path: root/shell.c

#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(p_queue, pid, int)

enum modes { word_separation, whole_word };
#if 0
enum {
    new_line        = 10,
    whitespace      = ' ',
    tab             = 9,
    backslash       = '\\',
    double_quotes   = '"'
};

/* two-letter tokens */
enum {
    append          = '>' + 1,
    and             = '&' + 1,
    or              = '|' + 1
};

/* storing file names to redirect standard input/output streams */
struct io_type {
    char *input_stream;
    char *output_stream;
    char *output_stream_to_append;
};

struct param_type {
    int is_word;
    int escape_sequences;
    unsigned int double_quotes_counter;
    char stored_symbol;
    int empty_word_flag;
    int tokens;
    int wrong_command;
    struct io_type streams;
    int last_execution_status;
    int pipeline;
};
#endif

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

static void print_error()
{
    fprintf(stderr, "Error: unmatched quotes\n");
}

/* 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);
}
#if 0
static int is_double_quotes_pair(struct param_type params)
{
    return !(params.double_quotes_counter % 2);
}
static int check_separation(int ch, struct param_type params)
{
    return (ch == whitespace || ch == tab) && params.is_word &&
            !params.escape_sequences;
}
#endif
int filename_waiting(struct param_type *params)
{
    if(params->tokens == '<' || params->tokens == '>' ||
            params->tokens == append) {
        if(!params->is_word)
            params->wrong_command = 1;
        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;
}

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;
}

#if 0
static int is_double_token(struct param_type *params)
{
    return params->tokens == and || params->tokens == or ||
            params->tokens == append;
}
static int is_redirect_token(int ch, int next_ch)
{
    return ch == '<' || ch == '>' || (ch == '>' && next_ch == '>');
}
static int validate_redirections(int ch, int next_ch, struct param_type *params)
{
    return (ch == '<' && params->streams.input_stream == NULL) ||
            ((ch == '>' || (ch == '>' && next_ch == '>')) &&
             params->streams.output_stream == NULL &&
             params->streams.output_stream_to_append == NULL);
}
static void add_word_or_filename(struct w_queue *word_chain,
                                 struct dynamic_array *tmp_word,
                                 struct param_type *params)
{
    /* filenames */
    if(filename_waiting(params) && !params->wrong_command)
            add_filename(tmp_word, params);
    /* execute command */
    else if(params->is_word)
        add_word(word_chain, tmp_word, params);
}

static int stream_redirect_tokens(struct w_queue *word_chain,
                                  struct dynamic_array *tmp_word, int ch,
                                  struct param_type *params)
{
    int next_ch;
    next_ch = getchar();
    ungetc(next_ch, stdin);

    if(is_redirect_token(ch, next_ch)) {
        add_word_or_filename(word_chain, tmp_word, params);

        if(params->wrong_command)
            return 0;

        if(validate_redirections(ch, next_ch, params)) {
            params->tokens = (ch == '>' && next_ch == '>') ? append : ch;
            if(is_double_token(params))
                getchar();
            return 1;
        } else {
            fprintf(stderr, "syntax error\n");
            params->wrong_command = 1;
        }
    }
    return 0;
}
#endif

static void clean_input_buffer()
{
    int ch;
    while((ch = getchar()) != new_line)
    {}
}
#if 0
static int is_special_token(int ch)
{
    return ch == and || ch == or || ch == '&' || ch == ';' || ch == '|';
}
static int wrong_streams_redirection(struct param_type *params)
{
    return
        (!params->pipeline && (params->tokens == '>' ||
                               params->tokens == append)) ||
        (params->pipeline && (params->tokens == '>' ||
                              params->tokens == append ||
                              params->tokens == '<'));
}
#endif

