Read very large strings of UNKNOWN length

char buffer[10];
    char *s = 0;
    size_t cur_len = 0;
    while (fgets(buffer, sizeof(buffer), stdin) != 0)
    {
        size_t buf_len = strlen(buffer);
        char *extra = realloc(s, buf_len + cur_len + 1);
        if (extra == 0)
            break;
        s = extra;
        strcpy(s + cur_len, buffer);
        cur_len += buf_len;
    }