Building SUSI.AI Android App with FDroid

Fdroid is an app store for Free and Open Source Software (FOSS). Building and hosting an app on Fdroid is not an easy process compared to when we host one on Google Play. A certain set of build checks are required to be done prior to making a merge request (which is similar to a pull request in GitHub) in the fdroid-data GitLab repository. SUSI.AI Android app has undergone through all these checks and tests and is now ready for the merge request to be made.

Setting up the fdroid-server and fdroid-data repositories is a separate thing and is fairly easy. Building the app using the tools provided by fdroid is another thing and is the one that causes the most problems. It will involve quite a few steps to get started. Fdroid requires all the apps need to be built using:

$ fdroid build -v -l ai.susi

This will output a set of logs which tell us what went wrong in the builds. The usual one in a first time app is obviously the build is not taking place at all. The reason is our metadata file needs to be changed to initiate a build.

The metadata file is used for the build process and contains all the information about the app. The metadata file for a.susi package was a .yaml file.

Builds:

 – versionName: 1.0.10

   versionCode: 11

   commit: 1ad2fd0e858b1256617e652c6c8ce1b8372473e6

   subdir: app

   gradle:

     – fdroid

This is the metadata reference file’s build section that is used for the build process using the command that was mentioned above.The versionName a nd versionCode is found in the build.gradle file in the app and commit denotes the commit-id of the latest commit that will be checked out and built, subdir shows the subdirectory of the app, here the subdirectory is the app file.

Next is the interesting stuff, since we are using flavors in the app, we have to mention in the gradle the flavor which we are using, in our case we are using the flavor by the name of “fdroid” and by mentioning this we can build only the “fdroid” flavor in the app.

Also when building the app there were many blockers that were faced, the reason for the usual build fails were :

1 actionable task: 1 executed
INFO: Scanning source for common problems…
ERROR: Found usual suspect ‘youtube.*android.*player.*api’ at app/libs/YouTubeAndroidPlayerApi.jar
WARNING: Found JAR file at app/libs/YouTubeAndroidPlayerApi.jar
WARNING: Found possible binary at app/src/main/assets/snowboy/alexa_02092017.umdl
WARNING: Found possible binary at app/src/main/assets/snowboy/common.res
ERROR: Found shared library at app/src/main/jniLibs/arm64-v8a/libsnowboy-detect-android.so
ERROR: Found shared library at app/src/main/jniLibs/armeabi-v7a/libsnowboy-detect-android.so
INFO: Removing gradle-wrapper.jar at gradle/wrapper/gradle-wrapper.jar
ERROR: Could not build app ai.susi: Can‘t build due to 3 errors while scanning
INFO: Finished
INFO: 1 build failed

The reason for these build fails were that fdroid does not allow us to use prebuilt files and any proprietary software if present, the above log indicates the two prebuilt files which should be removed and also the YouTubeAndroidPlayerApi.jar which is proprietary software and hence needs to removed. So, to remove the files that are not used in the fdroid flavor and exclude them in the build process, we have to include the following statements in the build section of the metadata reference file :

   rm:
     – app/src/main/jniLibs/arm64-v8a/libsnowboy-detect-android.so
     – app/src/main/jniLibs/armeabi-v7a/libsnowboy-detect-android.so
     – app/libs/YouTubeAndroidPlayerApi.jar

Once the metadata file is complete we are ready to run the build command once again. If you have properly set the environment in your local PC, build will end successfully assuming there were no Java or any other language syntax errors.

It is worth to mention few other facts which are common to Android software projects. Usually the source code is packed in a folder named “app” inside the repository and this is the common scenario if Android Studio builds up the project from scratch. If this “app” folder is one level below the root, that is “android/app”, the build instructions shown above will throw an error as it cannot find the project files.

The reason for this is as it is mentioned “subdir=app” in the metadata file. Change this to “subdir=android/app” and run the build again. The idea is to direct the build to find where the project files are.

