As I’m now permanently installed at our University (yeah!) I probably need to use skype more often than desired. However, I still try to avoid proprietary software, and skype is the worst of all. Skype is an

obfuscated malicious binary blob with network capabilities

as jvoisin beautifully put into words. I came in contact with skype multiple times and it was always a mess. Ok, but what are the options if I need skype? So far I’ve been using a virtual box if I needed to call somebody who insisted on using skype, but now that I’ll be using skype more often I need an alternative to running a second OS on my machine. My friend Tom meant to make a joke about using Docker and … TA-DAH! … Turns out it’s actually possible to jail a usable skype inside a Docker container! Guided by jvoisin’s article Running Skype in docker I created my own setup:

The Dockerfile

The Dockerfile is available from the skype-on-docker project on GitHub. Just clone the project and change into the directory:

$ git clone https://github.com/binfalse/skype-on-docker.git
$ cd skype-on-docker
$ ls -l
total 12
-rw-r--r-- 1 martin martin   32 Jan  4 17:26 authorized_keys
-rw-r--r-- 1 martin martin 1144 Jan  4 17:26 Dockerfile
-rw-r--r-- 1 martin martin  729 Jan  4 17:26 README.md

The Docker image is based on a Debian:stable. It will install an OpenSSH server (it exposes 22) and download the skype binaries. It will also install the authorized_keys file in the home directories of root and the unprivileged user. Thus, to be able to connect to the container you need to copy your public SSH key into that file:

$ cat ~/.ssh/id_rsa.pub >> authorized_keys

Good so far? Ok, then go for it! Build a docker image:

$ docker build -t binfalse/skype .

This might take a while. Docker will execute the commands given in the Dockerfile and create a new Docker image with the name binfalse/skype. Feel free to choose a different name.. As soon as that’s finished you can instantiate and run a new container using:

$ docker run -d -p 127.0.0.1:55757:22 --name skype_container binfalse/skype

This will start the container as a daemon (-d) with the name skype_container (--name skype_container) and the host’s port 55757 mapped to the container’s port 22 (-p 127.0.0.1:55757:22). Give it a millisecond to come up and then you should be able to connect to that container via ssh. From that shell you should be able to start an configure skype:

$ ssh -X -p 55555 docker@127.0.0.1

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Mon Jan  4 23:07:37 2016 from 172.17.42.1
$ skype

You can immediately go and do your chats and stuff, but you can also just configure skype. Do setup everything just like you want to find it when starting skype, for example tick the auto-login button to get rid of the login screen etc. As soon as that’s done, commit the changes to build a new image reflecting your preferences:

$ docker commit skype_container binfalse/deb-skype

Now you’ll have an image called binfalse/deb-skype that contains a fully configured skype installation. Just kill the other container:

$ docker stop skype_container
$ docker rm skype_container

And now your typical workflow might look like:

docker run -d -p 127.0.0.1:55757:22 --name skype__ binfalse/deb-skype
sleep 1
ssh -X -p 55757 docker@127.0.0.1 skype && docker rm -f skype__

Feel free to cast it in a mould just as I did. The script is also available from my apt repo, it’s name is bf-skype-on-docker:

echo "deb http://apt.binfalse.de binfalse main" > /etc/apt/sources.list.d/binfalse.list
apt-get update && apt-get install bf-skype-on-docker

You know, … you just got this new floppy disk with very important material but you cannot access it because you’re not in the system’s floppy group and, thus, you’re not allowed to access the floppy device. Solution is easy: add your current user to the floppy group! Sounds easy, doesn’t it? The annoying thing is that those changes won’t take affect in the current session. You need to log out and log in again – quite annoying, especially if you’re into something with lots of windows and stuff. Just happened to me with docker again..

However, there are two methods to get into the new groups without the need to kill the current session:

• su yourself: let’s say your username is myname you just need to su myname to get a prompt with the new group memberships.
• ssh localhost: that also gives you a new session with updated affiliations.

That way, you do not need to start a new session. However, you still need to start all applications/tools from that terminal - might be odd to those who are used to the gnome/kde menues.. :)

Supplemental material

Display group membership:

 groups USERNAME

Add a new system group:

 groupadd GROUPNAME

Add a user to a group:

 useradd -G GROUPNAME USERNAME

I’m running CyanogenMod on my phone and I have the firewall AFWall+ installed.

To update the list of available updates the application CM Updater need to be able to connect to the internet. It will contact a website from within the google empire and ask for available images.

In order to download a new image the application Media Storage, Download Manager, Downloads needs internet access, as this app is in charge of downloading the actual image file.

To be remembered.

