mirror of
https://github.com/SerenityOS/serenity
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129 lines
4.2 KiB
C++
129 lines
4.2 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <AK/Assertions.h>
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#include <AK/ByteBuffer.h>
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#include <LibCore/ArgsParser.h>
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#include <LibCore/File.h>
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#include <errno.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#define DEFAULT_LINE_COUNT 10
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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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const auto& 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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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::IODevice::SeekMode::FromEndPosition, &pos)) {
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fprintf(stderr, "Failed to find end of file: %s\n", 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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const auto& 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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int main(int argc, char* argv[])
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{
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if (pledge("stdio rpath", nullptr) < 0) {
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perror("pledge");
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return 1;
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}
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bool follow = false;
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int line_count = DEFAULT_LINE_COUNT;
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const char* file = nullptr;
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Core::ArgsParser args_parser;
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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(argc, argv);
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auto f = Core::File::construct(file);
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if (!f->open(Core::IODevice::ReadOnly)) {
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fprintf(stderr, "Error opening file %s: %s\n", file, strerror(errno));
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exit(1);
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}
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if (pledge("stdio", nullptr) < 0) {
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perror("pledge");
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return 1;
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}
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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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