Reference:

  1. Metadata : https://f-droid.org/docs/Build_Metadata_Reference/#Build
  2. Publish an app on fdroid: https://blog.fossasia.org/publish-an-open-source-app-on-fdroid/
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Adding Open Event Orga App as a Product Flavor on FDroid

To release the orga app on fdroid, product flavors need to be added to the app. This means that 2 different packages need to be maintained that handle the code for fdroid and playstore separately. For eg. There are certain proprietary software that are used in the app such as Google Play services which won’t get accepted on fdroid. Hence alternatives need to be found out and separate code has to be maintained.  

Steps:

  • Go to the build.gradle file where in the Android section add the following line of code in the groovy language. We specify the flavorDimension to be default and then add the productFlavor tag. Inside this tag there will be 2 more sub tags namely fdroid and playStore. These are the 2 different flavors we will be maintaining in the app. Because of this command, 4 different build variants will be created namely : fdroidDebug, fdroidRelease, playStoreDebug and playStoreRelease. The dimension for each is specified to be default.
flavorDimensions “default”

productFlavors {
  fdroid {
      dimension “default”
  }

  playStore {
      dimension “default”
  }
}
  • Now as testCoverage is being used in the app the file name also need to be changed from debug to playStore. So firstly go to the travis.yml file and change the testDebugUnitCoverage command to testPlayStoreDebugUnitCoverage. Hence when the travis will build, the modified command will be executed rather than the old command. We could also have used testfdroidDebugUnitCoverage.Following is the code snippet from the travis.yml file.
script:
./gradlew build
./gradlew testPlayStoreDebugUnitTestCoverage
  • Now command for testCoverage also needs to be changed in the config.yml. So navigate to this file and modify the command.
– run:
  name: Test Coverage
  command: ./gradlew testPlayStoreDebugUnitTestCoverage
  • Now navigate to the update-apk.sh script where we will change the name of the output apk in case of fdroid build and playStore build. As can be seen below we have first changed the name of the json file in each build. Also the name of the folder where they get generated are changed.
\cp -r ../app/build/outputs/apk/playStore/*/**.apk .
\cp -r ../app/build/outputs/apk/fdroid/*/**.apk .
\cp -r ../app/build/outputs/apk/playStore/debug/output.json playStore-debug-output.json
\cp -r ../app/build/outputs/apk/playStore/release/output.json playStore-release-output.json
\cp -r ../app/build/outputs/apk/fdroid/debug/output.json fdroid-debug-output.json
\cp -r ../app/build/outputs/apk/fdroid/release/output.json fdroid-release-output.json
  • Also the apk names in fastlane  are changed for playStore with the help of the following code.
gem install fastlane
fastlane supply –apk app-playStore-release.apk –track alpha –json_key ../scripts/fastlane.json –package_name $PACKAGE_NAME

Resources

  1. Official fdroid website https://f-droid.org/en/
  2. Google Developer website https://developer.android.com/studio/build/build-variants
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Use Travis to extract testing APKs for PSLab

Travis CI is a popular continuous integration tool built to test software and deployments done at GitHub repositories. They provide free plans to open source projects. PSLab Android is using Travis to ensure that all the pull requests made and the merges are build-bug frees. Travis can do this pretty well, but that is not all it can do. It’s a powerful tool and we can think of it as a virtual machine (with high specs) installed in a server for us to utilize efficiently.

There was a need in PSLab development that, if we want to test the functionalities of code at a branch. To fulfil this need, one has to download the branch to his local machine and use gradle to build a new apk. This is a tedious task, not to mention reviewers, even developers wouldn’t like to do this.

If the apk files were generated and in a branch, we can simply download them using a console command.

$ wget https://raw.github.com/fossasia/<repository>/<branch>/<file with extension>

 

With the help of Travis integration, we can create a simple script to generate these apks for us. This is done as follows;

Once the Travis build is complete for a triggering event such as a pull request, it will run it’s “after_success” block. We are going to execute a script at this point. Simply add the following code snippet.

after_success:
  - 'if [ "$TRAVIS_PULL_REQUEST" == "false" ]; then bash <script-name>.sh; fi'

 

This will run the script you have mentioned using bash. Here we will have the following code snippets in the specified bash script.