• The first sentence of each doc comment should be a summary sentence
• Write the description to be implementation-independent, but specifying such dependencies where necessary. (what is required, what is allowed)
• wrap keywords in <code>...</code>

typical meta annotations

• @author is not critical, because it is not included when generating the API specification
• @version SCCS string "%I%, %G%", which converts to something like “ 1.39, 02/28/97” (mm/dd/yy) when the file is checked out of SCCS
• @since specify the product version when the Java name was added to the API specification (if different from the implementation)

typical method definition

• @param parameter-name description
  • followed by the name (not data type) of the parameter, followed by a description of the parameter
  • the first noun in the description is the data type
• @return description
  • omit for methods that return void and for constructors
  • include it for all other methods, even if its content is entirely redundant with the method description
• @throws class-name description should be included for any checked exceptions (previously, it was @exception)

additional annotations

• {@value package.class#field}
  • when {@value} is used (without any argument) in the doc comment of a static field, it displays the value of that constant: The value of this constant is {@value}.
  • otherwise it displays the value of the specified constant: Evaluates the script starting with {@value #SCRIPT_START}.
• {@code text}
  • Equivalent to <code>{@literal}</code>.

linking

• @see reference
  • Adds a "See Also" heading
  • reference is a string: Adds a text entry for string. No link is generated. The string is a book or other reference to information not available by URL.
  • reference is an <a href="URL#value">label</a>: Adds a link as defined by URL#value. The URL#value is a relative or absolute URL.
  • reference is an package.class#member label: Adds a link (with optional visible text label) that points to the documentation for the specified name in the Java Language that is referenced.
• {@link package.class#member label}
  • in-line link with visible text label that points to the documentation for the specified package, class or member name of a referenced class
  • not necessary to add links for all API names in a doc comment
• @serial (or @serialField or @serialData) for interoperability with alternative implementations of a Serializable class and to document class evolution

deprecation

• @deprecated deprecated-text
  • the first sentence should at least tell the user when the API was deprecated and what to use as a replacement
  • a {@link} tag should be included that points to the replacement method

example

/**
 * The Class CombineArchive to create/read/manipulate/store etc.
 * CombineArchives.
 * <p>
 * We directly operate on the ZIP file, which will be kept open. Therefore, do
 * not forget to finally close the CombineArchive when you're finished.
 * 
 * @see <a href="https://sems.uni-rostock.de/projects/combinearchive/">
 *      sems.uni-rostock.de/projects/combinearchive</a>
 * @author martin scharm
 */
public class CombineArchive
    extends MetaDataHolder
    implements Closeable
{
    /* ... */

    /**
     * Gets the the first main entry of this archive, if defined. As of RC2 of the spec there may be more than one main entry, so you should use {@link #getMainEntries()} instead.
     * 
     * @return the first main entry, or <code>null</code> if there is no main entry
     * @deprecated as of version 0.8.2, replaced by {@link #getMainEntries()}
     */
    public ArchiveEntry getMainEntry ()
    {
        if (mainEntries == null)
            return null;
        return mainEntries.size () > 0 ? mainEntries.get (0) : null;
    }
    
    /**
     * Gets the main entries as defined in the archive.
     *
     * @return the main entries in this archive
     */
    public List<ArchiveEntry> getMainEntries ()
    {
        return mainEntries;
    }

    /**
     * Replace the file associated with a certain entry while keeping the meta
     * data.
     * 
     * @param toInsert
     *          the new file to insert
     * @param oldEntry
     *          the old entry whose file should be replaced
     * @return the new entry
     * @throws IOException If an input or output exception occurred
     */
    public ArchiveEntry replaceFile (File toInsert, ArchiveEntry oldEntry) throws IOException
    {
        addEntry (toInsert, oldEntry.getFilePath (), oldEntry.getFormat (), false);
        entries.put (oldEntry.getFilePath (), oldEntry);
        return oldEntry;
    }
}

References

• oracle.com/technetwork/java/javase/documentation
• docs.oracle.com/javase/7/docs/technotes/tools/solaris/javadoc

Using AdAway on your Android phones it is very easy to block a set of URLs.

AdAway (available from F-Droid, source from GitHub) is an ad-blocker. The application basically maintains a list of resources containing lists to ad-servers, see figure for example, e.g.:

# dest ip   url
127.0.0.1   some.ad.server.com

This entry will redirect all traffic meant for some.ad.server.com to the server 127.0.0.1, which is your localhost. Entries from different resources are merged. Thus, all requests to typical ad-servers will fail → annoying advertisements won’t be delivered. It’s quite powerful and gives impressive results. However, I didn’t want to talk about ad-stuff. The cool thing is

AdAway allows for extensions with own hosts files!

You can simply add another link to a file containing further host entries. I created my own AdAway file, uploaded it to https://stuff.lesscomplex.org/adaway.txt and added it to AdAway, as you can see in the figure. The current version contains a few entries for:

• facebook/yahoo/etc: I’m not using facebook or stuff, all these request shouldn’t leave my phone
• captive portal detection: To detect captive portals the phone downloads a few bytes from a google server and checks if it is able to access the real internet or just a captive portal
• swift key: I’m using swift key, but do not want it to communicate to the internet. Thus, I’m blocking a few URLs that swiftkey wants to talk to. As I’m already using a firewall this just adds another layer of privacy.

Feel free to use my “extension”, but I expect it to change over time. :)

Shortcomings

This method only works if applications load contents from URLs. As soon as the IPs are hard-coded the hosts file