Forem: Krishnanand

Simple Telegram Bot in Go

Krishnanand — Fri, 08 May 2020 07:40:48 +0000

The adoption of chat-bots are at a peak now. Since facebook opened up its developer platform and opened the world of possibilities for chat-bots many platforms supported bots. Telegram is one of the leading platforms with bot functionality.

There is almost a bot for everything on telegram. For memes, searching movies, downloading youtube videos, dating and many more. Businesses engage with users through these bots. Crypto companies do airdrops, giveaways using these bots. Bots are literally everywhere.

Today we are going to checkout how to build a telegram bot using Golang. So if you don't know Go this article is not for you.
We are not using any telegram bot api wrapper libraries .We are using only the net/http package to have a better understanding how things work under the hood. Let's dive right in.

Getting started

First thing you have to do is to get a bot token after creating a bot using botfather bot on telegram and declare a constant.

const botToken = "BOT_TOKEN"

Let's start by creating a main.go file.

The first thing we need is the net/http package we also require the log package for logging the errors so import them and code the main function which looks like this.

func main() {
    err := http.ListenAndServe(":8080", http.HandlerFunc(webHookHandler))
    if err != nil {
        log.Fatal(err)
        return
    }
}

Yep that's it . That' how much it takes to make a simple http server in go.It listens at the port 8080 and invokes the function webHookHandler on recieving a http Request the next line is just how we handle errors in go.

Now that we have setup a server we want to create the webHookHandler function. You may think why the name webHookhandler its because we are using the webHooks. You can find more details here on Telegram bot docs.

Now lets take a look at the webHookHandler function.
The bot we are going to built reply's with a random joke when the user sends the command "/joke". For this we use a free API http://api.icndb.com/jokes/random.

Our WebHookHandler Function looks like this

func webHookHandler(rw http.ResponseWriter, req *http.Request) {

    // Create our web hook request body type instance
    body := &webHookReqBody{}

    // Decodes the incoming request into our cutom webhookreqbody type
    if err := json.NewDecoder(req.Body).Decode(body); err != nil {
        log.Printf("An error occured (webHookHandler)")
        log.Panic(err)
        return
    }

    // If the command /joke is recieved call the sendReply function
    if strings.ToLower(body.Message.Text) == "/joke" {
        err := sendReply(body.Message.Chat.ID)
        if err != nil {
            log.Panic(err)
            return
        }
    }
}

Whenever a message is received by the bot our http Server gets a request and we handle the request using this function.
You can see a webHookReqBody type which is a struct to which we decode the data received via http Request.

The webHookReqBody struct declaration :
We need to import the encoding/json package for this

type webHookReqBody struct {
    Message struct {
        Text string `json:"text"`
        Chat struct {
            ID int64 `json:"id"`
        } `json:"chat"`
    } `json:"message"`
}

Now whenever our bot recieves a message an http request is recieved by our server and that http request body is decoded into the webHookHandler struct. Then we check if the message is "/joke" if it is then we call the sendReply Function :

func sendReply(chatID int64) error {
    fmt.Println("sendReply called")

    // calls the joke fetcher fucntion and gets a random joke from the API
    text, err := jokeFetcher()
    if err != nil {
        return err
    }

    //Creates an instance of our custom sendMessageReqBody Type
    reqBody := &sendMessageReqBody{
        ChatID: chatID,
        Text:   text,
    }

    // Convert our custom type into json format
    reqBytes, err := json.Marshal(reqBody)

    if err != nil {
        return err
    }

    // Make a request to send our message using the POST method to the telegram bot API
    resp, err := http.Post(
        "https://api.telegram.org/bot"+botToken+"/"+"sendMessage",
        "application/json",
        bytes.NewBuffer(reqBytes),
    )

    if err != nil {
        return err
    }

    defer resp.Body.Close()

    if resp.StatusCode != http.StatusOK {
        return errors.New("unexpected status" + resp.Status)
    }

    return err
}

sendReply takes an argument the CHATID which is used to identify the telegram user inside the sendReply we first generate the text to be sent using the jokFetcher function which calls our API and gets a random joke for us.

