Decode file descriptor from the correct offset.

Fix a few bugs in nativeDecodeFileDescriptor:
1. Restore the FD's offset when exiting the function.
2. Copy the data when potentially using an SkImageRef.
   The old behavior would have continued to modify the
   file descriptor's offset each time a new decode was
   required. The copy ensures that the file descriptor
   remains unchanged.
3. Buffer the file stream.
   Prior to this change, if the image was not a PNG,
   the stream would be rewound to the beginning of the
   file, even if the file descriptor was passed in with
   an offset. Thanks to the buffer, the stream is only
   rewound to the original offset.

Depends on https://googleplex-android-review.googlesource.com/#/c/415821/1
in external/skia

BUG:12807677
BUG:12895876
Change-Id: I38b8cf5d210dbbc0107e6562e3884867de57fc4b

1 files changed, 42 insertions, 21 deletions

diff --git a/core/jni/android/graphics/BitmapFactory.cpp b/core/jni/android/graphics/BitmapFactory.cpp
index 3e1f26a..fae93ba 100644
--- a/core/jni/android/graphics/BitmapFactory.cpp
+++ b/core/jni/android/graphics/BitmapFactory.cpp
@@ -474,6 +474,12 @@ static jobject doDecode(JNIEnv* env, SkStreamRewindable* stream, jobject padding
             bitmapCreateFlags, ninePatchChunk, layoutBounds, -1);
 }
 
+// Need to buffer enough input to be able to rewind as much as might be read by a decoder
+// trying to determine the stream's format. Currently the most is 64, read by
+// SkImageDecoder_libwebp.
+// FIXME: Get this number from SkImageDecoder
+#define BYTES_TO_BUFFER 64
+
 static jobject nativeDecodeStream(JNIEnv* env, jobject clazz, jobject is, jbyteArray storage,
         jobject padding, jobject options) {
 
@@ -481,11 +487,8 @@ static jobject nativeDecodeStream(JNIEnv* env, jobject clazz, jobject is, jbyteA
     SkAutoTUnref<SkStream> stream(CreateJavaInputStreamAdaptor(env, is, storage));
 
     if (stream.get()) {
-        // Need to buffer enough input to be able to rewind as much as might be read by a decoder
-        // trying to determine the stream's format. Currently the most is 64, read by
-        // SkImageDecoder_libwebp.
-        // FIXME: Get this number from SkImageDecoder
-        SkAutoTUnref<SkStreamRewindable> bufferedStream(SkFrontBufferedStream::Create(stream, 64));
+        SkAutoTUnref<SkStreamRewindable> bufferedStream(
+                SkFrontBufferedStream::Create(stream, BYTES_TO_BUFFER));
         SkASSERT(bufferedStream.get() != NULL);
         // for now we don't allow purgeable with java inputstreams
         bitmap = doDecode(env, bufferedStream, padding, options, false, false);
@@ -506,30 +509,48 @@ static jobject nativeDecodeFileDescriptor(JNIEnv* env, jobject clazz, jobject fi
         return nullObjectReturn("fstat return -1");
     }
 
-    bool isPurgeable = optionsPurgeable(env, bitmapFactoryOptions);
-    bool isShareable = optionsShareable(env, bitmapFactoryOptions);
-    bool weOwnTheFD = false;
-    if (isPurgeable && isShareable) {
-        int newFD = ::dup(descriptor);
-        if (-1 != newFD) {
-            weOwnTheFD = true;
-            descriptor = newFD;
-        }
-    }
+    // Restore the descriptor's offset on exiting this function.
+    AutoFDSeek autoRestore(descriptor);
 
     FILE* file = fdopen(descriptor, "r");
     if (file == NULL) {
         return nullObjectReturn("Could not open file");
     }
 
-    SkAutoTUnref<SkFILEStream> stream(new SkFILEStream(file,
-            weOwnTheFD ? SkFILEStream::kCallerPasses_Ownership :
+    SkAutoTUnref<SkFILEStream> fileStream(new SkFILEStream(file,
                          SkFILEStream::kCallerRetains_Ownership));
 
-    /* Allow purgeable iff we own the FD, i.e., in the puregeable and
-       shareable case.
-    */
-    return doDecode(env, stream, padding, bitmapFactoryOptions, weOwnTheFD);
+    SkAutoTUnref<SkStreamRewindable> stream;
+
+    // Retain the old behavior of allowing purgeable if both purgeable and
+    // shareable are set to true.
+    bool isPurgeable = optionsPurgeable(env, bitmapFactoryOptions)
+                       && optionsShareable(env, bitmapFactoryOptions);
+    if (isPurgeable) {
+        // Copy the stream, so the image can be decoded multiple times without
+        // continuing to modify the original file descriptor.
+        // Copy beginning from the current position.
+        const size_t fileSize = fileStream->getLength() - fileStream->getPosition();
+        void* buffer = sk_malloc_flags(fileSize, 0);
+        if (buffer == NULL) {
+            return nullObjectReturn("Could not make a copy for ashmem");
+        }
+
+        SkAutoTUnref<SkData> data(SkData::NewFromMalloc(buffer, fileSize));
+
+        if (fileStream->read(buffer, fileSize) != fileSize) {
+            return nullObjectReturn("Could not read the file.");
+        }
+
+        stream.reset(new SkMemoryStream(data));
+    } else {
+        // Use a buffered stream. Although an SkFILEStream can be rewound, this
+        // ensures that SkImageDecoder::Factory never rewinds beyond the
+        // current position of the file descriptor.
+        stream.reset(SkFrontBufferedStream::Create(fileStream, BYTES_TO_BUFFER));
+    }
+
+    return doDecode(env, stream, padding, bitmapFactoryOptions, isPurgeable);
 }
 
 static jobject nativeDecodeAsset(JNIEnv* env, jobject clazz, jlong native_asset,