First of all we have to define the branch we want to build. This can be done using a variable assignment.

export DEVELOPMENT_BRANCH=${DEVELOPMENT_BRANCH:-development}

 

Once the build is complete, there will be new folders in the virtual machine. One of them is the app folder. Inside this folder contains the build folder where all the apk files are generated. So the next step is to copy these apk files to a place of our preference. I am using a folder named apk to make it much sense.

cd apk
\cp -r ../app/build/outputs/apk/*/**.apk .
\cp -r ../app/build/outputs/apk/debug/output.json debug-output.json
\cp -r ../app/build/outputs/apk/release/output.json release-output.json
\cp -r ../README.md .

 

Usually, the build folder has following apk files

  • app-debug.apk
  • app-release-unsigned.apk
  • app-release.apk

Release apks are usually signed with a key and it would cause issues while installation. So we have to filter out the debug apk that we usually use for debugging and get it as the output apk. This involves simple file handling operations in Linux and a bit of git.

First of all, rename the apk file so that it will be different from other files.

# Rename apks with dev prefixes
mv app-debug.apk app-dev-debug.apk

 

Then add and commit them to a specific branch where we want the output from.

git add -A
git commit -am "Travis build pushed [development]"
git push origin apk --force --quiet> /dev/null

 

Once it is all done, you will have a branch created and updated with the apk files you have defined.

 

Figure 1: UI of pslab-android apk branch

Reference:

  1. https://travis-ci.org/
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Building PSLab Android app with Fdroid

Fdroid is a place for open source enthusiasts and developers to host their Free and Open Source Software (FOSS) for free and get more people onboard into their community. Hosting an app in Fdroid is not a fairly easy process just like hosting one in Google Play. We need to perform a set of build checks prior to making a merge request (which is similar to pull request in GitHub) in the fdroid-data GitLab repository. PSLab Android app by FOSSASIA has undergone through all these checks and tests and now ready to be published.

Setting up the fdroid-server and fdroid-data repositories is one thing. Building our app using the tools provided by fdroid is another thing. It will involve quite a few steps to get started. Fdroid requires all the apps need to be built using:

$ fdroid build -v -l org.fossasia.pslab

 

This will output a set of logs which tell us what went wrong in the builds. The usual one in a first time app is obviously the build is not taking place at all. The reason is our metadata file needs to be changed to initiate a build.

Build:<versioncode>,<versionname>
    commit=<commit which has the build mentioned in versioncode>
    subdir=app
    gradle=yes

 

When a metadata file is initially created, this build is disabled by default and commit is set to “?”. We need to fill in those blanks. Once completed, it will look like the snippet above. There can be many blocks of “Build” can be added to the end of metadata file as we are advancing and upgrading through the app. As an example, the latest PSLab Android app has the following metadata “Build” block:

Build:1.1.5,7
    commit=0a50834ccf9264615d275a26feaf555db42eb4eb
    subdir=app
    gradle=yes

 

In case of an update, add another “Build” block and mention the version you want to appear on the Fdroid repository as follows:

Auto Update Mode:Version v%v
Update Check Mode:Tags
Current Version:1.1.5
Current Version Code:7

 

Once it is all filled, run the build command once again. If you have properly set the environment in your local PC, build will end successfully assuming there were no Java or any other language syntax errors.

It is worth to mention few other facts which are common to Android software projects. Usually the source code is packed in a folder named “app” inside the repository and this is the common scenario if Android Studio builds up the project from scratch. If this “app” folder is one level below the root, that is “android/app”, the build instructions shown above will throw an error as it cannot find the project files.

The reason behind this is we have mentioned “subdir=app” in the metadata file. Change this to “subdir=android/app” and run the build again. The idea is to direct the build to find where the project files are.

Apart from that, the commit can be represented by a tag instead of a long commit hash. As an example, if we had merge commits in PSLab labeled as “v.<versioncode>”, we can simply use “commit=v.1.1.5” instead of the hash code. It is just a matter of readability.

Happy Coding!