func jokeFetcher() (string, error) {
    resp, err := http.Get("http://api.icndb.com/jokes/random")
    c := &joke{}
    if err != nil {
        return "", err
    }
    err = json.NewDecoder(resp.Body).Decode(c)
    return c.Value.Joke, err
}

We have joke struct into which the joke gets decoded into

type joke struct {
    Value struct {
        Joke string `json:"joke"`
    } `json:"value"`
}

In the senReply Function we have sendMessageReqBody struct whose declaration is as follows :

type sendMessageReqBody struct {
    ChatID int64  `json:"chat_id"`
    Text   string `json:"text"`
}

Check out the full code here main.go

Now in order to test our bot you should first install ngrok on your system

then run

ngrok http 8080

Now you will get a screen containing an https url copy that url and run the command

curl -F "url=YOUR_NGROK_URL_HERE" https://api.telegram.org/botYOUR_BOT_TOKEN_HERE/setWebhook

Now run your main.go file then send your bot a message "/joke". Enjoy .!!!

Dart Basics -Flutter #2

Krishnanand — Mon, 30 Mar 2020 17:07:21 +0000

In the previous article in this series, we have gone through the basic syntax of Dart.
Cool Is'nt it ? told ya.. Dart is a simple and easy to learn programming language for anyone with basic programming knowledge.
This article is another quick run through dart basics and mainly deals with the different datatypes available in dart.

Datatypes

String

Strings are sequences of characters which we use to represent text.We can use single,double or triple quotes to represent strings in dart

void main() { 
   String name1 = 'Sachin';
   String name2 = "Virat Kohli";
   String name3 = '''MS Dhoni''';
   print('$name1,$name2,$name3');
}

We can join two strings easily with the help of the + operator.

void main() { 
  String firstName = 'Sachin';
  String lastName = 'Tendulkar';
  String fullName = firstName +' ' + lastName;
  print(fullName);
}

Dart also has many builtin methods within the String class which simplifies certain string operations(eg:toUpper()) As this is a quick intro to datatypes in dart these concepts are out of the cope of this article.

Numbers

Numbers are mainly represented in dart as int or double.int Stands for integer.
double is the keyword used for 64bit floating point numbers.
Here is how we declare numbers in dart.

int num1 = 10;
double num2 = 10.5;

We will come across instances when we have to convert String into num.
We can do that.

void main() { 
  String num1='10';
  int num2=num.parse(num1);
  print(num2);
}

List

We all know about arrays.Lists are similar to arrays they are simply an ordered group of objects.
The easiest way for declaring a list is using the assignment operator to assign a variable to an empty list.
Check out the example below

   var emptyList = [];
   var snackList = [ 'Burger' , 'Sandwich' ];

We can also explicitly explicitly specify whether a variable is a list or not so that the variable can only be assigned to List type.
for example :

   List nameList = [ 'Rahul' , 'Goutham' , 'Nirmal' , 'Shivani' ];

If we want the list to be a list of String we can also explicitly specify that within '<>'.
Checkout this code snippet

   List<String> nameList = [ 'Rahul' , 'Goutham' , 'Nirmal' , 'Shivani' ];
   List<num> numberList =[1,2,4];

Apart from these above techniques if we want to declare a List with a specific size we can use : List(listsize)

var newList = List(3);

Accessing List Items

Checkout this list of fruits.

List<String> fruitList = ['Apple' , 'Orange' , 'Banana' , 'Strawberry'];

We can use listname[index] to access a particular item in a list
fruitList[0] is 'Apple'.
We can also use it to modify an item in the list.

void main() { 
  List<String> fruitList = ['Apple' , 'Orange' , 'Banana' , 'Strawberry'];
  fruitList[0] = 'Pineapple';
  print(fruitList);
}

The output will be : [Pineapple, Orange, Banana, Strawberry]

Adding Items to a List

We can use the List.add() method to add an item to end of the List or List.insert( index, element) to add an item to a particular index.

void main() { 
  List<String> fruitList = ['Apple' , 'Orange' , 'Banana' , 'Strawberry'];
  fruitList.add('Grapes');
  print(fruitList);
  fruitList.insert(2, 'Mango');
  print(fruitList);
}

There are a lot of properties and methods within the List class that will be of great use when we start building flutter apps.
Do check out the official documentation for more info.

