path: root/shell.c

#include "shell.h"
#include "queue.h"
#include "dynamic_array.h"
#include "lexical_analysis.h"

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <signal.h>
#include <errno.h>

MAKE_QUEUE_INIT(w_queue)
MAKE_QUEUE_INIT(p_queue)
MAKE_QUEUE_PUSH(w_queue, word, char*)
MAKE_QUEUE_PUSH(c_queue, cmdline, char**)
MAKE_QUEUE_PUSH(p_queue, pid, int)

enum modes { word_separation, whole_word };

static void show_invitation()
{
    printf("> ");
}

/* remove background zombie processes */
static void handler(int signal)
{
    int save_errno = errno;
    int pid;

    if(signal == SIGCHLD) {
        do {
            pid = wait4(-1, NULL, WNOHANG, NULL);
        } while(pid > 0);
    }
    errno = save_errno;
}

static void init_params(struct param_type *params, enum modes *current_mode)
{
    params->is_word = 0;
    params->escape_sequences = 0;
    params->double_quotes_counter = 0;
    params->stored_symbol = ' ';
    params->empty_word_flag = 0;
    params->tokens = 0;
    params->wrong_command = 0;
    params->streams.input_stream = NULL;
    params->streams.output_stream = NULL;
    params->streams.output_stream_to_append = NULL;
    /* 0 - success, 1 - error */
    params->last_execution_status = 0;
    params->pipeline = 0;
    *current_mode = word_separation;
}

static void clear_filename(struct param_type *params)
{
    if(params->streams.input_stream)
        free(params->streams.input_stream);
    if(params->streams.output_stream)
        free(params->streams.output_stream);
    if(params->streams.output_stream_to_append)
        free(params->streams.output_stream_to_append);
    params->streams.input_stream = NULL;
    params->streams.output_stream = NULL;
    params->streams.output_stream_to_append = NULL;
}

static void reset_params(struct param_type *params,
                         enum modes *current_mode,
                         struct w_queue *word_chain,
                         struct c_queue *cmdlines,
                         struct dynamic_array *tmp_word)
{
    w_queue_clear(word_chain);
    c_queue_clear(cmdlines);
    dynarr_drop_word(tmp_word);
    clear_filename(params);
    init_params(params, current_mode);
}

static void add_letter(int ch, struct dynamic_array *tmp_word,
                       struct param_type *params)
{
    dynarr_push_back(tmp_word, ch);
    params->is_word = 1;
    params->escape_sequences = 0;
}

static void clean_input_buffer()
{
    int ch;
    while((ch = getchar()) != new_line)
    {}
}

static void print_error_msg(const char *error_msg)
{
    if(error_msg)
        fprintf(stderr, "%s\n", error_msg);
}

static const char* error_code_to_token(int error_code)
{
    switch(error_code) {
    case err_filename_expected:             return "expected file name";
    case err_redirect_stream_again:         return "stream redirected again";
    case err_redirect_stream_in_pipeline:   return "bad stream redirect in pipe";
    case err_bg_process:                    return "extra characters after &";
    case err_empty_command:                 return "empty command";
    case err_extra_chars_after_filename:    return "extra chars after filename";
    case err_odd_double_quotes:             return "odd number of double quotes";
    }
    return NULL;
}

void error_identification(const struct param_type *params)
{
    print_error_msg(error_code_to_token(params->wrong_command));
}

static int special_token_handling(struct w_queue *word_chain,
                                  struct c_queue *cmdlines,
                                  struct dynamic_array *tmp_word, int ch,
                                  struct param_type *params)
{
    return
        stream_redirect_tokens(word_chain, tmp_word, ch, params) ?
            1 : special_tokens(word_chain, cmdlines, tmp_word, ch, params);
}

static void wait_for_process_to_complete(struct p_queue *pid_store)
{
    int total_process_counter, current_process_counter, wait_pid;
    total_process_counter = p_queue_get_process_quantity(pid_store);
    current_process_counter = 0;

    do {
        wait_pid = wait(NULL);
        if(p_queue_find_pid(pid_store, wait_pid))
            ++current_process_counter;
    } while(total_process_counter != current_process_counter);

