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96edcbc27c
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.
126 lines
3.5 KiB
C++
126 lines
3.5 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/Optional.h>
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#include <AK/Stream.h>
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namespace AK {
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class InputBitStream final : public InputStream {
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public:
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explicit InputBitStream(InputStream& stream)
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: m_stream(stream)
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{
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}
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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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size_t nread = 0;
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if (bytes.size() >= 1) {
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if (m_next_byte.has_value()) {
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bytes[0] = m_next_byte.value();
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m_next_byte.clear();
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++nread;
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}
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}
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return nread + m_stream.read(bytes.slice(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_next_byte.has_value() && m_stream.unreliable_eof(); }
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bool discard_or_error(size_t count) override
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{
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if (count >= 1) {
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if (m_next_byte.has_value()) {
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m_next_byte.clear();
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--count;
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}
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}
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return m_stream.discard_or_error(count);
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}
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u32 read_bits(size_t count)
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{
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u32 result = 0;
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size_t nread = 0;
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while (nread < count) {
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if (m_stream.has_any_error()) {
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set_fatal_error();
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return 0;
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}
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if (m_next_byte.has_value()) {
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const auto bit = (m_next_byte.value() >> m_bit_offset) & 1;
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result |= bit << nread;
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++nread;
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if (m_bit_offset++ == 7)
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m_next_byte.clear();
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} else {
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m_stream >> m_next_byte;
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m_bit_offset = 0;
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}
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}
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return result;
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}
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bool read_bit() { return static_cast<bool>(read_bits(1)); }
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void align_to_byte_boundary()
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{
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if (m_next_byte.has_value())
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m_next_byte.clear();
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}
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private:
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Optional<u8> m_next_byte;
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size_t m_bit_offset { 0 };
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InputStream& m_stream;
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};
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}
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using AK::InputBitStream;
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