Add a buffered SkStream class.

include/utils/SkFrontBufferedStream.h

Index: include/utils/SkFrontBufferedStream.h
diff --git a/include/utils/SkFrontBufferedStream.h b/include/utils/SkFrontBufferedStream.h
new file mode 100644
index 0000000000000000000000000000000000000000..9f7f4a03c71c1bcf1675e596327dc6b94da8cd5e
--- /dev/null
+++ b/include/utils/SkFrontBufferedStream.h
@@ -0,0 +1,69 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkStream.h"
+#include "SkTypes.h"
+
+/**
+ *  Specialized stream that only buffers the first X bytes of a stream,
+ *  where X is passed in by the user. Note that unlike some buffered
+ *  stream APIs, once more than those bytes are read, no more buffering
+ *  is done. This stream is designed for a use case where the caller
+ *  knows that rewind will only be called from within X bytes (inclusive),
+ *  and the wrapped stream is not necessarily able to rewind at all.
+ */
+class SkFrontBufferedStream : public SkStreamRewindable {

[scroggo, 2013/09/18 15:15:44]

Patch set 4 ONLY changes the name of SkBufferedStream to SkFrontBufferedStream
(and adds the comment above the class definition), so that the changes to code
can be more easily seen.

+public:
+    /**
+     *  Creates a new stream that wraps and buffers SkStream.
+     *  @param stream SkStream to buffer. If NULL, NULL is returned. After
+     *      this call, unref stream and do not refer to it.
+     *      SkFrontBufferedStream is expected to be its only owner.
+     *  @param bufferSize Exact size of the buffer to be used.
+     *  @return An SkStream that can buffer up to bufferSize.
+     */
+    static SkFrontBufferedStream* Create(SkStream* stream, size_t bufferSize);
+
+    virtual size_t read(void* buffer, size_t size) SK_OVERRIDE;
+
+    virtual bool isAtEnd() const SK_OVERRIDE;
+
+    virtual bool rewind() SK_OVERRIDE;
+
+    virtual bool hasPosition() const SK_OVERRIDE { return true; }
+
+    virtual size_t getPosition() const SK_OVERRIDE { return fOffset; }
+
+    virtual bool hasLength() const SK_OVERRIDE;
+
+    virtual size_t getLength() const SK_OVERRIDE;
+
+    virtual SkStreamRewindable* duplicate() const SK_OVERRIDE { return NULL; }
+
+private:
+    SkAutoTUnref<SkStream>  fStream;
+    // Current offset into the stream. Always >= 0.
+    size_t                  fOffset;
+    // Amount that has been buffered by calls to read. Will always be less than
+    // fBufferSize.
+    size_t                  fBufferedSoFar;
+    // Total size of the buffer.
+    const size_t            fBufferSize;
+    SkAutoTMalloc<char>     fBuffer;
+
+    // Unimplemented.
+    SkFrontBufferedStream();
+
+    // Private. Use Create.
+    SkFrontBufferedStream(SkStream*, size_t bufferSize);
+
+    char* getBufferAtOffset() {
+        return fBuffer.get() + fOffset;
+    }
+
+    typedef SkStream INHERITED;
+};