# gRPC Reflection

Enable gRPC reflection for development tools and service discovery.

## Overview

gRPC reflection allows clients to discover available services and their methods at runtime without needing .proto files. This enables:

- ✅ **grpcurl** - Command-line testing
- ✅ **Postman** - GUI testing
- ✅ **BloomRPC** - Desktop gRPC client
- ✅ **Service discovery** - Dynamic client generation
- ✅ **Development** - Faster iteration

## Setup

### Install Package

```bash
dotnet add package Grpc.AspNetCore.Server.Reflection
```

### Enable Reflection

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

builder.Services.AddGrpc();
builder.Services.AddGrpcReflection();  // Add reflection

var app = builder.Build();

app.MapGrpcService<CommandServiceImpl>();
app.MapGrpcService<QueryServiceImpl>();
app.MapGrpcReflectionService();  // Map reflection service

app.Run();
```

## Using grpcurl

### Installation

**macOS:**
```bash
brew install grpcurl
```

**Windows:**
```powershell
choco install grpcurl
```

**Linux:**
```bash
# Download from GitHub releases
wget https://github.com/fullstorydev/grpcurl/releases/download/v1.8.9/grpcurl_1.8.9_linux_x86_64.tar.gz
tar -xvf grpcurl_1.8.9_linux_x86_64.tar.gz
sudo mv grpcurl /usr/local/bin/
```

### List Services

```bash
grpcurl -plaintext localhost:5001 list
```

**Output:**
```
grpc.reflection.v1alpha.ServerReflection
myapp.CommandService
myapp.QueryService
```

### Describe Service

```bash
grpcurl -plaintext localhost:5001 describe myapp.CommandService
```

**Output:**
```
myapp.CommandService is a service:
service CommandService {
  rpc CreateUser ( .myapp.CreateUserCommand ) returns ( .myapp.CreateUserResponse );
  rpc DeleteUser ( .myapp.DeleteUserCommand ) returns ( .google.protobuf.Empty );
}
```

### Describe Message

```bash
grpcurl -plaintext localhost:5001 describe myapp.CreateUserCommand
```

**Output:**
```
myapp.CreateUserCommand is a message:
message CreateUserCommand {
  string name = 1;
  string email = 2;
  int32 age = 3;
}
```

### Call Method

```bash
grpcurl -plaintext \
  -d '{"name": "John Doe", "email": "john@example.com", "age": 25}' \
  localhost:5001 \
  myapp.CommandService/CreateUser
```

**Response:**
```json
{
  "userId": 42
}
```

### With Metadata

```bash
grpcurl -plaintext \
  -H "Authorization: Bearer eyJhbGc..." \
  -H "X-Request-ID: abc-123" \
  -d '{"userId": 42}' \
  localhost:5001 \
  myapp.QueryService/GetUser
```

## Using Postman

### Setup

1. Create new gRPC request
2. Enter server URL: `localhost:5001`
3. Click "Use Server Reflection"
4. Postman discovers all services

### Making Requests

1. Select service (e.g., `CommandService`)
2. Select method (e.g., `CreateUser`)
3. Fill in message fields
4. Click "Invoke"
5. View response

### Adding Headers

1. Click "Metadata" tab
2. Add key-value pairs:
   - Key: `Authorization`
   - Value: `Bearer token...`
3. Click "Invoke"

## Using BloomRPC

### Installation

Download from: https://github.com/bloomrpc/bloomrpc

### Setup

1. Launch BloomRPC
2. Click "+" to add server
3. Enter address: `localhost:5001`
4. Enable "Use Server Reflection"
5. Services appear in left panel

### Making Requests

1. Select method from tree
2. Edit JSON request
3. Click play button
4. View response

## Production Considerations

### Disable in Production

```csharp
if (app.Environment.IsDevelopment())
{
    app.MapGrpcReflectionService();
}
```

### Conditional Registration

```csharp
builder.Services.AddGrpc();

if (builder.Configuration.GetValue<bool>("EnableGrpcReflection"))
{
    builder.Services.AddGrpcReflection();
}

var app = builder.Build();

if (app.Configuration.GetValue<bool>("EnableGrpcReflection"))
{
    app.MapGrpcReflectionService();
}
```

### With Authentication

```csharp
app.MapGrpcReflectionService().RequireAuthorization("AdminOnly");
```

## Alternatives to Reflection

### Static .proto Files

Distribute .proto files to clients:

```bash
# Client downloads .proto files
curl https://api.example.com/protos/cqrs_services.proto > cqrs_services.proto

# Generate client code
protoc --csharp_out=. --grpc_out=. cqrs_services.proto
```

### Client Libraries

Publish NuGet package with generated client code:

```xml
<ItemGroup>
  <Protobuf Include="Protos\cqrs_services.proto" GrpcServices="Client" />
</ItemGroup>
```

```bash
dotnet pack -c Release
dotnet nuget push MyApi.Client.1.0.0.nupkg
```

## Best Practices

### ✅ DO

- Use reflection in development
- Disable reflection in production (or secure it)
- Use grpcurl for quick testing
- Document gRPC endpoints
- Version your services

### ❌ DON'T

- Don't expose reflection publicly without auth
- Don't rely on reflection for production clients
- Don't skip .proto file documentation

## See Also

- [gRPC Integration Overview](README.md)
- [Getting Started](getting-started-grpc.md)
- [gRPC Clients](grpc-clients.md)
- [grpcurl Documentation](https://github.com/fullstorydev/grpcurl)