Reference:

  1. Metadata : https://f-droid.org/docs/Build_Metadata_Reference/#Build
  2. PSLab Android app Fdroid : https://gitlab.com/fdroid/fdroiddata/merge_requests/3271/diffs
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Auto Updating SUSI Android APK and App Preview on appetize.io

This blog will cover the way in which the SUSI Android APK is build automatically after each commit and pushed to “apk” branch in the github repo. Other thing which will be covered is that how the app preview on appetize.io can be updated after each commit. This is basically for the testers who wish to test the SUSI Android App. There are four ways to test the SUSI Android App. One is to simply download the alpha version of the app from the Google PlayStore. Here is the link to the app. Join the alpha testing and report bugs on the github issue tracker of the repo. Other way is to build the app from Android Studio but you may need to set the complete project. If you are looking to contribute in the project, this is the advised way to test the app. The other two ways are explained below.

Auto Building of APK and pushing to “apk” branch

We have written a script which does following steps whenever a PR is merged:

  1. Checks if the commit is of a PR or a commit to repo
  2. If not of PR, configures a user whose github account will be used to push the APKs.
  3. Clones the repo, generates the debug and release APK.
  4. Deletes everything in the apk branch.
  5. Commits and Pushes new changes to apk branch.

This script is written for people or testers who do not have android studio installed in their computer and want to test the app. So, they can directly download the apk from the apk branch and install it in their phone. The APK is always updated after each commit. So, whenever a tester downloads the APK from apk branch, he will always get the latest app.

if [[ $CIRCLE_BRANCH != pull* ]]
then
    git config --global user.name "USERNAME"
    git config --global user.email "EMAIL"

    git clone --quiet --branch=apk https://USERNAME:[email protected]/fossasia/susi_android apk > /dev/null
    ls
    cp -r ${HOME}/${CIRCLE_PROJECT_REPONAME}/app/build/outputs/apk/app-debug.apk apk/susi-debug.apk
    cp -r ${HOME}/${CIRCLE_PROJECT_REPONAME}/app/build/outputs/apk/app-release-unsigned.apk apk/susi-release.apk
    cd apk

    git checkout --orphan workaround
    git add -A

    git commit -am "[Circle CI] Update Susi Apk"

    git branch -D apk
    git branch -m apk

    git push origin apk --force --quiet > /dev/null
fi

Auto Updating of App Preview on appetize.io

The APKs generated in the above step can now be used to set up the preview of the app on the appetize.io. Appetize.io is an online simulator to run mobile apps ( IOS and Android). Appetize.io provides a nice virtual mobile frame to run native apps with various options like screen size, mobile, OS version, etc. Appetize.io provides some API to update/publish the app. In SUSI, we once uploaded the app on appetize.io and now we are using the API provided by them to update the APK everytime a commit is pushed in the repository.

API information (Derived from official docs of appetize.io):

You may upload a new version of an existing app, or update app settings.

Send an HTTP POST request to

https://[email protected]/v1/apps/PUBLICKEY

Replace APITOKEN with your API token and PUBLICKEY with the public key of the app you’re updating. Your API token must be permissioned to the same account as was used to upload the app. The POST body must be a JSON object. To delete a previously set field, use a value of null.

Optional Fields

  1. url: (string) a publicly accessible link to your .zip, .tar.gz, or .apk file, used to upload a new version of your app.
  2. note: (string) a note for your own purposes, will appear on your management dashboard.

For the url parameter, we have used https://github.com/fossasia/susi_android/raw/apk/susi-debug.apk and note can be anything. We have used Update SUSI Preview.

curl https://[email protected]/v1/apps/mbpprq4xj92c119j7nxdhttjm0 -H 'Content-Type: application/json' -d '{"url":"https://github.com/fossasia/susi_android/raw/apk/susi-debug.apk", "note": "Update SUSI Preview"}'

Summary

This blog covered about how to implement an automatic structure to generate APKs for testing and using that APK to build a preview on websites like appetize.io and then using the APIs provided by them to update the APK after each PR merge in the repo. Check out the resources below to learn more about the topic. So, if you are thinking of contributing to SUSI Android App, this may help you a little in testing the app. But if not, then you can also use the similar technique for your android app as well and ease the life of testers.

