Once in a while it is useful to dismiss abstractions and layers that makes daily routines easier and take the raw approach. Like when debugging a software problem that doesn’t make sense, it is nice to see the underlying basic stuff is behaving nicely, to better be able to locate where the unexpected occurs.
In the IP world of the internet, the swiss army knife for debugging interprocess communications in a totally protocol agnostic way is called ‘telnet’. Telnet opens up a communication channel between your local computer and a daemon/server on a specific port on a specific IP address. Then it gets out of the way for you to talk directly to the daemon in clear text.
Knowledge of how to interact using a specific protocol can be very useful to check server availability and functionality. All common protocols in use on the internet (like DNS, HTTP, SMTP, POP3, IMAP, XMPP etc.) can be debugged like this, because all of them transfers data in clear text (or at least initiates other transfer types from a clear text session). Full specifications for the HTTP protocol can be found in IETF RFC2616. I keep forgetting this, and end up digging around for it when needed, therefore this blog post.
Below is a basic HTTP session to my web server www.mikini.dk using telnet on the command line.
Red text is local text input by me. Blue text is local text by telnet application. Green text is server response.
$ telnet www.mikini.dk 80 Trying 92.61.152.47… Connected to 92-61-152-47.static.servage.net. Escape character is ‘^]’. GET /index.php/2010/06 HTTP/1.1 Host: www.mikini.dk
HTTP/1.1 200 OK Date: Wed, 21 Jul 2010 09:19:13 GMT Server: Apache X-Pingback: http://www.mikini.dk/xmlrpc.php Transfer-Encoding: chunked Content-Type: text/html; charset=UTF-8
2bd2 <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd“>
<… remainder of HTML document dropped …>
We are asking the server at www.mikini.dk port 80 (default http port) for the document at path /index.php/2010/06 (“GET /index.php/2010/06”). Notice the two CRLF characters after the Host header field, this indicates to the server that the request header is done, and that it should begin parsing header and send its response. Also notice that even though you tell the telnet program on the commandline that you want to access www.mikini.dk, you have to tell it again to the server in th HTTP Host field. Thats because telnet is only concerned about the IP address of the server, it resolves www.mikini.dk to the IP 92.61.152.47 through DNS and forgets about it. From the servers point of view, it needs to know which of its virtual hosts you want to talk to, cause one server application on one port on one ip can potentially host thousands of separate websites (virtual hosts).
Below is the same session using nc (netcat) as a one-liner (wow, old PHP at Hostinger, better get that move to a self-administered box going).
$ echo -ne "GET /index.php/2010/06 HTTP/1.1\r\nHost:www.mikini.dk\r\n\r\n"|nc www.mikini.dk 80 | head -10 HTTP/1.1 200 OK Date: Thu, 05 Jul 2018 16:30:07 GMT Server: Apache X-Powered-By: PHP/5.5.35 Link: <http://www.mikini.dk/wp-json/>; rel="https://api.w.org/" Content-Length: 32356 Content-Type: text/html; charset=UTF-8 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> $
2018-07-05: nc command line added
Today I managed to get a Huawei E1752 3G modem (USB id 12d1:1446/140c, usually called E1552 by lsusb) running on Ubuntu 10.04 without all the hassle described elsewhere (see this, this or this or this …).
This particular modem came from the danish cable ISP YouSee, in an offering known as Mobilt Bredbånd (mobile broadband), targeting their existing cable internet customers. Pricing starts at lowest offering of 1 Mbit/384 kbit transmission speed with 1GiB/month data limit at DKK 99/month (~USD 16.5 ~EUR 13.3).
As many recent USB modems, this one is a mode switching type with multiple personalities (Option ZeroCD(TM)). At plugin it defaults to an emulated CD mass storage drive (USB ID 12d1:1446), with an onboard Windows driver and dialer (Mobile Partner). When detected by a driver knowing it’s schizophrenic nature, it can be manipulated, utilizing psychotherapeutic tricks, to switch it’s personality to the modem it actually is (USB ID 12d1:140c). Hence, on non-Windows systems some magic needs to be established to make the modem actually behave like a modem.
One incarnation (se discussion about other stuff here) of this magic is called usb_modeswitch. That is also the solution chosen by the Ubuntu distribution team, and it is present in the repositories and configured for the Huawei E1752 in Ubuntu 10.04 ‘Lucid Lynx’, so we just need to know that we need it. You do now…
Activating usb_modeswitch is a matter of installing the usb-modeswitch package. Find it in Synaptic or issue the following in a terminal:
sudo apt-get install usb-modeswitch
Now all you have to do is insert the modem and check (we like to be certain, right?) with lsusb that you have the 12d1:140c modem device instead of the 12d1:1446 mass storage device.
The Gnome Network Manager should now pick up on the new modem device, and offer you the possibility of adding a new mobile broadband connection. In my case, it defaulted to an Oister connection, but removing that and using the wizard to create a TDC connection (YouSee is a part of/close associate of TDC) did the trick, after reinserting the modem once more.
Now I wonder why my own E160G modem works without usb_modeswitch installed…
A quick note about my feelings and observations after using my new Samsung N210 (white) netbook for a couple of hours during the last 2 days.
The new fellow was bought at danish netshop Proshop.dk (product page) for DKK 2551 (~342.75 EUR ~420.50 USD). Delivery was DKK 59 and took from order at thursday 17th until delivered monday 21st (danish mail is not to blame, I expected it to arrive friday, on stock and all but Proshop decided to wait until sunday 20th before processing the order).
Even though I’m a software junkie, I’m by no means a commercial hardware junkie (software is the enabler anyway, ya ‘now!). I don’t buy off-the-shelf systems every other day, or have a job where I try out a horde of different netbooks/notebooks. Bear that in mind; these observations come from a newbie netbook user, with experience from larger more gfx capable laptops.
All of the below are under the overall judgement that says: I like this machine very much, it will indeed fellow me in many a journey in the time to come.
Oh, and of course, it needs a name! My N210 is named khandro, after a tibetian deity, meaning “cloud fairy” or “she who traverses the sky’.
Let the fairytales begin…
Just bumped into the LISP dialect Clojure. In short, its a Java enclosed runtime interpreted functional programming language/environment which seems to have some rather interresting features. Its easy and acessibly, in fact 2 mins. after reading about it, I was throwing UI dialogs all over my screen. There’s even a danish user group (dcug).
Of couse its open source/free software (EPL 1.0 licensed) and development is community driven, or I wouldn’t mention it by many words.
Will be interesting to learn more about this, and see if it kicks in. Kind of reminds me about Carl Sassenrath’s little known environment REBOL, even though REBOL is a little more ‘itself’, where Closure draws on the large LISP heritage.
Velcome to Mikini Services.
We do stuff! Like foobar, null pointer dereferences, DND and N/A. Oh, and also fluffy, squeaky things!
