42sh/src/execution/execution.c

#include "execution.h"

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#include "../utils/ast/ast.h"

/**
 * @brief converts a linked list of command arguments to an argv array. Don't
 * forget to free the result
 *
 * @param cmd_list Linked list of command arguments
 * @return char** Array of command arguments suitable for execvp. Terminated by
 * NULL
 */
static char **list_to_argv(struct list *cmd_list)
{
    size_t len = 0;
    struct list *cur = cmd_list;

    while (cur)
    {
        len++;
        cur = cur->next;
    }

    char **argv = calloc(len + 1, sizeof(char *));
    if (!argv)
    {
        return NULL;
    }
    cur = cmd_list;

    for (size_t i = 0; i < len; i++)
    {
        argv[i] = (char *)cur->data;
        cur = cur->next;
    }

    argv[len] = NULL;
    return argv;
}

/**
 * @brief Executes a command represented by an ast_cmd structure
 *
 * @param cmd The command to execute
 * @return int The exit status of the command
 */
static int exec_command(struct ast_cmd *cmd)
{
    if (!cmd || !(cmd->cmd))
    {
        return -1;
    }

    char **argv = list_to_argv(cmd->cmd);

    if (!argv || !(argv[0]))
    {
        free(argv);
        return -1;
    }

    pid_t pid = fork();

    if (pid < 0) // Fork failed
    {
        perror("fork");
        free(argv);
        return -1;
    }

    if (pid == 0) // If child process
    {
        execvp(argv[0], argv);
        perror("execvp"); // If execvp returns, there was an error
        exit(EXIT_FAILURE); // Exit child process
    }

    int status = 0;
    waitpid(pid, &status, 0);
    free(argv);

    if (WIFEXITED(status))
    {
        return WEXITSTATUS(status);
    }

    return -1; // Should not happen
}

/**
 * @brief Executes the AST returned by the parser
 *
 * @param ast The AST to execute
 * @return int The exit status of the last executed command.
 */
int execution(struct ast *ast)
{
    if (!ast)
    {
        return 0;
    }

    switch (ast->type)
    {
    case AST_END: {
        return 0;
    }
    case AST_CMD: {
        struct ast_cmd *cmd = ast_get_cmd(ast);
        return exec_command(cmd); // It's recursive
    }
    case AST_IF: {
        struct ast_if *if_node = ast_get_if(ast);
        int cond = execution(if_node->condition);
        if (cond == 0) // True
        {
            return execution(if_node->then_clause);
        }
        else // False
        {
            return execution(if_node->else_clause);
        }
    }
    default: {
        return -1; // Should not happen
    }
    }
}