153 lines
3.7 KiB
C++
153 lines
3.7 KiB
C++
/*
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* Copyright 2003-2018 The Music Player Daemon Project
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* http://www.musicpd.org
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#include "RewindInputStream.hxx"
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#include "ProxyInputStream.hxx"
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#include <assert.h>
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#include <string.h>
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class RewindInputStream final : public ProxyInputStream {
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/**
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* The read position within the buffer. Undefined as long as
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* ReadingFromBuffer() returns false.
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*/
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size_t head;
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/**
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* The write/append position within the buffer.
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*/
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size_t tail = 0;
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/**
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* The size of this buffer is the maximum number of bytes
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* which can be rewinded cheaply without passing the "seek"
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* call to CURL.
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*
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* The origin of this buffer is always the beginning of the
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* stream (offset 0).
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*/
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char buffer[64 * 1024];
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public:
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explicit RewindInputStream(InputStreamPtr _input)
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:ProxyInputStream(std::move(_input)) {}
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/* virtual methods from InputStream */
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void Update() noexcept override {
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if (!ReadingFromBuffer())
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ProxyInputStream::Update();
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}
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bool IsEOF() noexcept override {
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return !ReadingFromBuffer() && ProxyInputStream::IsEOF();
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}
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size_t Read(std::unique_lock<Mutex> &lock,
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void *ptr, size_t size) override;
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void Seek(std::unique_lock<Mutex> &lock, offset_type offset) override;
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private:
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/**
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* Are we currently reading from the buffer, and does the
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* buffer contain more data for the next read operation?
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*/
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bool ReadingFromBuffer() const noexcept {
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return tail > 0 && offset < input->GetOffset();
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}
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};
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size_t
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RewindInputStream::Read(std::unique_lock<Mutex> &lock,
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void *ptr, size_t read_size)
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{
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if (ReadingFromBuffer()) {
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/* buffered read */
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assert(head == (size_t)offset);
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assert(tail == (size_t)input->GetOffset());
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if (read_size > tail - head)
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read_size = tail - head;
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memcpy(ptr, buffer + head, read_size);
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head += read_size;
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offset += read_size;
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return read_size;
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} else {
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/* pass method call to underlying stream */
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size_t nbytes = input->Read(lock, ptr, read_size);
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if (input->GetOffset() > (offset_type)sizeof(buffer))
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/* disable buffering */
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tail = 0;
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else if (tail == (size_t)offset) {
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/* append to buffer */
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memcpy(buffer + tail, ptr, nbytes);
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tail += nbytes;
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assert(tail == (size_t)input->GetOffset());
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}
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CopyAttributes();
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return nbytes;
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}
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}
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void
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RewindInputStream::Seek(std::unique_lock<Mutex> &lock, offset_type new_offset)
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{
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assert(IsReady());
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if (tail > 0 && new_offset <= (offset_type)tail) {
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/* buffered seek */
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assert(!ReadingFromBuffer() ||
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head == (size_t)offset);
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assert(tail == (size_t)input->GetOffset());
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head = (size_t)new_offset;
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offset = new_offset;
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} else {
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/* disable the buffer, because input has left the
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buffered range now */
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tail = 0;
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ProxyInputStream::Seek(lock, new_offset);
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}
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}
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InputStreamPtr
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input_rewind_open(InputStreamPtr is)
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{
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assert(is != nullptr);
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assert(!is->IsReady() || is->GetOffset() == 0);
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if (is->IsReady() && is->IsSeekable())
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/* seekable resources don't need this plugin */
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return is;
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return std::make_unique<RewindInputStream>(std::move(is));
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}
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