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f67b9cb680
This is useful for a situation when handling a small file than 512 KiB or being under low system memory pressure.
112 lines
3.7 KiB
C++
112 lines
3.7 KiB
C++
/*
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* Copyright (c) 2023, the SerenityOS developers.
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/Checked.h>
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#include <LibCore/ArgsParser.h>
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#include <LibCore/File.h>
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#include <LibCore/System.h>
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#include <LibFileSystem/FileSystem.h>
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#include <LibMain/Main.h>
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static ErrorOr<void> seek_and_read(size_t offset, ByteBuffer& buffer, Core::File& file)
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{
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TRY(file.seek(offset, SeekMode::SetPosition));
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TRY(file.read_until_filled(buffer));
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return {};
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}
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static ErrorOr<void> seek_and_write(size_t offset, ByteBuffer& buffer, Core::File& file)
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{
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TRY(file.seek(offset, SeekMode::SetPosition));
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TRY(file.write_until_depleted(buffer));
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return {};
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}
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static ErrorOr<void> process_file(Core::File& file, size_t block_size, size_t file_size, size_t file_size_rounded)
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{
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size_t head = 0;
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size_t tail = file_size_rounded - block_size;
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size_t const last_block_size = file_size - tail;
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auto head_buffer = TRY(ByteBuffer::create_uninitialized(block_size));
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auto tail_buffer = TRY(ByteBuffer::create_uninitialized(last_block_size));
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auto stdout = TRY(Core::File::standard_output());
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// Overwrite the current block (after saving its contents to a temporary buffer) with the last block until we've processed half of the blocks in the file.
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while (head <= tail) {
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TRY(seek_and_read(head, head_buffer, file));
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TRY(seek_and_read(tail, tail_buffer, file));
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TRY(seek_and_write(head, tail_buffer, file));
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TRY(file.truncate(tail));
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TRY(stdout->write_until_depleted(head_buffer));
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if (tail_buffer.size() != block_size)
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TRY(tail_buffer.try_resize(block_size));
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head += block_size;
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tail -= block_size;
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};
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size_t remaining_size = file_size - head;
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// Note that we iterate downwards from the end of the file, as the above algorithm left all of the remaining blocks in reverse order.
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while (remaining_size) {
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size_t to_write = remaining_size >= block_size ? block_size : last_block_size;
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tail_buffer.trim(to_write, true);
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TRY(seek_and_read(tail, tail_buffer, file));
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TRY(file.truncate(tail));
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TRY(stdout->write_until_depleted(tail_buffer));
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tail -= to_write;
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remaining_size -= to_write;
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}
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return {};
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}
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ErrorOr<int> serenity_main(Main::Arguments arguments)
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{
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TRY(Core::System::pledge("stdio cpath rpath wpath"));
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StringView path;
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size_t block_size_in_kib = 256;
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Core::ArgsParser args_parser;
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args_parser.set_general_help("Print file to stdout, while progressively deleting read segments.");
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args_parser.add_option(block_size_in_kib, "Base Block size in KiB, defaults to 256 KiB", "block-size", 'b', "base block size");
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args_parser.add_positional_argument(path, "File path", "path", Core::ArgsParser::Required::Yes);
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args_parser.parse(arguments);
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if (block_size_in_kib < 1)
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return Error::from_string_literal("Invalid block size");
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if (Checked<size_t>::multiplication_would_overflow(block_size_in_kib, KiB))
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return Error::from_string_literal("Overflow in block size");
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size_t block_size = block_size_in_kib * KiB;
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if (!FileSystem::exists(path))
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return Error::from_errno(ENOENT);
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auto file = TRY(Core::File::open(path, Core::File::OpenMode::ReadWrite));
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size_t file_size = TRY(file->seek(0, SeekMode::FromEndPosition));
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if (file_size < block_size * 2)
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return Error::from_string_literal("Input file too small");
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size_t file_size_rounded = TRY(file->seek(ceil_div(file_size, block_size) * block_size, SeekMode::SetPosition));
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TRY(process_file(*file, block_size, file_size, file_size_rounded));
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TRY(FileSystem::remove(path, FileSystem::RecursionMode::Disallowed));
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return 0;
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}
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