MagiWOL 2.20

After very long time (more than a year!) here is update to my Wake-On-LAN program.

This update consists mostly of bug-fixes with single new feature. One can define custom wait period between sending packets. This change will not be used much but for situations where you need to wake hundred of computers without burning fusebox it is definitely crucial.

Additional small tweak that may stop some frustration is change of console tool to wol.exe. This way one working in command-line can write only three letters instead of eight (it was magiwolc.exe).

Download is ready.

GPS Should Stop

One error that creeps quite often in Android applications is not handling being in background gracefully. It is error that is really easy to make since your application works as it normally would. However, it does use more resources than it is needed and resources usually map to battery life.

One example of bad behavior that comes to mind is updating location non-stop. Most often application needs to update their location only when user is looking at it. Once application is in background GPS should be turned off (although there are some application that have good reason to leave it going).

Easiest way to do it is just handling all GPS “subscriptions” in onResume and onPause methods. Those methods get called each time application comes to foreground (onResume) or leaves it (onPause).

Generic solution would look something like this:

private LocationManager thisLocationManager;

@Override
public void onCreate(Bundle savedInstanceState) {
   ...
   thisLocationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
}

@Override
protected void onResume() {
    thisLocationManager.requestLocationUpdates("gps", 0, 0, gpsLocationListener);
    super.onResume();
}

@Override
protected void onPause() {
    thisLocationManager.removeUpdates(gpsLocationListener);
    super.onPause();
}

private LocationListener gpsLocationListener = new LocationListener() {
   ...
};

P.S. Do note that this code is not optimal in any way (e.g. hard-coding “gps” as provider name). Intention is just to illustrate concept.

Getting GUID Value After SQL Insert

Whoever used identity columns in SQL Server probably used SCOPE_IDENTITY in order to retrieve newest identity value after insert.

For example, if we have two columns, one named Id and declared as identity column and other named Test with text inside, we would use something like this in order to insert new row:

INSERT INTO Example(Test) VALUES('test'); SELECT SCOPE_IDENTITY();

Once we use ExecuteScalar, we would get newly inserted identity value (in column Id).

Once we enter world of Guids, we cannot do that. Guid is not considered identity value and same rules do not apply to it. In order to have similar example we shall have also two columns here. However, this time Id column will be of uniqueidentifier type and it will have it’s default set to NEWID(). This way client behavior is same. Once we insert new row (without specifying Id value) we will get Id assigned to us.

In order to retrieve value for Id column, we need to change SQL a little:

INSERT INTO Example(Test) OUTPUT INSERTED.Id VALUES('test');

Antena

Another issue of scratching-an-itch with new application is my newest Android application. I had to mount my terrestrial TV antenna and I figured that there should be easier way to align it with DVB-T signal towers.

Result of that “one night stand” is Antena. Application that will show you all towers in 100 km radius and signal you when alignment is made. For that purpose it needs something to give it location (GPS?) and compass.

Unfortunately it is usable only in Croatia. There are no plans to make it work in others countries.

P.S. If someone is really interested in making it work somewhere else, all that is needed are GPS coordinates of towers and a beer. With those two items we can make it work anywhere.

Private Mercury

Sharing source with Mercurial is not hard. There is quite a good guide at Martin’s Blog and, indeed, first part of this post will mostly follow his setup.

Sharing sources with password authentication is still not hard but (at least from my perspective) is not obvious. This post will document my efforts of creating private and password protected Mercurial storage.

This procedure is tested on Ubuntu 10.04.1 LTS but I would expect it to work on older versions as well.

First we need to install it’s package.

sudo apt-get install mercurial
 Reading package lists... Done
 Building dependency tree       
 Reading state information... Done
 The following extra packages will be installed:
   mercurial-common
 Suggested packages:
   qct vim emacs kdiff3 tkdiff meld xxdiff python-mysqldb python-pygments
 The following NEW packages will be installed:
   mercurial mercurial-common
 0 upgraded, 2 newly installed, 0 to remove and 63 not upgraded.
 Need to get 1,182kB of archives.
 After this operation, 4,956kB of additional disk space will be used.
 Do you want to continue [Y/n]? Y
 Get:1 http://hr.archive.ubuntu.com/ubuntu/ lucid/universe mercurial-common 1.4.3-1 [1,131kB]
 Get:2 http://hr.archive.ubuntu.com/ubuntu/ lucid/universe mercurial 1.4.3-1 [50.7kB]
 Fetched 1,182kB in 3s (388kB/s)
 Selecting previously deselected package mercurial-common.
 (Reading database ... 124142 files and directories currently installed.)
 Unpacking mercurial-common (from .../mercurial-common_1.4.3-1_all.deb) ...
 Selecting previously deselected package mercurial.
 Unpacking mercurial (from .../mercurial_1.4.3-1_i386.deb) ...
 Processing triggers for man-db ...
 Setting up mercurial-common (1.4.3-1) ...
 Setting up mercurial (1.4.3-1) ...
 Creating config file /etc/mercurial/hgrc.d/hgext.rc with new version
 Processing triggers for python-support ...