Resources

  1. Docs of appetize.io to learn more about the API https://appetize.io/docs
  2. Tutorial on using curl to make API requests https://curl.haxx.se/docs/httpscripting.html
  3. Tutorial on writing basic shell scripts https://ryanstutorials.net/bash-scripting-tutorial/
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Implementing a Custom Serializer for Yaydoc

At the crux of it, Yaydoc is comprised of a number of specialized bash scripts which perform various tasks such as generating documentation, publishing it to github pages, heroku, etc. These bash scripts also serve as the central communication portal for various technologies used in Yaydoc. The core generator is composed of several Python modules extending the sphinx documentation generator. The web Interface has been built using Node, Express, etc. Yaydoc also contains a Python package dedicated to reading configuration options from a Yaml file.

Till now the options were read and then converted to strings irrespective of the actual data type, based on some simple rules.

  • List was converted to a comma separated string.(Nested lists were not handled)
  • Boolean values were converted to true | false respectively.
  • None was converted to an empty string.

While these simple rules were enough at that time, It was certain that a better solution would be required as the project grew in size. It was also getting tough to maintain because a lot of hard-coding was required when we wanted to convert those strings to python objects. To handle these cases, I decided to create a custom serialization format which would be simple for our use cases and easily parseable from a bash script yet can handle all edge cases. The format is mostly similar to its earlier form apart from lists where it takes heavy inspiration from the python language itself.

With the new implementation, Lists would get converted to comma separated strings enclosed by square brackets. This allowed us to encode the type of the object in the string so that it can later be decoded. This handled the case of an empty list or a list with single element well. The implementation also handled nested lists.

Two methods were created namely serialize and deserialize which detected the type of the corresponding object using several heuristics and applied the proper serialization or deserialization rule.

def serialize(value):
    """
    Serializes a python object to a string.
    None is serialized to an empty string.
    bool values are converted to strings True False.
    list or tuples are recursively handled and are comma separated.
    """
    if value is None:
        return ''
    if isinstance(value, str):
        return value
    if isinstance(value, bool):
        return "true" if value else "false"
    if isinstance(value, (list, tuple)):
        return '[' + ','.join(serialize(_) for _ in value) + ']'
    return str(value)

To deserialize we also had to handle the case of nested lists. The following snippet does that properly.

def deserialize(value, numeric=True):
    """
    Deserializes a string to a python object.
    Strings True False are converted to bools.
    `numeric` controls whether strings should be converted to
    ints or floats if possible. List strings are handled recursively.
    """
    if value.lower() in ("true", "false"):
        return value.lower() == "true"
    if numeric and _is_numeric(value):
        return _to_numeric(value)
    if value.startswith('[') and value.endswith(']'):
        split = []
        element = ''
        level = 0
        for c in value:
            if c == '[':
                level += 1
                if level != 1:
                    element += c
            elif c == ']':
                if level != 1:
                    element += c
                level -= 1
            elif c == ',' and level == 1:
                split.append(element)
                element = ''
            else:
                element += c
        if split or element:
            split.append(element)
        return [deserialize(_, numeric) for _ in split]
    return value

With this new approach, we are able to handle much more cases as compared to the previous implementation and is much more robust. It does however still lacks lacks certain features such as serializing dictionaries. That may be be implemented in the future if need be.

Resources

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Deploying Yacy with Docker on Different Cloud Platforms

To make deploying of yacy easier we are now supporting Docker based installation.

Following the steps below one could successfully run Yacy on docker.

  1. You can pull the image of Yacy from https://hub.docker.com/r/nikhilrayaprolu/yacygridmcp/ or buid it on your own with the docker file present at https://github.com/yacy/yacy_grid_mcp/blob/master/docker/Dockerfile

One could pull the docker image using command:

docker pull nikhilrayaprolu/yacygridmcp

 

2) Once you have an image of yacygridmcp you can run it by typing

docker run <image_name>

 

You can access the yacygridmcp endpoint at localhost:8100

Installation of Yacy on cloud servers:

Installing Yacy and all microservices with just one command:

  • One can also download,build and run Yacy and all its microservices (presently supported are yacy_grid_crawler, yacy_grid_loader, yacy_grid_ui, yacy_grid_parser, and yacy_grid_mcp )
  • To build all these microservices in one command, run this bash script productiondeployment.sh
    • `bash productiondeployment.sh build` will install all required dependencies and build microservices by cloning them from github repositories.
    • `bash productiondeployment.sh run` will run all services and starts them.
    • Right now all repositories are cloned into ~/yacy and you can make customisations and your own changes to this code and build your own customised yacy.

