grpc-graphql-gateway

A high-performance Rust gateway that bridges gRPC services to GraphQL with full Apollo Federation v2 support.

Transform your gRPC microservices into a unified GraphQL API with zero GraphQL code. This gateway dynamically generates GraphQL schemas from protobuf descriptors and routes requests to your gRPC backends via Tonic, providing a seamless bridge between gRPC and GraphQL ecosystems.

✨ Features

Core Capabilities

• 🚀 Dynamic Schema Generation - Automatic GraphQL schema from protobuf descriptors
• ⚡ Full Operation Support - Queries, Mutations, and Subscriptions
• 🔌 WebSocket Subscriptions - Real-time data via GraphQL subscriptions (graphql-ws protocol)
• 📤 File Uploads - Multipart form data support for file uploads
• 🎯 Type Safety - Leverages Rust's type system for robust schema generation

Federation & Enterprise

• 🌐 Apollo Federation v2 - Complete federation support with entity resolution
• 🔄 Entity Resolution - Production-ready resolver with DataLoader batching
• 🚫 No N+1 Queries - Built-in DataLoader prevents performance issues
• 🔗 All Federation Directives - @key, @external, @requires, @provides, @shareable
• 📊 Batch Operations - Efficient entity resolution with automatic batching

Developer Experience

• 🛠️ Code Generation - protoc-gen-graphql-template generates starter gateway code
• 🔧 Middleware Support - Extensible middleware for auth, logging, and observability
• 📝 Rich Examples - Complete working examples for all features
• 🧪 Well Tested - Comprehensive test coverage

🚀 Quick Start

Installation

[dependencies]
grpc-graphql-gateway = "0.1"
tokio = { version = "1", features = ["full"] }
tonic = "0.12"

Basic Gateway

use grpc_graphql_gateway::{Gateway, GrpcClient};

const DESCRIPTORS: &[u8] = include_bytes!(concat!(env!("OUT_DIR"), "/graphql_descriptor.bin"));

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let gateway = Gateway::builder()
        .with_descriptor_set_bytes(DESCRIPTORS)
        .add_grpc_client(
            "greeter.Greeter",
            GrpcClient::builder("http://127.0.0.1:50051").connect_lazy()?,
        )
        .build()?;

    gateway.serve("0.0.0.0:8888").await?;
    Ok(())
}

Your gateway is now running!

• GraphQL HTTP: http://localhost:8888/graphql
• GraphQL WebSocket: ws://localhost:8888/graphql/ws

Generate Descriptors

Add to your build.rs:

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let out_dir = std::env::var("OUT_DIR")?;
    
    tonic_build::configure()
        .build_server(false)
        .build_client(false)
        .file_descriptor_set_path(
            std::path::PathBuf::from(&out_dir).join("graphql_descriptor.bin")
        )
        .compile_protos(&["proto/your_service.proto"], &["proto"])?;
    
    Ok(())
}

📖 Usage Examples

Queries, Mutations & Subscriptions

Annotate your proto file with GraphQL directives:

service UserService {
  option (graphql.service) = {
    host: "localhost:50051"
    insecure: true
  };

  // Query
  rpc GetUser(GetUserRequest) returns (User) {
    option (graphql.schema) = {
      type: QUERY
      name: "user"
    };
  }

  // Mutation
  rpc CreateUser(CreateUserRequest) returns (User) {
    option (graphql.schema) = {
      type: MUTATION
      name: "createUser"
      request { name: "input" }
    };
  }

  // Subscription (server streaming)
  rpc WatchUser(WatchUserRequest) returns (stream User) {
    option (graphql.schema) = {
      type: SUBSCRIPTION
      name: "userUpdates"
    };
  }
}

GraphQL operations:

# Query
query {
  user(id: "123") {
    id
    name
    email
  }
}

# Mutation
mutation {
  createUser(input: { name: "Alice", email: "alice@example.com" }) {
    id
    name
  }
}

# Subscription
subscription {
  userUpdates(id: "123") {
    id
    name
    status
  }
}

File Uploads

The gateway automatically supports GraphQL file uploads via multipart requests:

message UploadAvatarRequest {
  string user_id = 1;
  bytes avatar = 2;  // Maps to Upload scalar in GraphQL
}

curl http://localhost:8888/graphql \
  --form 'operations={"query": "mutation($file: Upload!) { uploadAvatar(input:{userId:\"123\", avatar:$file}) { userId size } }", "variables": {"file": null}}' \
  --form 'map={"0": ["variables.file"]}' \
  --form '0=@avatar.png'

Field-Level Control

message User {
  string id = 1 [(graphql.field) = { required: true }];
  string email = 2 [(graphql.field) = { name: "emailAddress" }];
  string internal_id = 3 [(graphql.field) = { omit: true }];
  string password_hash = 4 [(graphql.field) = { omit: true }];
}

🌐 Apollo Federation v2

Build federated GraphQL architectures with multiple subgraphs.

