Wallpaper Strategy for Meilix Generator

We were first hosting the wallpaper uploaded by user on the Heroku server which was downloaded by the Travis CI which was previous solution for sending wallpaper to the Travis CI, but the problem was that wallpaper was downloaded only when build started building the ISO.

Downloading the hosted wallpaper was not a problem but the problem in that method was that the wallpaper hosted can be changed if another user also starts the build using Meilix Generator and uploads the wallpaper which will replace the previous wallpaper so simultaneous builds was not possible in previous method and resulted in conflicts.

So we thought of a sending the wallpaper to the Travis CI server for that we used base64 to and encoded it to a string using this.

with open(filename,'rb') as f:
    os.environ["Wallpaper"] = str(base64.b64encode(f.read()))[1:]

 

After uploading we send it as a variable to Travis CI and decode it. We will receive a binary file after decoding now we need to detect the mime type of the file and rename it accordingly before applying for that we use a script like this.

#renaming wallpaper according to extension png or jpg
for f in wallpaper; do
    type=$( file "$f" | grep -oP '\w+(?= image data)' )
    case $type in  
        PNG)  newext=png ;;
        JPEG) newext=jpg ;;
        *)    echo "??? what is this: $f"; continue ;;
    esac
    mv "$f" "${f%.*}.$newext"
done

 

After fixing the wallpaper extension we can apply it using the themes by replacing it with the theme wallpaper.

Resources

Base64 python documentation

How to Send a Script as Variable to the Meilix ISO with Travis and Meilix Generator

We wanted to add more features to Melix Generator web app to be able to customize Meilix ISO with more features so we thought of sending every customization we want to apply as a different variable and then use the scripts from Meilix Generator repo to generate ISO but that idea was bad as many variables are to be made and need to be maintained on both Heroku and Travis CI and keep growing with addition of features to web app.

So we thought of a better idea of creating a combined script with web app for each feature to be applied to ISO and send it as a variable to Travis CI.

Now another problem was how to send script as a variable after generating it as json do not support special characters inside the script. We tried escaping the special characters and the data was successfully sent to Travis CI and was shown in config but when setting that variable as an environment variable in Travis CI the whole value of variable was not taken as we had spaces in the script.

So to eliminate that problem we encoded the variable in the app as base64 and sent it to Travis CI and used it using following code.

To generate the variable from script.

with open('travis_script_1.sh','rb') as f:
    os.environ["TRAVIS_SCRIPT"] = str(base64.b64encode(f.read()))[1:]

 

For this we have to import base64 module and open the script generated in binary mode and using base64 we encode the script and using Travis CI API we send variable as script to the Travis CI to build the ISO with script in chroot we were also required to make changes in Meilix to be able to decode the script and then copy it into chroot during the ISO build.

sudo su <<EOF
echo "$TRAVIS_SCRIPT" > edit/meilix-generator.sh
mv browser.sh edit/browser.sh
EOF 

 

Using script inside chroot.

chmod +x meilix-generator.sh browser.sh
echo "$(<meilix-generator.sh)" #to test the file
./browser.sh
rm browser.sh

Resources

Base64 python documentation from docs.python.org

Base64 bash tutorial from scottlinux.com by Scott Miller

su in a script from unix.stackexchange.com answered by Ankit

Encoding and Saving Images as Strings in Preferences in SUSI Android App

In this blog post, I’ll be telling about how to store images in preferences by encoding them into Strings and also how to retrieve them back. Many a times, you need to store an image in preferences for various purposes and then need to retrieve it back when required. In SUSI Android App, we need to store an image in preference to set the chat background. We just simply select image from gallery, convert image to a byte array, then do a Base 64 encoding to string, store it in preferences and later decode it and set the chat background.

Base64 Encoding-Decoding in Java

You may already know what Base 64 is but still here is a link to Wikipedia article explaining it. So, how to do a Base64 encoding-decoding in java? For that java has a class with all such methods already present. https://docs.oracle.com/javase/8/docs/api/java/util/Base64.html

According to the docs:

This class consists exclusively of static methods for obtaining encoders and decoders for the Base64 encoding scheme. The implementation of this class supports the following types of Base64 as specified in RFC 4648 and RFC 2045.

  • Basic
  • URL and Filename safe
  • MIME

So, you may just use Base64.encode to encode a byte array and Base64.decode to decode a byte array.

Implementation

1. Selecting image from gallery

    

Start Image Picker Intent and pick an image from gallery. After selecting you may also start a Crop Intent to crop image also. After selecting and cropping image, you will get a URI of the image.

override fun openImagePickerActivity() {
   val i = Intent(Intent.ACTION_PICK, android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI)
   startActivityForResult(i, SELECT_PICTURE)
}
val thePic = data.extras.getParcelable<Bitmap>("data")
val encodedImage = ImageUtils.Companion.cropImage(thePic)
chatPresenter.cropPicture(encodedImage)

2. Getting image from the URI using inputstream

Next step is to get the image from file using URI from the previous step and InputStream class and store it in a BitMap variable.

val imageStream: InputStream = context.contentResolver.openInputStream(selectedImageUri)
   val selectedImage: Bitmap
   val filePathColumn = arrayOf(MediaStore.Images.Media.DATA)
   val cursor = context.contentResolver.query(getImageUrl(context.applicationContext, selectedImageUri), filePathColumn, null, null, null)
   cursor?.moveToFirst()
   selectedImage = BitmapFactory.decodeStream(imageStream)

3. Converting the bitmap to ByteArray

Now, just convert the Bitmap thus obtained to a ByteArray using below code.

val baos = ByteArrayOutputStream()
   selectedImage.compress(Bitmap.CompressFormat.JPEG, 100, baos)
   val b = baos.toByteArray()

4. Base64 encode the ByteArray and store in preference

Encode the the byte array obtained in last step to a String and store it in preferences.

 val encodedImage = Base64.encodeToString(b, Base64.DEFAULT)
//now you have a string. You can store it in preferences

5. Decoding the String to image

Now whenever you want, you can just decode the stored Base64 encoded string to a byte array and then from byte array to a bitmap and use wherever you want.

fun decodeImage(context: Context, previouslyChatImage: String): Drawable {
   val b = Base64.decode(previouslyChatImage, Base64.DEFAULT)
   val bitmap = BitmapFactory.decodeByteArray(b, 0, b.size)
   return BitmapDrawable(context.resources, bitmap)
}

Summary

So, the main aim of this blog was to give an idea about how can you store images in preferences. There is no way to store them directly. So, you have to convert them to String by encoding them in Base64 format and then decoding it to use it. You also have other ways to store images like storing it in database etc but this one is simpler and fast.

Resources

  1. Stackoverflow answer to “How to save image as String” https://stackoverflow.com/questions/31502566/save-image-as-string-with-sharedpreferences
  2. Other Stackoverflow answer about “Saving Images in preferences” https://stackoverflow.com/questions/18072448/how-to-save-image-in-shared-preference-in-android-shared-preference-issue-in-a
  3. Official docs of Base64 class https://docs.oracle.com/javase/8/docs/api/java/util/Base64.html
  4. Wikipedia link for learning about Base64 https://en.wikipedia.org/wiki/Base64
  5. Stackoverflow answer for “What is Base64 encoding used for?” https://stackoverflow.com/questions/201479/what-is-base-64-encoding-used-for