Add a detachAsStream to SkDynamicMemoryWStream.

src/core/SkStream.cpp

Index: src/core/SkStream.cpp
===================================================================
--- src/core/SkStream.cpp	(revision 10125)
+++ src/core/SkStream.cpp	(working copy)
@@ -661,6 +661,125 @@
     }
 }
 
+class SkBlockMemoryRefCnt : public SkRefCnt {
+public:
+    SkBlockMemoryRefCnt(SkDynamicMemoryWStream::Block* head) : fHead(head) { }
+
+    virtual ~SkBlockMemoryRefCnt() {
+        SkDynamicMemoryWStream::Block* block = fHead;
+        while (block != NULL) {
+            SkDynamicMemoryWStream::Block* next = block->fNext;
+            sk_free(block);
+            block = next;
+        }
+    }
+
+    SkDynamicMemoryWStream::Block* const fHead;
+};
+
+class SkBlockMemoryStream : public SkStreamAsset {
+public:
+    SkBlockMemoryStream(SkDynamicMemoryWStream::Block* head, size_t size)
+        : fBlockMemory(new SkBlockMemoryRefCnt(head)), fCurrent(head), fSize(size)
+        , fOffset(0), fCurrentOffset(0) { }
+
+    SkBlockMemoryStream(SkBlockMemoryRefCnt* headRef, size_t size)
+        : fBlockMemory(SkRef(headRef)), fCurrent(fBlockMemory->fHead), fSize(size)
+        , fOffset(0), fCurrentOffset(0) { }
+
+    virtual size_t read(void* buffer, size_t rawCount) SK_OVERRIDE {
+        size_t count = rawCount;
+        if (fOffset + count > fSize) {
+            count = fSize - fOffset;
+        }
+        size_t bytesLeftToRead = count;
+        while (fCurrent != NULL) {
+            size_t bytesLeftInCurrent = fCurrent->written() - fCurrentOffset;
+            size_t bytesFromCurrent = bytesLeftToRead <= bytesLeftInCurrent
+                                    ? bytesLeftToRead  : bytesLeftInCurrent;
+            if (buffer) {
+                memcpy(buffer, fCurrent->start() + fCurrentOffset, bytesFromCurrent);
+            }
+            if (bytesLeftToRead <= bytesFromCurrent) {
+                fCurrentOffset += bytesFromCurrent;
+                fOffset += count;
+                return count;
+            }
+            bytesLeftToRead -= bytesFromCurrent;
+            buffer = (void*) ((char* ) buffer + bytesFromCurrent);
+            fCurrent = fCurrent->fNext;
+            fCurrentOffset = 0;
+        }
+        SkASSERT(false);
+        return 0;
+    }
+
+    virtual bool isAtEnd() const SK_OVERRIDE {
+        return fOffset == fSize;
+    }
+
+    virtual bool rewind() SK_OVERRIDE {
+        fCurrent = fBlockMemory->fHead;
+        fCurrentOffset = 0;
+        fOffset = 0;
+        return true;
+    }
+    virtual SkBlockMemoryStream* duplicate() const SK_OVERRIDE {
+        return new SkBlockMemoryStream(fBlockMemory.get(), fSize);
+    }
+
+    virtual size_t getPosition() const SK_OVERRIDE {
+        return fOffset;
+    }
+    virtual bool seek(size_t position) SK_OVERRIDE {
+        if (position >= fOffset) {
+            size_t skipAmount = position - fOffset;
+            return this->skip(skipAmount) == skipAmount;
+        }
+        return this->rewind() && this->skip(position) == position;
+    }
+    virtual bool move(long offset) SK_OVERRIDE {
+        return seek(fOffset + offset);
+    }
+    virtual SkBlockMemoryStream* fork() const SK_OVERRIDE {
+        SkAutoTUnref<SkBlockMemoryStream> that(this->duplicate());
+        that->fOffset = this->fOffset;
+        that->fCurrent = this->fCurrent;
+        that->fCurrentOffset = this->fCurrentOffset;
+        return that.detach();
+    }
+
+    virtual size_t getLength() const SK_OVERRIDE {
+        return fSize;
+    }
+
+    virtual const void* getMemoryBase() SK_OVERRIDE {
+        if (fBlockMemory->fHead->fNext == NULL) {
+            return fBlockMemory->fHead->start();
+        }
+        return false;
+    }
+
+private:
+    SkAutoTUnref<SkBlockMemoryRefCnt> fBlockMemory;
+    SkDynamicMemoryWStream::Block const * fCurrent;
+    size_t const fSize;
+    size_t fOffset;
+    size_t fCurrentOffset;
+};
+
+SkStreamAsset* SkDynamicMemoryWStream::detatchAsStream() {
+    if (fCopy) {
+        SkMemoryStream* stream = new SkMemoryStream(fCopy);
+        this->reset();
+        return stream;
+    }
+    SkBlockMemoryStream* stream = new SkBlockMemoryStream(fHead, fBytesWritten);
+    fHead = 0;
+    this->reset();
+    return stream;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 void SkDebugWStream::newline()