Smali Payload Directory Creator

This is a function I created called the createPayloadDirectory function. This function determines the appropriate name for a directory where payload files will be placed within an Android APK. It does so by analyzing the existing directories in the decompiled APK and creating a new directory name based on the naming conventions used in the APK's "smali" directory structure.

This new directory is intended to hold the payload-specific files before generating the final modified APK.

What Does This Function Do?

ℹ️ Info

1. It takes an array of files as input, which represents the list of files and directories in a decompiled APK folder.

2. It defines an array called ignoreDirs, containing directory names that should be ignored during the process. These directories are typically common directories in Android apps that don't need to be considered for payload placement.

3. It filters the files array to get a list of directories that are not in the ignoreDirs list. This filtered list is stored in the smaliList variable.

4. It sorts the smaliList array in ascending order using a custom collator with numeric comparison.

5. It checks if the last item in the sorted smaliList array is named "smali". If it is, the function sets the payloadSmaliFolder variable to '/smali_classes2' and returns it.

6. If the last item in the smaliList array is not named "smali", the function extracts a number from its name using a regular expression and increments that number. It then constructs a new directory name in the format '/smali_classes' + newSmaliNumber and returns it.

How do we use this Function?

🧑‍💻 Code

• declare the needed imports for the function.

const fs = require('fs-extra');
const apkFolder = 'path/to/decompiled/apk'

• declare the createPayloadDirectory function itself.

var createPayloadDirectory = (files) => {
    var ignoreDirs = ['original',
        'res',
        'build',
        'kotlin',
        'lib',
        'assets',
        'META-INF',
        'unknown',
        'smali_assets'];
    var smaliList = files.filter((item) => item.isDirectory() && !(ignoreDirs.includes(item.name))).map((item) => item.name);
    var collator = new Intl.Collator([], {
        numeric: true
    });
    smaliList.sort((a, b) => collator.compare(a, b));
    var lastSmali = smaliList[smaliList.length - 1];

    if (lastSmali == "smali") {
        payloadSmaliFolder = '/smali_classes2';
        return payloadSmaliFolder;
    } else {
        var extractSmaliNumber = lastSmali.match(/[a-zA-Z_]+|[0-9]+/g);
        var lastSmaliNumber = parseInt(extractSmaliNumber[1]);
        var newSmaliNumber = lastSmaliNumber + 1;
        var payloadSmaliFolder = '/smali_classes' + newSmaliNumber;
        return payloadSmaliFolder;
    }
};

• Run the function and handle it's output like so.

var someFunction = (apkFolder) => {

    // Read the Decompiled APK folder
    console.log('[★] Reading the Decompiled Original Application...')
    fs.readdir(apkFolder, {
        withFileTypes: true
    }, (error, files) => {
        if (error) {
            console.log('[x] Failed to Read the Decompiled Original Application!\n' + error);
            return;
        }

        // create the smali payload directory
        console.log(`[★] Creating the ${payloadSmaliFolder} Directory...`);
        const payloadSmaliFolder = createPayloadDirectory(files);
        const targetPayloadFolder = path.join(apkFolder, payloadSmaliFolder);
        fs.mkdir(targetPayloadFolder, {
            recursive: true
        }, (error) => {
            if (error) {
                console.log(`[x] Unable to Create the ${payloadSmaliFolder} Directory!\n` + error);
                return;
            }

            // do something with the newly created smali directory such as copy over android payload files.
        });
    });
}