From fd3efb080ef6ce4280389c7420e10e7104ca5d5b Mon Sep 17 00:00:00 2001
From: David Renshaw <dwrenshaw@gmail.com>
Date: Sun, 9 Nov 2014 16:32:51 -0500
Subject: [PATCH] add a Zeroing test and fix some bugs

---
 .../scala/org/capnproto/EncodingTest.scala    | 30 ++++++++++++++++++-
 .../java/org/capnproto/MessageBuilder.java    | 17 +++++++----
 .../main/java/org/capnproto/WireHelpers.java  |  5 ++++
 3 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/compiler/src/test/scala/org/capnproto/EncodingTest.scala b/compiler/src/test/scala/org/capnproto/EncodingTest.scala
index 4e97eab..c998a85 100644
--- a/compiler/src/test/scala/org/capnproto/EncodingTest.scala
+++ b/compiler/src/test/scala/org/capnproto/EncodingTest.scala
@@ -50,7 +50,7 @@ class EncodingSuite extends FunSuite {
     TestUtil.initTestMessage(allTypes);
 
     val message2 = new MessageBuilder();
-    val allTypes2 = message.initRoot(TestAllTypes.factory);
+    val allTypes2 = message2.initRoot(TestAllTypes.factory);
 
     allTypes2.setStructField(allTypes.asReader());
     TestUtil.checkTestMessage(allTypes2.getStructField());
@@ -58,6 +58,34 @@ class EncodingSuite extends FunSuite {
     TestUtil.checkTestMessage(reader);
   }
 
+  test("Zeroing") {
+    val message = new MessageBuilder();
+    val allTypes = message.initRoot(TestAllTypes.factory);
+
+    val structList = allTypes.initStructList(3);
+    TestUtil.initTestMessage(structList.get(0));
+
+    val structField = allTypes.initStructField();
+    TestUtil.initTestMessage(structField);
+
+    TestUtil.initTestMessage(structList.get(1));
+    TestUtil.initTestMessage(structList.get(2));
+    TestUtil.checkTestMessage(structList.get(0));
+    allTypes.initStructList(0);
+
+    TestUtil.checkTestMessage(allTypes.getStructField());
+    val allTypesReader = allTypes.asReader();
+    TestUtil.checkTestMessage(allTypesReader.getStructField());
+
+    val any = message.initRoot(AnyPointer.factory);
+    val segments = message.getSegmentsForOutput();
+    for (segment <- segments) {
+      for (jj <- 0 to segment.limit - 1) {
+        segment.get(jj) should equal (0);
+      }
+    }
+  }
+
   test("Generics") {
     val message = new MessageBuilder();
     val factory = TestGenerics.newFactory(TestAllTypes.factory, Text.factory);
diff --git a/runtime/src/main/java/org/capnproto/MessageBuilder.java b/runtime/src/main/java/org/capnproto/MessageBuilder.java
index 6983bf9..d8ec266 100644
--- a/runtime/src/main/java/org/capnproto/MessageBuilder.java
+++ b/runtime/src/main/java/org/capnproto/MessageBuilder.java
@@ -46,13 +46,18 @@ public final class MessageBuilder {
 
     public <T> T initRoot(FromPointerBuilder<T> factory) {
         SegmentBuilder rootSegment = this.arena.segments.get(0);
-        int location = rootSegment.allocate(1);
-        if (location == SegmentBuilder.FAILED_ALLOCATION) {
-            throw new Error("could not allocate root pointer");
+        if (rootSegment.currentSize() == 0) {
+            int location = rootSegment.allocate(1);
+            if (location == SegmentBuilder.FAILED_ALLOCATION) {
+                throw new Error("could not allocate root pointer");
+            }
+            if (location != 0) {
+                throw new Error("First allocated word of new segment was not at offset 0");
+            }
+           return factory.initFromPointerBuilder(rootSegment, location, 0);
+        } else {
+           return factory.initFromPointerBuilder(rootSegment, 0, 0);
         }
-
-        AnyPointer.Builder ptr = new AnyPointer.Builder(rootSegment, location);
-        return ptr.initAs(factory);
     }
 
     public final java.nio.ByteBuffer[] getSegmentsForOutput() {
diff --git a/runtime/src/main/java/org/capnproto/WireHelpers.java b/runtime/src/main/java/org/capnproto/WireHelpers.java
index 5669022..91f27c5 100644
--- a/runtime/src/main/java/org/capnproto/WireHelpers.java
+++ b/runtime/src/main/java/org/capnproto/WireHelpers.java
@@ -48,6 +48,11 @@ final class WireHelpers {
                                    int amount, // in words
                                    byte kind) {
 
+        long ref = segment.get(refOffset);
+        if (!WirePointer.isNull(ref)) {
+            zeroObject(segment, refOffset);
+        }
+
         if (amount == 0 && kind == WirePointer.STRUCT) {
             WirePointer.setKindAndTargetForEmptyStruct(segment.buffer, refOffset);
             return new AllocateResult(refOffset, refOffset, segment);