Merge branch 'stsypanov/asm-master'

asm/src/main/java/org/objectweb/asm/ClassReader.java

@@ -88,6 +88,9 @@ public class ClassReader {
    */
   static final int EXPAND_ASM_INSNS = 256;
 
+  /** The maximum size of array to allocate. */
+  private static final int MAX_BUFFER_SIZE = 1024 * 1024;
+
   /** The size of the temporary byte array used to read class input streams chunk by chunk. */
   private static final int INPUT_STREAM_DATA_CHUNK_SIZE = 4096;
 
@@ -310,13 +313,19 @@ public class ClassReader {
     if (inputStream == null) {
       throw new IOException("Class not found");
     }
+    int bufferSize = calculateBufferSize(inputStream);
     try (ByteArrayOutputStream outputStream = new ByteArrayOutputStream()) {
-      byte[] data = new byte[INPUT_STREAM_DATA_CHUNK_SIZE];
+      byte[] data = new byte[bufferSize];
       int bytesRead;
-      while ((bytesRead = inputStream.read(data, 0, data.length)) != -1) {
+      int readCount = 0;
+      while ((bytesRead = inputStream.read(data, 0, bufferSize)) != -1) {
         outputStream.write(data, 0, bytesRead);
+        readCount++;
       }
       outputStream.flush();
+      if (readCount == 1) {
+        return data;
+      }
       return outputStream.toByteArray();
     } finally {
       if (close) {
@@ -325,6 +334,20 @@ public class ClassReader {
     }
   }
 
+  private static int calculateBufferSize(final InputStream inputStream) throws IOException {
+    int expectedLength = inputStream.available();
+    /*
+     * Some implementations can return 0 while holding available data
+     * (e.g. new FileInputStream("/proc/a_file"))
+     * Also in some pathological cases a very small number might be returned,
+     * and in this case we use default size
+     */
+    if (expectedLength < 256) {
+      return INPUT_STREAM_DATA_CHUNK_SIZE;
+    }
+    return Math.min(expectedLength, MAX_BUFFER_SIZE);
+  }
+
   // -----------------------------------------------------------------------------------------------
   // Accessors
   // -----------------------------------------------------------------------------------------------