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    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
    * under the terms of the Eclipse Distribution License v1.0 which
    * accompanies this distribution, is reproduced below, and is
    * available at http://www.eclipse.org/org/documents/edl-v10.php
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  package org.eclipse.jgit.util;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  
  import java.util.Arrays;
  
  import org.eclipse.jgit.lib.Constants;
  
  /**
   * Utility functions related to quoted string handling.
   */
  public abstract class QuotedString {
  	/** Quoting style that obeys the rules Git applies to file names */
  	public static final GitPathStyle GIT_PATH = new GitPathStyle(true);
  
  	/**
  	 * Quoting style that obeys the rules Git applies to file names when
  	 * {@code core.quotePath = false}.
  	 *
  	 * @since 5.6
  	 */
  	public static final QuotedString GIT_PATH_MINIMAL = new GitPathStyle(false);
  
  	/**
  	 * Quoting style used by the Bourne shell.
  	 * <p>
  	 * Quotes are unconditionally inserted during {@link #quote(String)}. This
  	 * protects shell meta-characters like <code>$</code> or <code>~</code> from
  	 * being recognized as special.
  	 */
  	public static final BourneStyle BOURNE = new BourneStyle();
  
  	/** Bourne style, but permits <code>~user</code> at the start of the string. */
  	public static final BourneUserPathStyle BOURNE_USER_PATH = new BourneUserPathStyle();
  
  	/**
  	 * Quote an input string by the quoting rules.
  	 * <p>
  	 * If the input string does not require any quoting, the same String
  	 * reference is returned to the caller.
  	 * <p>
  	 * Otherwise a quoted string is returned, including the opening and closing
  	 * quotation marks at the start and end of the string. If the style does not
  	 * permit raw Unicode characters then the string will first be encoded in
  	 * UTF-8, with unprintable sequences possibly escaped by the rules.
  	 *
  	 * @param in
  	 *            any non-null Unicode string.
  	 * @return a quoted string. See above for details.
  	 */
  	public abstract String quote(String in);
  
  	/**
  	 * Clean a previously quoted input, decoding the result via UTF-8.
  	 * <p>
  	 * This method must match quote such that:
 	 *
 	 * <pre>
 	 * a.equals(dequote(quote(a)));
 	 * </pre>
 	 *
 	 * is true for any <code>a</code>.
 	 *
 	 * @param in
 	 *            a Unicode string to remove quoting from.
 	 * @return the cleaned string.
 	 * @see #dequote(byte[], int, int)
 	 */
 	public String dequote(String in) {
 		final byte[] b = Constants.encode(in);
 		return dequote(b, 0, b.length);
 	}
 
 	/**
 	 * Decode a previously quoted input, scanning a UTF-8 encoded buffer.
 	 * <p>
 	 * This method must match quote such that:
 	 *
 	 * <pre>
 	 * a.equals(dequote(Constants.encode(quote(a))));
 	 * </pre>
 	 *
 	 * is true for any <code>a</code>.
 	 * <p>
 	 * This method removes any opening/closing quotation marks added by
 	 * {@link #quote(String)}.
 	 *
 	 * @param in
 	 *            the input buffer to parse.
 	 * @param offset
 	 *            first position within <code>in</code> to scan.
 	 * @param end
 	 *            one position past in <code>in</code> to scan.
 	 * @return the cleaned string.
 	 */
 	public abstract String dequote(byte[] in, int offset, int end);
 
 	/**
 	 * Quoting style used by the Bourne shell.
 	 * <p>
 	 * Quotes are unconditionally inserted during {@link #quote(String)}. This
 	 * protects shell meta-characters like <code>$</code> or <code>~</code> from
 	 * being recognized as special.
 	 */
 	public static class BourneStyle extends QuotedString {
 		@Override
 		public String quote(String in) {
 			final StringBuilder r = new StringBuilder();
 			r.append('\'');
 			int start = 0, i = 0;
 			for (; i < in.length(); i++) {
 				switch (in.charAt(i)) {
 				case '\'':
 				case '!':
 					r.append(in, start, i);
 					r.append('\'');
 					r.append('\\');
 					r.append(in.charAt(i));
 					r.append('\'');
 					start = i + 1;
 					break;
 				}
 			}
 			r.append(in, start, i);
 			r.append('\'');
 			return r.toString();
 		}
 
 		@Override
 		public String dequote(byte[] in, int ip, int ie) {
 			boolean inquote = false;
 			final byte[] r = new byte[ie - ip];
 			int rPtr = 0;
 			while (ip < ie) {
 				final byte b = in[ip++];
 				switch (b) {
 				case '\'':
 					inquote = !inquote;
 					continue;
 				case '\\':
 					if (inquote || ip == ie)
 						r[rPtr++] = b; // literal within a quote
 					else
 						r[rPtr++] = in[ip++];
 					continue;
 				default:
 					r[rPtr++] = b;
 					continue;
 				}
 			}
 			return RawParseUtils.decode(UTF_8, r, 0, rPtr);
 		}
 	}
 
