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/*
* Copyright 2003-2020 The Music Player Daemon Project
* http://www.musicpd.org
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "RewindInputStream.hxx"
#include "ProxyInputStream.hxx"
#include <cassert>
#include <string.h>
class RewindInputStream final : public ProxyInputStream {
/**
* The read position within the buffer. Undefined as long as
* ReadingFromBuffer() returns false.
*/
size_t head;
/**
* The write/append position within the buffer.
*/
size_t tail = 0;
/**
* The size of this buffer is the maximum number of bytes
* which can be rewinded cheaply without passing the "seek"
* call to CURL.
*
* The origin of this buffer is always the beginning of the
* stream (offset 0).
*/
char buffer[64 * 1024];
public:
explicit RewindInputStream(InputStreamPtr _input)
:ProxyInputStream(std::move(_input)) {}
/* virtual methods from InputStream */
void Update() noexcept override {
if (!ReadingFromBuffer())
ProxyInputStream::Update();
}
[[nodiscard]] bool IsEOF() const noexcept override {
return !ReadingFromBuffer() && ProxyInputStream::IsEOF();
}
size_t Read(std::unique_lock<Mutex> &lock,
void *ptr, size_t size) override;
void Seek(std::unique_lock<Mutex> &lock, offset_type offset) override;
private:
/**
* Are we currently reading from the buffer, and does the
* buffer contain more data for the next read operation?
*/
[[nodiscard]] bool ReadingFromBuffer() const noexcept {
return tail > 0 && offset < input->GetOffset();
}
};
size_t
RewindInputStream::Read(std::unique_lock<Mutex> &lock,
void *ptr, size_t read_size)
{
if (ReadingFromBuffer()) {
/* buffered read */
assert(head == (size_t)offset);
assert(tail == (size_t)input->GetOffset());
if (read_size > tail - head)
read_size = tail - head;
memcpy(ptr, buffer + head, read_size);
head += read_size;
offset += read_size;
return read_size;
} else {
/* pass method call to underlying stream */
size_t nbytes = input->Read(lock, ptr, read_size);
if (input->GetOffset() > (offset_type)sizeof(buffer))
/* disable buffering */
tail = 0;
else if (tail == (size_t)offset) {
/* append to buffer */
memcpy(buffer + tail, ptr, nbytes);
tail += nbytes;
assert(tail == (size_t)input->GetOffset());
}
CopyAttributes();
return nbytes;
}
}
void
RewindInputStream::Seek(std::unique_lock<Mutex> &lock, offset_type new_offset)
{
assert(IsReady());
if (tail > 0 && new_offset <= (offset_type)tail) {
/* buffered seek */
assert(!ReadingFromBuffer() ||
head == (size_t)offset);
assert(tail == (size_t)input->GetOffset());
head = (size_t)new_offset;
offset = new_offset;
} else {
/* disable the buffer, because input has left the
buffered range now */
tail = 0;
ProxyInputStream::Seek(lock, new_offset);
}
}
InputStreamPtr
input_rewind_open(InputStreamPtr is)
{
assert(is != nullptr);
assert(!is->IsReady() || is->GetOffset() == 0);
if (is->IsReady() && is->IsSeekable())
/* seekable resources don't need this plugin */
return is;
return std::make_unique<RewindInputStream>(std::move(is));
}
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