Well, I finally finished off the initial test where I can run an app on my phone or tablet anywhere, click something and it fetches a random image from my PC at home.
The updated sources can be found HERE.
Author Archive: csnorwood
Android load and scale a bitmap
Before I move onto the application itself, I was testing out loading in and scaling a bitmap, when I came across a very annoying Out Of Memory error. The image I was testing was ~4000 x ~3500 pixels and the test was running in the android emulator.
Initially, after using the android logging I found the image wasn’t being scaled and I couldn’t load it in and then scale it. And I didn’t want to up the memory on the emulator.
I know I needed an AsyncTask to do this, plus I needed to figure out how to implement them anyway as I’ve used Async’s in GWT extensively.
Eventually after a bit of digging around I eventually found out how to get everything done and it doesn’t waste any memory.
After this has been done, I want to figure out how to display a large image with a zoom option.
See below for the code…
[snippet id=”15″]
Notes on encryption and security
An important part of communicating over the internet is having some security in place. For my own project this will have the server setup so that it only accepts connections from known devices. It will also encrypt data before it is sent and decrypted when the server receives it.
Encryption:
There are many ways to encrypt data:
- Inverting all bits in the data being sent. This was handy in the very old days of 8-bit cpu’s to hide data in memory to stop people spying on code and data in memory.
- Apply a key to the data. A good method of securing data which could be a password protected to unlock on the receiving side. However, it doesn’t take long for key to be found.
- Apply a key and add salt. Skewing the data like in method 2 is good, but when adding salt, it makes it almost impossible to decrypt without having access to the code.
I’ll be using a system which adds a key and pours in some salt. Now how this is done is using a key to skew the data, and then by splitting the bits of the data up randomly and adding random bits in between, the bitstream will be larger but impossible to decrypt. 2 things will be needed to decrypt the data, the code itself and the key.
Security:
Most of the time, security means logging in with a username and password. The final project will require the device to first log in which will have a timeout feature on it. This is just like session handling in GWT for the web. The login data will still be sent encrypted.
Fortunately, I’ve worked with encryption since 8-bit cpu’s, so this shouldn’t pose a problem for me at all. I’ll have some generic classes written that can be used on both client and server for de/encryption. Apart from the usual login credentials, the client and server will have some hardcoded (still encrypted) transport keys, which can be updated when software is updated. The server can also handle software updates which includes data security updates. This will mean that software that isn’t updated will no-longer work unless it gets an update.
Obviously, this means a lot of boilerplate code, but it will be worth it. And hiding it from a web interface by using TCP, it will be more secure.
One last thing to note about security is server/port attacks. On each socket connection, the server will log the number of requests from an IP address. It it gets too many then it will ignore that IP address for 30 minutes or another set time. This will reduce DoS attacks on the servers port/s.
When the application is transferring data back and forth to the server, most of the communication will be done in one connection. Too many connection attempts will simply be denied.
TCP home server test client
With the previous post setup I’ve written a very basic example of how to test the server. At the moment, there are no back and forth communications, just a simple send of a 4 byte header.
Run the server program first, and then run the test. These can actually be run in the same order from Eclipse.
The good news is, this also works over the internet. The ‘Global’ in the code hold a string of my web server address and also the port that my router has open.
So, all working as expected.
[snippet id=”11″]
The output from the server will be:
WLGfx Home Server - Starting up Shutdown hook attached TCP Server thread started... TCP Incoming socket handler Got header: HEAD
Java server test 1 [UPDATED]
My first test for Java as a console daemon. There’s not much here at the moment and the project is in Eclipse IDE.
From Eclipse, right click on the project and select export and then export as a runnable jar. Then in the terminal just type:
java -jar myexportedjar.jar
The JVM will continue to run as long as there are non daemon threads still running as in the below code. Also note that the hook handler allows catching of CTRL+C and other errors.
UPDATE:
I’ve now added the actually tcp server code which has a timeout on the server socket to allow for the thread to shut down safely. And a thread to handle each incoming connection.
[snippet id=”9″]
(I’m currently not well at the moment but I’m plodding on with some studies.)
Testing out TCP server over the web (my IoT stuff)
So I have this idea where I can take photos on my phone or save images from the web and then send them directly to my PC.
I’m currently using a Sky router in which I have enabled a port redirect to my PC. That’s all working. And I’ve got an external web address which re-routes to my PC also. That’s all working as I can host a website on my PC and access from outside.
The first pitfall was I started a console application in Qt to be a TCP server, but, deploying Qt applications to anywhere can be a huge pain in the butt.
So now I’ve decided to pick between a Java server or a C/C++ server. The issue I will have with a standard C/C++ server is image handling when it comes to working with them in the future, whereas Java has built in Bitmap libraries. Although I could add a 3rd party library to get around this, Java has lots of other libraries.
The other issue is speed. C/C++ has raw speed and that it. But because its a server, speed shouldn’t really be an issue for most things.
I’ve already successfully got the address of my PC over the internet and in the past had a basic TCP communication test working. This time it’s for real.
Okay, I’ll try out a Java project and see how it goes.
My current stack development
Linux headless server
Once everything is deployed, the linux distribution will have the desktop stripped and left to run headless.
UDP server
General broadcasting of the servers location on the network along with the current time 4 times a second as the end point devices have no internet connection and no time.
TCP server
Used for communication between the server and devices. Content is managed through TCP instead of FTP as it is more secure.
C/C++
The software manages the servers UDP and TCP communication and also handles other commands when necessary from the web server. UDP is used for streaming DVB-T data across the network. Continually running daemon in linux.
Apache Tomcat 7
The Java based web server.
Google Web Toolkit (GWT)
The web framework for both front and back end web server. Used to manage user logins and session authentication. Manages the devices deployment. Mainly in Java. The web server is a large project.
