blob: 519609f1183317baea339aa6820ba6865019ffe0 [file] [log] [blame]
/*
* 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 "include/codec/SkCodec.h"
#include "include/core/SkStream.h"
#include "FrontBufferedStream.h"
#include <algorithm>
namespace {
class FrontBufferedStream : public SkStreamRewindable {
public:
// Called by Make.
FrontBufferedStream(std::unique_ptr<SkStream>, size_t bufferSize);
~FrontBufferedStream() override;
bool failedToAllocateBuffer() const { return !fBuffer; }
size_t read(void* buffer, size_t size) override;
size_t peek(void* buffer, size_t size) const override;
bool isAtEnd() const override;
bool rewind() override;
bool hasLength() const override { return fHasLength; }
size_t getLength() const override { return fLength; }
private:
SkStreamRewindable* onDuplicate() const override { return nullptr; }
std::unique_ptr<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;
char* fBuffer;
static constexpr size_t kStorageSize = SkCodec::MinBufferedBytesNeeded();
char fStorage[kStorageSize];
// Read up to size bytes from already buffered data, and copy to
// dst, if non-nullptr. 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-
// nullptr. 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-
// nullptr. 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;
};
} // anonymous namespace
namespace android {
namespace skia {
std::unique_ptr<SkStreamRewindable> FrontBufferedStream::Make(std::unique_ptr<SkStream> stream,
size_t bufferSize) {
if (!stream) {
return nullptr;
}
auto frontBufferedStream = std::unique_ptr<::FrontBufferedStream>(
new ::FrontBufferedStream(std::move(stream), bufferSize));
if (frontBufferedStream->failedToAllocateBuffer()) {
return nullptr;
}
// Work around a warning regarding a copy on older compilers.
return std::move(frontBufferedStream);
}
} // namespace skia
} // namespace android
namespace {
FrontBufferedStream::FrontBufferedStream(std::unique_ptr<SkStream> stream, size_t bufferSize)
: fStream(std::move(stream))
, fHasLength(fStream->hasPosition() && fStream->hasLength())
, fLength(fStream->getLength() - fStream->getPosition())
, fOffset(0)
, fBufferedSoFar(0)
, fBufferSize(bufferSize)
, fBuffer(bufferSize <= kStorageSize ? fStorage
: reinterpret_cast<char*>(malloc(bufferSize))) {}
FrontBufferedStream::~FrontBufferedStream() {
if (fBuffer != fStorage) {
free(fBuffer);
}
}
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 = std::min(size, fBufferedSoFar - fOffset);
if (dst != nullptr) {
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 = std::min(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 != nullptr) {
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 && fBuffer != fStorage) {
free(fBuffer);
fBuffer = nullptr;
}
return bytesReadDirectly;
}
size_t FrontBufferedStream::peek(void* dst, size_t size) const {
// Keep track of the offset so we can return to it.
const size_t start = fOffset;
if (start >= fBufferSize) {
// This stream is not able to buffer.
return 0;
}
size = std::min(size, fBufferSize - start);
FrontBufferedStream* nonConstThis = const_cast<FrontBufferedStream*>(this);
const size_t bytesRead = nonConstThis->read(dst, size);
nonConstThis->fOffset = start;
return bytesRead;
}
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 != nullptr) {
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 != nullptr) {
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;
}
} // anonymous namespace