support Java 5.0 Signature attribute and small refactorings

git-svn-id: https://wala.svn.sourceforge.net/svnroot/wala/trunk@546 f5eafffb-2e1d-0410-98e4-8ec43c5233c4

com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/AttributeReader.java

@@ -0,0 +1,91 @@
+/*******************************************************************************
+ * Copyright (c) 2002,2006 IBM Corporation.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     IBM Corporation - initial API and implementation
+ *******************************************************************************/
+package com.ibm.wala.shrikeCT;
+
+/**
+ * This is a base class for "attribute readers", the classes which provide
+ * access to the contents of attributes.
+ */
+public abstract class AttributeReader {
+  protected ClassReader cr;
+  protected int attr;
+  protected int length;
+
+  /**
+   * Construct a reader for a particular attribute.
+   * 
+   * @param attr
+   *          a valid attribute iterator pointing at the attribute to read
+   * @param expectedName
+   *          the name the attribute must have
+   */
+  protected AttributeReader(ClassReader.AttrIterator attr, String expectedName) throws InvalidClassFileException {
+    attr.verifyValid();
+    this.cr = attr.cr;
+    this.attr = attr.offset;
+    this.length = attr.size;
+
+    String n = attr.getName();
+    if (expectedName != n && !expectedName.equals(n)) {
+      throw new IllegalArgumentException("Attribute " + n + " is not a " + expectedName + " attribute");
+    }
+  }
+
+  /**
+   * @return the class reader the attribute belongs to
+   */
+  public final ClassReader getClassReader() {
+    return cr;
+  }
+
+  /**
+   * @return the offset of the raw attribute data (including the attribute
+   *         header)
+   */
+  public final int getRawOffset() {
+    return attr;
+  }
+
+  /**
+   * @return the size of the raw attribute data (including the attribute header)
+   */
+  public final int getRawSize() {
+    return length;
+  }
+
+  /**
+   * Ensure that the len bytes starting at offset fall within the attribute
+   * data.
+   * 
+   * @throws InvalidClassFileException
+   *           if the bytes fall outside the data
+   */
+  protected final void checkSize(int offset, int len) throws InvalidClassFileException {
+    if (length < offset - attr + len) {
+      throw new InvalidClassFileException(offset, "Attribute data too short, expected " + len + " bytes, got "
+          + (length + attr - offset));
+    }
+  }
+
+  /**
+   * Ensure that the len bytes starting at offset end at the end of the
+   * attribute data.
+   * 
+   * @throws InvalidClassFileException
+   *           if the bytes do not end at the end of the attribute
+   */
+  protected final void checkSizeEquals(int offset, int len) throws InvalidClassFileException {
+    if (length != offset - attr + len) {
+      throw new InvalidClassFileException(offset, "Attribute data invalid length, expected " + len + " bytes, got "
+          + (length + attr - offset));
+    }
+  }
+}