Teach RawParseUtil how to format base 10 numbers it reads

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

/*
 *  Copyright (C) 2008  Shawn Pearce <spearce@spearce.org>
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public
 *  License, version 2, as published by the Free Software Foundation.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301
 */
package org.spearce.jgit.util;

import java.nio.ByteBuffer;
import java.nio.charset.Charset;
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[] author = Constants.encodeASCII("author ");

        private static final byte[] committer = Constants.encodeASCII("committer ");

        private static final byte[] encoding = Constants.encodeASCII("encoding ");

        private static final byte[] digits;

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

        private 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.
         * <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 = digits[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 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 LF at.
         * @param chrA
         *            character to find.
         * @return new position just after chr.
         */
        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 + 1;
                        else
                                ptr++;
                }
                return ptr;
        }

        /**
         * 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 LF at.
         * @param chrA
         *            character to find.
         * @return new position just after the first chrA or chrB 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 + 1;
                        else
                                ptr++;
                }
                return ptr;
        }

        /**
         * 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 = next(b, ptr, '\n');
                return match(b, ptr, committer);
        }

        /**
         * 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 = next(b, ptr, '\n');
                }
                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 = next(b, enc, '\n');
                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 int when = parseBase10(raw, emailE + 1, ptrout);
                final int tz = parseTimeZoneOffset(raw, ptrout.value);

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

        /**
         * Decode a region of the buffer under the specified character set.
         * 
         * @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) {
                final ByteBuffer b = ByteBuffer.wrap(buffer, start, end - start);
                return cs.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.
                //
                while (ptr < sz && b[ptr] != '\n')
                        ptr = next(b, ptr, '\n');
                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 ptr
         *            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, int ptr) {
                final int sz = b.length;
                while (ptr < sz && b[ptr] != '\n')
                        ptr = next(b, ptr, '\n');
                if (ptr < sz && b[ptr] == '\n')
                        return ptr - 1;
                return sz;
        }

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