The related PRs of this work are https://github.com/yacy/yacy_grid_mcp/pull/21 and https://github.com/yacy/yacy_grid_mcp/pull/20 and https://github.com/yacy/yacy_grid_mcp/pull/13

Resources:

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Displaying selective logs in Yaydoc with downloadable detailed logs

Yaydoc, our automatic documentation generation and deployment project, at the crux of it consists of bash scripts. These bash scripts perform various actions, including documentation generation, deployment to Github and deployment to Heroku.

Since the inception of the User Interface of the Web UI, we have been spitting out the output of the bash script directly to the console output block without any filter. We understand that the output contains a lot of jargon that provides no essential information to the user. Hence, to improve the user experience of our platform, we decided to separate the Detailed logs and show only basic logs outlining the flow of the processes.

To implement this, we append all the logs to a unique file, sending only basic logs to stdout and stderr. Since we attend to store logs and display them in the console block of Web UI simultaneously we use the tee command, piping it with echo commands.

function print_log {
  if [ -n “$LOGFILE” ]; then
    echo -e $1 | tee -a ${LOGFILE}
  else
    echo -e $1
  fi
}

${LOGFILE}  is a unique file that has the same name as the preview directory and the compressed repository. After storing the logs in the file, the contents of the file are outputted using the cat command and is then shown to the user in a modal which is after the Detailed Logs button is clicked.

$(“#btnLogs”).click(function () {
  socket.emit(‘retrieve-detailed-logs’, data);
  ....
});

socket.on(‘retrieve-detailed-logs’, function (data) {
  var process = spawn(‘cat’, [‘temp/’+data.email+’/’+data.uniqueId+’.txt’]);
  process.stdout.setEncoding(‘utf-8’);
  process.stdout.on(‘data’, function (data)) {
    socket.emit(‘file-content’, data);
  }
});

To keep the indentation of the logs, we display the content inside the HTML pre tags. Along with displaying the detailed logs, we also let our two additional functionalities. These are ‘Copy to Clipboard’ and ‘Download as text file’. The ‘copy to clipboard’ functionality is achieved using the clipboard.js jQuery library while the `Download` functionality is achieved using res.download(file) function of ExpressJS response.

socket.on(‘file-content’, function (data) {
  new Clipboard(‘#copy-button’);
  $(‘#detailed-logs’).html(data);
  $(‘#detailed-logs-modal’).modal(‘show’);
});

Resources:

  1. https://clipboardjs.com – A modern approach to copy text to clipboard
  2. https://socket.io/ – The fastest and most reliable real-time engine
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Editing files and piped data with “sed” in Loklak server

What is sed ?

“sed” is used in “Loklak Server” one of the most popular projects of FOSSASIA. “sed” is acronym for “Stream Editor” used for filtering and transforming text, as mentioned in the manual page of sed. Stream can be a file or input from a pipeline or even standard input. Regular expressions are used to filter the text and transformation are carried out using sed commands, either inline or from a file. So, most of the time writing a single line does the work of text substitution, removal or to obtaining a value from a text file.

Basic Syntax of “sed”

$sed [options]... {inline commands or file having sed commands} [input_file]...

Loklak Server uses a config.properties file – contains key-value pairs – which is the basis of the server as it contains configuration values, used by the server during runtime for various operations.

Let’s go through a simple sed example that prints line containing word “https” at the beginning in the config.properties file.

$sed -n '/^https/p' config.properties

Here “-n” option suppresses automatically printing of pattern space (pattern space is where each line is put that is to be processed by sed). Without “-n” option sed will print the whole file.

