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Using custom cache object with AngularJS $http


At work, I’ve been bitten by the way AngularJS handles cache by default when using $https service. This post will show a simple way to improve cache handling with $http service.

The service I’m working on must perform the followings tasks:

  • retrieve data from a remote server.
  • save data to the same server.
  • retrieve the saved data and some extra information generated by the server to update a UI

At first, I’ve naively used $http.get cache parameter to enable or disable caching using a sequence like:

  1. $http.get(url, {cache: true} )
  2. $
  3. $http.get(url, {cache: false})
  4. $http.get(url, {cache: true})

Let’s say the calls above use the following data:

  1. $http.get(url, {cache: true}) returns “foo”
  2. $ stores “bar”
  3. $http.get(url, {cache: false}) returns “bar”

I expected the next call $http.get(url, {cache: false}) to return “bar”. But no, I got “foo”, i.e. the obsolete data.

Turns out that cache object is completely left alone when {cache: false} is passed to $http.get.

ok. Fair enough. But this means that the value of the cache parameter should not change for a given URL. The default cache provided by $https cannot be cleared. (Well, actually, you can clear the cache under AngularJS’s hood, but that will probably not improve the readability of your code).

The naive approach does not work. Let’s try another solution by using a custom cache object as suggested by AngularJS doc. This cache object should be created by $cacheFactory service.

This cache object can then be passed to $http.get to be used as cache. When needed, the cache can be cleared. In the example above, the cache must be cleared after saving some data to the remote service.

There’s 2 possibilities to clear a cache:

  • Completely flush the cache using removeAll() function.
  • Clear the cache for the specific URL using remove(key) function. The only hitch is that the “key” used by $http is not documented.

So, we have to use the first solution and create a cache object for each API entry point:

angular.module('app').factory('myService', function ($http, $cacheFactory) {
  var myFooUrl = '/foo-rest-service';
  // create cache object. The cache id must be unique
  var fooCache = $cacheFactory(''); 
  function getFooData () {
    return $http.get( myFooUrl, { cache: fooCache });
  function saveFooData(data) {
    return $ myFooUrl, { cache: fooCache }).then(function() {
      myCache.removeAll() ;

The code above ensures that:

  • cached data for foo service is always consistent
  • http get requests are not sent more than necessary

This simple approach has the following limitations:

  • cache is not refreshed if the data on the server are updated by another client
  • cache is flushed when only the browser page is reloaded

If you need more a more advance cache mechanism, you may want to check jmdobry’s angular cache project

All the best


How to automount optical media on Debian Linux for Kodi


This problem has been bugging me for a while: how to setup my Kodi based home cinema to automatically mount an optical media ?

Turns out the solution is quite simple, now that Debian has switched for systemd. Just add the following line to /etc/fstab:

/dev/sr0 /media/bluray auto defaults,nofail,x-systemd.automount 0 2


  • /dev/sr0 is the device file. You can also use one of the symbolic links setup by udev in /dev/disk/by-id
  • /media/bluray is the mount point. You can choose another mount point
  • nofail is required to avoid failure report when booting without a disc in the optical drive
  • x-systemd.automount is the option to configure systemd to automatically mount the inserted disc

Do not specify noauto: this would prevent systemd to automatically mount a disc, which defeats the purpose.

To test you setup:

  • Run the command journalctl -x -f in a terminal to check what is going on with systemd
  • Reload systemd configuration with sudo systemctl daemon-reload.
  • load a disc in your optical drive

Then, journalctl should show something like:

Sept. 27 16:07:01 frodo systemd[1]: Mounted /media/bluray.

And that’s it. No need to have obsolete packages like udisk-glue or autofs.

Last but not least: this blog is moderated, please do not waste your time (and mine) posting rants about systemd.

Edited: I’ve later realised that the instruction contained in this post works only if the mount point is opened, e.g. a program opens the mount point directory to check its content. Unfortunately, it’s not enough for kodi: once a media is plugged, systemd makes sure that the plugged device is ready to be mounted, but kodi does not know this. See this Automount usb devices with systemd for a solution.

All the best.

