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95 lines
2.7 KiB
C++
95 lines
2.7 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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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 <LibMain/Main.h>
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#include <stdlib.h>
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#include <unistd.h>
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#define DEFAULT_LINE_COUNT 10
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static int tail_from_pos(Core::File& file, off_t startline, bool want_follow)
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{
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if (!file.seek(startline + 1))
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return 1;
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while (true) {
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auto const& b = file.read(4096);
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if (b.is_empty()) {
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if (!want_follow) {
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break;
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} else {
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while (!file.can_read()) {
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// FIXME: would be nice to have access to can_read_from_fd with an infinite timeout
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usleep(100);
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}
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continue;
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}
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}
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if (write(STDOUT_FILENO, b.data(), b.size()) < 0)
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return 1;
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}
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return 0;
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}
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static off_t find_seek_pos(Core::File& file, int wanted_lines)
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{
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// Rather than reading the whole file, start at the end and work backwards,
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// stopping when we've found the number of lines we want.
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off_t pos = 0;
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if (!file.seek(0, Core::SeekMode::FromEndPosition, &pos)) {
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warnln("Failed to find end of file: {}", file.error_string());
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return 1;
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}
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off_t end = pos;
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int lines = 0;
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// FIXME: Reading char-by-char is only OK if IODevice's read buffer
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// is smart enough to not read char-by-char. Fix it there, or fix it here :)
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for (; pos >= 0; pos--) {
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file.seek(pos);
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auto const& ch = file.read(1);
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if (ch.is_empty()) {
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// Presumably the file got truncated?
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// Keep trying to read backwards...
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} else {
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if (*ch.data() == '\n' && (end - pos) > 1) {
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lines++;
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if (lines == wanted_lines)
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break;
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}
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}
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}
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return pos;
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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 rpath"));
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bool follow = false;
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int line_count = DEFAULT_LINE_COUNT;
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char const* file = nullptr;
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Core::ArgsParser args_parser;
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args_parser.set_general_help("Print the end ('tail') of a file.");
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args_parser.add_option(follow, "Output data as it is written to the file", "follow", 'f');
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args_parser.add_option(line_count, "Fetch the specified number of lines", "lines", 'n', "number");
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args_parser.add_positional_argument(file, "File path", "file");
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args_parser.parse(arguments);
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auto f = TRY(Core::File::open(file, Core::OpenMode::ReadOnly));
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TRY(Core::System::pledge("stdio"));
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auto pos = find_seek_pos(*f, line_count);
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return tail_from_pos(*f, pos, follow);
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}
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