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;
}

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;
}
#if 0
static int pipeline_token_processing(struct w_queue *word_chain,
                                     struct c_queue *cmdlines,
                                     struct dynamic_array *tmp_word,
                                     struct param_type *params)
{
    char **cmdline = NULL;
    if(is_stream_redirection_set(params) &&
            wrong_streams_redirection(params)) {
        /* TODO: add error codes */
        params->wrong_command = 1;
        return 0;
    }
    params->tokens = '|';
    params->pipeline = 1;
    cmdline =
        create_cmdline(word_chain, w_queue_get_word_count(word_chain));

    c_queue_push(cmdlines, cmdline);
    w_queue_clear(word_chain);
    dynarr_drop_word(tmp_word);
    return 1;
}

static int special_tokens(struct w_queue *word_chain,
                          struct c_queue *cmdlines,
                          struct dynamic_array *tmp_word, int ch,
                          struct param_type *params)
{
    int next_ch;
    next_ch = getchar();
    ungetc(next_ch, stdin);

    if(is_special_token(ch)) {
        add_word_or_filename(word_chain, tmp_word, params);

        if(params->wrong_command)
            return 0;

        if(ch == '|' && next_ch == '|')
            params->tokens = or;
        else if(ch == '|') {
            if(!pipeline_token_processing(word_chain, cmdlines, tmp_word,
                                          params))
                return 0;
        } else if(ch == '&' && next_ch == '&')
            params->tokens = and;
        else if(ch == '&') {
            while((ch = getchar()) != new_line) {
                if(ch != whitespace && ch != tab) {
                    fprintf(stderr, "incorrect command\n");
                    params->wrong_command = 1;
                    return 0;
                }
            }
            params->tokens = '&';
        }
        if(is_double_token(params))
                getchar();
        return 1;
    }
    return 0;
}
#endif

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);
}
#if 0
static int ignore_spaces(int ch, struct param_type params)
{
    return (ch == whitespace || ch == tab) && !params.escape_sequences;
}

static int change_mode(int ch, struct param_type params)
{
    return ch == '"' && !params.escape_sequences;
}

static int start_escape_sequence(int ch, struct param_type params)
{
    return ch == backslash && !params.escape_sequences;
}

/* name of file for opening stream already exists */

static int excessive_words(int ch, const struct param_type *params)
{
    int next_ch;

    if(filename_waiting(params)) {
        if(ch == new_line)
            return 0;
        while((next_ch = getchar()) != new_line) {
            if(next_ch == ' ')
                continue;
            if(!is_special_token(next_ch) && next_ch != '<' && next_ch != '>')
                return 1;
            else
                break;
        }
        ungetc(next_ch, stdin);
    }
    return 0;
}
#endif

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 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 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);
    }
}

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 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 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);
                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 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);
    }
}

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;

    /* and odd number of double quotes  */
    if(!is_double_quotes_pair(*params)) {
        print_error();
        reset_params(params, current_mode, word_chain, cmdlines, tmp_word);
        show_invitation();
        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 == '<') {
                fprintf(stderr, "read in the last pipline element\n");
                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 0
    if(params->empty_word_flag || params->is_word) {
        if(filename_waiting(params)) {
            if(excessive_words(ch, params)) {
                fprintf(stderr, "too many args\n");
                goto clean;
            }
            if(params->pipeline) {
                if(params->tokens == '>' || params->tokens == append)
                    add_filename(tmp_word, params);
                else if(params->tokens == '<') {
                    fprintf(stderr, "read in the last pipline element\n");
                    goto clean;
                }
            } else
                add_filename(tmp_word, params);
        } else
            add_word(word_chain, tmp_word, params);

    } else if(filename_waiting(params)) {
        fprintf(stderr, "filename expected\n");
        goto clean;
    }
#endif

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

    if(word_chain->first == NULL) {
        fprintf(stderr, "empty command\n");
        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:
    if(params->tokens == '&' || params->tokens == 0 || ch == new_line)
        show_invitation();
    reset_params(params, current_mode, word_chain, cmdlines, tmp_word);
}

#if 0
static int is_empty_word(int ch, struct param_type params)
{
    return (ch == whitespace || ch == tab) && !params.is_word &&
            params.empty_word_flag;
}

static int command_execution_condition(struct param_type *params)
{
    return
        (!filename_waiting(params) && !params->pipeline) ||
        (params->pipeline && params->tokens == '&');
}
#endif

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) {
        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)) {
            clean_input_buffer();
            reset_params(params, current_mode, word_chain, cmdlines, tmp_word);
            fprintf(stderr, "too many args\n");
            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);
}

#if 0
static int escape_double_quotes_or_backslash(int ch, struct param_type params)
{
    return params.escape_sequences &&
        (ch == double_quotes || ch == backslash);
}

static int double_quotes_again(int ch, struct param_type params)
{
    return ch == double_quotes && !params.is_word &&
        params.stored_symbol == '"';
}
#endif

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;
}