 	/** Bourne style, but permits <code>~user</code> at the start of the string. */
 	public static class BourneUserPathStyle extends BourneStyle {
 		@Override
 		public String quote(String in) {
 			if (in.matches("^~[A-Za-z0-9_-]+$")) { //$NON-NLS-1$
 				// If the string is just "~user" we can assume they
 				// mean "~user/".
 				//
 				return in + "/"; //$NON-NLS-1$
 			}
 
 			if (in.matches("^~[A-Za-z0-9_-]*/.*$")) { //$NON-NLS-1$
 				// If the string is of "~/path" or "~user/path"
 				// we must not escape ~/ or ~user/ from the shell.
 				//
 				final int i = in.indexOf('/') + 1;
 				if (i == in.length())
 					return in;
 				return in.substring(0, i) + super.quote(in.substring(i));
 			}
 
 			return super.quote(in);
 		}
 	}
 
 	/** Quoting style that obeys the rules Git applies to file names */
 	public static final class GitPathStyle extends QuotedString {
 		private static final byte[] quote;
 		static {
 			quote = new byte[128];
 			Arrays.fill(quote, (byte) -1);
 
 			for (int i = '0'; i <= '9'; i++)
 				quote[i] = 0;
 			for (int i = 'a'; i <= 'z'; i++)
 				quote[i] = 0;
 			for (int i = 'A'; i <= 'Z'; i++)
 				quote[i] = 0;
 			quote[' '] = 0;
 			quote['$'] = 0;
 			quote['%'] = 0;
 			quote['&'] = 0;
 			quote['*'] = 0;
 			quote['+'] = 0;
 			quote[','] = 0;
 			quote['-'] = 0;
 			quote['.'] = 0;
 			quote['/'] = 0;
 			quote[':'] = 0;
 			quote[';'] = 0;
 			quote['='] = 0;
 			quote['?'] = 0;
 			quote['@'] = 0;
 			quote['_'] = 0;
 			quote['^'] = 0;
 			quote['|'] = 0;
 			quote['~'] = 0;
 
 			quote['\u0007'] = 'a';
 			quote['\b'] = 'b';
 			quote['\f'] = 'f';
 			quote['\n'] = 'n';
 			quote['\r'] = 'r';
 			quote['\t'] = 't';
 			quote['\u000B'] = 'v';
 			quote['\\'] = '\\';
 			quote['"'] = '"';
 		}
 
 		private final boolean quoteHigh;
 
 		@Override
 		public String quote(String instr) {
 			if (instr.isEmpty()) {
 				return "\"\""; //$NON-NLS-1$
 			}
 			boolean reuse = true;
 			final byte[] in = Constants.encode(instr);
 			final byte[] out = new byte[4 * in.length + 2];
 			int o = 0;
 			out[o++] = '"';
 			for (int i = 0; i < in.length; i++) {
 				final int c = in[i] & 0xff;
 				if (c < quote.length) {
 					final byte style = quote[c];
 					if (style == 0) {
 						out[o++] = (byte) c;
 						continue;
 					}
 					if (style > 0) {
 						reuse = false;
 						out[o++] = '\\';
 						out[o++] = style;
 						continue;
 					}
 				} else if (!quoteHigh) {
 					out[o++] = (byte) c;
 					continue;
 				}
 
 				reuse = false;
 				out[o++] = '\\';
 				out[o++] = (byte) (((c >> 6) & 03) + '0');
 				out[o++] = (byte) (((c >> 3) & 07) + '0');
 				out[o++] = (byte) (((c >> 0) & 07) + '0');
 			}
 			if (reuse) {
 				return instr;
 			}
 			out[o++] = '"';
 			return new String(out, 0, o, UTF_8);
 		}
 
 		@Override
 		public String dequote(byte[] in, int inPtr, int inEnd) {
 			if (2 <= inEnd - inPtr && in[inPtr] == '"' && in[inEnd - 1] == '"')
 				return dq(in, inPtr + 1, inEnd - 1);
 			return RawParseUtils.decode(UTF_8, in, inPtr, inEnd);
 		}
 
 		private static String dq(byte[] in, int inPtr, int inEnd) {
 			final byte[] r = new byte[inEnd - inPtr];
 			int rPtr = 0;
 			while (inPtr < inEnd) {
 				final byte b = in[inPtr++];
 				if (b != '\\') {
 					r[rPtr++] = b;
 					continue;
 				}
 
 				if (inPtr == inEnd) {
 					// Lone trailing backslash. Treat it as a literal.
 					//
 					r[rPtr++] = '\\';
 					break;
 				}
 
 				switch (in[inPtr++]) {
 				case 'a':
 					r[rPtr++] = 0x07 /* \a = BEL */;
 					continue;
 				case 'b':
 					r[rPtr++] = '\b';
 					continue;
 				case 'f':
 					r[rPtr++] = '\f';
 					continue;
 				case 'n':
 					r[rPtr++] = '\n';
 					continue;
 				case 'r':
 					r[rPtr++] = '\r';
 					continue;
 				case 't':
 					r[rPtr++] = '\t';
 					continue;
 				case 'v':
 					r[rPtr++] = 0x0B/* \v = VT */;
 					continue;
 
 				case '\\':
 				case '"':
 					r[rPtr++] = in[inPtr - 1];
 					continue;
 
 				case '0':
 				case '1':
 				case '2':
 				case '3': {
 					int cp = in[inPtr - 1] - '0';
 					for (int n = 1; n < 3 && inPtr < inEnd; n++) {
 						final byte c = in[inPtr];
 						if ('0' <= c && c <= '7') {
 							cp <<= 3;
 							cp |= c - '0';
 							inPtr++;
 						} else {
 							break;
 						}
 					}
 					r[rPtr++] = (byte) cp;
 					continue;
 				}
 
 				default:
 					// Any other code is taken literally.
 					//
 					r[rPtr++] = '\\';
 					r[rPtr++] = in[inPtr - 1];
 					continue;
 				}
 			}
 
 			return RawParseUtils.decode(UTF_8, r, 0, rPtr);
 		}
 
 		private GitPathStyle(boolean doQuote) {
 			quoteHigh = doQuote;
 		}
 	}
 }