API_gRPC

Definitions

Main-Source

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# gRPC

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# What does it mean?

g	gRPC
R	Remote
P	Procedure
C	Calls

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# What is it used for?

• Client ⇔ Server Communication
• Server ⇔ Server Communication
• X ⇔ Y Communication

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# Transport channel (ツ)

gRPC is agnostic about the transport channel.

For client server communication in a web application we use gRPC over HTTP.

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# Why use it rather than [X] ?

• Efficient serialization → Small message size
• Interface definition can easily be shared (.protobuf files)
• Support for both server-side code generation and client generation for many languages
• Integrating systems in different languages

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# Programming Model

ClientServerDoSomething()responseDataClientServer

A client application calls a method on a server application on a different machine as if it were a local object.

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# Multiple Different Clients

MethodCall()ResponseMethodCall()ResponseClient AC#Client BC++ServerC#

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# Message Format

By default gRPC uses Protocol Buffers

// This is how you define services and message types.
 
service Greeter {
  rpc SayHello (HelloRequest) returns (HelloReply);
}
 
message HelloRequest {
  string firstName = 1;
  string lastName = 2;
}
 
message HelloReply {
  string greeting = 1;
}

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# Adding gRPC and Protobuf to a .NET Solution

You need three projects.

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• Install NuGet Packages in Shared project:

Grpc.Net.Client
Google.Protobuf
Grpc.Tools

• Add folder Grpc in Shared project
• Add reward.proto file in that folder

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// File: reward.proto
syntax = "proto3";
option csharp_namespace = "SavingsPlanner.Shared.Grpc";
package Rewards;
 
service Rewards {
  rpc GetRewards (RewardRequest) returns (RewardReply);
}
 
message RewardRequest {}
 
message RewardReply {
  repeated RewardItem rewards = 1;
}
 
message RewardItem {
  int32 id = 1;
  string title = 2;
  double targetAmount = 3;
  string description = 4;
}

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Add code in Shared .csproj file

<ItemGroup>
  <Protobuf 
    Include="Grpc/reward.proto" 
    GrpcServices="Server,Client">
  </Protobuf>
</ItemGroup>

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• Install NuGet Packages in Client project:

Grpc.Net.Client.Web

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// Add in Program.cs of client project
builder.Services.AddSingleton(services =>
{
  var httpClient = new HttpClient(
    new GrpcWebHandler(
      GrpcWebMode.GrpcWeb, 
      new HttpClientHandler()));
  var baseUri = services
    .GetRequiredService<NavigationManager>()
    .BaseUri;
  var channel = GrpcChannel
    .ForAddress(
      baseUri, 
      new GrpcChannelOptions { HttpClient = httpClient });
  return new Rewards.RewardsClient(channel);   
});

If you have a seperate Client-Server architecture - add the following line:

builder.Services.AddSingleton(services =>  
{  
    var httpClient = new HttpClient(  
        ...
    !--
    var baseUri = @"http://localhost:5125";  
    !--
    var channel = GrpcChannel  
        ...  
    return new School.SchoolClient(channel);     
});

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// in a Blazor component on the client
@inject Rewards.RewardsClient RewardsClient
 
private async Task LoadDataAsync()
{
  var rewardsResponse = 
    await RewardsClient.GetRewardsAsync(new RewardsRequest());
  rewards = rewardsResponse.Rewards.ToArray();
}

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• Install NuGet Packages in Server project:

Grpc.AspNetCore.Web
Grpc.AspNetCore

• Implement a service by deriving from generated classes in Shared project (next slide)

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public class RewardService : Rewards.RewardsBase
{
  private readonly IRepository<Reward> _repository;
  public override async Task<RewardReply> GetRewards(
    RewardRequest request, serverCallContext context)
  {
    var reply = new RewardReply();
    var items = await _repository.GetAllAsync<RewardItem>();
    reply.Rewards.AddRange(items);
    return reply;
  }
}

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// in Program.cs of Server project
builder.Services.AddGrpc();
app.UseGrpcWeb();
app.MapGrpcService<RewardService>().EnableGrpcWeb();

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// Automapper configuration 
// for transformation to generated type
CreateMap<Reward, RewardItem>()
  .ForMember(
    r => r.TargetAmount,
    opt => opt.MapFrom(src => (double)src.TargetAmount));