff. This field is initialized by initBlock(). */ private BZip2CompressorInputStream.Data data; /** * Constructs a new BZip2CompressorInputStream which decompresses bytes read from the * specified stream. * * @throws IOException * if the stream content is malformed or an I/O error occurs. * @throws NullPointerException * if <tt>in == null</tt> */ public BZip2CompressorInputStream(final InputStream in) throws IOException { super(); this.in = in; init(); } /** {@inheritDoc} */ public int read() throws IOException { if (this.in != null) { return read0(); } else { throw new IOException("stream closed"); } } /* * (non-Javadoc) * * @see java.io.InputStream#read(byte[], int, int) */ public int read(final byte[] dest, final int offs, final int len) throws IOException { if (offs < 0) { throw new IndexOutOfBoundsException("offs(" + offs + ") < 0."); } if (len < 0) { throw new IndexOutOfBoundsException("len(" + len + ") < 0."); } if (offs + len > dest.length) { throw new IndexOutOfBoundsException( "offs(" + offs + ") + len(" + len + ") > dest.length(" + dest.length + ")."); } if (this.in == null) { throw new IOException("stream closed"); } final int hi = offs + len; int destOffs = offs; for (int b; (destOffs < hi) && ((b = read0()) >= 0);) { dest[destOffs++] = (byte) b; } return (destOffs == offs) ? -1 : (destOffs - offs); } private void makeMaps() { final boolean[] inUse = this.data.inUse; final byte[] seqToUnseq = this.data.seqToUnseq; int nInUseShadow = 0; for (int i = 0; i < 256; i++) { if (inUse[i]) seqToUnseq[nInUseShadow++] = (byte) i; } this.nInUse = nInUseShadow; } private int read0() throws IOException { final int retChar = this.currentChar; switch (this.currentState) { case EOF: return -1; case START_BLOCK_STATE: throw new IllegalStateException(); case RAND_PART_A_STATE: throw new IllegalStateException(); case RAND_PART_B_STATE: setupRandPartB(); break; case RAND_PART_C_STATE: setupRandPartC(); break; case NO_RAND_PART_A_STATE: throw new IllegalStateException(); case NO_RAND_PART_B_STATE: setupNoRandPartB(); break; case NO_RAND_PART_C_STATE: setupNoRandPartC(); break; default: throw new IllegalStateException(); } return retChar; } private void init() throws IOException { if (null == in) { throw new IOException("No InputStream"); } checkMagicChar('B', "first"); checkMagicChar('Z', "second"); checkMagicChar('h', "third"); int blockSize = this.in.read(); if ((blockSize < '1') || (blockSize > '9')) { throw new IOException("Stream is not BZip2 formatted: illegal " + "blocksize " + (char) blockSize); } this.blockSize100k = blockSize - '0'; initBlock(); setupBlock(); } private void checkMagicChar(char expected, String position) throws IOException { int magic = this.in.read(); if (magic != expected) { throw new IOException("Stream is not BZip2 formatted: expected '" + expected + "' as " + position + " byte but got '" + (char) magic + "'"); } } private void initBlock() throws IOException { char magic0 = bsGetUByte(); char magic1 = bsGetUByte(); char magic2 = bsGetUByte(); char magic3 = bsGetUByte(); char magic4 = bsGetUByte(); char magic5 = bsGetUByte(); if (magic0 == 0x17 && magic1 == 0x72 && magic2 == 0x45 && magic3 == 0x38 && magic4 == 0x50 && magic5 == 0x90) { complete(); // end of file } else if (magic0 != 0x31 || // '1' magic1 != 0x41 || // ')' magic2 != 0x59 || // 'Y' magic3 != 0x26 || // '&' magic4 != 0x53 || // 'S' magic5 != 0x59 // 'Y' ) { this.currentState = EOF; throw new IOException("bad block header"); } else { this.storedBlockCRC = bsGetInt(); this.blockRandomised = bsR(1) == 1; /** * Allocate data here instead in constructor, so we do not allocate * it if the input file is empty. */ if (this.data == null) { this.data = new Data(this.blockSize100k); } // currBlockNo++; getAndMoveToFrontDecode(); this.crc.initialiseCRC(); this.currentState = START_BLOCK_STATE; } } private void endBlock() throws IOException { this.computedBlockCRC = this.crc.getFinalCRC(); // A bad CRC is considered a fatal error. if (this.storedBlockCRC != this.computedBlockCRC) { // make next blocks readable without error // (repair feature, not yet documented, not tested) this.computedCombinedCRC = (this.storedCombinedCRC << 1) | (this.storedCombinedCRC >>> 31); this.computedCombinedCRC ^= this.storedBlockCRC; throw new IOException("BZip2 CRC error"); } this.computedCombinedCRC = (this.computedCombinedCRC << 1) | (this.computedCombinedCRC >>> 31); this.computedCombinedCRC ^= this.computedBlockCRC; } private void complete() throws IOException { this.storedCombinedCRC = bsGetInt(); this.currentState = EOF; this.data = null; if (this.storedCombinedCRC != this.computedCombinedCRC) { throw new IOException("BZip2 CRC error"); } } public void close() throws IOException { InputStream inShadow = this.in; if (inShadow != null) { try { if (inShadow != System.in) { inShadow.close(); } } finally { this.data = null; this.in = null; } } } private int bsR(final int n) throws IOException { int bsLiveShadow = this.bsLive; int bsBuffShadow = this.bsBuff; if (bsLiveShadow < n) { final InputStream inShadow = this.in; do { int thech = inShadow.read(); if (thech < 0) { throw new IOException("unexpected end of stream"); } bsBuffShadow = (bsBuffShadow << 8) | thech; bsLiveShadow += 8; } while (bsLiveShadow < n); this.bsBuff = bsBuffShadow; } this.bsLive = bsLiveShadow - n; return (bsBuffShadow >> (bsLiveShadow - n)) & ((1 << n) - 1); } private boolean bsGetBit() throws IOException { int bsLiveShadow = this.bsLive; int bsBuffShadow = this.bsBuff; if (bsLiveShadow < 1) { int thech = this.in.read(); if (thech < 0) { throw new IOException("unexpected end of stream"); } bsBuffShadow = (bsBuffShadow << 8) | thech; bsLiveShadow += 8; this.bsBuff = bsBuffShadow; } this.bsLive = bsLiveShadow - 1; return ((bsBuffShadow >> (bsLiveShadow - 1)) & 1) != 0; } private char bsGetUByte() throws IOException { return (char) bsR(8); } private int bsGetInt() throws IOException { return (((((bsR(8) << 8) | bsR(8)) << 8) | bsR(8)) << 8) | bsR(8); } /** * Called by createHuffmanDecodingTables() exclusively. */ private static void hbCreateDecodeTables(final int[] limit, final int[] base, final int[] perm, final char[] length, final int minLen, final int maxLen, final int alphaSize) { for (int i = minLen, pp = 0; i <= maxLen; i++) { for (int j = 0; j < alphaSize; j++) { if (length[j] == i) { perm[pp++] = j; } } } for (int i = MAX_CODE_LEN; --i > 0;) { base[i] = 0; limit[i] = 0; } for (int i = 0; i < alphaSize; i++) { base[length[i] + 1]++; } for (int i = 1, b = base[0]; i < MAX_CODE_LEN; i++) { b += base[i]; base[i] = b; } for (int i = minLen, vec = 0, b = base[i]; i <= maxLen; i++) { final int nb = base[i + 1]; vec += nb - b; b = nb; limit[i] = vec - 1; vec <<= 1; } for (int i = minLen + 1; i <= maxLen; i++) { base[i] = ((limit[i - 1] + 1) << 1) - base[i]; } } private void recvDecodingTables() throws IOException { final Data dataShadow = this.data; final boolean[] inUse = dataShadow.inUse; final byte[] pos = dataShadow.recvDecodingTables_pos; final byte[] selector = dataShadow.selector; final byte[] selectorMtf = dataShadow.selectorMtf; int inUse16 = 0; /* Receive the mapping table */ for (int i = 0; i < 16; i++) { if (bsGetBit()) { inUse16 |= 1 << i; } } for (int i = 256; --i >= 0;) { inUse[i] = false; } for (int i = 0; i < 16; i++) { if ((inUse16 & (1 << i)) != 0) { final int i16 = i << 4; for (int j = 0; j < 16; j++) { if (bsGetBit()) { inUse[i16 + j] = true; } } } } makeMaps(); final int alphaSize = this.nInUse + 2; /* Now the selectors */ final int nGroups = bsR(3); final int nSelectors = bsR(15); for (int i = 0; i < nSelectors; i++) { int j = 0; while (bsGetBit()) { j++; } selectorMtf[i] = (byte) j; } /* Undo the MTF values for the selectors. */ for (int v = nGroups; --v >= 0;) { pos[v] = (byte) v; } for (int i = 0; i < nSelectors; i++) { int v = selectorMtf[i] & 0xff; final byte tmp = pos[v]; while (v > 0) { // nearly all times v is zero, 4 in most other cases pos[v] = pos[v - 1]; v--; } pos[0] = tmp; selector[i] = tmp; } final char[][] len = dataShadow.temp_charArray2d; /* Now the coding tables */ for (int t = 0; t < nGroups; t++) { int curr = bsR(5); final char[] len_t = len[t]; for (int i = 0; i < alphaSize; i++) { while (bsGetBit()) { curr += bsGetBit() ? -1 : 1; } len_t[i] = (char) curr; } } // finally create the Huffman tables createHuffmanDecodingTables(alphaSize, nGroups); } /** * Called by recvDecodingTables() exclusively. */ private void createHuffmanDecodingTables(final int alphaSize, final int nGroups) { final Data dataShadow = this.data; final char[][] len = dataShadow.temp_charArray2d; final int[] minLens = dataShadow.minLens; final int[][] limit = dataShadow.limit; final int[][] base = dataShadow.base; final int[][] perm = dataShadow.perm; for (int t = 0; t < nGroups; t++) { int minLen = 32; int maxLen = 0; final char[] len_t = len[t]; for (int i = alphaSize; --i >= 0;) { final char lent = len_t[i]; if (lent > maxLen) { maxLen = lent; } if (lent < minLen) { minLen = lent; } } hbCreateDecodeTables(limit[t], base[t], perm[t], len[t], minLen, maxLen, alphaSize); minLens[t] = minLen; } } private void getAndMoveToFrontDecode() throws IOException { this.origPtr = bsR(24); recvDecodingTables(); final InputStream inShadow = this.in; final Data dataShadow = this.data; final byte[] ll8 = dataShadow.ll8; final int[] unzftab = dataShadow.unzftab; final byte[] selector = dataShadow.selector; final byte[] seqToUnseq = dataShadow.seqToUnseq; final char[] yy = dataShadow.getAndMoveToFrontDecode_yy; final int[] minLens = dataShadow.minLens; final int[][] limit = dataShadow.limit; final int[][] base = dataShadow.base; final int[][] perm = dataShadow.perm; final int limitLast = this.blockSize100k * 100000; /* * Setting up the unzftab entries here is not strictly necessary, but it * does save having to do