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AK: Lower the requirements for InputStream::eof and rename it.

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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.
This commit is contained in:
asynts 2020-09-13 12:24:17 +02:00 • committed by Andreas Kling
parent 8a21c528ad
commit 96edcbc27c
12 changed files with 61 additions and 89 deletions
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53
Libraries/LibCore/FileStream.h
View file

@ -68,25 +68,8 @@ public:
if (has_any_error())
return 0;
auto nread = m_buffered.bytes().copy_trimmed_to(bytes);
m_buffered.bytes().slice(nread, m_buffered.size() - nread).copy_to(m_buffered);
m_buffered.trim(m_buffered.size() - nread);
while (nread < bytes.size()) {
if (m_file->eof())
return nread;
if (m_file->has_error()) {
set_fatal_error();
return 0;
}
const auto buffer = m_file->read(bytes.size() - nread);
nread += buffer.bytes().copy_to(bytes.slice(nread));
}
return nread;
const auto buffer = m_file->read(bytes.size());
return buffer.bytes().copy_to(bytes);
}
bool read_or_error(Bytes bytes) override
@ -99,34 +82,9 @@ public:
return true;
}
bool discard_or_error(size_t count) override
{
u8 buffer[4096];
bool discard_or_error(size_t count) override { return m_file->seek(count, IODevice::SeekMode::FromCurrentPosition); }
size_t ndiscarded = 0;
while (ndiscarded < count && !eof())
ndiscarded += read({ buffer, min<size_t>(count - ndiscarded, sizeof(buffer)) });
if (eof()) {
set_fatal_error();
return false;
}
return true;
}
bool eof() const override
{
if (m_buffered.size() > 0)
return false;
if (m_file->eof())
return true;
m_buffered = m_file->read(4096);
return m_buffered.size() == 0;
}
bool unreliable_eof() const override { return m_file->eof(); }
void close()
{
@ -137,8 +95,7 @@ public:
private:
InputFileStream() = default;
mutable NonnullRefPtr<File> m_file;
mutable ByteBuffer m_buffered;
NonnullRefPtr<File> m_file;
};
class OutputFileStream : public OutputStream {