Android Studio and Qt 5.7
Used to write the software for the end point devices.
GWT IFrame DialogBox example
In GWT, being able to load external pages comes in extremely handy when you want to pass on a lot of the design work to another team. This can be achieved by loading an external page elsewhere on the web server into an IFrame and wrapping the existing widgets.
Most GWT widgets can be wrapped, buttons, DIV’s, check boxes, etc.
Unfortunately I’ve not found a way of wrapping a HTML table. The only way around that is to have the table on the existing HTML page in a DIV, clear the DIV and programmatically add the new table which can be styled using the pages CSS. However, another problem arises with CSS which is you cannot use table header and footers CSS.
Anyway, below is a quick and simple way of loading an external page into a DialogBox using an IFrame and wrapping the buttons. You might notice that I’ve cleared the DialogBox CSS style.
[snippet id=”7″]
More stuff August 2016
Very rarely do I update my website. That’s because I work all day and get very little time at home to actually work on my own stuff. However, I can update on a few things.
- My knowledge of Java has improved vastly that now it’s rare I use google to solve my problems for me. Personally I wouldn’t use it for my own projects, except for the web server I will eventually start work on. Lots of people still say that there is now speed difference between Java and C++, but there is when you are running constant loops in code.
- Google Web Toolkit or GWT. I’ve used this extensively for over a year now and I do actually like it more and more as the months go by. More recently, I’ve figured out how to manage logged in users and session management. I usually have a tomcat user assigned in Linux which the back-end can use, away from the web server to do it’s storage and data crunching. LibGDX also uses GWT and with the experience I’ve had, I’ve got a few things up my sleeve.
- Qt… What more can I say. Every new version that comes out it gets more and more support. Recently I have figured how to call Java functions from Qt’s C++ on the Android platform which can be used for lots of missing features from native.
- I still haven’t got round to playing around more with Python which I really want to do. As a scripting language it looks great. And for it’s mega bloated support for everything and anything (API’s etc), there’s no end to what it can do. Ideally once I get to getting good at it I want to be able to quickly prototype stuff to be redone in C++ or Java.
For the time being that’s it.
My plan for the very near future is to get some more stuff done on my website using the GWT back-end.
Work ‘Smarter’ not ‘Harder’ as a programmer
I’ve just come across a question posted on Quora which I tend to peruse through daily out of interest, and I can across the question:
What are some uncommon ways to work smarter instead of harder?
One person gave a list of answers which were very interesting and tickled my fancy. In short before I explain my personal experiences, here they are:
- Learn to say “No.”
- Sleep at least 8-9 hours
- Don’t be a night Owl. Work in between 5am-10pm not from 10pm-5am
- Stop multitasking.
- Take more breaks: respect your natural attention spans
- Spend time in nature
- Move around and work in blocks
- Limit your to-do list
- Measure your results, not your time
- Build “getting ready to work” routines
- Track what you’re wasting time on
- Exercise daily even if you think you have no time
- Believe that you can do it
And being employed now for a while as a professional programmer after a lifetime of being a hobbyist here’s my thoughts on those points…
Learn to say “No.”
This is probably one of my failings because I’m quick to tell others they ought to ‘learn to say no’, it’s hard to actually do it yourself. There are times when I need some wind down time and I’m needed elsewhere at other times which doesn’t help me get that proper chill time at the weekends especially.
Sleep at least 8-9 hours
On average I get about 7 hours. Usually at the weekends, I fight the urge to sleep during the day in order to keep my sleep pattern regular.
Don’t be a night Owl. Work in between 5am-10pm not from 10pm-5am
Going from a hobbyist programmer to an employed programmer has seen a huge change in the hours I code. Years ago I would work through the night until the sun came back up. Now, I get home and just read stuff online and do no coding in my spare time.
Stop multitasking.
A programmer needs to focus on the project they are working on. Ask them to do something that doesn’t relate will throw them miles off track. Just just distractions can take them right out of the zone just for saying ‘hi’ to them.
Take more breaks: respect your natural attention spans
I’ve found that taking breaks regular helps immensely. I used to often find myself getting stuck at points and clock watching before I left the screen. That was counter productive to progress. Now when I get so far and need to give my thoughts and brain a rest, I get up and go for a quick wonder around.
Spend time in nature
Oh… Errr… Maybe I’ll plan for this one.
Move around and work in blocks
With working on large projects, I now tend to break it up into many smaller chunks and work through each piece.
Limit your to-do list
Just like the above, but when it comes to planning, I never set too many targets for the next days worth of coding. It’s usually just about two things I plan to get through and if I do manage more then it makes me feel better for it.
Measure your results, not your time
This is learning patience too. Working on large project is extremely time consuming. As I mentioned above, by breaking the project down into many smaller parts, it makes it easier to see progress being made.
Build “getting ready to work” routines
I do… I get to work… Make a brew… Read some interesting stuff for at least half an hour… Then within an hour after work starts, I am getting into the zone. Sometimes I get quickly zapped out of it when other members of staff start having loud conversations.
Track what you’re wasting time on
This is definitely another matter that I’ve learnt over the past couple of years. There’s been times when I’ve tried out something and dumped all the code only to start again a few times. Now I make small unit tests to make sure I know what I am doing before it gets implemented into the project. So much time can be wasted by having to backtrack a shed load of junk code.
Exercise daily even if you think you have no time
I don’t have time… I really need to but I haven’t yet got around to it. I will do as soon as I possibly can.
Believe that you can do it
This is not an issue with me. When I first started at the position I’m in now, I was thrown in the deep end and I had to create my own paddles and floats. Nowadays, it seems that after a few unit tests per awkward section, anything is possible.
…
As you can see, I’m not perfect, but I still very much enjoy day to day coding…