serenity/AK/MemoryStream.h

/*
 * Copyright (c) 2020, the SerenityOS developers.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include <AK/ByteBuffer.h>
#include <AK/MemMem.h>
#include <AK/Stream.h>
#include <AK/Vector.h>

namespace AK {

class InputMemoryStream final : public InputStream {
public:
    InputMemoryStream(ReadonlyBytes bytes)
        : m_bytes(bytes)
    {
    }

    bool eof() const override { return m_offset >= m_bytes.size(); }

    size_t read(Bytes bytes) override
    {
        const auto count = min(bytes.size(), remaining());
        __builtin_memcpy(bytes.data(), m_bytes.data() + m_offset, count);
        m_offset += count;
        return count;
    }

    bool read_or_error(Bytes bytes) override
    {
        if (remaining() < bytes.size()) {
            set_recoverable_error();
            return false;
        }

        __builtin_memcpy(bytes.data(), m_bytes.data() + m_offset, bytes.size());
        m_offset += bytes.size();
        return true;
    }

    bool discard_or_error(size_t count) override
    {
        if (remaining() < count) {
            set_recoverable_error();
            return false;
        }

        m_offset += count;
        return true;
    }

    void seek(size_t offset)
    {
        ASSERT(offset < m_bytes.size());
        m_offset = offset;
    }

    u8 peek_or_error() const
    {
        if (remaining() == 0) {
            set_recoverable_error();
            return 0;
        }

        return m_bytes[m_offset];
    }

    // LEB128 is a variable-length encoding for integers
    bool read_LEB128_unsigned(size_t& result)
    {
        const auto backup = m_offset;

        result = 0;
        size_t num_bytes = 0;
        while (true) {
            // Note. The implementation in AK::BufferStream::read_LEB128_unsigned read one
            //       past the end, this is fixed here.
            if (eof()) {
                m_offset = backup;
                set_recoverable_error();
                return false;
            }

            const u8 byte = m_bytes[m_offset];
            result = (result) | (static_cast<size_t>(byte & ~(1 << 7)) << (num_bytes * 7));
            ++m_offset;
            if (!(byte & (1 << 7)))
                break;
            ++num_bytes;
        }

        return true;
    }

    // LEB128 is a variable-length encoding for integers
    bool read_LEB128_signed(ssize_t& result)
    {
        const auto backup = m_offset;

        result = 0;
        size_t num_bytes = 0;
        u8 byte = 0;

        do {
            // Note. The implementation in AK::BufferStream::read_LEB128_unsigned read one
            //       past the end, this is fixed here.
            if (eof()) {
                m_offset = backup;
                set_recoverable_error();
                return false;
            }

            byte = m_bytes[m_offset];
            result = (result) | (static_cast<size_t>(byte & ~(1 << 7)) << (num_bytes * 7));
            ++m_offset;
            ++num_bytes;
        } while (byte & (1 << 7));

        if (num_bytes * 7 < sizeof(size_t) * 4 && (byte & 0x40)) {
            // sign extend
            result |= ((size_t)(-1) << (num_bytes * 7));
        }

        return true;
    }

    ReadonlyBytes bytes() const { return m_bytes; }
    size_t offset() const { return m_offset; }
    size_t remaining() const { return m_bytes.size() - m_offset; }

private:
    ReadonlyBytes m_bytes;
    size_t m_offset { 0 };
};

// All data written to this stream can be read from it. Reading and writing is done
// using different offsets, meaning that it is not necessary to seek to the start
// before reading; this behaviour differs from BufferStream.
class DuplexMemoryStream final : public DuplexStream {
public:
    static constexpr size_t chunk_size = 4 * 1024;

    bool eof() const override { return m_write_offset == m_read_offset; }

    bool discard_or_error(size_t count) override
    {
        if (m_write_offset - m_read_offset < count) {
            set_recoverable_error();
            return false;
        }

        m_read_offset += count;
        try_discard_chunks();
        return true;
    }

    Optional<size_t> offset_of(ReadonlyBytes value) const
    {
        if (value.size() > remaining())
            return {};