it later in a separate pass, and so saves a * block's worth of cache misses. */ for (int i = 256; --i >= 0;) { yy[i] = (char) i; unzftab[i] = 0; } int groupNo = 0; int groupPos = G_SIZE - 1; final int eob = this.nInUse + 1; int nextSym = getAndMoveToFrontDecode0(0); int bsBuffShadow = this.bsBuff; int bsLiveShadow = this.bsLive; int lastShadow = -1; int zt = selector[groupNo] & 0xff; int[] base_zt = base[zt]; int[] limit_zt = limit[zt]; int[] perm_zt = perm[zt]; int minLens_zt = minLens[zt]; while (nextSym != eob) { if ((nextSym == RUNA) || (nextSym == RUNB)) { int s = -1; for (int n = 1; true; n <<= 1) { if (nextSym == RUNA) { s += n; } else if (nextSym == RUNB) { s += n << 1; } else { break; } if (groupPos == 0) { groupPos = G_SIZE - 1; zt = selector[++groupNo] & 0xff; base_zt = base[zt]; limit_zt = limit[zt]; perm_zt = perm[zt]; minLens_zt = minLens[zt]; } else { groupPos--; } int zn = minLens_zt; // Inlined: // int zvec = bsR(zn); while (bsLiveShadow < zn) { final int thech = inShadow.read(); if (thech >= 0) { bsBuffShadow = (bsBuffShadow << 8) | thech; bsLiveShadow += 8; continue; } else { throw new IOException("unexpected end of stream"); } } int zvec = (bsBuffShadow >> (bsLiveShadow - zn)) & ((1 << zn) - 1); bsLiveShadow -= zn; while (zvec > limit_zt[zn]) { zn++; while (bsLiveShadow < 1) { final int thech = inShadow.read(); if (thech >= 0) { bsBuffShadow = (bsBuffShadow << 8) | thech; bsLiveShadow += 8; continue; } else { throw new IOException("unexpected end of stream"); } } bsLiveShadow--; zvec = (zvec << 1) | ((bsBuffShadow >> bsLiveShadow) & 1); } nextSym = perm_zt[zvec - base_zt[zn]]; } final byte ch = seqToUnseq[yy[0]]; unzftab[ch & 0xff] += s + 1; while (s-- >= 0) { ll8[++lastShadow] = ch; } if (lastShadow >= limitLast) { throw new IOException("block overrun"); } } else { if (++lastShadow >= limitLast) { throw new IOException("block overrun"); } final char tmp = yy[nextSym - 1]; unzftab[seqToUnseq[tmp] & 0xff]++; ll8[lastShadow] = seqToUnseq[tmp]; /* * This loop is hammered during decompression, hence avoid * native method call overhead of System.arraycopy for very * small ranges to copy. */ if (nextSym <= 16) { for (int j = nextSym - 1; j > 0;) { yy[j] = yy[--j]; } } else { System.arraycopy(yy, 0, yy, 1, nextSym - 1); } yy[0] = tmp; if (groupPos == 0) { groupPos = G_SIZE - 1; zt = selector[++groupNo] & 0xff; base_zt = base[zt]; limit_zt = limit[zt]; perm_zt = perm[zt]; minLens_zt = minLens[zt]; } else { groupPos--; } int zn = minLens_zt; // Inlined: // int zvec = bsR(zn); while (bsLiveShadow < zn) { final int thech = inShadow.read(); if (thech >= 0) { bsBuffShadow = (bsBuffShadow << 8) | thech; bsLiveShadow += 8; continue; } else { throw new IOException("unexpected end of stream"); } } int zvec = (bsBuffShadow >> (bsLiveShadow - zn)) & ((1 << zn) - 1); bsLiveShadow -= zn; while (zvec > limit_zt[zn]) { zn++; while (bsLiveShadow < 1) { final int thech = inShadow.read(); if (thech >= 0) { bsBuffShadow = (bsBuffShadow << 8) | thech; bsLiveShadow += 8; continue; } else { throw new IOException("unexpected end of stream"); } } bsLiveShadow--; zvec = (zvec << 1) | ((bsBuffShadow >> bsLiveShadow) & 1); } nextSym = perm_zt[zvec - base_zt[zn]]; } } this.last = lastShadow; this.bsLive = bsLiveShadow; this.bsBuff = bsBuffShadow; } private int getAndMoveToFrontDecode0(final int groupNo) throws IOException { final InputStream inShadow = this.in; final Data dataShadow = this.data; final int zt = dataShadow.selector[groupNo] & 0xff; final int[] limit_zt = dataShadow.limit[zt]; int zn = dataShadow.minLens[zt]; int zvec = bsR(zn); int bsLiveShadow = this.bsLive; int bsBuffShadow = this.bsBuff; while (zvec > limit_zt[zn]) { zn++; while (bsLiveShadow < 1) { final int thech = inShadow.read(); if (thech >= 0) { bsBuffShadow = (bsBuffShadow << 8) | thech; bsLiveShadow += 8; continue; } else { throw new IOException("unexpected end of stream"); } } bsLiveShadow--; zvec = (zvec << 1) | ((bsBuffShadow >> bsLiveShadow) & 1); } this.bsLive = bsLiveShadow; this.bsBuff = bsBuffShadow; return dataShadow.perm[zt][zvec - dataShadow.base[zt][zn]]; } private void setupBlock() throws IOException { if (this.data == null) { return; } final int[] cftab = this.data.cftab; final int[] tt = this.data.initTT(this.last + 1); final byte[] ll8 = this.data.ll8; cftab[0] = 0; System.arraycopy(this.data.unzftab, 0, cftab, 1, 256); for (int i = 1, c = cftab[0]; i <= 256; i++) { c += cftab[i]; cftab[i] = c; } for (int i = 0, lastShadow = this.last; i <= lastShadow; i++) { tt[cftab[ll8[i] & 0xff]++] = i; } if ((this.origPtr < 0) || (this.origPtr >= tt.length)) { throw new IOException("stream corrupted"); } this.su_tPos = tt[this.origPtr]; this.su_count = 0; this.su_i2 = 0; this.su_ch2 = 256; /* not a char and not EOF */ if (this.blockRandomised) { this.su_rNToGo = 0; this.su_rTPos = 0; setupRandPartA(); } else { setupNoRandPartA(); } } private void setupRandPartA() throws IOException { if (this.su_i2 <= this.last) { this.su_chPrev = this.su_ch2; int su_ch2Shadow = this.data.ll8[this.su_tPos] & 0xff; this.su_tPos = this.data.tt[this.su_tPos]; if (this.su_rNToGo == 0) { this.su_rNToGo = Rand.rNums(this.su_rTPos) - 1; if (++this.su_rTPos == 512) { this.su_rTPos = 0; } } else { this.su_rNToGo--; } this.su_ch2 = su_ch2Shadow ^= (this.su_rNToGo == 1) ? 1 : 0; this.su_i2++; this.currentChar = su_ch2Shadow; this.currentState = RAND_PART_B_STATE; this.crc.updateCRC(su_ch2Shadow); } else { endBlock(); initBlock(); setupBlock(); } } private void setupNoRandPartA() throws IOException { if (this.su_i2 <= this.last) { this.su_chPrev = this.su_ch2; int su_ch2Shadow = this.data.ll8[this.su_tPos] & 0xff; this.su_ch2 = su_ch2Shadow; this.su_tPos = this.data.tt[this.su_tPos]; this.su_i2++; this.currentChar = su_ch2Shadow; this.currentState = NO_RAND_PART_B_STATE; this.crc.updateCRC(su_ch2Shadow); } else { this.currentState = NO_RAND_PART_A_STATE; endBlock(); initBlock(); setupBlock(); } } private void setupRandPartB() throws IOException { if (this.su_ch2 != this.su_chPrev) { this.currentState = RAND_PART_A_STATE; this.su_count = 1; setupRandPartA(); } else if (++this.su_count >= 4) { this.su_z = (char) (this.data.ll8[this.su_tPos] & 0xff); this.su_tPos = this.data.tt[this.su_tPos]; if (this.su_rNToGo == 0) { this.su_rNToGo = Rand.rNums(this.su_rTPos) - 1; if (++this.su_rTPos == 512) { this.su_rTPos = 0; } } else { this.su_rNToGo--; } this.su_j2 = 0; this.currentState = RAND_PART_C_STATE; if (this.su_rNToGo == 1) { this.su_z ^= 1; } setupRandPartC(); } else { this.currentState = RAND_PART_A_STATE; setupRandPartA(); } } private void setupRandPartC() throws IOException { if (this.su_j2 < this.su_z) { this.currentChar = this.su_ch2; this.crc.updateCRC(this.su_ch2); this.su_j2++; } else { this.currentState = RAND_PART_A_STATE; this.su_i2++; this.su_count = 0; setupRandPartA(); } } private void setupNoRandPartB() throws IOException { if (this.su_ch2 != this.su_chPrev) { this.su_count = 1; setupNoRandPartA(); } else if (++this.su_count >= 4) { this.su_z = (char) (this.data.ll8[this.su_tPos] & 0xff); this.su_tPos = this.data.tt[this.su_tPos]; this.su_j2 = 0; setupNoRandPartC(); } else { setupNoRandPartA(); } } private void setupNoRandPartC() throws IOException { if (this.su_j2 < this.su_z) { int su_ch2Shadow = this.su_ch2; this.currentChar = su_ch2Shadow; this.crc.updateCRC(su_ch2Shadow); this.su_j2++; this.currentState = NO_RAND_PART_C_STATE; } else { this.su_i2++; this.su_count = 0; setupNoRandPartA(); } } private static final class Data extends Object { // (with blockSize 900k) final boolean[] inUse = new boolean[256]; // 256 byte final byte[] seqToUnseq = new byte[256]; // 256 byte final byte[] selector = new byte[MAX_SELECTORS]; // 18002 byte final byte[] selectorMtf = new byte[MAX_SELECTORS]; // 18002 byte /** * Freq table collected to save a pass over the data during * decompression. */ final int[] unzftab = new int[256]; // 1024 byte final int[][] limit = new int[N_GROUPS][MAX_ALPHA_SIZE]; // 6192 byte final int[][] base = new int[N_GROUPS][MAX_ALPHA_SIZE]; // 6192 byte final int[][] perm = new int[N_GROUPS][MAX_ALPHA_SIZE]; // 6192 byte final int[] minLens = new int[N_GROUPS]; // 24 byte final int[] cftab = new int[257]; // 1028 byte final char[] getAndMoveToFrontDecode_yy = new char[256]; // 512 byte final char[][] temp_charArray2d = new char[N_GROUPS][MAX_ALPHA_SIZE]; // 3096 // byte final byte[] recvDecodingTables_pos = new byte[N_GROUPS]; // 6 byte // --------------- // 60798 byte int[] tt; // 3600000 byte byte[] ll8; // 900000 byte // --------------- // 4560782 byte // =============== Data(int blockSize100k) { super(); this.ll8 = new byte[blockSize100k * BZip2Constants.BASEBLOCKSIZE]; } /** * Initializes the {@link #tt} array. * * This method is called when the required length of the array is known. * I don't initialize it at construction time to avoid unneccessary * memory allocation when compressing small files. */ int[] initTT(int length) { int[] ttShadow = this.tt; // tt.length should always be >= length, but theoretically // it can happen, if the compressor mixed small and large // blocks. Normally only the last block will be smaller // than others. if ((ttShadow == null) || (ttShadow.length < length)) { this.tt = ttShadow = new int[length]; } return ttShadow; } } /** * Checks if the signature matches what is expected for a bzip2 file. * * @param signature * the bytes to check * @param length * the number of bytes to check * @return true, if this stream is a bzip2 compressed stream, false otherwise * * @since Apache Commons Compress 1.1 */ public static boolean matches(byte[] signature, int length) { if (length < 3) { return false; } if (signature[0] != 'B') { return false; } if (signature[1] != 'Z') { return false; } if (signature[2] != 'h') { return false; } return true; } }