Major bug fix for cme update copyright command


Previous version of libconfig-model-dpkg-perl had 2 bugs related to copyright update command :

  • Too many directory paragraphs (like src/foo/*) were removed during update.
  • Some file paragraph were not merged, leading to needless paragraphs in debian/copyright file. This bug is less severe as no information is lost

Version 2.067 of libconfig-model-dpkg-perl fixes both issues. This version is available in unstable.

To use cme update dpkg-copyright command, the following packages are required:

All the best

Improving update of existing debian/copyright file


One of my last blog introduced the new cme update dpkg-copyright command and explained how to use this command to create a debian/copyright file from scratch.

We will see in this blog how cme update dpkg-copyright command can also be used if a debian/copyright file already exists.

During the lifetime of a package, creating a new debian/copyright copyright file should only happen once. When updating a package to a new upstream version, the content of the copyright file should be modified to reflect upstream changes by:

  • adding or removing file entries
  • updating © years or owners
  • updating licenses

cme update dpkg-copyright can be run with an existing debian/copyright file: the information extracted by licensecheck are merged in debian/copyright. Unfortunately, this merge may bring back the errors coming from licensecheck that you’ve cleaned up manually last time.

This last part is not optimal as the manual clean up must be repeated after cme update dpkg-copyright is run.

Here’s a way to avoid the last problem: cme update dpkg-copyright supports a way to modify the content of debian/copyright after the merge: the optional file debian/fix.scanned.copyright contains instructions to tweak the content of debian/copyright. (See Config::Model::Dpkg::Copyright man page for more details)

You may remember that Config::Model handles all configuration information as a tree. The information contained in the copyright file is also stored in a tree structure. debian/fix.scanned.copyright contains instructions to navigate this tree and modify the content of the tree.

Imagine that there’s a robot (or a monkey) in that configuration tree. Each instruction tells the robot either to move in the tree or to perform an operation.

The most useful instructions for debian/fix.scanned.copyright are:

  • ! to move to the root of the tree
  • = to assign a value , e.g: short_name=MIT or Copyright="2014, FooBar" (use double quotes when the value white space or other fancy characters).
  • .= to append to a value, e.g Copyright.=" Appended info."
  • =~ to apply a substitution with a Perl regexp, e.g. Copyright=~"/©\s*//g"
  • : to move a Files element, e.g. Files:"foo/baz.c"
  • :~ to remove a Files element, e.g. Files:~"bogus.c"


  • Comments with # or // must begin at the beginning of the line
  • Instructions are separated by space(s) or new lines

Let’s see a commented example:

# go to the root of the tree (with '!')
# and remove a bogus Files entry (with ":~")
! Files:~"foo/bogus.c"

// go to a Files entry and append (operator '.=') some info to © owner
! Files:"foo/bar.h"
  Copyright.=" Appended info."

# go back to tree root and assign © info
! Files:"foo/baz.c" Copyright="2014, FooBar"

# add a global license and a file entry missed by licensecheck
# global license must be set before using it in Files entry
# note: MIT text license is provided by cme
! License=MIT
! Files:"3rdparty/missed.c" Copyright="2005 FooBar" License short_name=MIT

Other possible instructions for this file are described in Config::Model::Loader doc.

The number of instructions depends on the accuracy of licencecheck command. Hopefully, this number can be reduced by improving licensecheck.

Last but not least, the following packages are required:

You may want to install also libconfig-model-tkui-perl to update the copyright file with cme GUI.

In summary, the command cme updated dpkg-copyright associated with instructions stored in debian/fix.scanned.copyright enable Debian packagers to update with less effort debian/copyright file when updating a package.

All the best

The #newinjessie game: automatic configuration upgrade and other stuff in Debian/Jessie

Here are my contribution for the #newinjessie game, i.e. what new stuff I’ve contributed to the Jessie release of Debian.

See you in 2 years for Stretch release

All the best

Improving creation of debian copyright file


In my opinion, creating and maintaining Debian copyright file is the most boring task required to create a Debian package. Unfortunately, this file is also one of the most important of a package: it specifies some legal aspect regarding the use of the software.

Debian copyright file is scrutinized by ftp masters gatekeepers when accepting a new package in Debian project: this file must accurately describe the copyright and licenses of all files of a source package, preferably using a specific syntax. (Kudos to the ftp-masters team: reading copyright files must be even more boring than writing them).