        // First, find which chunk we're in.
        auto chunk_index = (m_read_offset - m_base_offset) / chunk_size;
        auto last_written_chunk_index = (m_write_offset - m_base_offset) / chunk_size;
        auto first_chunk_index = chunk_index;
        auto last_written_chunk_offset = m_write_offset % chunk_size;
        auto first_chunk_offset = m_read_offset % chunk_size;
        size_t last_chunk_offset = 0;
        auto found_value = false;

        for (; chunk_index <= last_written_chunk_index; ++chunk_index) {
            auto chunk_bytes = m_chunks[chunk_index].bytes();
            size_t chunk_offset = 0;
            if (chunk_index == last_written_chunk_index) {
                chunk_bytes = chunk_bytes.slice(0, last_written_chunk_offset);
            }
            if (chunk_index == first_chunk_index) {
                chunk_bytes = chunk_bytes.slice(first_chunk_offset);
                chunk_offset = first_chunk_offset;
            }

            // See if 'value' is in this chunk,
            auto position = AK::memmem(chunk_bytes.data(), chunk_bytes.size(), value.data(), value.size());
            if (!position)
                continue; // Not in this chunk either :(

            // We found it!
            found_value = true;
            last_chunk_offset = (const u8*)position - chunk_bytes.data() + chunk_offset;
            break;
        }

        if (found_value) {
            if (first_chunk_index == chunk_index)
                return last_chunk_offset - first_chunk_offset;

            return (chunk_index - first_chunk_index) * chunk_size + last_chunk_offset - first_chunk_offset;
        }

        // No dice.
        return {};
    }

    size_t read_without_consuming(Bytes bytes) const
    {
        size_t nread = 0;
        while (bytes.size() - nread > 0 && m_write_offset - m_read_offset - nread > 0) {
            const auto chunk_index = (m_read_offset - m_base_offset) / chunk_size;
            const auto chunk_bytes = m_chunks[chunk_index].bytes().slice(m_read_offset % chunk_size).trim(m_write_offset - m_read_offset - nread);
            nread += chunk_bytes.copy_trimmed_to(bytes.slice(nread));
        }

        return nread;
    }

    size_t read(Bytes bytes) override
    {
        const auto nread = read_without_consuming(bytes);

        m_read_offset += nread;
        try_discard_chunks();

        return nread;
    }

    bool read_or_error(Bytes bytes) override
    {
        if (m_write_offset - m_read_offset < bytes.size()) {
            set_recoverable_error();
            return false;
        }

        read(bytes);
        return true;
    }

    size_t write(ReadonlyBytes bytes) override
    {
        size_t nwritten = 0;
        while (bytes.size() - nwritten > 0) {
            if ((m_write_offset + nwritten) % chunk_size == 0)
                m_chunks.append(ByteBuffer::create_uninitialized(chunk_size));

            nwritten += bytes.copy_trimmed_to(m_chunks.last().bytes().slice(m_write_offset % chunk_size));
        }

        m_write_offset += nwritten;
        return nwritten;
    }

    bool write_or_error(ReadonlyBytes bytes) override
    {
        write(bytes);
        return true;
    }

    ByteBuffer copy_into_contiguous_buffer() const
    {
        auto buffer = ByteBuffer::create_uninitialized(remaining());

        const auto nread = read_without_consuming(buffer);
        ASSERT(nread == buffer.size());

        return buffer;
    }

    size_t roffset() const { return m_read_offset; }
    size_t woffset() const { return m_write_offset; }

    size_t remaining() const { return m_write_offset - m_read_offset; }

private:
    void try_discard_chunks()
    {
        while (m_read_offset - m_base_offset >= chunk_size) {
            m_chunks.take_first();
            m_base_offset += chunk_size;
        }
    }

    Vector<ByteBuffer> m_chunks;
    size_t m_write_offset { 0 };
    size_t m_read_offset { 0 };
    size_t m_base_offset { 0 };
};

class OutputMemoryStream final : public OutputStream {
public:
    size_t write(ReadonlyBytes bytes) override { return m_stream.write(bytes); }
    bool write_or_error(ReadonlyBytes bytes) override { return m_stream.write_or_error(bytes); }

    ByteBuffer copy_into_contiguous_buffer() const { return m_stream.copy_into_contiguous_buffer(); }

    Optional<size_t> offset_of(ReadonlyBytes value) const { return m_stream.offset_of(value); }

    size_t size() const { return m_stream.woffset(); }

private:
    DuplexMemoryStream m_stream;
};

}

using AK::DuplexMemoryStream;
using AK::InputMemoryStream;
using AK::InputStream;
using AK::OutputMemoryStream;