Make SnappyOutputStream.close() idempotent; guard against writing to closed stream

src/main/java/org/xerial/snappy/SnappyOutputStream.java

@@ -65,10 +65,12 @@ public class SnappyOutputStream extends OutputStream {
     private final BufferAllocator inputBufferAllocator;
     private final BufferAllocator outputBufferAllocator;
 
-    protected final byte[] inputBuffer;
-    protected final byte[] outputBuffer;
+    // The input and output buffer fields are set to null when closing this stream:
+    protected byte[] inputBuffer;
+    protected byte[] outputBuffer;
     private int inputCursor = 0;
     private int outputCursor = 0;
+    private boolean closed;
 
     public SnappyOutputStream(OutputStream out) {
         this(out, DEFAULT_BLOCK_SIZE);
@@ -231,6 +233,9 @@ private boolean hasSufficientOutputBufferFor(int inputSize) {
      * @throws IOException
      */
     public void rawWrite(Object array, int byteOffset, int byteLength) throws IOException {
+        if (closed) {
+            throw new IOException("Stream is closed");
+        }
         int cursor = 0;
         while(cursor < byteLength) {
             int readLen = Math.min(byteLength - cursor, blockSize - inputCursor);
@@ -258,6 +263,9 @@ public void rawWrite(Object array, int byteOffset, int byteLength) throws IOExce
      */
     @Override
     public void write(int b) throws IOException {
+        if (closed) {
+            throw new IOException("Stream is closed");
+        }
         if(inputCursor >= inputBuffer.length) {
             compressInput();
         }
@@ -269,6 +277,9 @@ public void write(int b) throws IOException {
      */
     @Override
     public void flush() throws IOException {
+        if (closed) {
+            throw new IOException("Stream is closed");
+        }
         compressInput();
         dumpOutput();
         out.flush();
@@ -320,12 +331,18 @@ protected void compressInput() throws IOException {
      */
     @Override
     public void close() throws IOException {
+        if (closed) {
+            return;
+        }
         try {
             flush();
             out.close();
         } finally {
+            closed = true;
             inputBufferAllocator.release(inputBuffer);
             outputBufferAllocator.release(outputBuffer);
+            inputBuffer = null;
+            outputBuffer = null;
         }
     }
 

src/test/java/org/xerial/snappy/SnappyOutputStreamTest.java

@@ -29,8 +29,13 @@
 import java.io.BufferedInputStream;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.lang.ref.WeakReference;
 
 import org.junit.Test;
+import org.xerial.snappy.buffer.BufferAllocatorFactory;
+import org.xerial.snappy.buffer.CachedBufferAllocator;
+import org.xerial.snappy.buffer.DefaultBufferAllocator;
 import org.xerial.util.FileResource;
 import org.xerial.util.log.Logger;
 
@@ -157,6 +162,83 @@ public void batchingOfWritesShouldNotAffectCompressedDataSize() throws Exception
         }
     }
 
+    @Test
+    public void closeShouldBeIdempotent() throws Exception {
+        // Regression test for issue #107, a bug where close() was non-idempotent and would release
+        // its buffers to the allocator multiple times, which could cause scenarios where two open
+        // SnappyOutputStreams could share the same buffers, leading to stream corruption issues.
+        final BufferAllocatorFactory bufferAllocatorFactory = CachedBufferAllocator.factory;
+        final int BLOCK_SIZE = 4096;
+        // Create a stream, use it, then close it once:
+        ByteArrayOutputStream ba1 = new ByteArrayOutputStream();
+        SnappyOutputStream os1 = new SnappyOutputStream(ba1, BLOCK_SIZE, bufferAllocatorFactory);
+        os1.write(42);
+        os1.close();
+        // Create a new output stream, which should end up re-using the first stream's freed buffers
+        ByteArrayOutputStream ba2 = new ByteArrayOutputStream();
+        SnappyOutputStream os2 = new SnappyOutputStream(ba2, BLOCK_SIZE, bufferAllocatorFactory);
+        // Close the first stream a second time, which is supposed to be safe due to idempotency:
+        os1.close();
+        // Allocate a third output stream, which is supposed to get its own fresh set of buffers:
+        ByteArrayOutputStream ba3 = new ByteArrayOutputStream();
+        SnappyOutputStream os3 = new SnappyOutputStream(ba3, BLOCK_SIZE, bufferAllocatorFactory);
+        // Since the second and third streams should have distinct sets of buffers, writes to these
+        // streams should not interfere with one another:
+        os2.write(2);
+        os3.write(3);
+        os2.close();
+        os3.close();
+        SnappyInputStream in2 = new SnappyInputStream(new ByteArrayInputStream(ba2.toByteArray()));
+        assertEquals(2, in2.read());
+        in2.close();
+        SnappyInputStream in3 = new SnappyInputStream(new ByteArrayInputStream(ba3.toByteArray()));
+        assertEquals(3, in3.read());
+        in3.close();
+    }
+
+    @Test
+    public void writingToClosedStreamShouldThrowIOException() throws IOException {
+        ByteArrayOutputStream b = new ByteArrayOutputStream();
+        SnappyOutputStream os = new SnappyOutputStream(b);
+        os.close();
+        try {
+            os.write(4);
+            fail("Expected write() to throw IOException");
+        } catch (IOException e) {
+            // Expected exception
+        }
+        try {
+            os.write(new int[] { 1, 2, 3, 4});
+            fail("Expected write() to throw IOException");
+        } catch (IOException e) {
+            // Expected exception
+        }
+    }
+
+    @Test
+    public void flushingClosedStreamShouldThrowIOException() throws IOException {
+        ByteArrayOutputStream b = new ByteArrayOutputStream();
+        SnappyOutputStream os = new SnappyOutputStream(b);
+        os.close();
+        try {
+            os.flush();
+        } catch (IOException e) {
+            // Expected exception
+        }
+    }
+
+    @Test
+    public void closingStreamShouldMakeBuffersEligibleForGarbageCollection() throws IOException {
+        ByteArrayOutputStream b = new ByteArrayOutputStream();
+        SnappyOutputStream os = new SnappyOutputStream(b, 4095, DefaultBufferAllocator.factory);
+        WeakReference<byte[]> inputBuffer = new WeakReference<byte[]>(os.inputBuffer);
+        WeakReference<byte[]> outputBuffer = new WeakReference<byte[]>(os.inputBuffer);
+        os.close();
+        System.gc();
+        assertNull(inputBuffer.get());
+        assertNull(outputBuffer.get());
+    }
+
     @Test
     public void longArrayCompress() throws Exception {
         long[] l = new long[10];