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LibCore: Add an automatically allocating MemoryStream

Similar to AK::DuplexStream, this writes to the end and reads from the
beginning of a dynamically allocated buffer.
This commit is contained in:
Tim Schumacher 2022-12-07 17:43:31 +01:00 committed by Linus Groh
parent 8dbc7aa63f
commit f205f62a44
3 changed files with 200 additions and 0 deletions

View file

@ -1,5 +1,6 @@
/*
* Copyright (c) 2021, kleines Filmröllchen <filmroellchen@serenityos.org>.
* Copyright (c) 2022, Tim Schumacher <timschumi@gmx.de>.
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -124,4 +125,123 @@ size_t FixedMemoryStream::remaining() const
return m_bytes.size() - m_offset;
}
ErrorOr<Bytes> AllocatingMemoryStream::read(Bytes bytes)
{
size_t read_bytes = 0;
while (read_bytes < bytes.size()) {
VERIFY(m_write_offset >= m_read_offset);
auto range = TRY(next_read_range());
if (range.size() == 0)
break;
auto copied_bytes = range.copy_trimmed_to(bytes.slice(read_bytes));
read_bytes += copied_bytes;
m_read_offset += copied_bytes;
}
cleanup_unused_chunks();
return bytes.trim(read_bytes);
}
ErrorOr<size_t> AllocatingMemoryStream::write(ReadonlyBytes bytes)
{
size_t written_bytes = 0;
while (written_bytes < bytes.size()) {
VERIFY(m_write_offset >= m_read_offset);
auto range = TRY(next_write_range());
auto copied_bytes = bytes.slice(written_bytes).copy_trimmed_to(range);
written_bytes += copied_bytes;
m_write_offset += copied_bytes;
}
return written_bytes;
}
ErrorOr<void> AllocatingMemoryStream::discard(size_t count)
{
VERIFY(m_write_offset >= m_read_offset);
if (count > used_buffer_size())
return Error::from_string_literal("Number of discarded bytes is higher than the number of allocated bytes");
m_read_offset += count;
cleanup_unused_chunks();
return {};
}
bool AllocatingMemoryStream::is_eof() const
{
return used_buffer_size() == 0;
}
bool AllocatingMemoryStream::is_open() const
{
return true;
}
void AllocatingMemoryStream::close()
{
}
size_t AllocatingMemoryStream::used_buffer_size() const
{
return m_write_offset - m_read_offset;
}
ErrorOr<ReadonlyBytes> AllocatingMemoryStream::next_read_range()
{
VERIFY(m_write_offset >= m_read_offset);
size_t const chunk_index = m_read_offset / chunk_size;
size_t const chunk_offset = m_read_offset % chunk_size;
size_t const read_size = min(chunk_size - m_read_offset % chunk_size, m_write_offset - m_read_offset);
if (read_size == 0)
return ReadonlyBytes { static_cast<u8*>(nullptr), 0 };
VERIFY(chunk_index < m_chunks.size());
return ReadonlyBytes { m_chunks[chunk_index].data() + chunk_offset, read_size };
}
ErrorOr<Bytes> AllocatingMemoryStream::next_write_range()
{
VERIFY(m_write_offset >= m_read_offset);
size_t const chunk_index = m_write_offset / chunk_size;
size_t const chunk_offset = m_write_offset % chunk_size;
size_t const write_size = chunk_size - m_write_offset % chunk_size;
if (chunk_index >= m_chunks.size())
TRY(m_chunks.try_append(TRY(Chunk::create_uninitialized(chunk_size))));
VERIFY(chunk_index < m_chunks.size());
return Bytes { m_chunks[chunk_index].data() + chunk_offset, write_size };
}
void AllocatingMemoryStream::cleanup_unused_chunks()
{
// FIXME: Move these all at once.
while (m_read_offset >= chunk_size) {
VERIFY(m_write_offset >= m_read_offset);
auto buffer = m_chunks.take_first();
m_read_offset -= chunk_size;
m_write_offset -= chunk_size;
m_chunks.append(move(buffer));
}
}
}

View file

@ -47,4 +47,31 @@ private:
bool m_writing_enabled { true };
};
/// A stream class that allows for writing to an automatically allocating memory area
/// and reading back the written data afterwards.
class AllocatingMemoryStream final : public Stream {
public:
virtual ErrorOr<Bytes> read(Bytes) override;
virtual ErrorOr<size_t> write(ReadonlyBytes) override;
virtual ErrorOr<void> discard(size_t) override;
virtual bool is_eof() const override;
virtual bool is_open() const override;
virtual void close() override;
size_t used_buffer_size() const;
private:
// Note: We set the inline buffer capacity to zero to make moving chunks as efficient as possible.
using Chunk = AK::Detail::ByteBuffer<0>;
static constexpr size_t chunk_size = 4096;
ErrorOr<ReadonlyBytes> next_read_range();
ErrorOr<Bytes> next_write_range();
void cleanup_unused_chunks();
Vector<Chunk> m_chunks;
size_t m_read_offset = 0;
size_t m_write_offset = 0;
};
}