Wtf is Grpc? Part 1: Authentication and Authorization in Flutter and Golang.

Greetings, fellow tech enthusiasts, and welcome to a tech journey like no other! 🚀 Today, we're embarking on a roller-coaster ride through the fascinating world of gRPC, Flutter, and Golang, but with a twist – we've spiced it up with a generous serving of humor. Buckle up; it's going to be a wild ride!

In our three-part series, we'll explore the ins and outs of gRPC, the delightful dance between Flutter and Golang, and discover how these technologies can come together to create harmonious applications that can bring a smile to even the most stoic developer's face.

Table of Contents

1. Introduction

   • gRPC: A Not-So-Boring Bookish and Slightly Amusing Definition
   • gRPC vs REST: The Iron Throne of APIs
   • Types of gRPC

2. Prerequisites

   • Create project
   • Setup Database model
   • Password Hashing
   • Environment
   • JWT

3. Basic of Protocol Buffer

   • Service
   • Message

4. Setup Basic Project in Golang

5. Create Protocol Buffers

6. Generate Golang code

7. Authentication in Go

8. Setup Server and Middleware

9. Start Server

10. Flutter Project

    • Setup Project
    • Output

11. Conclusion

    • Source Code
    • Follow Me

A Quick Peek

• Part 1: Authentication & Authorization
• Part 2: Custom Flutter Notifications
• Part 3: Chat Applications with gRPC

gRPC: A Not-So-Boring Bookish and Slightly Amusing Definition

Alright, time to don our academic spectacles and approach this with a hint of whimsy. Imagine you're at a fancy library soirée, and someone asks, "What, pray tell, is gRPC?" You respond with a grin:

"Gentlefolk, gRPC, which stands for 'Google Remote Procedure Call,' is like the telegraph system of the digital realm. It's a meticulously structured, high-tech method for different programs to chit-chat with each other, just like sending telegrams back in the day, but without the Morse code."

"But wait, there's more! Instead of tapping out dots and dashes, gRPC uses Protocol Buffers, which is like encoding your messages in secret spy code, only it's not so secret. This makes your data compact and zippy, perfect for today's speedy world."

"Picture it as a virtual switchboard operator connecting your apps with finesse. Plus, it plays nice with HTTP/2, which is like giving your data a sleek, sports car to zoom around in, making it super fast."

"So, in essence, gRPC is the gentleman's agreement between software, ensuring they can communicate efficiently and reliably, like two well-mannered tea-drinking robots having a chat. It's the technological equivalent of a courteous bow, allowing different systems to exchange information harmoniously."

gRPC vs REST: The Iron Throne of APIs

Types of gRPC

Here are the primary types of gRPC communication:

• Unary RPC (Request-Response): This is the simplest form of gRPC communication. The client sends a single request to the server and waits for a single response. It's similar to traditional request-response interactions.

• Server Streaming RPC: In this pattern, the client sends a single request, but the server responds with a stream of messages. It's useful when the server needs to push multiple pieces of data to the client, such as real-time updates.

• Client Streaming RPC: Here, the client sends a stream of messages to the server, and the server responds with a single message. This can be beneficial for scenarios like uploading large files.

• Bidirectional Streaming RPC: In this type, both the client and server can send a stream of messages to each other concurrently. It's ideal for interactive and real-time applications like chat or gaming.

In this we are going to explore unary gRPC using login,signup and get-user request.

Prerequisites

• Basic understanding of Golang,Flutter and MongoDb.
• Excitement to learn something new.

Setup Basic Project in Golang

• Create new project ```

go mod init

- Install Mongo package for go

go get go.mongodb.org/mongo-driver

- Setup Database Model
    - Create package `db` 
      - Create Struct to access database
        

  


  - Create new model `user.go`



    

    





  




Password hashing : we are going to create function for hashing password and check password, Never store password in simple text.


Create package utils in root.
Install required package go get golang.org/x/crypto/bcrypt.
Create HashPasword and CheckPassword function in password.go






  




Setup Environment: We required few environment variable like server_address,mongodburl and jwt_key etc.



Install Viper package for loading app.env.


go get github.com/spf13/viper



    

    

for more information read about viper

• Create function in utils to load app.env file.

• Create app.env in root folder.

DB_NAME=grpc 
DB_SOURCE=mongodb://localhost:27017
RPC_SERVER_ADDRESS=0.0.0.0:9090
GIN_MODE=debug
TOKEN_SYMMETRIC_KEY=12345678123456781234567812345678
ACCESS_TOKEN_DURATION=600m

• Setup Jwt: We need authorization in few requests so its going to bearer token based authentication.
  • Install required Jwt package

     go get github.com/dgrijalva/jwt-go

Note: Not Going to cover Jwt Basics.

• Create new package token and create interface to create token and verify token.

Basic of Protocol Buffer (.proto).

• Service: A unary service in gRPC involves a single request from the client to the server, which then sends a single response back to the client. To define a unary service, you need to create a .proto file that describes the service and the message types it uses.

• Message: A message is a data structure that represents the information being sent between the client and server. It's defined in your .proto file using the message keyword. Here's a simple example:

syntax = "proto3";

message MyRequest {
string name = 1;
int32 age = 2;
}

message MyResponse {
string greeting = 1;
}

In this example, we have two messages, `MyRequest`and `MyResponse`. `MyRequest` has two fields, name and age, while `MyResponse` has a single field, greeting.

