# gRPC Integration Overview

Expose commands and queries via high-performance gRPC services with automatic code generation.

## What is gRPC Integration?

The `Svrnty.CQRS.Grpc` package with `Svrnty.CQRS.Grpc.Generators` source generator provides automatic gRPC service implementations for all registered commands and queries.

**Key Features:**
- ✅ **Automatic service generation** - Source generators create implementations
- ✅ **Google Rich Error Model** - Structured validation errors
- ✅ **High performance** - Binary Protocol Buffers
- ✅ **Strong typing** - Compile-time safety
- ✅ **gRPC reflection** - Tool support (grpcurl, Postman)
- ✅ **Bidirectional streaming** - Real-time communication
- ✅ **Cross-platform** - Works with any gRPC client

## Quick Start

### Installation

```bash
dotnet add package Svrnty.CQRS.Grpc
dotnet add package Svrnty.CQRS.Grpc.Generators
dotnet add package Grpc.AspNetCore
```

### Basic Setup

**1. Define .proto file:**

```protobuf
syntax = "proto3";

package myapp;

import "google/protobuf/empty.proto";

service CommandService {
  rpc CreateUser (CreateUserCommand) returns (CreateUserResponse);
  rpc DeleteUser (DeleteUserCommand) returns (google.protobuf.Empty);
}

service QueryService {
  rpc GetUser (GetUserQuery) returns (UserDto);
}

message CreateUserCommand {
  string name = 1;
  string email = 2;
}

message CreateUserResponse {
  int32 user_id = 1;
}

message DeleteUserCommand {
  int32 user_id = 1;
}

message GetUserQuery {
  int32 user_id = 1;
}

message UserDto {
  int32 id = 1;
  string name = 2;
  string email = 3;
}
```

**2. Configure services:**

```csharp
var builder = WebApplication.CreateBuilder(args);

// Register CQRS services
builder.Services.AddSvrntyCQRS();
builder.Services.AddDefaultCommandDiscovery();
builder.Services.AddDefaultQueryDiscovery();

// Register commands and queries
builder.Services.AddCommand<CreateUserCommand, int, CreateUserCommandHandler>();
builder.Services.AddCommand<DeleteUserCommand, DeleteUserCommandHandler>();
builder.Services.AddQuery<GetUserQuery, UserDto, GetUserQueryHandler>();

// Add gRPC
builder.Services.AddGrpc();

var app = builder.Build();

// Map auto-generated service implementations
app.MapGrpcService<CommandServiceImpl>();
app.MapGrpcService<QueryServiceImpl>();

// Enable reflection for tools
app.MapGrpcReflectionService();

app.Run();
```

**3. Source generator automatically creates:**
- `CommandServiceImpl` class implementing `CommandService.CommandServiceBase`
- `QueryServiceImpl` class implementing `QueryService.QueryServiceBase`

## How It Works

```
┌─────────────────────────────┐
│  Build Time                 │
├─────────────────────────────┤
│  1. Read .proto files       │
│  2. Discover commands/queries│
│  3. Generate service impls  │
│  4. Compile into assembly   │
└─────────────────────────────┘
            │
            ▼
┌─────────────────────────────┐
│  Runtime                    │
├─────────────────────────────┤
│  gRPC Request               │
│  → Deserialize protobuf     │
│  → Validate                 │
│  → Authorize                │
│  → Execute handler          │
│  → Serialize response       │
└─────────────────────────────┘
```

## Commands via gRPC

### Command Without Result

```csharp
public record DeleteUserCommand
{
    public int UserId { get; init; }
}

public class DeleteUserCommandHandler : ICommandHandler<DeleteUserCommand>
{
    public async Task HandleAsync(DeleteUserCommand command, CancellationToken cancellationToken)
    {
        // Delete user logic
    }
}
```

**.proto definition:**
```protobuf
service CommandService {
  rpc DeleteUser (DeleteUserCommand) returns (google.protobuf.Empty);
}

message DeleteUserCommand {
  int32 user_id = 1;
}
```

**gRPC Client:**
```csharp
var client = new CommandService.CommandServiceClient(channel);

var request = new DeleteUserCommand { UserId = 123 };
await client.DeleteUserAsync(request);
```

### Command With Result

```csharp
public record CreateUserCommand
{
    public string Name { get; init; } = string.Empty;
    public string Email { get; init; } = string.Empty;
}

public class CreateUserCommandHandler : ICommandHandler<CreateUserCommand, int>
{
    public async Task<int> HandleAsync(CreateUserCommand command, CancellationToken cancellationToken)
    {
        // Create user and return ID
        return newUserId;
    }
}
```

**.proto definition:**
```protobuf
service CommandService {
  rpc CreateUser (CreateUserCommand) returns (CreateUserResponse);
}

message CreateUserCommand {
  string name = 1;
  string email = 2;
}

message CreateUserResponse {
  int32 user_id = 1;
}
```

**gRPC Client:**
```csharp
var client = new CommandService.CommandServiceClient(channel);

var request = new CreateUserCommand
{
    Name = "John Doe",
    Email = "john@example.com"
};

var response = await client.CreateUserAsync(request);
var userId = response.UserId;
```

## Queries via gRPC

```csharp
public record GetUserQuery
{
    public int UserId { get; init; }
}

public record UserDto
{
    public int Id { get; init; }
    public string Name { get; init; } = string.Empty;
    public string Email { get; init; } = string.Empty;
}

public class GetUserQueryHandler : IQueryHandler<GetUserQuery, UserDto>
{
    public async Task<UserDto> HandleAsync(GetUserQuery query, CancellationToken cancellationToken)
    {
        // Fetch and return user
    }
}
```

