Add initial support for new Java 9 class file format (JDK-8148785) (#97)

Add initial support for new Java 9 class file format (Java 9 b119, see JDK-8148785, JDK-8150011)

src/main/java/de/thetaphi/forbiddenapis/AsmUtils.java

@@ -16,11 +16,20 @@
 
 package de.thetaphi.forbiddenapis;
 
+import java.io.EOFException;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.PushbackInputStream;
 import java.net.URISyntaxException;
 import java.net.URL;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
 import java.util.Locale;
 import java.util.regex.Pattern;
 
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.Opcodes;
+
 /** Some static utilities for analyzing with ASM, also constants. */
 public final class AsmUtils {
 
@@ -146,5 +155,27 @@ public static String getModuleName(URL jrtUrl) {
       return null;
     }
   }
+
+  private static void patchClassMajorVersion(byte[] header, int versionFrom, int versionTo) {
+    final ByteBuffer buf = ByteBuffer.wrap(header).order(ByteOrder.BIG_ENDIAN);
+    if (buf.getShort(6) == versionFrom) {
+      buf.putShort(6, (short) versionTo);
+    }
+  }
+
+  /** Utility method to load class files of Java 9 by patching them, so ASM can read them. */
+  public static ClassReader readAndPatchClass(InputStream in) throws IOException {
+    final byte[] b = new byte[8];
+    final PushbackInputStream pbin = new PushbackInputStream(in, b.length);
+    for (int upto = 0; upto < b.length;) {
+      final int read = pbin.read(b, upto, b.length - upto);
+      if (read == -1)
+        throw new EOFException("Not enough bytes available to read header of class file.");
+      upto += read;
+    }
+    patchClassMajorVersion(b, Opcodes.V1_8 + 1, Opcodes.V1_8);
+    pbin.unread(b);
+    return new ClassReader(pbin);
+  }
 
 }

src/main/java/de/thetaphi/forbiddenapis/Checker.java

@@ -245,7 +245,7 @@ private ClassSignature loadClassFromJigsaw(String classname) throws IOException
     }
 
     try {
-      return new ClassSignature(new ClassReader(in), AsmUtils.isRuntimeModule(moduleName), false);
+      return new ClassSignature(AsmUtils.readAndPatchClass(in), AsmUtils.isRuntimeModule(moduleName), false);
     } finally {
       in.close();
     }
@@ -297,7 +297,7 @@ private ClassSignature getClassFromClassLoader(final String clazz) throws ClassN
         final boolean isRuntimeClass = isRuntimeClass(conn);
         final InputStream in = conn.getInputStream();
         try {
-          classpathClassCache.put(clazz, c = new ClassSignature(new ClassReader(in), isRuntimeClass, false));
+          classpathClassCache.put(clazz, c = new ClassSignature(AsmUtils.readAndPatchClass(in), isRuntimeClass, false));
         } finally {
           in.close();
         }
@@ -528,7 +528,7 @@ private void parseSignaturesFile(Reader reader, boolean isBundled) throws IOExce
   public void addClassToCheck(final InputStream in) throws IOException {
     final ClassReader reader;
     try {
-      reader = new ClassReader(in);
+      reader = AsmUtils.readAndPatchClass(in);
     } finally {
       in.close();
     }

src/tools/java/de/thetaphi/forbiddenapis/DeprecatedGen.java

@@ -69,7 +69,7 @@ protected boolean isDeprecated(int access) {
   protected void parseClass(InputStream in) throws IOException {
     final ClassReader reader;
     try {
-      reader = new ClassReader(in);
+      reader = AsmUtils.readAndPatchClass(in);
     } catch (IllegalArgumentException iae) {
       // unfortunately the ASM IAE has no message, so add good info!
       throw new IllegalArgumentException("The class file format of your runtime seems to be too recent to be parsed by ASM (may need to be upgraded).");