Map

Map is also a type of collection in which we can store data in the form of key-value pairs.If you are coming from a python background then you can think of Maps as dictionaries in python.
For example, consider a case where we have to store data of a phone. It will contain different details like the Brand name, Model Name, Price, etc.
We can easily store these details in a map.

var phone1={
    'Brand': 'Samsung',
    'Model' : 'Galaxy S10',
    'Price' : 30000,
  };

Accessing and Modifying data in a Map

We can access a particualar value using Map['key_name'] and also modify a field using the same.

void main() { 
  var phone1={
    'Brand': 'Samsung',
    'Model' : 'Galaxy S10',
    'price' : 30000,
  };
  phone1['price'] =35000; //modifying a field in a map
  print('${phone1['Brand']} ,${phone1['price']}');
}

Output: Samsung ,35000

So that's a very quick intro to datatypes in dart.
Stay tuned for more content..

Dart Basics - Flutter #1

Krishnanand — Sat, 28 Mar 2020 10:31:33 +0000

So Trying to learn Flutter Huh📱? Let's begin with a Hello World program in dart.
Dart is the programming language in which you are going to write code for creating beautiful flutter apps.

Without further due, let's jump right in...

So the first thing we will need is a place where we can code.
As our main goal is to learn flutter and not dart in specific we don't have to go through the process of setting up the dart SDK separately and run dart on your local machine when tools like dartpad are here to make our lives simpler.

So if you prefer to learn dart deeply and want to set up dart development environment locally in your system go ahead and google your way into it.

Here We Go

void main(){
  print('Hello World!!');
}

Thats it..!! simple and humble..
There is nothing much to explain in this code snippet. It's just the definition of a function named 'main',
which returns a void type and displays 'Hello World!!" .
Simple as that.

Now it's important that you try it out. Go to dartpad and code it in and fire🔥 that run button.

A quick run through dart language

Variables

We can use the var keyword in dart to declare variables apart from that if we want a variable to only have values of a particular datatype we can use the datatype name instead of the var keyword.

void main(){
  //var is the keyword used by dart to declare variables

  var name1='Ronaldo'; //here we are storing the String 'Ronaldo' to the variable name1
  var number1=7;//here integer value of 7 is stored to the variable number2

  //to enable type checking we can use the Datatype name instead of the var keyword
  //eg:

  String name2='Messi';//here name2 can only accept String datatype
  //if we provide anyother datatype(eg:int,double) it will throw an error
  int number2=10;

  print(name1);
  print(number1);
  print(name2);
  print(number2);
}

Output :

Ronaldo
7
Messi
10

Lets check what will happen if we provide a different datatype to a variable declared with a static type .

For this, we are going to change the String name2 and pass it an int.

String name2=10

now, this code will throw an error :

main.dart:15:16:
Error: A value of type 'int' can't be assigned to a variable of type 'String'.
  String name2=10;
               ^
Error: Compilation failed.

But if we change name1 to 7 or any other integer dart will not complain because we haven't specified a datatype for that variable.

Now the variables which are declared without a static type that is the variables declared using var keyword can accept any type that is given to it.such variables are said to be of dynamic type meaning it can accept any datatype given to it.

So instead of using the var keyword, we can use dynamic to declare dynamic type independent variables.
eg:

dynamic name='Ronaldo'

`final` and `const`

Now let's play with some constants. Yes!! constants.
final and const are two keywords that we use to declare immutable objects.
Now there is some difference between these two keywords but for the time being let's consider them to be the same.
Both of them are used to declare an immutable object.
After it's declared we cannot change it.

Remember they have their differences as we dive deep into flutter and dart you'll figure it out.

void main(){
  final name1='Ronaldo'; //final variable declaration of dynamic type
  final String name2='Messi'; //final variable declaration with type specified
  const name3='Sachin Tendulkar';//using the const keyword for declaring a constant
  const name4='Virat Kohli';

  print('$name1 ,$name2 ,$name3 ,$name4'); 
  //here we used a special syntax
  //to embed the value of a variable within a String
  // we can use the '$' sign and the the variable name         
  //($variable_name)
}

Go try it out on dartpad.
What will happen if we try to modify a const or final value. Obviously it will throw an error.
Let's try it.

void main(){
  const name1='Ronaldo'; //final variable declaration of dynamic type
  name1='Ibrahimović';
}

Output :

Error: Setter not found: 'name1'.
  name1='Ibrahimović';
  ^^^^^
Error: Compilation failed.

