Add support for decoding WebP images

ios/web/public/webp_decoder.h

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IOS_WEB_PUBLIC_WEBP_DECODER_H_
+#define IOS_WEB_PUBLIC_WEBP_DECODER_H_
+
+#include "base/mac/scoped_nsobject.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "third_party/libwebp/webp/decode.h"
+
+@class NSData;
+
+namespace web {
+
+// Decodes a WebP image into either JPEG, PNG or uncompressed TIFF.
+class WebpDecoder : public base::RefCountedThreadSafe<WebpDecoder> {
+ public:
+  // Format of the decoded image.
+  // This enum is used for UMA reporting, keep it in sync with the histogram
+  // definition.
+  enum DecodedImageFormat {
+    JPEG = 1,
+    PNG,
+    TIFF,
+    DECODED_FORMAT_COUNT
+  };
+
+  class Delegate : public base::RefCountedThreadSafe<WebpDecoder::Delegate> {
+   public:
+    virtual void OnFinishedDecoding(bool success) = 0;
+    virtual void SetImageFeatures(size_t total_size,  // In bytes.
+                                  DecodedImageFormat format) = 0;
+    virtual void OnDataDecoded(NSData* data) = 0;
+
+   protected:
+    friend class base::RefCountedThreadSafe<WebpDecoder::Delegate>;
+    virtual ~Delegate() {}
+  };
+
+  explicit WebpDecoder(WebpDecoder::Delegate* delegate);
+
+  // For tests.
+  static size_t GetHeaderSize();
+
+  // Main entry point.
+  void OnDataReceived(const base::scoped_nsobject<NSData>& data);
+
+  // Stops the decoding.
+  void Stop();
+
+ private:
+  struct WebPIDecoderDeleter {
+    inline void operator()(WebPIDecoder* ptr) const { WebPIDelete(ptr); }
+  };
+
+  enum State {
+    READING_FEATURES,
+    READING_DATA,
+    DONE
+  };
+
+  friend class base::RefCountedThreadSafe<WebpDecoder>;
+  virtual ~WebpDecoder();
+
+  // Implements WebP image decoding state machine steps.
+  void DoReadFeatures(NSData* data);
+  void DoReadData(NSData* data);
+  bool DoSendData();
+
+  scoped_refptr<WebpDecoder::Delegate> delegate_;
+  WebPDecoderConfig config_;
+  WebpDecoder::State state_;
+  scoped_ptr<WebPIDecoder, WebPIDecoderDeleter> incremental_decoder_;
+  base::scoped_nsobject<NSData> output_buffer_;
+  base::scoped_nsobject<NSMutableData> features_;
+  int has_alpha_;
+};
+
+}  // namespace web
+
+#endif  // IOS_WEB_PUBLIC_WEBP_DECODER_H_