138 lines
3.1 KiB
C++
138 lines
3.1 KiB
C++
// SPDX-License-Identifier: GPL-2.0-or-later
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// Copyright The Music Player Daemon Project
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#include "RewindInputStream.hxx"
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#include "ProxyInputStream.hxx"
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#include <cassert>
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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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std::byte 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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[[nodiscard]] bool IsEOF() const 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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std::span<std::byte> dest) 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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[[nodiscard]] 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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std::span<std::byte> dest)
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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 (dest.size() > tail - head)
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dest = dest.first(tail - head);
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memcpy(dest.data(), buffer + head, dest.size());
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head += dest.size();
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offset += dest.size();
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return dest.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, dest);
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if (std::cmp_greater(input->GetOffset(), 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, dest.data(), 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 && std::cmp_less_equal(new_offset, 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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