    /* return of background process zombie cleanup */
    signal(SIGCHLD, handler);
}

static void clean_up_memory(struct w_queue *word_chain,
                            struct c_queue *cmdlines, struct param_type *params)
{
    w_queue_clear(word_chain);
    c_queue_clear(cmdlines);
    clear_filename(params);
}

static void close_files(int input_fd, int output_fd)
{
    if(input_fd)
        close(input_fd);
    if(output_fd)
        close(output_fd);
}

static void postprocessing(struct w_queue *word_chain, struct c_queue *cmdlines,
                           struct p_queue *pid_store, struct param_type *params,
                           int input_fd, int output_fd)
{
    clean_up_memory(word_chain, cmdlines, params);
    close_files(input_fd, output_fd);
    if(params->tokens != '&')
        wait_for_process_to_complete(pid_store);
    p_queue_clear(pid_store);
}

static void set_signal_disposition(struct param_type *params)
{
    if(params->tokens == '&')
        /* zombie process termination on signal */
        signal(SIGCHLD, handler);
    else
        /* the parent process will wait for the process to complete;
           default signal disposition
         */
        signal(SIGCHLD, SIG_DFL);
}

static void change_streams(int input_fd, int output_fd, int is_pipeline,
                           int is_begin_pipeline)
{
    if((!is_pipeline && input_fd) ||
            (is_pipeline && is_begin_pipeline && input_fd)) {
        dup2(input_fd, 0);
        close(input_fd);
    }
    if((!is_pipeline && output_fd) ||
            (is_pipeline && !is_begin_pipeline && output_fd)) {
        dup2(output_fd, 1);
        close(output_fd);
    }
}

int is_stream_redirection_set(const struct param_type *params)
{
    return params->streams.input_stream || params->streams.output_stream ||
            params->streams.output_stream_to_append;
}

static void make_pipeline(struct w_queue *word_chain, struct c_queue *cmdlines,
                          struct param_type *params,
                          int input_fd, int output_fd)
{
    struct p_queue pid_store;
    p_queue_init(&pid_store);
    char **cmdline = NULL;
    int fd[2];
    int save_read_fd, pid;

    pipe(fd);
    cmdline = c_queue_pop(cmdlines);
    set_signal_disposition(params);
    pid = fork();

    if(pid == 0) {
        close(fd[0]);
        dup2(fd[1], 1);
        close(fd[1]);
        if(is_stream_redirection_set(params))
            change_streams(input_fd, output_fd, 1, 1);
        execvp(cmdline[0], cmdline);
        perror(cmdline[0]);
        exit(1);
    }

    close(fd[1]);
    p_queue_push(&pid_store, pid);

    while(!c_queue_is_empty(cmdlines)) {
        cmdline = c_queue_pop(cmdlines);
        /* if not last process in pipeline*/
        if(!c_queue_is_empty(cmdlines)) {
            save_read_fd = fd[0];
            pipe(fd);
        }
        pid = fork();
        if(pid == 0) {
            if(!c_queue_is_empty(cmdlines)) {
                dup2(save_read_fd, 0);
                close(save_read_fd);
                close(fd[0]);
                dup2(fd[1], 1);
                close(fd[1]);
            } else {
                dup2(fd[0], 0);
                close(fd[0]);
            }
            /* for last process in pipeline */
            if(c_queue_is_empty(cmdlines))
                if(is_stream_redirection_set(params))
                    change_streams(input_fd, output_fd, 1, 0);
            execvp(cmdline[0], cmdline);
            perror(cmdline[0]);
            exit(1);
        }
        if(!c_queue_is_empty(cmdlines)) {
            close(save_read_fd);
            close(fd[1]);
        } else
            close(fd[0]);
        p_queue_push(&pid_store, pid);
    }
    postprocessing(word_chain, cmdlines, &pid_store, params, input_fd,
                   output_fd);
}

static void open_files(const struct param_type *params, int *input_fd,
                      int *output_fd)
{
    if(params->streams.input_stream)
        *input_fd = open(params->streams.input_stream, O_RDONLY);
    if(params->streams.output_stream)
        *output_fd = open(params->streams.output_stream, O_WRONLY | O_CREAT |
                          O_TRUNC, 0666);
    if(params->streams.output_stream_to_append)
        *output_fd = open(params->streams.output_stream_to_append, O_WRONLY |
                          O_APPEND, 0666);
}

