Move PacketLineIn hex parsing to RawParseUtils

[egit/graphgui.git] / org.spearce.jgit / src / org / spearce / jgit / util / RawParseUtils.java

/*
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 * - Neither the name of the Git Development Community nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.spearce.jgit.util;

import static org.spearce.jgit.lib.ObjectChecker.author;
import static org.spearce.jgit.lib.ObjectChecker.committer;
import static org.spearce.jgit.lib.ObjectChecker.encoding;
import static org.spearce.jgit.lib.ObjectChecker.tagger;

import java.nio.ByteBuffer;
import java.nio.charset.CharacterCodingException;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CodingErrorAction;
import java.util.Arrays;

import org.spearce.jgit.lib.Constants;
import org.spearce.jgit.lib.PersonIdent;

/** Handy utility functions to parse raw object contents. */
public final class RawParseUtils {
        private static final byte[] digits10;

        private static final byte[] digits16;

        static {
                digits10 = new byte['9' + 1];
                Arrays.fill(digits10, (byte) -1);
                for (char i = '0'; i <= '9'; i++)
                        digits10[i] = (byte) (i - '0');

                digits16 = new byte['f' + 1];
                Arrays.fill(digits16, (byte) -1);
                for (char i = '0'; i <= '9'; i++)
                        digits16[i] = (byte) (i - '0');
                for (char i = 'a'; i <= 'f'; i++)
                        digits16[i] = (byte) ((i - 'a') + 10);
                for (char i = 'A'; i <= 'F'; i++)
                        digits16[i] = (byte) ((i - 'A') + 10);
        }

        /**
         * Determine if b[ptr] matches src.
         *
         * @param b
         *            the buffer to scan.
         * @param ptr
         *            first position within b, this should match src[0].
         * @param src
         *            the buffer to test for equality with b.
         * @return ptr + src.length if b[ptr..src.length] == src; else -1.
         */
        public static final int match(final byte[] b, int ptr, final byte[] src) {
                if (ptr + src.length > b.length)
                        return -1;
                for (int i = 0; i < src.length; i++, ptr++)
                        if (b[ptr] != src[i])
                                return -1;
                return ptr;
        }

        private static final byte[] base10byte = { '0', '1', '2', '3', '4', '5',
                        '6', '7', '8', '9' };

        /**
         * Format a base 10 numeric into a temporary buffer.
         * <p>
         * Formatting is performed backwards. The method starts at offset
         * <code>o-1</code> and ends at <code>o-1-digits</code>, where
         * <code>digits</code> is the number of positions necessary to store the
         * base 10 value.
         * <p>
         * The argument and return values from this method make it easy to chain
         * writing, for example:
         * </p>
         * 
         * <pre>
         * final byte[] tmp = new byte[64];
         * int ptr = tmp.length;
         * tmp[--ptr] = '\n';
         * ptr = RawParseUtils.formatBase10(tmp, ptr, 32);
         * tmp[--ptr] = ' ';
         * ptr = RawParseUtils.formatBase10(tmp, ptr, 18);
         * tmp[--ptr] = 0;
         * final String str = new String(tmp, ptr, tmp.length - ptr);
         * </pre>
         * 
         * @param b
         *            buffer to write into.
         * @param o
         *            one offset past the location where writing will begin; writing
         *            proceeds towards lower index values.
         * @param value
         *            the value to store.
         * @return the new offset value <code>o</code>. This is the position of
         *         the last byte written. Additional writing should start at one
         *         position earlier.
         */
        public static int formatBase10(final byte[] b, int o, int value) {
                if (value == 0) {
                        b[--o] = '0';
                        return o;
                }
                final boolean isneg = value < 0;
                while (value != 0) {
                        b[--o] = base10byte[value % 10];
                        value /= 10;
                }
                if (isneg)
                        b[--o] = '-';
                return o;
        }

