Treat output length as a maximum length for CALL operations (#236)

* Fix corner case where Memory did not clear target destination if the new bytes to set was empty.

* Use BytesValue.EMPTY instead of Bytes32.EMPTY to make it clear that it's a 0 length BytesValues rather than 32 bytes of zeross.

* Treat outputLength for call operations as a maximum length - when the actual data to output is shorter than outputLength, do not zero out the tail end of the memory range.

ethereum/core/src/main/java/tech/pegasys/pantheon/ethereum/mainnet/precompiles/ECRECPrecompiledContract.java

@@ -72,7 +72,7 @@ public class ECRECPrecompiledContract extends AbstractPrecompiledContract {
     try {
       final Optional<PublicKey> recovered = PublicKey.recoverFromSignature(h, signature);
       if (!recovered.isPresent()) {
-        return Bytes32.EMPTY;
+        return BytesValue.EMPTY;
       }
 
       final Bytes32 hashed = Hash.hash(recovered.get().getEncodedBytes());
@@ -80,7 +80,7 @@ public class ECRECPrecompiledContract extends AbstractPrecompiledContract {
       hashed.slice(12).copyTo(result, 12);
       return result;
     } catch (final IllegalArgumentException e) {
-      return Bytes32.EMPTY;
+      return BytesValue.EMPTY;
     }
   }
 }

ethereum/core/src/main/java/tech/pegasys/pantheon/ethereum/vm/AbstractCallOperation.java

@@ -195,9 +195,17 @@ public abstract class AbstractCallOperation extends AbstractOperation {
 
     final UInt256 outputOffset = outputDataOffset(frame);
     final UInt256 outputSize = outputDataLength(frame);
-    frame.writeMemory(outputOffset, outputSize, childFrame.getOutputData());
+    final BytesValue outputData = childFrame.getOutputData();
+    final int outputSizeAsInt = outputSize.toInt();
 
-    frame.setReturnData(childFrame.getOutputData());
+    if (outputSizeAsInt > outputData.size()) {
+      frame.expandMemory(outputOffset.toLong(), outputSizeAsInt);
+      frame.writeMemory(outputOffset, UInt256.of(outputData.size()), outputData);
+    } else {
+      frame.writeMemory(outputOffset, outputSize, outputData);
+    }
+
+    frame.setReturnData(outputData);
     frame.addLogs(childFrame.getLogs());
     frame.addSelfDestructs(childFrame.getSelfDestructs());
     frame.incrementGasRefund(childFrame.getGasRefund());

ethereum/core/src/main/java/tech/pegasys/pantheon/ethereum/vm/Memory.java

@@ -361,8 +361,9 @@ public class Memory {
     ensureCapacityForBytes(start, length);
 
     // We've properly expanded memory as needed. We now have simply have to copy the
-    // min(length, value.size()) first bytes of value.
+    // min(length, value.size()) first bytes of value and clear any bytes that exceed value's length
     if (taintedValue.isEmpty()) {
+      clearBytes(location, numBytes);
       return;
     }
     final BytesValue value;

ethereum/core/src/test/java/tech/pegasys/pantheon/ethereum/vm/MemoryTest.java

@@ -123,6 +123,30 @@ public class MemoryTest {
     assertThat(memory.getWord(UInt256.of(64))).isEqualTo(WORD3);
   }
 
+  @Test
+  public void shouldClearMemoryWhenSourceDataIsEmpty() {
+    memory.setWord(UInt256.of(64), WORD3);
+    assertThat(memory.getWord(UInt256.of(64))).isEqualTo(WORD3);
+
+    memory.setBytes(UInt256.ZERO, UInt256.of(96), BytesValue.EMPTY);
+
+    assertThat(memory.getWord(UInt256.of(0))).isEqualTo(Bytes32.ZERO);
+    assertThat(memory.getWord(UInt256.of(32))).isEqualTo(Bytes32.ZERO);
+    assertThat(memory.getWord(UInt256.of(64))).isEqualTo(Bytes32.ZERO);
+  }
+
+  @Test
+  public void shouldClearMemoryWhenSourceDataIsEmptyWithSourceOffset() {
+    memory.setWord(UInt256.of(64), WORD3);
+    assertThat(memory.getWord(UInt256.of(64))).isEqualTo(WORD3);
+
+    memory.setBytes(UInt256.ZERO, UInt256.ZERO, UInt256.of(96), BytesValue.EMPTY);
+
+    assertThat(memory.getWord(UInt256.of(0))).isEqualTo(Bytes32.ZERO);
+    assertThat(memory.getWord(UInt256.of(32))).isEqualTo(Bytes32.ZERO);
+    assertThat(memory.getWord(UInt256.of(64))).isEqualTo(Bytes32.ZERO);
+  }
+
   private static Bytes32 fillBytes32(final long value) {
     return Bytes32.fromHexString(Strings.repeat(Long.toString(value), 64));
   }