Dear monks,

I am sending a request to a game server and getting some buffer back via UDP, which works fine. I'm now trying to parse the buffer.

I have a class name package_reader as a member of another class for this. Reading a string works fine: I have created the following function to do it:

Notes:
* $self->index() gets the current position in the buffer
* $self->size() gets the total length() the buffer
* $self->skip(n) sets index += n

## read a string until a '\x00' is encountered (-> null termination of
+ strings in C!)
sub read_complete_string {
    my ($self) = @_;
    my $string = "";

    ## return empty string if we're already at the end of the buffer
    if($self->index() >= $self->size()) {
        return $string;
    }

    my $end_of_string = index($self->buffer(), "\x00", $self->index())
+;

    if(!($end_of_string)) {
            ## just read the rest of the buffer if there is no termina
+tion
            $string =  $self->read_buffer($self->size() - $self->index
+());
    }
    else {
        $string = $self->read_buffer($end_of_string - $self->index());
        ## ignore the nullbyte '\x00'
        $self->skip(1);
    }

    return $string;
}
[download]

The function read_buffer() and skip() are used in the code above and therefor also shown here:

## read the specified number of bytes from buffer, called by the other
+ read_* functions
sub read_buffer {
    my ($self , $user_length) = @_;
    my $length = 1;
    $length = $user_length if $user_length;

    if(($self->index() + $length) > $self->size()) { print "$tag: WARN
+ING: ##### read_buffer(): not enough data left, ignoring request to r
+ead $length bytes! #####\n"; return 0; }

    my $val = substr($self->buffer(), $self->index(), $length);
    $self->index($self->index() + $length);

    print "$tag: DEBUG: read_buffer(): read raw data '$val' of length 
+$length, now at $self->{_index} (" . $self->data_left() . " bytes of 
+" . $self->size() . " left)\n";

    return $val;
}

## skips the given number of bytes
sub skip {
    my ($self, $user_length) = @_;
    my $default_length;
    my $length;
    $default_length = 1;

    $length = $default_length;
    $length = $user_length if $user_length;

    $self->index($self->index() + $length);

    return $length;
}
[download]

I do now need to parse the following C struct from the data:

struct client_t {
  short ping;
  int rate;
  char name[32]; // NULL-terminated
  byte clanTagPosition; // 0: prefix, 1: suffix
  char clanTag[32]; // NULL-terminated
  byte isBot;
};
[download]

And I'm trying to get the ping of this client with the following code:

sub read_short {
    my ($self) = @_;

    my $sys_short_length = $Config{shortsize};
    my $short = unpack('S', $self->read_buffer($sys_short_length));

    return $short;
}


# elsewhere in the code:
print "ping: " . $self->package_reader->read_short() . "\n";
[download]

I'm getting a number sometimes, but most of the time it's just empty or nonsense.

Two questions:
1) Is the read_short() function broken or do I have to do anything special when I print its return value (like use printf and format it properly)?
2) How do I unpack the byte from the C struct shown above? How do I know how long it is (how many characters do I have to read from my buffer)? Which template for 'unpack()' do I use?

Thanks in advance,

dichtfux

---

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