        /**
         * Parse a base 10 numeric from a sequence of ASCII digits into an int.
         * <p>
         * Digit sequences can begin with an optional run of spaces before the
         * sequence, and may start with a '+' or a '-' to indicate sign position.
         * Any other characters will cause the method to stop and return the current
         * result to the caller.
         * 
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position within buffer to start parsing digits at.
         * @param ptrResult
         *            optional location to return the new ptr value through. If null
         *            the ptr value will be discarded.
         * @return the value at this location; 0 if the location is not a valid
         *         numeric.
         */
        public static final int parseBase10(final byte[] b, int ptr,
                        final MutableInteger ptrResult) {
                int r = 0;
                int sign = 0;
                try {
                        final int sz = b.length;
                        while (ptr < sz && b[ptr] == ' ')
                                ptr++;
                        if (ptr >= sz)
                                return 0;

                        switch (b[ptr]) {
                        case '-':
                                sign = -1;
                                ptr++;
                                break;
                        case '+':
                                ptr++;
                                break;
                        }

                        while (ptr < sz) {
                                final byte v = digits10[b[ptr]];
                                if (v < 0)
                                        break;
                                r = (r * 10) + v;
                                ptr++;
                        }
                } catch (ArrayIndexOutOfBoundsException e) {
                        // Not a valid digit.
                }
                if (ptrResult != null)
                        ptrResult.value = ptr;
                return sign < 0 ? -r : r;
        }

        /**
         * Parse a base 10 numeric from a sequence of ASCII digits into a long.
         * <p>
         * Digit sequences can begin with an optional run of spaces before the
         * sequence, and may start with a '+' or a '-' to indicate sign position.
         * Any other characters will cause the method to stop and return the current
         * result to the caller.
         * 
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position within buffer to start parsing digits at.
         * @param ptrResult
         *            optional location to return the new ptr value through. If null
         *            the ptr value will be discarded.
         * @return the value at this location; 0 if the location is not a valid
         *         numeric.
         */
        public static final long parseLongBase10(final byte[] b, int ptr,
                        final MutableInteger ptrResult) {
                long r = 0;
                int sign = 0;
                try {
                        final int sz = b.length;
                        while (ptr < sz && b[ptr] == ' ')
                                ptr++;
                        if (ptr >= sz)
                                return 0;

                        switch (b[ptr]) {
                        case '-':
                                sign = -1;
                                ptr++;
                                break;
                        case '+':
                                ptr++;
                                break;
                        }

                        while (ptr < sz) {
                                final byte v = digits10[b[ptr]];
                                if (v < 0)
                                        break;
                                r = (r * 10) + v;
                                ptr++;
                        }
                } catch (ArrayIndexOutOfBoundsException e) {
                        // Not a valid digit.
                }
                if (ptrResult != null)
                        ptrResult.value = ptr;
                return sign < 0 ? -r : r;
        }

        /**
         * Parse 4 character base 16 (hex) formatted string to unsigned integer.
         * <p>
         * The number is read in network byte order, that is, most significant
         * nybble first.
         *
         * @param bs
         *            buffer to parse digits from; positions {@code [p, p+4)} will
         *            be parsed.
         * @param p
         *            first position within the buffer to parse.
         * @return the integer value.
         * @throws ArrayIndexOutOfBoundsException
         *             if the string is not hex formatted.
         */
        public static final int parseHexInt16(final byte[] bs, final int p) {
                int r = digits16[bs[p]] << 4;

                r |= digits16[bs[p + 1]];
                r <<= 4;

                r |= digits16[bs[p + 2]];
                r <<= 4;

                r |= digits16[bs[p + 3]];
                if (r < 0)
                        throw new ArrayIndexOutOfBoundsException();
                return r;
        }

