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Consider the following snippet: void foo(InputStream& stream) { if(!stream.eof()) { u8 byte; stream >> byte; } } There is a very subtle bug in this snippet, for some input streams eof() might return false even if no more data can be read. In this case an error flag would be set on the stream. Until now I've always ensured that this is not the case, but this made the implementation of eof() unnecessarily complicated. InputFileStream::eof had to keep a ByteBuffer around just to make this possible. That meant a ton of unnecessary copies just to get a reliable eof(). In most cases it isn't actually necessary to have a reliable eof() implementation. In most other cases a reliable eof() is avaliable anyways because in some cases like InputMemoryStream it is very easy to implement.
193 lines
5.9 KiB
C++
193 lines
5.9 KiB
C++
/*
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* Copyright (c) 2020, the SerenityOS developers.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <AK/Stream.h>
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namespace AK {
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// FIXME: Implement Buffered<T> for DuplexStream.
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template<typename StreamType, size_t Size = 4096, typename = void>
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class Buffered;
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template<typename StreamType, size_t Size>
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class Buffered<StreamType, Size, typename EnableIf<IsBaseOf<InputStream, StreamType>::value>::Type> final : public InputStream {
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public:
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template<typename... Parameters>
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explicit Buffered(Parameters&&... parameters)
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: m_stream(forward<Parameters>(parameters)...)
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{
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}
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bool has_recoverable_error() const override { return m_stream.has_recoverable_error(); }
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bool has_fatal_error() const override { return m_stream.has_fatal_error(); }
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bool has_any_error() const override { return m_stream.has_any_error(); }
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bool handle_recoverable_error() override { return m_stream.handle_recoverable_error(); }
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bool handle_fatal_error() override { return m_stream.handle_fatal_error(); }
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bool handle_any_error() override { return m_stream.handle_any_error(); }
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void set_recoverable_error() const override { return m_stream.set_recoverable_error(); }
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void set_fatal_error() const override { return m_stream.set_fatal_error(); }
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size_t read(Bytes bytes) override
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{
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if (has_any_error())
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return 0;
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auto nread = buffer().trim(m_buffer_remaining).copy_trimmed_to(bytes);
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m_buffer_remaining -= nread;
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buffer().slice(nread, m_buffer_remaining).copy_to(buffer());
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if (nread < bytes.size()) {
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m_buffer_remaining = m_stream.read(buffer());
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if (m_buffer_remaining == 0)
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return nread;
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nread += read(bytes.slice(nread));
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}
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return nread;
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}
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bool read_or_error(Bytes bytes) override
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{
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if (read(bytes) < bytes.size()) {
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set_fatal_error();
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return false;
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}
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return true;
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}
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bool unreliable_eof() const override { return m_buffer_remaining == 0 && m_stream.unreliable_eof(); }
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bool eof() const
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{
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if (m_buffer_remaining > 0)
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return false;
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m_buffer_remaining = m_stream.read(buffer());
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return m_buffer_remaining == 0;
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}
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bool discard_or_error(size_t count) override
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{
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size_t ndiscarded = 0;
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while (ndiscarded < count) {
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u8 dummy[Size];
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if (!read_or_error({ dummy, min(Size, count - ndiscarded) }))
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return false;
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ndiscarded += min(Size, count - ndiscarded);
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}
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return true;
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}
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private:
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Bytes buffer() const { return { m_buffer, Size }; }
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mutable StreamType m_stream;
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mutable u8 m_buffer[Size];
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mutable size_t m_buffer_remaining { 0 };
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};
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template<typename StreamType, size_t Size>
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class Buffered<StreamType, Size, typename EnableIf<IsBaseOf<OutputStream, StreamType>::value>::Type> final : public OutputStream {
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public:
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template<typename... Parameters>
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explicit Buffered(Parameters&&... parameters)
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: m_stream(forward<Parameters>(parameters)...)
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{
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}
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~Buffered()
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{
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flush();
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}
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bool has_recoverable_error() const override { return m_stream.has_recoverable_error(); }
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bool has_fatal_error() const override { return m_stream.has_fatal_error(); }
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bool has_any_error() const override { return m_stream.has_any_error(); }
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bool handle_recoverable_error() override { return m_stream.handle_recoverable_error(); }
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bool handle_fatal_error() override { return m_stream.handle_fatal_error(); }
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bool handle_any_error() override { return m_stream.handle_any_error(); }
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void set_recoverable_error() const override { return m_stream.set_recoverable_error(); }
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void set_fatal_error() const override { return m_stream.set_fatal_error(); }
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size_t write(ReadonlyBytes bytes) override
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{
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if (has_any_error())
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return 0;
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auto nwritten = bytes.copy_trimmed_to(buffer().slice(m_buffered));
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m_buffered += nwritten;
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if (m_buffered == Size) {
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flush();
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if (bytes.size() - nwritten >= Size)
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nwritten += m_stream.write_or_error(bytes);
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nwritten += write(bytes.slice(nwritten));
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}
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return nwritten;
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}
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bool write_or_error(ReadonlyBytes bytes) override
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{
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write(bytes);
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return true;
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}
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void flush()
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{
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m_stream.write_or_error({ m_buffer, m_buffered });
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m_buffered = 0;
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}
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private:
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Bytes buffer() { return { m_buffer, Size }; }
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StreamType m_stream;
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u8 m_buffer[Size];
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size_t m_buffered { 0 };
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};
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}
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using AK::Buffered;
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