Function runPipeline

programs/docker-init/docker-init.cpp:171–222

Run two commands connected by a pipe: lhs | rhs. Returns the exit code of the rhs process.

/// Run two commands connected by a pipe: lhs | rhs.
/// Returns the exit code of the rhs process.
int runPipeline(const std::vector<std::string> & lhs, const std::vector<std::string> & rhs)
{
    int pipefd[2];
    if (pipe(pipefd) < 0)
        return -1;

    pid_t lhs_pid = fork();
    if (lhs_pid < 0)
    {
        (void)close(pipefd[0]);
        (void)close(pipefd[1]);
        return -1;
    }
    if (lhs_pid == 0)
    {
        (void)close(pipefd[0]);
        (void)dup2(pipefd[1], STDOUT_FILENO);
        (void)close(pipefd[1]);
        auto argv = buildArgv(lhs);
        execvp(argv[0], argv.data());
        _exit(127);
    }

    pid_t rhs_pid = fork();
    if (rhs_pid < 0)
    {
        (void)close(pipefd[0]);
        (void)close(pipefd[1]);
        kill(lhs_pid, SIGTERM);
        while (waitpid(lhs_pid, nullptr, 0) < 0 && errno == EINTR) {}
        return -1;
    }
    if (rhs_pid == 0)
    {
        (void)close(pipefd[1]);
        (void)dup2(pipefd[0], STDIN_FILENO);
        (void)close(pipefd[0]);
        auto argv = buildArgv(rhs);
        execvp(argv[0], argv.data());
        _exit(127);
    }

    (void)close(pipefd[0]);
    (void)close(pipefd[1]);

    int lhs_status = 0;
    int rhs_status = 0;
    while (waitpid(lhs_pid, &lhs_status, 0) < 0 && errno == EINTR) {}
    while (waitpid(rhs_pid, &rhs_status, 0) < 0 && errno == EINTR) {}

    return WIFEXITED(rhs_status) ? WEXITSTATUS(rhs_status) : -1;
}

/// Returns true if the string is a safe ClickHouse identifier:
/// alphanumeric + underscore, not starting with a digit.