        /**
         * Parse 8 character base 16 (hex) formatted string to unsigned integer.
         * <p>
         * The number is read in network byte order, that is, most significant
         * nybble first.
         *
         * @param bs
         *            buffer to parse digits from; positions {@code [p, p+8)} will
         *            be parsed.
         * @param p
         *            first position within the buffer to parse.
         * @return the integer value.
         * @throws ArrayIndexOutOfBoundsException
         *             if the string is not hex formatted.
         */
        public static final int parseHexInt32(final byte[] bs, final int p) {
                int r = digits16[bs[p]] << 4;

                r |= digits16[bs[p + 1]];
                r <<= 4;

                r |= digits16[bs[p + 2]];
                r <<= 4;

                r |= digits16[bs[p + 3]];
                r <<= 4;

                r |= digits16[bs[p + 4]];
                r <<= 4;

                r |= digits16[bs[p + 5]];
                r <<= 4;

                r |= digits16[bs[p + 6]];

                final int last = digits16[bs[p + 7]];
                if (r < 0 || last < 0)
                        throw new ArrayIndexOutOfBoundsException();
                return (r << 4) | last;
        }

        /**
         * Parse a single hex digit to its numeric value (0-15).
         *
         * @param digit
         *            hex character to parse.
         * @return numeric value, in the range 0-15.
         * @throws ArrayIndexOutOfBoundsException
         *             if the input digit is not a valid hex digit.
         */
        public static final int parseHexInt4(final byte digit) {
                final byte r = digits16[digit];
                if (r < 0)
                        throw new ArrayIndexOutOfBoundsException();
                return r;
        }

        /**
         * Parse a Git style timezone string.
         * <p>
         * The sequence "-0315" will be parsed as the numeric value -195, as the
         * lower two positions count minutes, not 100ths of an hour.
         * 
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position within buffer to start parsing digits at.
         * @return the timezone at this location, expressed in minutes.
         */
        public static final int parseTimeZoneOffset(final byte[] b, int ptr) {
                final int v = parseBase10(b, ptr, null);
                final int tzMins = v % 100;
                final int tzHours = v / 100;
                return tzHours * 60 + tzMins;
        }

        /**
         * Locate the first position after a given character.
         * 
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position within buffer to start looking for chrA at.
         * @param chrA
         *            character to find.
         * @return new position just after chrA.
         */
        public static final int next(final byte[] b, int ptr, final char chrA) {
                final int sz = b.length;
                while (ptr < sz) {
                        if (b[ptr++] == chrA)
                                return ptr;
                }
                return ptr;
        }

        /**
         * Locate the first position after the next LF.
         * <p>
         * This method stops on the first '\n' it finds.
         *
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position within buffer to start looking for LF at.
         * @return new position just after the first LF found.
         */
        public static final int nextLF(final byte[] b, int ptr) {
                return next(b, ptr, '\n');
        }

        /**
         * Locate the first position after either the given character or LF.
         * <p>
         * This method stops on the first match it finds from either chrA or '\n'.
         * 
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position within buffer to start looking for chrA or LF at.
         * @param chrA
         *            character to find.
         * @return new position just after the first chrA or LF to be found.
         */
        public static final int nextLF(final byte[] b, int ptr, final char chrA) {
                final int sz = b.length;
                while (ptr < sz) {
                        final byte c = b[ptr++];
                        if (c == chrA || c == '\n')
                                return ptr;
                }
                return ptr;
        }

        /**
         * Index the region between <code>[ptr, end)</code> to find line starts.
         * <p>
         * The returned list is 1 indexed. Index 0 contains
         * {@link Integer#MIN_VALUE} to pad the list out.
         * <p>
         * Using a 1 indexed list means that line numbers can be directly accessed
         * from the list, so <code>list.get(1)</code> (aka get line 1) returns
         * <code>ptr</code>.
         * <p>
         * The last element (index <code>map.size()-1</code>) always contains
         * <code>end</code>.
         *
         * @param buf
         *            buffer to scan.
         * @param ptr
         *            position within the buffer corresponding to the first byte of
         *            line 1.
         * @param end
         *            1 past the end of the content within <code>buf</code>.
         * @return a line map indexing the start position of each line.
         */
        public static final IntList lineMap(final byte[] buf, int ptr, int end) {
                // Experimentally derived from multiple source repositories
                // the average number of bytes/line is 36. Its a rough guess
                // to initially size our map close to the target.
                //
                final IntList map = new IntList((end - ptr) / 36);
                map.fillTo(1, Integer.MIN_VALUE);
                for (; ptr < end; ptr = nextLF(buf, ptr))
                        map.add(ptr);
                map.add(end);
                return map;
        }