**.proto definition:**
```protobuf
service QueryService {
  rpc GetUser (GetUserQuery) returns (UserDto);
}

message GetUserQuery {
  int32 user_id = 1;
}

message UserDto {
  int32 id = 1;
  string name = 2;
  string email = 3;
}
```

**gRPC Client:**
```csharp
var client = new QueryService.QueryServiceClient(channel);

var request = new GetUserQuery { UserId = 123 };
var user = await client.GetUserAsync(request);
```

## Validation

### Automatic Validation with Rich Error Model

```csharp
public class CreateUserCommandValidator : AbstractValidator<CreateUserCommand>
{
    public CreateUserCommandValidator()
    {
        RuleFor(x => x.Name)
            .NotEmpty()
            .WithMessage("Name is required");

        RuleFor(x => x.Email)
            .EmailAddress()
            .WithMessage("Valid email address is required");
    }
}
```

**Validation failure response:**
```protobuf
google.rpc.Status {
  code: 3  // INVALID_ARGUMENT
  message: "Validation failed"
  details: [
    google.rpc.BadRequest {
      field_violations: [
        { field: "name", description: "Name is required" },
        { field: "email", description: "Valid email address is required" }
      ]
    }
  ]
}
```

**Client handling:**
```csharp
using Grpc.Core;
using Google.Rpc;

try
{
    var response = await client.CreateUserAsync(request);
}
catch (RpcException ex) when (ex.StatusCode == StatusCode.InvalidArgument)
{
    var status = ex.GetRpcStatus();
    var badRequest = status.GetDetail<BadRequest>();

    foreach (var violation in badRequest.FieldViolations)
    {
        Console.WriteLine($"{violation.Field}: {violation.Description}");
    }
}
```

## Performance Benefits

### Binary Protocol

gRPC uses Protocol Buffers (binary format) instead of JSON:

**JSON (HTTP):**
```json
{
  "id": 123,
  "name": "John Doe",
  "email": "john@example.com"
}
```
**Size:** ~71 bytes

**Protobuf (gRPC):**
```
Binary representation
```
**Size:** ~35 bytes

**Result:** ~50% smaller payload

### HTTP/2 Multiplexing

- Multiple requests over single connection
- Header compression
- Server push capability
- Bidirectional streaming

## gRPC vs HTTP Comparison

| Feature | gRPC | HTTP (Minimal API) |
|---------|------|-------------------|
| Protocol | HTTP/2 | HTTP/1.1 or HTTP/2 |
| Format | Protobuf (binary) | JSON (text) |
| Performance | Very fast | Fast |
| Payload Size | Small | Larger |
| Browser Support | Limited (grpc-web) | Full |
| Tooling | grpcurl, Postman | curl, Postman, Swagger |
| Streaming | Native bidirectional | Server-Sent Events |
| Code Generation | Automatic | Automatic |
| Type Safety | Strong | Strong |

### When to Use gRPC

✅ **Use gRPC for:**
- Microservices communication
- High-performance APIs
- Real-time bidirectional streaming
- Internal APIs
- Polyglot environments

### When to Use HTTP

✅ **Use HTTP for:**
- Public APIs
- Browser-based clients
- Simple REST APIs
- Legacy system integration
- Human-readable debugging

### Dual Protocol

**Best of both worlds:**
```csharp
// Same handlers, multiple protocols
builder.Services.AddCommand<CreateUserCommand, int, CreateUserCommandHandler>();

// HTTP endpoints
app.MapSvrntyCommands();

// gRPC endpoints
app.MapGrpcService<CommandServiceImpl>();
```

Clients choose their preferred protocol!

## Documentation

### [Getting Started](getting-started-grpc.md)

First gRPC service:

- Installation
- .proto file creation
- Service registration
- Testing with grpcurl

### [Proto File Setup](proto-file-setup.md)

.proto file creation:

- Syntax and conventions
- Message definitions
- Service definitions
- Importing common types

### [Source Generators](source-generators.md)

How code generation works:

- Build-time generation
- Generated code structure
- Customization options
- Troubleshooting

### [Service Implementation](service-implementation.md)

Generated service implementations:

- CommandServiceImpl
- QueryServiceImpl
- Validation integration
- Authorization integration

### [gRPC Reflection](grpc-reflection.md)

gRPC reflection for tools:

- Enabling reflection
- Using grpcurl
- Postman support
- Service discovery

### [gRPC Clients](grpc-clients.md)

Consuming gRPC services:

- C# client
- TypeScript client
- Go client
- Python client

### [gRPC Troubleshooting](grpc-troubleshooting.md)

Common issues:

- Connection errors
- Validation errors
- Code generation issues
- Performance tuning

## Best Practices

### ✅ DO

- Use gRPC for microservices
- Define clear .proto contracts
- Use gRPC reflection in development
- Handle RpcException properly
- Version your services
- Use deadlines/timeouts
- Enable compression

### ❌ DON'T

- Don't skip error handling
- Don't expose gRPC publicly without security
- Don't ignore validation
- Don't use gRPC for browser apps without grpc-web
- Don't forget cancellation tokens

## What's Next?

- **[Getting Started](getting-started-grpc.md)** - Create your first gRPC service
- **[Proto File Setup](proto-file-setup.md)** - Learn .proto file conventions
- **[Source Generators](source-generators.md)** - Understand code generation
- **[Service Implementation](service-implementation.md)** - Explore generated code
- **[gRPC Clients](grpc-clients.md)** - Build gRPC clients

## See Also

- [Commands Overview](../core-features/commands/README.md)
- [Queries Overview](../core-features/queries/README.md)
- [Validation Overview](../core-features/validation/README.md)
- [HTTP Integration](../http-integration/README.md)
- [Getting Started: Choosing HTTP or gRPC](../getting-started/06-choosing-http-or-grpc.md)