Create AAssetStreamAdaptor, for reading from AAssets

Bug: 135133301
Test: Ib84462ea5fa8a7779eaa44494775e182e52ecaca, once
      I4cf8bfb0aacfb8e22c3f9b1689bd614ed1253673 lands

AAssetStreamAdaptor lives in libjnigraphics, for use by AImageDecoder.

Change-Id: I4e2559c3c21c866d61fb431a0a1368150c7d39cb

native/graphics/jni/Android.bp

@@ -24,10 +24,15 @@ cc_library_shared {
 
     // our source files
     //
-    srcs: ["bitmap.cpp"],
+    srcs: [
+        "bitmap.cpp",
+        "aassetstreamadaptor.cpp",
+    ],
 
     shared_libs: [
+        "libandroid",
         "libandroid_runtime",
+        "liblog",
     ],
 
     arch: {

native/graphics/jni/aassetstreamadaptor.cpp

@@ -0,0 +1,117 @@
+/*
+ * Copyright 2019 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 "aassetstreamadaptor.h"
+
+#include <log/log.h>
+
+AAssetStreamAdaptor::AAssetStreamAdaptor(AAsset* asset)
+    : mAAsset(asset)
+{
+}
+
+bool AAssetStreamAdaptor::rewind() {
+    off64_t pos = AAsset_seek64(mAAsset, 0, SEEK_SET);
+    if (pos == (off64_t)-1) {
+        ALOGE("rewind failed!");
+        return false;
+    }
+    return true;
+}
+
+size_t AAssetStreamAdaptor::getLength() const {
+    return AAsset_getLength64(mAAsset);
+}
+
+bool AAssetStreamAdaptor::isAtEnd() const {
+    return AAsset_getRemainingLength64(mAAsset) == 0;
+}
+
+SkStreamRewindable* AAssetStreamAdaptor::onDuplicate() const {
+    // Cannot sensibly create a duplicate, since each AAssetStreamAdaptor
+    // would be modifying the same AAsset.
+    //return new AAssetStreamAdaptor(mAAsset);
+    return nullptr;
+}
+
+bool AAssetStreamAdaptor::hasPosition() const {
+    return AAsset_seek64(mAAsset, 0, SEEK_CUR) != -1;
+}
+
+size_t AAssetStreamAdaptor::getPosition() const {
+    const off64_t offset = AAsset_seek64(mAAsset, 0, SEEK_CUR);
+    if (offset == -1) {
+        ALOGE("getPosition failed!");
+        return 0;
+    }
+
+    return offset;
+}
+
+bool AAssetStreamAdaptor::seek(size_t position) {
+    if (AAsset_seek64(mAAsset, position, SEEK_SET) == -1) {
+        ALOGE("seek failed!");
+        return false;
+    }
+
+    return true;
+}
+
+bool AAssetStreamAdaptor::move(long offset) {
+    if (AAsset_seek64(mAAsset, offset, SEEK_CUR) == -1) {
+        ALOGE("move failed!");
+        return false;
+    }
+
+    return true;
+}
+
+size_t AAssetStreamAdaptor::read(void* buffer, size_t size) {
+    ssize_t amount;
+
+    if (!buffer) {
+        if (!size) {
+            return 0;
+        }
+
+        // asset->seek returns new total offset
+        // we want to return amount that was skipped
+        const off64_t oldOffset = AAsset_seek64(mAAsset, 0, SEEK_CUR);
+        if (oldOffset == -1) {
+            ALOGE("seek(oldOffset) failed!");
+            return 0;
+        }
+
+        const off64_t newOffset = AAsset_seek64(mAAsset, size, SEEK_CUR);
+        if (-1 == newOffset) {
+            ALOGE("seek(%zu) failed!", size);
+            return 0;
+        }
+        amount = newOffset - oldOffset;
+    } else {
+        amount = AAsset_read(mAAsset, buffer, size);
+    }
+
+    if (amount < 0) {
+        amount = 0;
+    }
+    return amount;
+}
+
+const void* AAssetStreamAdaptor::getMemoryBase() {
+    return AAsset_getBuffer(mAAsset);
+}
+

native/graphics/jni/aassetstreamadaptor.h

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2019 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.
+ */
+
+#pragma once
+
+#include "SkStream.h"
+
+#include <android/asset_manager.h>
+
+// Like AssetStreamAdaptor, but operates on AAsset, a public NDK API.
+class AAssetStreamAdaptor : public SkStreamRewindable {
+public:
+    /**
+     * Create an SkStream that reads from an AAsset.
+     *
+     * The AAsset must remain open for the lifetime of the Adaptor. The Adaptor
+     * does *not* close the AAsset.
+     */
+    explicit AAssetStreamAdaptor(AAsset*);
+
+    bool rewind() override;
+    size_t read(void* buffer, size_t size) override;
+    bool hasLength() const override { return true; }
+    size_t getLength() const override;
+    bool hasPosition() const override;
+    size_t getPosition() const override;
+    bool seek(size_t position) override;
+    bool move(long offset) override;
+    bool isAtEnd() const override;
+    const void* getMemoryBase() override;
+protected:
+    SkStreamRewindable* onDuplicate() const override;
+
+private:
+    AAsset* mAAsset;
+};
+