The content of the copyright file must reflect accurately the license of all files. This license is often specified in the comments of a source files. The licensecheck command is able to scan sources files and reports the copyright and licenses declared in there. But it does not summarize this information: a copyright line is generated for each file of a package.

licensecheck2dep5 (provided by cdbs package as /usr/lib/cdbs/licensecheck2dep5) does better: the output of licensecheck is consolidated and translated in Debian copyright format. The result is better, but must be heavily edited to be reviewable by ftp-masters team.

The new update subcommand of cme (available with libconfig-model-dpkg-perl 2.061 currently in experimental) goes further than licensecheck2deb:

  • copyright are coalesced when possible (i.e. 2001,2002,2003-2005 is changed to 2001-2005)
  • file entries same copyright owner and license are grouped, group of files may be represented with a wild card (‘*’)
  • license text is filled with actual text for the most popular licenses

For instance, here’s the (slightly edited) output of cme run for pan package starting without debian/copyright file:

$ cme update dpkg-copyright
Adding dummy license text for license public-domain 
for path pan/general/sorted-vector.h
Adding dummy license text for license BSD-2-clause 
for path pan/usenet-utils/MersenneTwister.h
$ cat debian/copyright

Files: *
Copyright: 1994-2001, Frank Pilhofer. The author may
License: GPL-2+

Files: pan/*
Copyright: 2002-2007, Charles Kerr 
License: GPL-2

Files: pan/data/
Copyright: 2011, Heinrich Müller 
  2002-2006, Charles Kerr 
License: GPL-2

Files: pan/general/
Copyright: 2000, 2001, Ximian, Inc
License: LGPL-2

Files: pan/general/locking.h
Copyright: 2007, Calin Culianu 
  2002-2007, Charles Kerr 
License: LGPL-2+

Files: pan/general/sorted-vector.h
Copyright: 2002, Martin Holzherr (
License: public-domain
 Please fill license public-domain from header
 of pan/general/sorted-vector.h

[ about 100 more lines including license text for Zlib and several 
  GPL licenses ]

This is a good start, but some modifications must be applied to get a correct license file:

  • add missing upstream information (Upstream-Name, Upstream-Contact and Source items)
  • remove irrelevant text from some copyright owner (e.g. remove “The author may” from Files: * entry).
  • add some missing license text (e.g. include text from sorted-vector.h comments to specify upstream author’s version of public-domain)

These modifications can be done:

  • directly after update by running cme update dpkg-copyright --edit
  • after update by running cme edit dpkg-copyright
  • with your favorite editor

This post has mentioned creation of Debian copyright file, but does not address the problem of updating an existing copyright file when packaging a new version of a software. This will be the subject of a next post.

I hope this new feature of cme will save hours of work for Debian packagers. As usual comments and suggestions are welcome.

See also Updating debian copyright file with cme wiki page on github

Last but not least, the following packages are required:

You may want to install also libconfig-model-tkui-perl to update the copyright file with cme GUI.

All the best



  • Removed -quiet option from cme example. This option is not recommended to learn cme update.
  • Added link to github wiki page

Performance improvement for ‘cme check dpkg’


Thanks to Devel::NYTProf, I’ve realized that Module::CoreList was used in a not optimal way (to say the least) in Config::Model::Dpkg::Dependency when checking the dependency between Perl packages. (Note that only Perl packages with many dependencies were affected by this lack of performance)

After a rework, the performance are much better. Here’s an example comparing check time before and after the modification of libconfig-model-dpkg-perl.

With libconfig-model-dpkg-perl 2.059:
$ time cme check dpkg
Using Dpkg
loading data
Reading package lists... Done
Building dependency tree
Reading state information... Done
checking data
check done

real 0m10.235s
user 0m10.136s
sys 0m0.088s

With libconfig-model-dpkg-perl 2.060:
$ time cme check dpkg
Using Dpkg
loading data
Reading package lists... Done
Building dependency tree
Reading state information... Done
checking data
check done

real 0m1.565s
user 0m1.468s
sys 0m0.092s


All in all, a 8x performance improvement on the dependency check.

Note that, due to the freeze, the new version of libconfig-model-dpkg-perl is available only in experimental.

All the best