Operators

As I said earlier I am assuming basic programming knowledge for every reader here. So everyone will be familiar with operator like,
= , == , != , < , > , >= , <= , / , * , % , ++ , -- etc ..

Apart from that. Logical operators like
AND && , OR |, NOT ! will also be familiar..

So no code snippets here 🤐

Decision making in dart

Here we are..! at the core of every programming language decision making.
The most basic unit of a decision-making program will be conditional statements and we all are familiar with the good old if and else statements. Apart from that, there are some other ways to write a conditional statement.
So let's analyze a code snippet. Make sure that you read each comment in the snippet :)

void main() { 
   var  num=1; 
   if (num>0) { 
      print("number is positive"); 
   }
  else if (num<0) {
    print("number is negative");
  }
  else{
    print("number is zero");
  }
}

Nothing fancy there just the good old familiar if..else if..if syntax.

Now with the help of some ternary operator, simple if-else statements can be converted into a single-liner.
When you dive deep into flutter you will use this a lot so make sure you practice it and make note of it 📝.

void main(){
  var num=2;
  //here we convert a if else statemet into a single liner with ternery operator
  num>0 ? print("number is positive") : print("number is either zero or negative");

  //now we are converting complex else if ladders to single liners but this not recomended
  //it is not a good practice to write single line code for a complex statement
  num>0 ? print("number is positive") : num==0 ? print("number is zero") : print("number is negative");
}

Now let me introduce to another special condition ??
?? checks whether the value of the operand is null. Let's look at an example.

void main(){
  var num1 = 2;
  var num2;

  var num3 = num1 ?? 10; //this means if num1 is null then make num3 = 10 
  var num4 = num2 ?? 10;//here since we have not given value for num2 it will be null
  //so the value of num4 will be 10

  print('$num3 , $num4');
}

output :

2, 10

`switch..case` statements

These statements are used when we have multiple cases to check. Check out the following code snippet.

  void main() { 
   var caseNum = 2; 
   switch(caseNum) { 
      case 1: {  print("Case number is one"); } 
      break; 

      case 2: {  print("Case number is two"); } 
      break; 

      case 3: {  print("Case number is three"); } 
      break; 

      case 4: {  print("Case number is four"); } 
      break; 

      default: { print("case number is $caseNum"); } 
      break; 
   } 
}

Depending upon the value of caseNum appropriate code is executed.
Can you guess the output here?
Also, don't forget to go and try it out on dartpad.

Loops

The interesting part of every programming language looooops!!.Let's dig right into while loop and for loop.

`while` loop

We all know while loops take in a boolean value as long as the boolean is true while loop keeps on running.
The following code prints out the first 5 numbers. Here the condition provided to the while loop is (num <= 5) unless this condition is false while loop keeps on running.

void main() { 
   var num = 1; 

   while(num <=5) {
     print(num);
      num++; 
   }  
}

`for` loop

Here is the for loop equivalent of the above code.

void main() { 
   var num = 1; 

   for( var i = num ; i<=5; i++ ) {
     print(num); 
     num++;
   } 
}

Apart from while and for loops dart also feature for..in loop to loop through properties of an object we will learn that when we learn about classes and as we dive deeper into flutter.

Those who have a mediocre programming knowledge know about break and continue statements for loop handling. Dart also supports these statements.
Since our main goal is to learn flutter we will try these out as we go.

So that's all for this post.
Next up in this series we will explore various datatypes in dart and also dive into object-oriented programming.

So stay tuned..

What is your view on tech courses getting pirated(the ethical ones)?

Krishnanand — Sat, 28 Mar 2020 05:16:28 +0000

Some websites like freetutorials.us allow users to download pirated tech courses but they argue that they have certain ethics. They do not pirate content of new creators and they only pirate those courses that had already made so many earnings. What is your opinion on this?

Personally I have seen so many students benefit from these pirated courses .

Explain what is garbage and garbage collection in a language like Iam 10 !!

Krishnanand — Fri, 27 Mar 2020 17:06:02 +0000