1 files changed, 63 insertions, 13 deletions

diff --git a/src/codec/SkStreamBuffer.h b/src/codec/SkStreamBuffer.h
index f04ddcbfd8..2b60775dd2 100644
--- a/src/codec/SkStreamBuffer.h
+++ b/src/codec/SkStreamBuffer.h
@@ -8,8 +8,10 @@
 #ifndef SkStreamBuffer_DEFINED
 #define SkStreamBuffer_DEFINED
 
+#include "SkData.h"
 #include "SkStream.h"
 #include "SkTypes.h"
+#include "../private/SkTHash.h"
 
 /**
  *  Helper class for reading from a stream that may not have all its data
@@ -25,28 +27,29 @@ public:
     // Takes ownership of the SkStream.
     SkStreamBuffer(SkStream*);
 
-    /**
-     *  Return a pointer the buffered data.
-     *
-     *  The number of bytes buffered is the sum of values returned by calls to
-     *  buffer() since the last call to flush().
-     */
-    const char* get() const { SkASSERT(fBytesBuffered >= 1); return fBuffer; }
+    ~SkStreamBuffer();
 
     /**
-     *  Bytes in the buffer.
+     *  Return a pointer the buffered data.
      *
-     *  Sum of the values returned by calls to buffer() since the last call to
-     *  flush().
+     *  The number of bytes buffered is the number passed to buffer()
+     *  after the last call to flush().
      */
-    size_t bytesBuffered() const { return fBytesBuffered; }
+    const char* get() const;
 
     /**
      *  Buffer from the stream into our buffer.
      *
-     *  Returns the number of bytes successfully buffered.
+     *  If this call returns true, get() can be used to access |bytes| bytes
+     *  from the stream. In addition, markPosition() can be called to mark this
+     *  position and enable calling getAtPosition() later to retrieve |bytes|
+     *  bytes.
+     *
+     *  @param bytes Total number of bytes desired.
+     *
+     *  @return Whether all bytes were successfully buffered.
      */
-    size_t buffer(size_t bytes);
+    bool buffer(size_t bytes);
 
     /**
      *  Flush the buffer.
@@ -54,15 +57,62 @@ public:
      *  After this call, no bytes are buffered.
      */
     void flush() {
+        if (fHasLengthAndPosition) {
+            if (fTrulyBuffered < fBytesBuffered) {
+                fStream->move(fBytesBuffered - fTrulyBuffered);
+            }
+            fTrulyBuffered = 0;
+        }
+        fPosition += fBytesBuffered;
         fBytesBuffered = 0;
     }
 
+    /**
+     *  Mark the current position in the stream to return to it later.
+     *
+     *  This is the position of the start of the buffer. After this call, a
+     *  a client can call getDataAtPosition to retrieve all the bytes currently
+     *  buffered.
+     *
+     *  @return size_t Position which can be passed to getDataAtPosition later
+     *      to retrieve the data currently buffered.
+     */
+    size_t markPosition();
+
+    /**
+     *  Retrieve data at position, as previously marked by markPosition().
+     *
+     *  @param position Position to retrieve data, as marked by markPosition().
+     *  @param length   Amount of data required at position.
+     *  @return SkData The data at position.
+     */
+    sk_sp<SkData> getDataAtPosition(size_t position, size_t length);
+
 private:
     static constexpr size_t kMaxSize = 256 * 3;
 
     std::unique_ptr<SkStream>   fStream;
+    size_t                      fPosition;
     char                        fBuffer[kMaxSize];
     size_t                      fBytesBuffered;
+    // If the stream has a length and position, we can make two optimizations:
+    // - We can skip buffering
+    // - During parsing, we can store the position and size of data that is
+    //   needed later during decoding.
+    const bool                  fHasLengthAndPosition;
+    // When fHasLengthAndPosition is true, we do not need to actually buffer
+    // inside buffer(). We'll buffer inside get(). This keeps track of how many
+    // bytes we've buffered inside get(), for the (non-existent) case of:
+    //  buffer(n)
+    //  get()
+    //  buffer(n + u)
+    //  get()
+    // The second call to get() needs to only truly buffer the part that was
+    // not already buffered.
+    mutable size_t              fTrulyBuffered;
+    // Only used if !fHasLengthAndPosition. In that case, markPosition will
+    // copy into an SkData, stored here.
+    SkTHashMap<size_t, SkData*> fMarkedData;
 };
 #endif // SkStreamBuffer_DEFINED