- Importing Data Structures from Another Package:

import "other_package.proto";

message MyRequest {
other_package.SomeMessage some_data = 1;
}

## Create Protocol buffers for our project:

- Services: We will have following services called `login`, `signup` and `get-user`. 

- Create `user.proto`, User object to return to the client.

syntax = "proto3";

package pb;
option go_package="github.com/djsmk123/server/pb";

message User{
int32 id=1;
string username=2;
string name=3;
}

- Create `rpc_login.proto`, it will have LoginRequestMessage and LoginReponseMessage

syntax="proto3";
package pb;
import "user.proto";
option go_package="github.com/djsmk123/server/pb";

message LoginRequestMessage{
string username=1;
string password=2;
}

message LoginResponseMessage{
User user=1;
string access_token=2;
}

- Same for `rpc_signup.proto`:

syntax="proto3";
package pb;
import "user.proto";
option go_package="github.com/djsmk123/server/pb";

message SignupRequestMessage{
string username=1;
string password=2;
string name=3;
}

message SignupResponseMessage{
User user=1;

}

- To create message `rpc_get_user.proto`: 

syntax="proto3";
package pb;
import "user.proto";
option go_package="github.com/djsmk123/server/pb";

message GetUserResponse{
User user=1;
}

- Create service `rpc_services.proto`

syntax="proto3";
package pb;
option go_package="github.com/djsmk123/server/pb";
import "empty_request.proto";
import "rpc_get_user.proto";
import "rpc_login.proto";
import "rpc_signup.proto";

service GrpcServerService {
rpc SignUp(SignupRequestMessage) returns (SignupResponseMessage){};

rpc login(LoginRequestMessage) returns (LoginResponseMessage){};
rpc GetUser(EmptyRequest) returns (GetUserResponse) {};

}
message EmptyRequest{

}

## Generate code for Golang

- Create `pb` package in root folder.
- Run command to generate equivalent code for golang 

protoc --proto_path=proto --go_out=pb --go_opt=paths=source_relative \
--go-grpc_out=pb --go-grpc_opt=paths=source_relative \
proto/*.proto

![image 1](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/xrjl4bhl3vh8woq1pzsv.png)

## Create Basic Auth function
- Create `Auth` Package: This package has basic function like `get-user`,`login`, `signup`,`tokenCreation` and function to convert MongoDB userModel to gRPC `user` Messsage.

- Create `converter.go` in `auth` package.

  




Create token_generate.go to generate token.






Create login.go





Create signup.go



  



Create get-user.go






  
  
  Setup Server and Middlware



Create server.go in gapi package struct to register GrpcServiceServer.



  



For creating middlware for Authentication, we will need Unary Interceptors but before that we will check,if request service required authentication or not, we will list all method that are not required token.
> Note by default all the method have restriction for auth token.


Create services.go


  



Create middlware.go




  


  
  
  Connect whole and start server


finally we are going to main function in main.go,lets load environment, connect database(MongoDb) and RunServer.


  


  
  
  Run Server

go run .

## Test server

You can test gRPC services using [`evans-cli`](https://github.com/ktr0731/evans).
- Start CLI Tool

evans --host localhost --port 9090 -r repl

- Call `login` service

call login

![output1](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/vkdhip9jx584ne8z3h8p.png)

!!!Oops,we forgot to define `login`,`get-user` and `signup` from `pb` interface.


- Create `auth.go` in `gapi` package.


  


  
  
  Try again






  
  
  Flutter Project



This Flutter application features four key pages: SplashScreen, LoginScreen, SignUpScreen, and HomeScreen.
SplashScreen: This initial page verifies the user's authentication status. If authenticated, it communicates with the gRPC server using the get-user service and redirects the user to the HomeScreen. Otherwise, it navigates to the LoginScreen.
LoginScreen: The LoginScreen presents fields for entering a username and password. Upon pressing the submit button, the application invokes the login service to authenticate the user. The access_token is saved to local storage, and the user is redirected to the HomeScreen.
SignUpScreen: The SignUpScreen offers fields for name, username, password, and confirmpassword. When the user submits the form, the application calls the signup service on the gRPC server.


> Note: Not going to create whole UI and remaining Login,but only will cover required parts. You are free to create your own ui or can refer from whole in github repo.

  
  
  Setup Project



Add following dependencies into pubspec.yaml

shared_preferences: ^2.2.1
protobuf: ^3.1.0
grpc: ^3.2.3

- Install `protoc_plugin` for dart.

dart pub global activate protoc_plugin

- Copy `.proto` files from server to root folder of the flutter project.

- Created equivalent code in dart

protoc --proto_path=proto --dart_out=grpc:lib/pb proto/*.proto

- Create channel for gRPC services `services/grpc_services.dart`

  



Create AuthServices for different method like login,signup and get-user




  



We are done just call function in presentation layer and add your own logic.


  
  
  OUTPUT














Thanks for joining me on this tech adventure! We hope you've enjoyed the journey through gRPC, Flutter, and Golang as much as I have. But wait, the fun doesn't stop here!

Stay tuned for my upcoming blogs, where I'll sprinkle more humor, insights, and tech wizardry into your day. Who knows, in my next episode, we might just unveil the secret to debugging code with a magic wand (disclaimer: we can't actually do that, but a coder can dream, right?).

Until then, keep coding, keep laughing, and keep those fingers ready on the refresh button because the next tech tale is just around the corner! 🚀✨"

  
  
  Source code


Github Repo

  
  
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