org.spearce.jgit/src/org/spearce/jgit/lib/ObjectLoader.java

   1 /*
   2  * Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
   3  * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
   4  *
   5  * All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or
   8  * without modification, are permitted provided that the following
   9  * conditions are met:
  10  *
  11  * - Redistributions of source code must retain the above copyright
  12  *   notice, this list of conditions and the following disclaimer.
  13  *
  14  * - Redistributions in binary form must reproduce the above
  15  *   copyright notice, this list of conditions and the following
  16  *   disclaimer in the documentation and/or other materials provided
  17  *   with the distribution.
  18  *
  19  * - Neither the name of the Git Development Community nor the
  20  *   names of its contributors may be used to endorse or promote
  21  *   products derived from this software without specific prior
  22  *   written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
  25  * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
  26  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  27  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  28  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  29  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  30  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  31  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  32  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  33  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  34  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  35  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  36  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  37  */
  38
  39 package org.spearce.jgit.lib;
  40
  41 import java.io.IOException;
  42 import java.security.MessageDigest;
  43
  44 /**
  45  * Base class for a set of loaders for different representations of Git objects.
  46  * New loaders are constructed for every object.
  47  */
  48 public abstract class ObjectLoader {
  49         private ObjectId objectId;
  50
  51         /**
  52          * @return the id of this object, possibly computed on demand
  53          * @throws IOException
  54          */
  55         public ObjectId getId() throws IOException {
  56                 if (objectId == null) {
  57                         final MessageDigest md = Constants.newMessageDigest();
  58                         md.update(Constants.encodedTypeString(getType()));
  59                         md.update((byte) ' ');
  60                         md.update(Constants.encodeASCII(getSize()));
  61                         md.update((byte) 0);
  62                         md.update(getCachedBytes());
  63                         objectId = ObjectId.fromRaw(md.digest());
  64                 }
  65                 return objectId;
  66         }
  67
  68         /**
  69          * @return true if id of loaded object is already known, false otherwise.
  70          */
  71         protected boolean hasComputedId() {
  72                 return objectId != null;
  73         }
  74
  75         /**
  76          * Set the SHA-1 id of the object handled by this loader
  77          *
  78          * @param id
  79          */
  80         protected void setId(final ObjectId id) {
  81                 if (objectId != null)
  82                         throw new IllegalStateException("Id already set.");
  83                 objectId = id;
  84         }
  85
  86         /**
  87          * @return Git in pack object type, see {@link Constants}.
  88          * @throws IOException
  89          */
  90         public abstract int getType() throws IOException;
  91
  92         /**
  93          * @return size of object in bytes
  94          * @throws IOException
  95          */
  96         public abstract long getSize() throws IOException;
  97
  98         /**
  99          * Obtain a copy of the bytes of this object.
 100          * <p>
 101          * Unlike {@link #getCachedBytes()} this method returns an array that might
 102          * be modified by the caller.
 103          *
 104          * @return the bytes of this object.
 105          * @throws IOException
 106          *             the object cannot be read.
 107          */
 108         public final byte[] getBytes() throws IOException {
 109                 final byte[] data = getCachedBytes();
 110                 final byte[] copy = new byte[data.length];
 111                 System.arraycopy(data, 0, copy, 0, data.length);
 112                 return data;
 113         }
 114
 115         /**
 116          * Obtain a reference to the (possibly cached) bytes of this object.
 117          * <p>
 118          * This method offers direct access to the internal caches, potentially
 119          * saving on data copies between the internal cache and higher level code.
 120          * Callers who receive this reference <b>must not</b> modify its contents.
 121          * Changes (if made) will affect the cache but not the repository itself.
 122          *
 123          * @return the cached bytes of this object. Do not modify it.
 124          * @throws IOException
 125          *             the object cannot be read.
 126          */
 127         public abstract byte[] getCachedBytes() throws IOException;
 128
 129         /**
 130          * @return raw object type from object header, as stored in storage (pack,
 131          *         loose file). This may be different from {@link #getType()} result
 132          *         for packs (see {@link Constants}).
 133          * @throws IOException
 134          *             when type cannot be read from the object header.
 135          */
 136         public abstract int getRawType() throws IOException;
 137
 138         /**
 139          * @return raw size of object from object header (pack, loose file).
 140          *         Interpretation of this value depends on {@link #getRawType()}.
 141          * @throws IOException
 142          *             when raw size cannot be read from the object header.
 143          */
 144         public abstract long getRawSize() throws IOException;
 145 }