Create location for Mercurial repositories at /srv/hg with cgi-bin at subdirectory:

sudo mkdir -p /srv/hg/cgi-bin
sudo cp /usr/share/doc/mercurial-common/examples/hgweb.cgi /srv/hg/cgi-bin/

Additionally we need “/srv/hg/cgi-bin/hgweb.config” (do not forget to sudo) with following lines:

[collections]
/srv/hg/ = /srv/hg/

In newer Mercurial installations you also need to edit “/srv/hg/cgi-bin/hgweb.cgi” in order to fix config parameter. Just change example config line with:

config = "/srv/hg/cgi-bin/hgweb.config"

Next thing to do is installing apache web server:

sudo apt-get install apache2
 Reading package lists... Done
 Building dependency tree       
 Reading state information... Done
 The following extra packages will be installed:
   apache2-mpm-worker apache2-utils apache2.2-bin apache2.2-common libapr1
   libaprutil1 libaprutil1-dbd-sqlite3 libaprutil1-ldap libssl0.9.8
 Suggested packages:
   apache2-doc apache2-suexec apache2-suexec-custom
 The following NEW packages will be installed:
   apache2 apache2-mpm-worker apache2-utils apache2.2-bin apache2.2-common
   libapr1 libaprutil1 libaprutil1-dbd-sqlite3 libaprutil1-ldap
 The following packages will be upgraded:
   libssl0.9.8
 1 upgraded, 9 newly installed, 0 to remove and 62 not upgraded.
 Need to get 6,343kB of archives.
 After this operation, 10.2MB of additional disk space will be used.
 Do you want to continue [Y/n]? Y
 Get:1 http://hr.archive.ubuntu.com/ubuntu/ lucid-updates/main libssl0.9.8 0.9.8k-7ubuntu8.1 [3,015kB]
 Get:2 http://hr.archive.ubuntu.com/ubuntu/ lucid/main libapr1 1.3.8-1build1 [116kB]
 Get:3 http://hr.archive.ubuntu.com/ubuntu/ lucid/main libaprutil1 1.3.9+dfsg-3build1 [85.4kB]
 Get:4 http://hr.archive.ubuntu.com/ubuntu/ lucid/main libaprutil1-dbd-sqlite3 1.3.9+dfsg-3build1 [27.1kB]
 Get:5 http://hr.archive.ubuntu.com/ubuntu/ lucid/main libaprutil1-ldap 1.3.9+dfsg-3build1 [25.1kB]
 Get:6 http://hr.archive.ubuntu.com/ubuntu/ lucid-updates/main apache2.2-bin 2.2.14-5ubuntu8.2 [2,622kB]
 Get:7 http://hr.archive.ubuntu.com/ubuntu/ lucid-updates/main apache2-utils 2.2.14-5ubuntu8.2 [159kB]
 Get:8 http://hr.archive.ubuntu.com/ubuntu/ lucid-updates/main apache2.2-common 2.2.14-5ubuntu8.2 [290kB]
 Get:9 http://hr.archive.ubuntu.com/ubuntu/ lucid-updates/main apache2-mpm-worker 2.2.14-5ubuntu8.2 [2,366B]
 Get:10 http://hr.archive.ubuntu.com/ubuntu/ lucid-updates/main apache2 2.2.14-5ubuntu8.2 [1,484B]
 Fetched 6,343kB in 14s (440kB/s)                                               
 Preconfiguring packages ...
 (Reading database ... 124530 files and directories currently installed.)
 Preparing to replace libssl0.9.8 0.9.8k-7ubuntu8 (using .../libssl0.9.8_0.9.8k-7ubuntu8.1_i386.deb) ...
 Unpacking replacement libssl0.9.8 ...
 Setting up libssl0.9.8 (0.9.8k-7ubuntu8.1) ...
 Processing triggers for libc-bin ...
 ldconfig deferred processing now taking place
 Selecting previously deselected package libapr1.
 (Reading database ... 124530 files and directories currently installed.)
 Unpacking libapr1 (from .../libapr1_1.3.8-1build1_i386.deb) ...
 Selecting previously deselected package libaprutil1.
 Unpacking libaprutil1 (from .../libaprutil1_1.3.9+dfsg-3build1_i386.deb) ...
 Selecting previously deselected package libaprutil1-dbd-sqlite3.
 Unpacking libaprutil1-dbd-sqlite3 (from .../libaprutil1-dbd-sqlite3_1.3.9+dfsg-3build1_i386.deb) ...
 Selecting previously deselected package libaprutil1-ldap.
 Unpacking libaprutil1-ldap (from .../libaprutil1-ldap_1.3.9+dfsg-3build1_i386.deb) ...
 Selecting previously deselected package apache2.2-bin.
 Unpacking apache2.2-bin (from .../apache2.2-bin_2.2.14-5ubuntu8.2_i386.deb) ...
 Selecting previously deselected package apache2-utils.
 Unpacking apache2-utils (from .../apache2-utils_2.2.14-5ubuntu8.2_i386.deb) ...
 Selecting previously deselected package apache2.2-common.
 Unpacking apache2.2-common (from .../apache2.2-common_2.2.14-5ubuntu8.2_i386.deb) ...
 Selecting previously deselected package apache2-mpm-worker.
 Unpacking apache2-mpm-worker (from .../apache2-mpm-worker_2.2.14-5ubuntu8.2_i386.deb) ...
 Selecting previously deselected package apache2.
 Unpacking apache2 (from .../apache2_2.2.14-5ubuntu8.2_i386.deb) ...
 Processing triggers for man-db ...
 Processing triggers for ufw ...
 Processing triggers for ureadahead ...
 ureadahead will be reprofiled on next reboot
 Setting up libapr1 (1.3.8-1build1) ...
 Setting up libaprutil1 (1.3.9+dfsg-3build1) ...
 Setting up libaprutil1-dbd-sqlite3 (1.3.9+dfsg-3build1) ...
 Setting up libaprutil1-ldap (1.3.9+dfsg-3build1) ...
 Setting up apache2.2-bin (2.2.14-5ubuntu8.2) ...
 Setting up apache2-utils (2.2.14-5ubuntu8.2) ...
 Setting up apache2.2-common (2.2.14-5ubuntu8.2) ...
 Enabling site default.
 Enabling module alias.
 Enabling module autoindex.
 Enabling module dir.
 Enabling module env.
 Enabling module mime.
 Enabling module negotiation.
 Enabling module setenvif.
 Enabling module status.
 Enabling module auth_basic.
 Enabling module deflate.
 Enabling module authz_default.
 Enabling module authz_user.
 Enabling module authz_groupfile.
 Enabling module authn_file.
 Enabling module authz_host.
 Enabling module reqtimeout.
 Setting up apache2-mpm-worker (2.2.14-5ubuntu8.2) ...
  * Starting web server apache2
 apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName
 Setting up apache2 (2.2.14-5ubuntu8.2) ...
 Processing triggers for libc-bin ...
 ldconfig deferred processing now taking place