static int is_cd_command(const char *arg)
{
    return !strcmp(arg, "cd");
}

static void change_directory(char **cmdline)
{
    int result;
    char *first_arg = cmdline[1];
    char *path = NULL;
    /* change to user home directory */
    if(first_arg == NULL) {
        path = getenv("HOME");
        if(!path) {
            perror("I don't know where's your home...");
            return;
        }
    } else {
        if(cmdline[2]) {
            perror("cd: too many arguments");
            return;
        }
        path = first_arg;
    }
    result = chdir(path);
    if(result == -1)
        perror(path);
}

static void run_external_program(struct w_queue *word_chain,
                                 struct c_queue *cmdlines,
                                 struct param_type *params)
{
    int pid, input_fd, output_fd;
    struct p_queue pid_store;
    p_queue_init(&pid_store);
    char **cmdline = NULL;
    input_fd = 0;
    output_fd = 0;

    if(is_stream_redirection_set(params))
        open_files(params, &input_fd, &output_fd);

    if(input_fd == -1 || output_fd == -1) {
        perror("can't open file");
        return;
    }
    if(params->pipeline) {
        make_pipeline(word_chain, cmdlines, params, input_fd, output_fd);
        return;
    }
    cmdline = c_queue_pop(cmdlines);
    if(is_cd_command(cmdline[0]))
        change_directory(cmdline);
    else {
        set_signal_disposition(params);
        pid = fork();
        if(pid == -1) {
            perror("fork error");
            exit(1);
        }
        /* child process */
        if(pid == 0) {
            if(is_stream_redirection_set(params))
                change_streams(input_fd, output_fd, 0, 0);
            execvp(cmdline[0], cmdline);
            params->last_execution_status = 1;
            perror(cmdline[0]);
            exit(1);
        }
        /* parent process */
        p_queue_push(&pid_store, pid);
        postprocessing(word_chain, cmdlines, &pid_store, params, input_fd,
                       output_fd);
    }
}

int filename_waiting(struct param_type *params)
{
    if(params->tokens == '<' || params->tokens == '>' ||
            params->tokens == append) {
        if(!params->is_word)
            params->wrong_command = err_filename_expected;
        return 1;
    } else
        return 0;
}

void add_filename(struct dynamic_array *tmp_word, struct param_type *params)
{
    dynarr_push_back(tmp_word, '\0');
    switch(params->tokens) {
    case '<':
        params->streams.input_stream = malloc(tmp_word->last_element_index+1);
        dynarr_copy_array(tmp_word, params->streams.input_stream);
        break;
    case '>':
        params->streams.output_stream = malloc(tmp_word->last_element_index+1);
        dynarr_copy_array(tmp_word, params->streams.output_stream);
        break;
    case append:
        params->streams.output_stream_to_append =
            malloc(tmp_word->last_element_index+1);
        dynarr_copy_array(tmp_word, params->streams.output_stream_to_append);
    }
    dynarr_drop_word(tmp_word);
    params->is_word = 0;
}

void add_word(struct w_queue *word_chain, struct dynamic_array *tmp_word,
              struct param_type *params)
{
    dynarr_push_back(tmp_word, 0);
    char *word = malloc(tmp_word->last_element_index+1);
    dynarr_copy_array(tmp_word, word);
    w_queue_push(word_chain, word);
    dynarr_drop_word(tmp_word);
    params->is_word = 0;
}

char** create_cmdline(const struct w_queue *word_chain, int word_counter)
{
    char **cmdline = malloc((word_counter + 1) * sizeof(char*));
    w_queue_copy_words_to_args(word_chain, cmdline);
    return cmdline;
}

static void command_processing(struct param_type *params,
                                enum modes *current_mode,
                                struct w_queue *word_chain,
                                struct c_queue *cmdlines,
                                struct dynamic_array *tmp_word, int ch)
{
    char **cmdline = NULL;

    /* odd number of double quotes  */
    if(!is_double_quotes_pair(*params)) {
        params->wrong_command = err_odd_double_quotes;
        goto clean;
        return;
    }
    if(filename_waiting(params)) {
        if(params->wrong_command)
            goto clean;
        if(params->pipeline) {
            if(params->tokens == '>' || params->tokens == append)
                add_filename(tmp_word, params);
            else if(params->tokens == '<') {
                params->wrong_command = err_redirect_stream_in_pipeline;
                goto clean;
            }
        } else
            add_filename(tmp_word, params);
    } else if(params->empty_word_flag || params->is_word)
        add_word(word_chain, tmp_word, params);

