tee.cpp

#include <AK/Vector.h>
#include <errno.h>
#include <fcntl.h>
#include <getopt.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>

static Vector<int> collect_fds(int argc, char** argv, int start, bool aflag, bool* err)
{
    int oflag;
    mode_t mode;
    if (aflag) {
        oflag = O_APPEND;
        mode = 0;
    } else {
        oflag = O_CREAT | O_WRONLY | O_TRUNC;
        mode = S_IROTH | S_IWOTH | S_IRGRP | S_IWGRP | S_IRUSR | S_IWUSR;
    }

    Vector<int> fds;
    for (int i = start; i < argc; ++i) {
        int fd = open(argv[i], oflag, mode);
        if (fd < 0) {
            perror("failed to open file for writing");
            *err = true;
        } else {
            fds.append(fd);
        }
    }
    fds.append(STDOUT_FILENO);
    return fds;
}

static void copy_stdin(Vector<int>& fds, bool* err)
{
    for (;;) {
        char buf[4096];
        ssize_t nread = read(STDIN_FILENO, buf, sizeof(buf));
        if (nread == 0)
            break;
        if (nread < 0) {
            perror("read() error");
            *err = true;
            // a failure to read from stdin should lead to an early exit
            return;
        }

        Vector<int> broken_fds;
        for (int i = 0; i < fds.size(); ++i) {
            auto fd = fds.at(i);
            int twrite = 0;
            while (twrite != nread) {
                ssize_t nwrite = write(fd, buf + twrite, nread - twrite);
                if (nwrite < 0) {
                    if (errno == EINTR) {
                        continue;
                    } else {
                        perror("write() failed");
                        *err = true;
                        broken_fds.append(fd);
                        // write failures to a successfully opened fd shall
                        // prevent further writes, but shall not block writes
                        // to the other open fds
                        break;
                    }
                } else {
                    twrite += nwrite;
                }
            }
        }

        // remove any fds which we can no longer write to for subsequent copies
        for (auto to_remove : broken_fds)
            fds.remove_first_matching([&](int fd) { return to_remove == fd; });
    }
}

static void close_fds(Vector<int>& fds)
{
    for (int fd : fds) {
        int closed = close(fd);
        if (closed < 0) {
            perror("failed to close output file");
        }
    }
}

static void int_handler(int)
{
    // pass
}

int main(int argc, char** argv)
{
    bool aflag = false, iflag = false;
    int c = 0;
    while ((c = getopt(argc, argv, "ai")) != -1) {
        switch (c) {
        case 'a':
            aflag = true;
            break;
        case 'i':
            iflag = true;
            break;
        }
    }

    if (iflag) {
        if (signal(SIGINT, int_handler) == SIG_ERR) {
            perror("failed to install SIGINT handler");
        }
    }

    bool err_open = false;
    bool err_write = false;
    auto fds = collect_fds(argc, argv, optind, aflag, &err_open);
    copy_stdin(fds, &err_write);
    close_fds(fds);

    return (err_open || err_write) ? 1 : 0;
}