We need new configuration for web interface of our repositories (“/etc/apache2/sites-available/hg”) with following content:

NameVirtualHost *
<VirtualHost *>
    ServerAdmin webmaster@localhost
    DocumentRoot /srv/hg/cgi-bin/
    <Directory "/srv/hg/cgi-bin/">
        SetHandler cgi-script
        AllowOverride None
        Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
        Order allow,deny
        Allow from all
    </Directory>
    ErrorLog /var/log/apache2/hg.log
    <Location />
        AuthType Basic
        AuthName "Mercurial"
        AuthUserFile  /srv/hg/.htpasswd
        Require valid-user
    </Location>
</VirtualHost>

Lines under Location are ones that ensure privacy of our repository.

We can now disable default web site and enable new one (and we can ignore all warnings) together with changes of ownership and rights:

sudo chown -R www-data /srv/hg

sudo chmod a+x /srv/hg/cgi-bin/hgweb.cgi

sudo a2dissite default
 Site default disabled.
 Run '/etc/init.d/apache2 reload' to activate new configuration!

sudo a2ensite hg
 Enabling site hg.
 Run '/etc/init.d/apache2 reload' to activate new configuration!

sudo /etc/init.d/apache2 reload
  * Reloading web server config apache2
 apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName
 [warn] NameVirtualHost *:80 has no VirtualHosts

If we try to access “http://localhost” now, we should be greeting with password prompt.

Thing that we are missing is “/srv/hg/.htpasswd” file. We can create all users we need with htpasswd command:

sudo htpasswd -c /srv/hg/.htpasswd testuser
 New password: 
 Re-type new password: 
 Adding password for user testuser

All further users are then added with slightly modified command (notice that -c is missing):

sudo htpasswd /srv/hg/.htpasswd testuser2
 New password: 
 Re-type new password: 
 Adding password for user testuser2

After creating repository itself

sudo hg init /srv/hg/TestRepo

we must also create “/srv/hg/TestRepo/.hg/hgrc” file with following content:

[web]
push_ssl=false
allow_push=testuser

This allows for using http (instead of https) and allows access to our “testuser” (if there are no restricturons, just put * for user name). Very last step in setup is actually allowing apache to use our repository for writing. Easiest thing to do here is just transferring ownership to it:

sudo chown -R www-data /srv/hg/TestRepo

Finally we can use “http://192.168.0.2/hgweb.cgi/TestRepo/” for pushing and pulling data from any Mercurial client.

P.S. To use https, check second post of a series.