    if((params->tokens == and || params->tokens == or) &&
            params->last_execution_status == 1) {
        /* ??? */
        fprintf(stderr, "cannot be performed\n");
        return;
    }

    if(word_chain->first == NULL) {
        params->wrong_command = err_empty_command;
        goto clean;
    }

    cmdline = create_cmdline(word_chain, w_queue_get_word_count(word_chain));
    c_queue_push(cmdlines, cmdline);
    run_external_program(word_chain, cmdlines, params);

clean:
    error_identification(params);
    if(params->tokens == '&' || params->tokens == 0 || ch == new_line)
        show_invitation();
    reset_params(params, current_mode, word_chain, cmdlines, tmp_word);
}

static void word_separation_processing(int ch, struct param_type *params,
                                       enum modes *current_mode,
                                       struct w_queue *word_chain,
                                       struct c_queue *cmdlines,
                                       struct dynamic_array *tmp_word)
{
    /* could be a marker for the beginning of a blank word */
    params->stored_symbol = ch;
    if(is_empty_word(ch, *params)) {
        dynarr_push_back(tmp_word, '\0');
        add_word(word_chain, tmp_word, params);
        params->empty_word_flag = 0;
        return;
    }
    params->empty_word_flag = 0;
    if(change_mode(ch, *params)) {
        ++params->double_quotes_counter;
        *current_mode = whole_word;
        return;
    }
    if(start_escape_sequence(ch, *params)) {
        params->escape_sequences = 1;
        return;
    }
    if(special_token_handling(word_chain, cmdlines, tmp_word, ch, params)) {
        if(command_execution_condition(params))
            command_processing(params, current_mode, word_chain, cmdlines,
                               tmp_word, ch);
        return;
    }
    if(params->wrong_command) {
        error_identification(params);
        clean_input_buffer();
        reset_params(params, current_mode, word_chain, cmdlines, tmp_word);
        show_invitation();
        return;
    }
    if(check_separation(ch, *params)) {
        if(excessive_words(ch, params)) {
            error_identification(params);
            clean_input_buffer();
            reset_params(params, current_mode, word_chain, cmdlines, tmp_word);
            show_invitation();
            return;
        }
        if(!filename_waiting(params)) {
            add_word(word_chain, tmp_word, params);
            params->is_word = 0;
        }
        return;
    }
    if(ignore_spaces(ch, *params))
        return;

    add_letter(ch, tmp_word, params);
}

static void whole_word_processing(int ch, struct param_type *params,
                                  enum modes *current_mode,
                                  struct w_queue *word_chain,
                                  struct dynamic_array *tmp_word)
{
    if(double_quotes_again(ch, *params)) {
        params->stored_symbol = '\0';
        params->empty_word_flag = 1;
        ++params->double_quotes_counter;
        *current_mode = word_separation;
        return;
    }
    params->stored_symbol = '\0';
    if(change_mode(ch, *params)) {
        ++params->double_quotes_counter;
        *current_mode = word_separation;
        return;
    }
    if(escape_double_quotes_or_backslash(ch, *params)) {
        dynarr_push_back(tmp_word, ch);
        params->escape_sequences = 0;
        params->is_word = 1;
        return;
    }
    if(start_escape_sequence(ch, *params)) {
        params->escape_sequences = 1;
        return;
    }
    /* backslash recovery */
    if(params->escape_sequences)
        dynarr_push_back(tmp_word, backslash);

    add_letter(ch, tmp_word, params);
}

int main()
{
    int ch;
    struct param_type params;
    struct w_queue word_chain;
    struct c_queue cmdlines;
    struct dynamic_array tmp_word;
    enum modes current_mode = word_separation;

    w_queue_init(&word_chain);
    c_queue_init(&cmdlines);
    dynarr_create_array(&tmp_word);
    init_params(&params, &current_mode);
    show_invitation();

    while((ch = getchar()) != EOF) {
        if(ch == new_line)
            command_processing(&params, &current_mode, &word_chain,
                               &cmdlines, &tmp_word, ch);
        else if(current_mode == word_separation)
            word_separation_processing(ch, &params, &current_mode, &word_chain,
                                       &cmdlines, &tmp_word);
        else if(current_mode == whole_word)
            whole_word_processing(ch, &params, &current_mode, &word_chain,
                                  &tmp_word);
    }
    putchar(new_line);
    dynarr_clear(&tmp_word);
    return 0;
}