path: root/src/Program.cpp

#include "../include/Program.hpp"
#include <unistd.h>
#include <sys/wait.h>
#include <sys/prctl.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <unordered_map>
#include <mutex>
#include <signal.h>

#define READ_END 0
#define WRITE_END 1

class CurrentThreadProgram {
public:
    void set(ReadProgram read_program) {
        std::lock_guard<std::mutex> lock(mutex);
        thread_current_program[std::this_thread::get_id()] = read_program;
    }

    void clear() {
        std::lock_guard<std::mutex> lock(mutex);
        thread_current_program.erase(std::this_thread::get_id());
    }

    void kill_in_thread(const std::thread::id &thread_id) {
        std::lock_guard<std::mutex> lock(mutex);
        auto it = thread_current_program.find(thread_id);
        if(it != thread_current_program.end()) {
            close(it->second.read_fd);
            kill(it->second.pid, SIGTERM);
        }
    }
private:
    std::unordered_map<std::thread::id, ReadProgram> thread_current_program;
    std::mutex mutex;
};

static CurrentThreadProgram current_thread_program;

int exec_program_pipe(const char **args, ReadProgram *read_program) {
    /* 1 arguments */
    if(args[0] == NULL)
        return -1;
    
    int fd[2];
    if(pipe(fd) == -1) {
        perror("Failed to open pipe");
        return -2;
    }

    pid_t parent_pid = getpid();

    pid_t pid = fork();
    if(pid == -1) {
        perror("Failed to fork");
        close(fd[READ_END]);
        close(fd[WRITE_END]);
        return -3;
    } else if(pid == 0) { /* child */
        if(prctl(PR_SET_PDEATHSIG, SIGTERM) == -1) {
            perror("prctl(PR_SET_PDEATHSIG, SIGTERM) failed");
            _exit(127);
        }

        /* Test if the parent died before the above call to prctl */
        if(getppid() != parent_pid)
            _exit(127);

        dup2(fd[WRITE_END], STDOUT_FILENO);
        close(fd[READ_END]);
        close(fd[WRITE_END]);

        execvp(args[0], (char* const*)args);
        perror("execvp");
        _exit(127);
    } else { /* parent */
        close(fd[WRITE_END]);
        read_program->pid = pid;
        read_program->read_fd = fd[READ_END];
        current_thread_program.set(*read_program);
        return 0;
    }
}

int exec_program(const char **args, ProgramOutputCallback output_callback, void *userdata, int buffer_size) {
    ReadProgram read_program;
    int res = exec_program_pipe(args, &read_program);
    if(res != 0)
        return res;

    int result = 0;
    int status;
    int exit_status;

    assert(buffer_size >= 1 && buffer_size <= 65536);
    char *buffer = (char*)alloca(buffer_size + 1);

    for(;;) {
        ssize_t bytes_read = read(read_program.read_fd, buffer, buffer_size);
        if(bytes_read == 0) {
            break;
        } else if(bytes_read == -1) {
            int err = errno;
            fprintf(stderr, "Failed to read from pipe to program %s, error: %s\n", args[0], strerror(err));
            result = -err;
            break;
        }

        buffer[bytes_read] = '\0';
        if(output_callback) {
            result = output_callback(buffer, bytes_read, userdata);
            if(result != 0)
                break;
        }
    }
    program_clear_current_thread();

    if(result != 0)
        kill(read_program.pid, SIGTERM);

    if(waitpid(read_program.pid, &status, 0) == -1) {
        perror("waitpid failed");
        result = -5;
        goto cleanup;
    }

    if(!WIFEXITED(status)) {
        result = -4;
        goto cleanup;
    }

    exit_status = WEXITSTATUS(status);
    if(exit_status != 0) {
        fprintf(stderr, "Failed to execute program (");
        const char **arg = args;
        while(*arg) {
            if(arg != args)
                fputc(' ', stderr);
            fprintf(stderr, "'%s'", *arg);
            ++arg;
        }
        fprintf(stderr, "), exit status %d\n", exit_status);
        result = -exit_status;
    }

    cleanup:
    close(read_program.read_fd);
    return result;
}

int wait_program(pid_t process_id) {
    int status;
    if(waitpid(process_id, &status, 0) == -1) {
        perror("waitpid failed");
        return -errno;
    }

    if(!WIFEXITED(status))
        return -4;

    return WEXITSTATUS(status);
}

int wait_program_non_blocking(pid_t process_id, int *status) {
    int s;
    int wait_result = waitpid(process_id, &s, WNOHANG);
    if(wait_result == -1) {
        perror("waitpid failed");
        *status = -errno;
        return 0;
    } else if(wait_result == 0) {
        /* the child process is still running */
        *status = 0;
        return 0;
    }

    if(!WIFEXITED(s)) {
        *status = -4;
        return 0;
    }

    *status = WEXITSTATUS(s);
    return 1;
}

int exec_program_async(const char **args, pid_t *result_process_id) {
    /* 1 arguments */
    if(args[0] == NULL)
        return -1;

    pid_t parent_pid = getpid();

    pid_t pid = fork();
    if(pid == -1) {
        int err = errno;
        perror("Failed to fork");
        return -err;
    } else if(pid == 0) { /* child */
        if(result_process_id) {
            if(prctl(PR_SET_PDEATHSIG, SIGTERM) == -1) {
                perror("prctl(PR_SET_PDEATHSIG, SIGTERM) failed");
                _exit(127);
            }

            /* Test if the parent died before the above call to prctl */
            if(getppid() != parent_pid)
                _exit(127);

            execvp(args[0], (char* const*)args);
            perror("execvp");
            _exit(127);
        } else {
            setsid();
            signal(SIGHUP, SIG_IGN);

            // Daemonize child to make the parent the init process which will reap the zombie child
            pid_t second_child = fork();
            if(second_child == 0) { // child
                execvp(args[0], (char* const*)args);
                perror("execvp");
                _exit(127);
            } else if(second_child != -1) {
                _exit(0);
            }
        }
    } else { /* parent */
        if(result_process_id)
            *result_process_id = pid;
        else
            waitpid(pid, nullptr, 0);
    }
    return 0;
}

void program_clear_current_thread() {
    current_thread_program.clear();
}

void program_kill_in_thread(const std::thread::id &thread_id) {
    current_thread_program.kill_in_thread(thread_id);
}