Now, the regular expression part,  “/^https” matches all the lines that has “https” at the start of line and “/p” is print command to print the output in console. Finally we provide the filename i.e. config.properties. If filename is not provided then sed waits for input from standard input.

Use cases of “sed” in Loklak Server

  • Displaying proper port number in message while starting or installing Loklak Server

The default port of loklak server is port number 9000, but it can be started in any non-occupied port by using “-p” flag with bin/start.sh and bin/installation.sh like

$ bin/installation.sh -p 8888

starts installation of Loklak Server in port 8888. To display the proper localhost address so that user can open it in a browser the port number in shortlink.urlstub parameter in config.properties needs to be changed. This is carried out by the function change_shortlink_urlstub in bin/utility.sh. The function is defined as

Now let’s try to understand what the sed command is doing.

“-i” option is used for in-place editing of the specified file i.e. config.properties in conf directory.

s” is substitute command of sed. The regular expression can be divided into two parts, between “/”:

  1. \(shortlink\.urlstub=http:.*:\)\(.*\) this is used to find the match in a line.
  2. \1′”$1″ is used to substitute the matched string in part 1.

The regular expressions can be split into groups so that operations can be performed on each group separately. A group is enclosed between “\(“ and “\)”. In our 1st part of regular expressions, there are two groups.

Dissecting the first group i.e. \(shortlink\.urlstub=http:.*:\):

  • shortlink\.urlstub=http:” will match the expression “shortlink.urlstub=http:”, here “\” is used as an escape sequence as “.” in regex represents any character.
  • “.*:”, “.” represents any character and “*” represents 0 or more characters of the previous character. So, it will basically match any expression. But, it ends with a “:”, which means any expression that ends with a “:”. Thus it matches the expression “//localhost:”.

So, the first group collectively matches the expression “shortlink.urlstub=http://localhost:”.

As described above second group i.e. \(.*\) will match any expression, here matches “9000”.

Now coming to the 2nd part of regular expression i.e. \1′”$1″:

  • “\1” represents the match of the first group in 1st part i.e. “shortlink.urlstub=http://localhost:”.
  • “$1” is the value of the first parameter provided to our function “change_shortlink_urlstub” which is an unused port where we want to run Loklak Server.

So 2nd part picks up the match from the first group and concatenates with the first parameter of the function. Assuming the first parameter to the function is “8888”, the expression for 2nd part becomes “shortlink.urlstub=http://localhost:8888” which replaces “shortlink.urlstub=http://localhost:9000”.

So a correct localhost address is displayed in the console while starting or installing Loklak Server.

  • Extracting value of a key from config.properties

“grep” and “sed” are used to extract the values of key from config.properties in bash scripts e.g. extracting default port, value of “port.http” in bin/start.sh, value of “shortlink.urlstub” in bin/start.sh and bin/installation.sh.

$ grep -iw 'port.http' conf/config.properties | sed 's/^[^=]*=//'

Here grep is used to filter a line and pass the filtered line to sed by piping the output. “i” flag is for ignoring case sensitivity and “w” flag is used for matching of word only. The output of

$ grep -iw 'port.http' conf/config.properties
port.http=9000

The aim is to get “9000”, the value of “port.http”. The approach used here is to substitute “port.http=” in the output of grep command above with a string of zero characters, that way only “9000” remains.

Let’s deconstruct the “sed” part, s/^[^=]*=//:

s” command of sed is used for substitution.  Here 1st part is “^[^=]*=” and 2nd part is nothing, as no characters are enclosed within “//”.

  • “^” means to match at the start.
  • [^characters] represents not to consider a set of characters. For matching a set of characters “^” is not used inside square brackets, [characters]. Here [^=] means not to include equal to – “=” symbol – and “*” after that makes it to match characters that are not “=”.

So “^[^=]*=” matches a sequence of characters that doesn’t start with “=” and followed by “=”. Thus the matched expression in this case is “http.port=” (“h” is not “=” and it ends with “=”), which is substituted by a string with zero characters which leaves “9000”.  Finally, “9000” is assigned to the required variable is bash script.

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