michael@0: /*
michael@0:  * Copyright 2013 Google Inc.
michael@0:  *
michael@0:  * Use of this source code is governed by a BSD-style license that can be
michael@0:  * found in the LICENSE file.
michael@0:  */
michael@0: 
michael@0: #include "SkFrontBufferedStream.h"
michael@0: #include "SkStream.h"
michael@0: #include "SkTemplates.h"
michael@0: 
michael@0: class FrontBufferedStream : public SkStreamRewindable {
michael@0: public:
michael@0:     // Called by Create.
michael@0:     FrontBufferedStream(SkStream*, size_t bufferSize);
michael@0: 
michael@0:     virtual size_t read(void* buffer, size_t size) SK_OVERRIDE;
michael@0: 
michael@0:     virtual bool isAtEnd() const SK_OVERRIDE;
michael@0: 
michael@0:     virtual bool rewind() SK_OVERRIDE;
michael@0: 
michael@0:     virtual bool hasPosition() const SK_OVERRIDE { return true; }
michael@0: 
michael@0:     virtual size_t getPosition() const SK_OVERRIDE { return fOffset; }
michael@0: 
michael@0:     virtual bool hasLength() const SK_OVERRIDE { return fHasLength; }
michael@0: 
michael@0:     virtual size_t getLength() const SK_OVERRIDE { return fLength; }
michael@0: 
michael@0:     virtual SkStreamRewindable* duplicate() const SK_OVERRIDE { return NULL; }
michael@0: 
michael@0: private:
michael@0:     SkAutoTUnref<SkStream>  fStream;
michael@0:     const bool              fHasLength;
michael@0:     const size_t            fLength;
michael@0:     // Current offset into the stream. Always >= 0.
michael@0:     size_t                  fOffset;
michael@0:     // Amount that has been buffered by calls to read. Will always be less than
michael@0:     // fBufferSize.
michael@0:     size_t                  fBufferedSoFar;
michael@0:     // Total size of the buffer.
michael@0:     const size_t            fBufferSize;
michael@0:     // FIXME: SkAutoTMalloc throws on failure. Instead, Create should return a
michael@0:     // NULL stream.
michael@0:     SkAutoTMalloc<char>     fBuffer;
michael@0: 
michael@0:     // Read up to size bytes from already buffered data, and copy to
michael@0:     // dst, if non-NULL. Updates fOffset. Assumes that fOffset is less
michael@0:     // than fBufferedSoFar.
michael@0:     size_t readFromBuffer(char* dst, size_t size);
michael@0: 
michael@0:     // Buffer up to size bytes from the stream, and copy to dst if non-
michael@0:     // NULL. Updates fOffset and fBufferedSoFar. Assumes that fOffset is
michael@0:     // less than fBufferedSoFar, and size is greater than 0.
michael@0:     size_t bufferAndWriteTo(char* dst, size_t size);
michael@0: 
michael@0:     // Read up to size bytes directly from the stream and into dst if non-
michael@0:     // NULL. Updates fOffset. Assumes fOffset is at or beyond the buffered
michael@0:     // data, and size is greater than 0.
michael@0:     size_t readDirectlyFromStream(char* dst, size_t size);
michael@0: 
michael@0:     typedef SkStream INHERITED;
michael@0: };
michael@0: 
michael@0: SkStreamRewindable* SkFrontBufferedStream::Create(SkStream* stream, size_t bufferSize) {
michael@0:     if (NULL == stream) {
michael@0:         return NULL;
michael@0:     }
michael@0:     return SkNEW_ARGS(FrontBufferedStream, (stream, bufferSize));
michael@0: }
michael@0: 
michael@0: FrontBufferedStream::FrontBufferedStream(SkStream* stream, size_t bufferSize)
michael@0:     : fStream(SkRef(stream))
michael@0:     , fHasLength(stream->hasPosition() && stream->hasLength())
michael@0:     , fLength(stream->getLength() - stream->getPosition())
michael@0:     , fOffset(0)
michael@0:     , fBufferedSoFar(0)
michael@0:     , fBufferSize(bufferSize)
michael@0:     , fBuffer(bufferSize) {}
michael@0: 
michael@0: bool FrontBufferedStream::isAtEnd() const {
michael@0:     if (fOffset < fBufferedSoFar) {
michael@0:         // Even if the underlying stream is at the end, this stream has been
michael@0:         // rewound after buffering, so it is not at the end.
michael@0:         return false;
michael@0:     }
michael@0: 
michael@0:     return fStream->isAtEnd();
michael@0: }
michael@0: 
michael@0: bool FrontBufferedStream::rewind() {
michael@0:     // Only allow a rewind if we have not exceeded the buffer.