        /**
         * Locate the "author " header line data.
         * 
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position in buffer to start the scan at. Most callers should
         *            pass 0 to ensure the scan starts from the beginning of the
         *            commit buffer and does not accidentally look at message body.
         * @return position just after the space in "author ", so the first
         *         character of the author's name. If no author header can be
         *         located -1 is returned.
         */
        public static final int author(final byte[] b, int ptr) {
                final int sz = b.length;
                if (ptr == 0)
                        ptr += 46; // skip the "tree ..." line.
                while (ptr < sz && b[ptr] == 'p')
                        ptr += 48; // skip this parent.
                return match(b, ptr, author);
        }

        /**
         * Locate the "committer " header line data.
         * 
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position in buffer to start the scan at. Most callers should
         *            pass 0 to ensure the scan starts from the beginning of the
         *            commit buffer and does not accidentally look at message body.
         * @return position just after the space in "committer ", so the first
         *         character of the committer's name. If no committer header can be
         *         located -1 is returned.
         */
        public static final int committer(final byte[] b, int ptr) {
                final int sz = b.length;
                if (ptr == 0)
                        ptr += 46; // skip the "tree ..." line.
                while (ptr < sz && b[ptr] == 'p')
                        ptr += 48; // skip this parent.
                if (ptr < sz && b[ptr] == 'a')
                        ptr = nextLF(b, ptr);
                return match(b, ptr, committer);
        }

        /**
         * Locate the "tagger " header line data.
         *
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position in buffer to start the scan at. Most callers should
         *            pass 0 to ensure the scan starts from the beginning of the tag
         *            buffer and does not accidentally look at message body.
         * @return position just after the space in "tagger ", so the first
         *         character of the tagger's name. If no tagger header can be
         *         located -1 is returned.
         */
        public static final int tagger(final byte[] b, int ptr) {
                final int sz = b.length;
                if (ptr == 0)
                        ptr += 48; // skip the "object ..." line.
                while (ptr < sz) {
                        if (b[ptr] == '\n')
                                return -1;
                        final int m = match(b, ptr, tagger);
                        if (m >= 0)
                                return m;
                        ptr = nextLF(b, ptr);
                }
                return -1;
        }

        /**
         * Locate the "encoding " header line.
         * 
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position in buffer to start the scan at. Most callers should
         *            pass 0 to ensure the scan starts from the beginning of the
         *            buffer and does not accidentally look at the message body.
         * @return position just after the space in "encoding ", so the first
         *         character of the encoding's name. If no encoding header can be
         *         located -1 is returned (and UTF-8 should be assumed).
         */
        public static final int encoding(final byte[] b, int ptr) {
                final int sz = b.length;
                while (ptr < sz) {
                        if (b[ptr] == '\n')
                                return -1;
                        if (b[ptr] == 'e')
                                break;
                        ptr = nextLF(b, ptr);
                }
                return match(b, ptr, encoding);
        }

        /**
         * Parse the "encoding " header into a character set reference.
         * <p>
         * Locates the "encoding " header (if present) by first calling
         * {@link #encoding(byte[], int)} and then returns the proper character set
         * to apply to this buffer to evaluate its contents as character data.
         * <p>
         * If no encoding header is present, {@link Constants#CHARSET} is assumed.
         * 
         * @param b
         *            buffer to scan.
         * @return the Java character set representation. Never null.
         */
        public static Charset parseEncoding(final byte[] b) {
                final int enc = encoding(b, 0);
                if (enc < 0)
                        return Constants.CHARSET;
                final int lf = nextLF(b, enc);
                return Charset.forName(decode(Constants.CHARSET, b, enc, lf - 1));
        }

