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