Issue 72: fix for infinite loop if allocate too large a buffer (due to invalid packet size)

src/main/java/net/schmizz/sshj/common/Buffer.java

@@ -74,10 +74,15 @@ public class Buffer<T extends Buffer<T>> {
     /** The default size for a {@code Buffer} (256 bytes) */
     public static final int DEFAULT_SIZE = 256;
 
+    /** The maximum valid size of buffer (i.e. biggest power of two that can be represented as an int - 2^30) */
+    public static final int MAX_SIZE = (1 << 30); 
+
     protected static int getNextPowerOf2(int i) {
         int j = 1;
-        while (j < i)
+        while (j < i) {
             j <<= 1;
+            if (j <= 0) throw new IllegalArgumentException("Cannot get next power of 2; "+i+" is too large"); 
+        }
         return j;
     }
 

src/main/java/net/schmizz/sshj/sftp/PacketReader.java

@@ -15,15 +15,16 @@
  */
 package net.schmizz.sshj.sftp;
 
-import net.schmizz.concurrent.Promise;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
+import net.schmizz.concurrent.Promise;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 public class PacketReader
         extends Thread {
 
@@ -65,7 +66,10 @@ public class PacketReader
     public SFTPPacket<Response> readPacket()
             throws IOException {
         int len = getPacketLength();
-
+        if (len > SFTPPacket.MAX_SIZE) {
+        	throw new IllegalStateException("Invalid packet: indicated length "+len+" too large");
+        }
+        
         packet.rpos(0);
         packet.wpos(0);
 

src/test/java/net/schmizz/sshj/common/BufferTest.java

@@ -0,0 +1,33 @@
+package net.schmizz.sshj.common;
+
+import static org.junit.Assert.fail;
+
+import net.schmizz.sshj.common.Buffer.PlainBuffer;
+
+import org.junit.Test;
+
+public class BufferTest {
+
+    // Issue 72: previously, it entered an infinite loop trying to establish the buffer size
+    @Test
+    public void shouldThrowOnTooLargeCapacity() {
+        PlainBuffer buffer = new PlainBuffer();
+        try {
+            buffer.ensureCapacity(Integer.MAX_VALUE);
+            fail("Allegedly ensured buffer capacity of size " + Integer.MAX_VALUE);
+        } catch (IllegalArgumentException e) {
+            // success
+        }
+    }
+
+    // Issue 72: previously, it entered an infinite loop trying to establish the buffer size
+    @Test
+    public void shouldThrowOnTooLargeInitialCapacity() {
+        try {
+            new PlainBuffer(Integer.MAX_VALUE);
+            fail("Allegedly created buffer with size " + Integer.MAX_VALUE);
+        } catch (IllegalArgumentException e) {
+            // success
+        }
+    }
+}

src/test/java/net/schmizz/sshj/sftp/PacketReaderTest.java

@@ -0,0 +1,71 @@
+package net.schmizz.sshj.sftp;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import java.io.DataOutputStream;
+import java.io.PipedInputStream;
+import java.io.PipedOutputStream;
+import java.util.Arrays;
+
+import net.schmizz.sshj.connection.channel.direct.Session.Subsystem;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+public class PacketReaderTest {
+
+    private DataOutputStream dataout;
+    private PacketReader reader;
+    private SFTPEngine engine;
+    private Subsystem subsystem;
+
+    @Before
+    public void setUp() throws Exception {
+        PipedOutputStream pipedout = new PipedOutputStream();
+        PipedInputStream pipedin = new PipedInputStream(pipedout);
+        dataout = new DataOutputStream(pipedout);
+
+        engine = Mockito.mock(SFTPEngine.class);
+        subsystem = Mockito.mock(Subsystem.class);
+        Mockito.when(engine.getSubsystem()).thenReturn(subsystem);
+        Mockito.when(subsystem.getInputStream()).thenReturn(pipedin);
+
+        reader = new PacketReader(engine);
+    }
+
+    // FIXME What is the byte format for the size? Big endian? Little endian?
+    @Test
+    public void shouldReadPacket() throws Exception {
+        byte[] bytes = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
+        dataout.writeInt(10);
+        dataout.write(bytes);
+        dataout.flush();
+        
+        SFTPPacket<Response> packet = reader.readPacket();
+        assertEquals(packet.available(), 10);
+        assertTrue("actual=" + Arrays.toString(packet.array()), Arrays.equals(bytes, subArray(packet.array(), 0, 10)));
+    }
+
+    @Test
+    public void shouldFailWhenPacketLengthTooLarge() throws Exception {
+        dataout.writeInt(Integer.MAX_VALUE);
+        dataout.flush();
+        
+        try {
+            reader.readPacket();
+            fail("Should have failed to read packet of size " + Integer.MAX_VALUE);
+        } catch (IllegalStateException e) {
+            e.printStackTrace();
+            // success; indicated packet size was too large
+        }
+    }
+
+    private byte[] subArray(byte[] source, int startIndex, int length) {
+        byte[] result = new byte[length];
+        System.arraycopy(source, startIndex, result, 0, length);
+        return result;
+    }
+}