        /**
         * Parse a name line (e.g. author, committer, tagger) into a PersonIdent.
         * <p>
         * When passing in a value for <code>nameB</code> callers should use the
         * return value of {@link #author(byte[], int)} or
         * {@link #committer(byte[], int)}, as these methods provide the proper
         * position within the buffer.
         * 
         * @param raw
         *            the buffer to parse character data from.
         * @param nameB
         *            first position of the identity information. This should be the
         *            first position after the space which delimits the header field
         *            name (e.g. "author" or "committer") from the rest of the
         *            identity line.
         * @return the parsed identity. Never null.
         */
        public static PersonIdent parsePersonIdent(final byte[] raw, final int nameB) {
                final Charset cs = parseEncoding(raw);
                final int emailB = nextLF(raw, nameB, '<');
                final int emailE = nextLF(raw, emailB, '>');

                final String name = decode(cs, raw, nameB, emailB - 2);
                final String email = decode(cs, raw, emailB, emailE - 1);

                final MutableInteger ptrout = new MutableInteger();
                final long when = parseLongBase10(raw, emailE + 1, ptrout);
                final int tz = parseTimeZoneOffset(raw, ptrout.value);

                return new PersonIdent(name, email, when * 1000L, tz);
        }

        /**
         * Decode a buffer under UTF-8, if possible.
         *
         * If the byte stream cannot be decoded that way, the platform default is tried
         * and if that too fails, the fail-safe ISO-8859-1 encoding is tried.
         * 
         * @param buffer
         *            buffer to pull raw bytes from.
         * @return a string representation of the range <code>[start,end)</code>,
         *         after decoding the region through the specified character set.
         */
        public static String decode(final byte[] buffer) {
                return decode(Constants.CHARSET, buffer, 0, buffer.length);
        }

        /**
         * Decode a buffer under the specified character set if possible.
         *
         * If the byte stream cannot be decoded that way, the platform default is tried
         * and if that too fails, the fail-safe ISO-8859-1 encoding is tried.
         * 
         * @param cs
         *            character set to use when decoding the buffer.
         * @param buffer
         *            buffer to pull raw bytes from.
         * @return a string representation of the range <code>[start,end)</code>,
         *         after decoding the region through the specified character set.
         */
        public static String decode(final Charset cs, final byte[] buffer) {
                return decode(cs, buffer, 0, buffer.length);
        }

        /**
         * Decode a region of the buffer under the specified character set if possible.
         *
         * If the byte stream cannot be decoded that way, the platform default is tried
         * and if that too fails, the fail-safe ISO-8859-1 encoding is tried.
         * 
         * @param cs
         *            character set to use when decoding the buffer.
         * @param buffer
         *            buffer to pull raw bytes from.
         * @param start
         *            first position within the buffer to take data from.
         * @param end
         *            one position past the last location within the buffer to take
         *            data from.
         * @return a string representation of the range <code>[start,end)</code>,
         *         after decoding the region through the specified character set.
         */
        public static String decode(final Charset cs, final byte[] buffer,
                        final int start, final int end) {
                try {
                        return decodeNoFallback(cs, buffer, start, end);
                } catch (CharacterCodingException e) {
                        // Fall back to an ISO-8859-1 style encoding. At least all of
                        // the bytes will be present in the output.
                        //
                        return extractBinaryString(buffer, start, end);
                }
        }

        /**
         * Decode a region of the buffer under the specified character set if
         * possible.
         *
         * If the byte stream cannot be decoded that way, the platform default is
         * tried and if that too fails, an exception is thrown.
         *
         * @param cs
         *            character set to use when decoding the buffer.
         * @param buffer
         *            buffer to pull raw bytes from.
         * @param start
         *            first position within the buffer to take data from.
         * @param end
         *            one position past the last location within the buffer to take
         *            data from.
         * @return a string representation of the range <code>[start,end)</code>,
         *         after decoding the region through the specified character set.
         * @throws CharacterCodingException
         *             the input is not in any of the tested character sets.
         */
        public static String decodeNoFallback(final Charset cs,
                        final byte[] buffer, final int start, final int end)
                        throws CharacterCodingException {
                final ByteBuffer b = ByteBuffer.wrap(buffer, start, end - start);
                b.mark();

