Joe’s Blog!

DOPE.

With moving into the new apartment it was inevitable that Motorboat would find a new place that was his. In the past he has claimed the bathroom as his domain, the new bathroom does not seem to be of his liking although he still likes toilet water. The first few days we heard a knocking from the kitchen but wasn’t sure what it was. Soon enough we found Motorboat was the cause, entering and exiting the same cabinet before and after naps. He has officially claimed a bottom cabinet of his own. Rather than fight it I put some towels in there for him and knock before entering.

While it seems that most (?) Erlangers use emacs as their editor of choice, I enjoy using gedit. Here’s what I do to get things just right for writing some code (many of the changes I found here):

• Plugins: Auto Completion, Bracket Completion, Document Statistics, Embedded Termal, File Browser Pane, Session Saver, Snippets, Spell Check (if you are rolling ubuntu, many of these can be installed via apt-get install gedit-plugins)
• Theme: Darkmate
• Font: droid sans mono

One additional change I make is to the snippet plugin. I have basically copied the code skeletons from erlang mode in emacs and put them into the snippets plugin. You can download my export file here. This file can be imported into the snippets plugin and will provide similar functionality to the skeletons in emacs.

Here’s what it looks like when I’m done, with an example of a snippet on the upper right.

Lately I have been working on a TCP server that works similar to D. J. Bernstein’s ucspi-tcp. Basically, it is a TCP server that sits in front of a executable of some sort and plays a middleman between the TCP client and the actual code that is performing functions on the data sent to the TCP server. More on ucspi-tcp in later post(s). The first portion of my TCP server code can be found here and blog post here. The portion of code for today is for sending and receiving messages to/from the executable in Erlang. This is done using an Erlang port, the Erlang docs have a good interoperability tutorial that should help anyone start out.

erl_portc.erl

-module(erl_portc).
-export([start/1, call_port/1, init/1, port_loop/1]).

start(Cmd) ->
% spawn a process connected to the executable
spawn(?MODULE, init, [Cmd]).

init(Cmd) ->
% register it and set things up
register(port, self()),
process_flag(trap_exit, true),
Port = open_port({spawn, Cmd}, []),
port_loop(Port).

call_port(Msg) ->
% send messages to the executable
port ! {call, self(), Msg},
receive
{port, Result} ->
Result
end.

port_loop(Port) ->
% recieve results from the executable
receive
{call, Caller, Msg} ->
Port ! {self(), {command, Msg}},
receive
{Port, {data, Data}} ->
Caller ! {port, Data};
stop ->
Port ! {self(), close},
receive
{Port, closed} ->
exit(normal)
end;
{‘EXIT’, Port, Reason} ->
exit(port_terminated)
end,
port_loop(Port)
end.

Here is an example of its usage using DJB’s qmail-smtpd executable.

[joe@box01 ~]$ erl
Erlang (BEAM) emulator version 5.6.3 [source] [smp:4] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.6.3 (abort with ^G)
1> erl_portc:start(‘/var/qmail/bin/qmail-smtpd’).
<0.32.0>
2> erl_portc:call_port(“”).
“220 mail.someaddress.com ESMTP\r\n”
3> erl_portc:call_port(“HELO mail.someaddress.com\r\n”).
“250 mail.someaddress.com\r\n”
4> erl_portc:call_port(“MAIL FROM: joe@someaddress.com\r\n”).
“250 ok\r\n”
5> erl_portc:call_port(“RCPT TO: joe@someaddress.com\r\n”).
CHKUSER accepted rcpt: from remote rcpt : found existing recipient
“250 ok\r\n”
6> erl_portc:call_port(“DATA\r\n”).
“354 go ahead\r\n”
7> erl_portc:call_port(“Subject: TEST123\r\n.\r\n”).
“250 ok 1229721933 qp 10176\r\n”
8> erl_portc:call_port(“QUIT\r\n”).
“221 mail.someaddress.com\r\n”

Shortly after running the above directives I received an email in my inbox with the subject “TEST123″. So it seems to be interfacing with the executable properly.

As with most of the code on this blog, this example can be checked out from subversion and viewed in WebSVN. Enjoy!

I have been posting photo’s from our trip from Saint Louis to Seattle on my flickr, here is the set. I will be doing updates when I can.