MySensors on Raspberry Pi with nRF24L01+

Recently I’ve learned that nRF24L01+ radio module can be connected directly to Raspberry Pi via GPIO pins in order for this Raspberry Pi to be used as MySensors library “gateway”.

I’ve successfully installed MySensors on Raspberry Pi using official instruction, but one thing wasn’t exactly clear – how do I specify channel for nRF24L01+? Without specifying proper channel, the “gateway” won’t be able to see other nodes.

It turned out to be quite simple actually – before doing make / sudo make install one has to run configure with these parameters:

./configure --my-transport=nrf24 --my-rf24-channel=123

The 123 is the number of channel to be used.

P.S. Remember to enable SPI via raspi-config.


DSLR focus control with gphoto2

If you read the documentation on gphoto2 regarding the focus control (“manual” focus as they call it) it mentions that focus control only works while liveview mode is on, and that seemed to be sufficient for Canon, but it turned out that for Nikon cameras there was more to it than just liveview.

First the necessary disclaimer though: I’ve only tried the Nikon D5100 here and Canon 550D and 600D, so YMMV.

But let’s start with liveview (or preview) mode itself first – this one is controlled by “/main/actions/viewfinder” setting in both Nikon and Canon. Continue reading

Spring MVC PreAuthorize and private/final methods

Spring MVC has nice feature for adding security controls to Controller methods via @PreAuthorize annotation, but there’s an interesting problem that might occur when those methods are mistakenly marked as private or final.

Spring uses CGLib proxy to add calls to authorization logic declared in @PreAuthorize before calling actual controller method, but CGLib fails to process private or final methods, producing error like this in console:

2016-11-28 17:19:14.186 INFO 97079 --- [ main] o.s.aop.framework.CglibAopProxy : Unable to proxy method [public final java.util.Map com.package.controller.MyController.someMethod(javax.servlet.http.HttpServletResponse)] because it is final: All calls to this method via a proxy will NOT be routed to the target instance.

Well, so far so good – nothing special happens, all is more/less expected.

The problem though is that among most console output produced by Spring MVC yet another INFO log line rarely gets noticed. So what actually happens with those private/final methods of SpringMVC controller? Here weird stuff begins.

Say you’re writing a controller method that has a @PreAuthorize added to it, and accidentally copy-paste in a return type with final predicate before it, thus making your method final. You miss the log line in console because it’s just INFO among many other similar lines. And then… all autowired or otherwise injected fields of a controller are somehow null when calling only that particular method. But we know that in Spring MVC every controller is a singleton, so how is this even possible?

The issue appears to be that we’re actually calling methods on a CGLib proxy, that can’t pass them down to actual controller class instance. But proxy itself looks just like the controller class instance, except all fields that were supposed to be injected by Spring are null. A weird looking symptom which does not intuitively lead us to the cause of the problem.

But once one encounters this issue, I bet one remembers well next time what it is a symptom of.

P.S. I’ve encountered this issue with final method, but seems other people had same issue with private methods.

Posted in MVC

Installing Cisco AnyConnect VPN on Ubuntu 16.04

Oracle, Unix and the world at large

I was struggling setting up a new VPN to connect to my servers at the office as was failing

# ./ 
Installing Cisco AnyConnect Secure Mobility Client...
Extracting installation files to /tmp/vpn.0Zgby3/vpninst625702875.tgz...
Unarchiving installation files to /tmp/vpn.0Zgby3...
Starting Cisco AnyConnect Secure Mobility Client Agent...
Failed to start vpnagentd.service: Unit vpnagentd.service not found.

I found a bunch of articles on the internet saying that this was due to missing libraries so started with the first batch of recommendations…

# apt install -y lib32z1 lib32ncurses5

This still didn’t work.

So I tried the next one, which was to also install the network-manager-openconnect package and reload the daemons

# apt install network-manager-openconnect

# systemctl daemon-reload


# ./ Installing Cisco AnyConnect Secure Mobility Client... Removing previous installation... mv: cannot stat '/opt/cisco/vpn/*.log': No such file or directory Extracting installation files to /tmp/vpn.yUyv15/vpninst922924093.tgz... Unarchiving installation files to /tmp/vpn.yUyv15... Starting Cisco AnyConnect Secure Mobility Client…

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Docker with xHyve on Mac – access stopped container files

I had a problem with Docker on Mac OS X – nowadays it comes with xHyve VM instead of VirtualBox, and the VM uses cow2 format for it’s disk image, so it wasn’t clear how can one access files in /var/lib/docker on the VM.

Why does one even have to access the files? Well, there can be number of reasons. In my case it was Mosquitto container where Mosquitto MQTT broker is a PID 1 process, and when it’s not running – the container isn’t running either. So while changing a config file for Mosquitto I had to do some experimenting, which caused Mosquitto to fail on startup due to bad configuration.

As you can probably guess, it wasn’t possible to fix Mosquitto config otherwise than via /var/lib/docker, because I could not start the container anymore. So it was either this, or start from scratch with new container.

Anyhow, I did not find any working way to mount cow2 image, but I have found a solution on Docker forums to get terminal into xHyve VM when docker was started:

screen ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/tty

The username is root with no password.

Thanks to Rohinton Kazak for posting that answer.

S3 mock endpoint

This post is incomplete and more of a note for oneself – be advices.

Here’s the way I’ve been trying to mock S3 for local testing, using Ruby FakeS3 app:

In order to make S3 endpoints point to localhost I had to create custom regions override XML and debug AWS Java SDK to figure out it’s format.

I also have to pass path of that file as system property in order for AWS Java SDK to use it:


I could not find a way to disable SSL (switch from HTTPS to HTTP) in Amason AWS SDK without modifying the code of apps (which I can’t do – otherwise I’d just set endpoint manually), thus I ran FakeS3 configured with some random certificates, and pass disableCertChecking property. Also RegionUtils.disableRemote property is included to reduce number of helper calls to actual AWS.

Still, I did not find any possibility to make AWS SDK use path style access – thus bucket name is prepended to my localhost:9000 URL configured in .aws-regions-override.xml file, and thus I still had to add some entries to /etc/hosts to make it point to localhost. But at least I did not break any real AWS URLs with that.

UPD: Also, in order for endpoint URI to change one has to call setRegion in code at least once. This works for Spring wrapper over AWS S3 SDK, but may not work for custom code, that instantiates S3 client without setting region.

The content of .aws-regions-override.xml is this (the “whatever” tag can have any name):