                // Try our built-in favorite. The assumption here is that
                // decoding will fail if the data is not actually encoded
                // using that encoder.
                //
                try {
                        return decode(b, Constants.CHARSET);
                } catch (CharacterCodingException e) {
                        b.reset();
                }

                if (!cs.equals(Constants.CHARSET)) {
                        // Try the suggested encoding, it might be right since it was
                        // provided by the caller.
                        //
                        try {
                                return decode(b, cs);
                        } catch (CharacterCodingException e) {
                                b.reset();
                        }
                }

                // Try the default character set. A small group of people
                // might actually use the same (or very similar) locale.
                //
                final Charset defcs = Charset.defaultCharset();
                if (!defcs.equals(cs) && !defcs.equals(Constants.CHARSET)) {
                        try {
                                return decode(b, defcs);
                        } catch (CharacterCodingException e) {
                                b.reset();
                        }
                }

                throw new CharacterCodingException();
        }

        /**
         * Decode a region of the buffer under the ISO-8859-1 encoding.
         *
         * Each byte is treated as a single character in the 8859-1 character
         * encoding, performing a raw binary->char conversion.
         *
         * @param buffer
         *            buffer to pull raw bytes from.
         * @param start
         *            first position within the buffer to take data from.
         * @param end
         *            one position past the last location within the buffer to take
         *            data from.
         * @return a string representation of the range <code>[start,end)</code>.
         */
        public static String extractBinaryString(final byte[] buffer,
                        final int start, final int end) {
                final StringBuilder r = new StringBuilder(end - start);
                for (int i = start; i < end; i++)
                        r.append((char) (buffer[i] & 0xff));
                return r.toString();
        }

        private static String decode(final ByteBuffer b, final Charset charset)
                        throws CharacterCodingException {
                final CharsetDecoder d = charset.newDecoder();
                d.onMalformedInput(CodingErrorAction.REPORT);
                d.onUnmappableCharacter(CodingErrorAction.REPORT);
                return d.decode(b).toString();
        }

        /**
         * Locate the position of the commit message body.
         * 
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position in buffer to start the scan at. Most callers should
         *            pass 0 to ensure the scan starts from the beginning of the
         *            commit buffer.
         * @return position of the user's message buffer.
         */
        public static final int commitMessage(final byte[] b, int ptr) {
                final int sz = b.length;
                if (ptr == 0)
                        ptr += 46; // skip the "tree ..." line.
                while (ptr < sz && b[ptr] == 'p')
                        ptr += 48; // skip this parent.

                // Skip any remaining header lines, ignoring what their actual
                // header line type is. This is identical to the logic for a tag.
                //
                return tagMessage(b, ptr);
        }

        /**
         * Locate the position of the tag message body.
         *
         * @param b
         *            buffer to scan.
         * @param ptr
         *            position in buffer to start the scan at. Most callers should
         *            pass 0 to ensure the scan starts from the beginning of the tag
         *            buffer.
         * @return position of the user's message buffer.
         */
        public static final int tagMessage(final byte[] b, int ptr) {
                final int sz = b.length;
                if (ptr == 0)
                        ptr += 48; // skip the "object ..." line.
                while (ptr < sz && b[ptr] != '\n')
                        ptr = nextLF(b, ptr);
                if (ptr < sz && b[ptr] == '\n')
                        return ptr + 1;
                return -1;
        }

        /**
         * Locate the end of a paragraph.
         * <p>
         * A paragraph is ended by two consecutive LF bytes.
         * 
         * @param b
         *            buffer to scan.
         * @param start
         *            position in buffer to start the scan at. Most callers will
         *            want to pass the first position of the commit message (as
         *            found by {@link #commitMessage(byte[], int)}.
         * @return position of the LF at the end of the paragraph;
         *         <code>b.length</code> if no paragraph end could be located.
         */
        public static final int endOfParagraph(final byte[] b, final int start) {
                int ptr = start;
                final int sz = b.length;
                while (ptr < sz && b[ptr] != '\n')
                        ptr = nextLF(b, ptr);
                while (0 < ptr && start < ptr && b[ptr - 1] == '\n')
                        ptr--;
                return ptr;
        }

        private RawParseUtils() {
                // Don't create instances of a static only utility.
        }
}