csci4061/p1-code/cmd.c

#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include "commando.h"

// Allocate a new cmd_t with the given argv[] array. Make string
// copies of each of the strings contained within argv[] using
// strdup() as they likely come from a source that will be
// altered. Ensure that cmd->argv[] is ended with NULL. Set the name
// field to be the argv[0]. Set finished to 0 (not finished yet). Set
// str_status to be "INIT" using snprintf(). Initialize the remaining
// fields to obvious default values such as -1s, and NULLs.
cmd_t *cmd_new(char *argv[]) {
    cmd_t *cmd = malloc(sizeof(cmd_t));
    strcpy(cmd->name, argv[0]);
    int i;
    for (i = 0; i < ARG_MAX; ++i) {
        if (!argv[i]) break;
        cmd->argv[i] = strdup(argv[i]);
    }
    cmd->pid = -1;
    cmd->status = -1;
    cmd->output = NULL;
    cmd->output_size = -1;
    cmd->argv[i] = NULL;
    cmd->finished = 0;
    snprintf(cmd->str_status, 5, "INIT");
    return cmd;
}

// Deallocate a cmd structure. Deallocate the strings in the argv[]
// array. Also deallocat the output buffer if it is not NULL. Finally,
// deallocate cmd itself.
void cmd_free(cmd_t *cmd) {
    for (int i = 0; cmd->argv[i]; ++i) {
        free(cmd->argv[i]);
    }
    if (cmd->output) free(cmd->output);
    free(cmd);
}

// Fork a process and start the command in cmd in it.  Change the
// str_status field to "RUN" using snprintf().  Create a pipe for
// out_pipe to capture standard output.  In the parent process, ensure
// that the pid field is set to the child PID.  In the child process,
// direct standard output to the pipe using the dup2() command. For
// both parent and child, ensure that unused file descriptors for the
// pipe are closed (write in the parent, read in the child).
void cmd_start(cmd_t *cmd) {
    snprintf(cmd->str_status, 4, "RUN");
    if (pipe(cmd->out_pipe)) {
        printf("pipe failed: %d\n", errno);
        exit(1);
        // immediately cause a kernel panic!!1!
    }
    pid_t child_pid = fork();
    if (child_pid == 0) {
        // child
        close(cmd->out_pipe[PREAD]);
        // dup2(cmd->out_pipe[PWRITE], STDOUT_FILENO);
        FILE *fp = fopen("lol", "r");
        dup2(cmd->out_pipe[PWRITE], fileno(fp));
        execvp(cmd->name, cmd->argv);
    } else {
        // parent
        cmd->pid = child_pid;
        close(cmd->out_pipe[PWRITE]);
    }
}

// If the finished flag is 1, do nothing. Otherwise, update the state
// of cmd.  Use waitpid() and the pid field of command to wait
// selectively for the given process. Pass the block argumnent, one of
// DOBLOCK or NOBLOCK, to waitpid() to cause either non-blocking or
// blocking waits.  Use the macro WIFEXITED to check the returned
// status for whether the command has exited. If so, set the finished
// field to 1 and set the cmd->status field to the exit status of the
// cmd using the WEXITSTATUS macro. Call cmd_fetch_output() to fill up
// the output buffer for later printing.
//
// When a command finishes (the first time), print a status update
// message of the form
//
// @!!! ls[#17331]: EXIT(0)
//
// which includes the command name, PID, and exit status.
void cmd_update_state(cmd_t *cmd, int block) {
    if (cmd->finished) return;
    int status = 0;
    int val = waitpid(cmd->pid, &status, block);
    if (val > 0) {
        if (WIFEXITED(status)) {
            cmd->status = WEXITSTATUS(status);
            snprintf(cmd->str_status, STATUS_LEN, "EXIT(%d)",
                     WEXITSTATUS(status));
            cmd->finished = 1;
            cmd_fetch_output(cmd);
            printf("@!!! %s[#%d]: EXIT(%d)\n", cmd->name, cmd->pid,
                   cmd->status);
        }
    }
    // printf("status of %d is %d\n", cmd->pid, status);
}

// Read all input from the open file descriptor fd. Store the results
// in a dynamically allocated buffer which may need to grow as more
// data is read.  Use an efficient grown scheme such as doubling the
// size of the buffer when additional space is needed. Use realloc()
// for resizing.  When no data is left in fd, set the integer pointed
// to by nread to the number of bytes read and return a pointer to the
// allocated buffer.
void *read_all(int fd, int *nread) {
    int size = BUFSIZE, total = 0, bytes;
    char *buf = (char *)malloc(size + 1);
    bytes = read(fd, buf, size / 2);
    total += bytes;
    while (bytes == size / 2) {
        size *= 2;
        buf = (char *)realloc(buf, size + 1);
        bytes = read(fd, buf + total, size / 2);
        if (!bytes) break;
        total += bytes;
    }
    buf[total] = '\0';
    *nread = total;
    return buf;
}

// If cmd->finished is zero, print an error message with the format
//
// ls[#12341] not finished yet
//
// Otherwise retrieves output from the cmd->out_pipe and fills
// cmd->output setting cmd->output_size to number of bytes in
// output. Data should be read() from the cmd's out_pipe into
// cmd->out_buf (allocated in this function). If out_buf runs out of
// space, realloc() it to a larger size and continue reading. Using a
// temporary buffer may help with this.
void cmd_fetch_output(cmd_t *cmd) {
    if (!cmd->finished) {
        printf("%s[#%d] not finished yet\n", cmd->name, (int)cmd->pid);
        return;
    }
    int nread;
    void *buf = read_all(cmd->out_pipe[PREAD], &nread);
    cmd->output = buf;
    cmd->output_size = nread;
    close(cmd->out_pipe[PREAD]);
}

// Print the output of the cmd contained in the output field if it is
// non-null. Print an error message like
//
// ls[#17251] has no output yet
//
// if output is NULL. The message includes the command name and PID.
void cmd_print_output(cmd_t *cmd) {
    if (!cmd->output) {
        printf("%s[#%d] has no output yet\n", cmd->name, (int)cmd->pid);
        return;
    }
    write(STDOUT_FILENO, cmd->output, cmd->output_size);
}