michael@0:     if (fOffset <= fBufferSize) {
michael@0:         fOffset = 0;
michael@0:         return true;
michael@0:     }
michael@0:     return false;
michael@0: }
michael@0: 
michael@0: size_t FrontBufferedStream::readFromBuffer(char* dst, size_t size) {
michael@0:     SkASSERT(fOffset < fBufferedSoFar);
michael@0:     // Some data has already been copied to fBuffer. Read up to the
michael@0:     // lesser of the size requested and the remainder of the buffered
michael@0:     // data.
michael@0:     const size_t bytesToCopy = SkTMin(size, fBufferedSoFar - fOffset);
michael@0:     if (dst != NULL) {
michael@0:         memcpy(dst, fBuffer + fOffset, bytesToCopy);
michael@0:     }
michael@0: 
michael@0:     // Update fOffset to the new position. It is guaranteed to be
michael@0:     // within the buffered data.
michael@0:     fOffset += bytesToCopy;
michael@0:     SkASSERT(fOffset <= fBufferedSoFar);
michael@0: 
michael@0:     return bytesToCopy;
michael@0: }
michael@0: 
michael@0: size_t FrontBufferedStream::bufferAndWriteTo(char* dst, size_t size) {
michael@0:     SkASSERT(size > 0);
michael@0:     SkASSERT(fOffset >= fBufferedSoFar);
michael@0:     // Data needs to be buffered. Buffer up to the lesser of the size requested
michael@0:     // and the remainder of the max buffer size.
michael@0:     const size_t bytesToBuffer = SkTMin(size, fBufferSize - fBufferedSoFar);
michael@0:     char* buffer = fBuffer + fOffset;
michael@0:     const size_t buffered = fStream->read(buffer, bytesToBuffer);
michael@0: 
michael@0:     fBufferedSoFar += buffered;
michael@0:     fOffset = fBufferedSoFar;
michael@0:     SkASSERT(fBufferedSoFar <= fBufferSize);
michael@0: 
michael@0:     // Copy the buffer to the destination buffer and update the amount read.
michael@0:     if (dst != NULL) {
michael@0:         memcpy(dst, buffer, buffered);
michael@0:     }
michael@0: 
michael@0:     return buffered;
michael@0: }
michael@0: 
michael@0: size_t FrontBufferedStream::readDirectlyFromStream(char* dst, size_t size) {
michael@0:     SkASSERT(size > 0);
michael@0:     // If we get here, we have buffered all that can be buffered.
michael@0:     SkASSERT(fBufferSize == fBufferedSoFar && fOffset >= fBufferSize);
michael@0: 
michael@0:     const size_t bytesReadDirectly = fStream->read(dst, size);
michael@0:     fOffset += bytesReadDirectly;
michael@0: 
michael@0:     // If we have read past the end of the buffer, rewinding is no longer
michael@0:     // supported, so we can go ahead and free the memory.
michael@0:     if (bytesReadDirectly > 0) {
michael@0:         fBuffer.reset(0);
michael@0:     }
michael@0: 
michael@0:     return bytesReadDirectly;
michael@0: }
michael@0: 
michael@0: size_t FrontBufferedStream::read(void* voidDst, size_t size) {
michael@0:     // Cast voidDst to a char* for easy addition.
michael@0:     char* dst = reinterpret_cast<char*>(voidDst);
michael@0:     SkDEBUGCODE(const size_t totalSize = size;)
michael@0:     const size_t start = fOffset;
michael@0: 
michael@0:     // First, read any data that was previously buffered.
michael@0:     if (fOffset < fBufferedSoFar) {
michael@0:         const size_t bytesCopied = this->readFromBuffer(dst, size);
michael@0: 
michael@0:         // Update the remaining number of bytes needed to read
michael@0:         // and the destination buffer.
michael@0:         size -= bytesCopied;
michael@0:         SkASSERT(size + (fOffset - start) == totalSize);
michael@0:         if (dst != NULL) {
michael@0:             dst += bytesCopied;
michael@0:         }
michael@0:     }
michael@0: 
michael@0:     // Buffer any more data that should be buffered, and copy it to the
michael@0:     // destination.
michael@0:     if (size > 0 && fBufferedSoFar < fBufferSize) {
michael@0:         const size_t buffered = this->bufferAndWriteTo(dst, size);
michael@0: 
michael@0:         // Update the remaining number of bytes needed to read
michael@0:         // and the destination buffer.
michael@0:         size -= buffered;
michael@0:         SkASSERT(size + (fOffset - start) == totalSize);
michael@0:         if (dst != NULL) {
michael@0:             dst += buffered;
michael@0:         }
michael@0:     }
michael@0: 
michael@0:     if (size > 0 && !fStream->isAtEnd()) {
michael@0:         SkDEBUGCODE(const size_t bytesReadDirectly =) this->readDirectlyFromStream(dst, size);
michael@0:         SkDEBUGCODE(size -= bytesReadDirectly;)
michael@0:         SkASSERT(size + (fOffset - start) == totalSize);
michael@0:     }
michael@0: 
michael@0:     return fOffset - start;
michael@0: }