AAPT2: Separate out the various steps

An early refactor. Some ideas became clearer as
development continued. Now the various phases are much
clearer and more easily reusable.

Also added a ton of tests!

Change-Id: Ic8f0a70c8222370352e63533b329c40457c0903e
diff --git a/tools/aapt2/unflatten/ResChunkPullParser.cpp b/tools/aapt2/unflatten/ResChunkPullParser.cpp
new file mode 100644
index 0000000..6f8bb1b
--- /dev/null
+++ b/tools/aapt2/unflatten/ResChunkPullParser.cpp
@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "unflatten/ResChunkPullParser.h"
+#include "util/Util.h"
+
+#include <androidfw/ResourceTypes.h>
+#include <cstddef>
+
+namespace aapt {
+
+using android::ResChunk_header;
+
+ResChunkPullParser::Event ResChunkPullParser::next() {
+    if (!isGoodEvent(mEvent)) {
+        return mEvent;
+    }
+
+    if (mEvent == Event::StartDocument) {
+        mCurrentChunk = mData;
+    } else {
+        mCurrentChunk = (const ResChunk_header*)
+                (((const char*) mCurrentChunk) + util::deviceToHost32(mCurrentChunk->size));
+    }
+
+    const std::ptrdiff_t diff = (const char*) mCurrentChunk - (const char*) mData;
+    assert(diff >= 0 && "diff is negative");
+    const size_t offset = static_cast<const size_t>(diff);
+
+    if (offset == mLen) {
+        mCurrentChunk = nullptr;
+        return (mEvent = Event::EndDocument);
+    } else if (offset + sizeof(ResChunk_header) > mLen) {
+        mLastError = "chunk is past the end of the document";
+        mCurrentChunk = nullptr;
+        return (mEvent = Event::BadDocument);
+    }
+
+    if (util::deviceToHost16(mCurrentChunk->headerSize) < sizeof(ResChunk_header)) {
+        mLastError = "chunk has too small header";
+        mCurrentChunk = nullptr;
+        return (mEvent = Event::BadDocument);
+    } else if (util::deviceToHost32(mCurrentChunk->size) <
+            util::deviceToHost16(mCurrentChunk->headerSize)) {
+        mLastError = "chunk's total size is smaller than header";
+        mCurrentChunk = nullptr;
+        return (mEvent = Event::BadDocument);
+    } else if (offset + util::deviceToHost32(mCurrentChunk->size) > mLen) {
+        mLastError = "chunk's data extends past the end of the document";
+        mCurrentChunk = nullptr;
+        return (mEvent = Event::BadDocument);
+    }
+    return (mEvent = Event::Chunk);
+}
+
+} // namespace aapt