Defining Entities

message User {
  option (graphql.entity) = {
    keys: "id"
    resolvable: true
  };
  
  string id = 1 [(graphql.field) = { required: true }];
  string email = 2 [(graphql.field) = { shareable: true }];
  string name = 3 [(graphql.field) = { shareable: true }];
}

message Product {
  option (graphql.entity) = {
    keys: "upc"
    resolvable: true
  };
  
  string upc = 1 [(graphql.field) = { required: true }];
  string name = 2 [(graphql.field) = { shareable: true }];
  int32 price = 3 [(graphql.field) = { shareable: true }];
  User created_by = 4 [(graphql.field) = { 
    name: "createdBy"
    shareable: true 
  }];
}

Entity Resolution with DataLoader

The gateway includes production-ready entity resolution with automatic batching:

use grpc_graphql_gateway::{
    Gateway, GrpcClient, EntityResolverMapping, GrpcEntityResolver
};

// Configure entity resolver with DataLoader batching
let resolver = GrpcEntityResolver::builder(client_pool)
    .register_entity_resolver(
        "User",
        EntityResolverMapping {
            service_name: "UserService".to_string(),
            method_name: "GetUser".to_string(),
            key_field: "id".to_string(),
        }
    )
    .build();

let gateway = Gateway::builder()
    .with_descriptor_set_bytes(DESCRIPTORS)
    .enable_federation()
    .with_entity_resolver(Arc::new(resolver))
    .add_grpc_client("UserService", user_client)
    .serve("0.0.0.0:8891")
    .await?;

Benefits:

• ✅ No N+1 Queries - DataLoader batches concurrent entity requests
• ✅ Automatic Batching - Multiple entities resolved in single operation
• ✅ Production Ready - Comprehensive error handling and logging

Extending Entities

message UserReviews {
  option (graphql.entity) = {
    extend: true
    keys: "id"
  };
  
  string id = 1 [(graphql.field) = {
    external: true
    required: true
  }];
  
  repeated Review reviews = 2 [(graphql.field) = {
    requires: "id"
  }];
}

Federation Directives

Running with Apollo Router

# Start your federation subgraphs
cargo run --bin federation

# Compose the supergraph
./examples/federation/compose_supergraph.sh

# Run Apollo Router
router --supergraph examples/federation/supergraph.graphql --dev

Query the federated graph:

query {
  product(upc: "123") {
    upc
    name
    price
    createdBy {
      id
      name
      email  # Resolved from User subgraph!
    }
  }
}

🔧 Advanced Features

Middleware

use grpc_graphql_gateway::middleware::{Middleware, Context};

struct AuthMiddleware;

#[async_trait::async_trait]
impl Middleware for AuthMiddleware {
    async fn call(
        &self,
        ctx: &mut Context,
        next: Box<dyn Fn(&mut Context) -> BoxFuture<'_, Result<()>>>,
    ) -> Result<()> {
        // Validate auth token
        let token = ctx.headers().get("authorization")
            .ok_or_else(|| Error::Unauthorized)?;
        
        // Add user info to context
        ctx.extensions_mut().insert(UserInfo { /* ... */ });
        
        next(ctx).await
    }
}

let gateway = Gateway::builder()
    .add_middleware(AuthMiddleware)
    .build()?;

Custom Error Handling

let gateway = Gateway::builder()
    .with_error_handler(|error| {
        // Log errors, send to monitoring, etc.
        tracing::error!("GraphQL Error: {}", error);
        error
    })
    .build()?;

Response Plucking

Extract nested fields as top-level responses:

message ListUsersResponse {
  repeated User users = 1;
  int32 total = 2;
}

rpc ListUsers(ListUsersRequest) returns (ListUsersResponse) {
  option (graphql.schema) = {
    type: QUERY
    name: "users"
    response {
      pluck: "users"  // Returns [User] instead of ListUsersResponse
    }
  };
}

📊 Type Mapping

🛠️ Code Generation

Generate a starter gateway:

# Install the generator
cargo install grpc-graphql-gateway --bin protoc-gen-graphql-template

# Generate gateway code
protoc \
  --plugin=protoc-gen-graphql-template=target/debug/protoc-gen-graphql-template \
  --graphql-template_out=. \
  --proto_path=proto \
  proto/federation_example.proto

# Run the generated gateway
cargo run --bin graphql

The generator creates:

• Complete gateway implementation
• Example queries/mutations/subscriptions
• Service configuration
• Ready-to-run code

📚 Examples

Greeter Example

Basic query, mutation, subscription, and file upload:

cargo run --bin greeter

Open http://localhost:8888/graphql and try:

query { hello(name: "World") { message } }
mutation { updateGreeting(input: {name: "GraphQL", salutation: "Hey"}) { message } }
subscription { streamHello(name: "Stream") { message } }

Federation Example

Complete federated microservices with entity resolution:

cargo run --bin federation

Demonstrates:

• 3 federated subgraphs (User, Product, Review)
• Entity resolution with DataLoader batching
• Cross-subgraph queries
• @shareable fields
• Entity extensions

🎯 Best Practices

Federation

1. Define Clear Boundaries - Each subgraph owns its entities
2. Use @shareable Wisely - Mark fields resolved by multiple subgraphs
3. Leverage DataLoader - Prevent N+1 queries with batch resolution
4. Composite Keys - Use when entities need multiple identifiers
5. Minimize @requires - Only specify truly required fields

Performance

1. Enable Connection Pooling - Reuse gRPC connections
2. Use Lazy Connections - Connect on first use
3. Implement Caching - Cache frequently accessed entities
4. Batch Operations - Use DataLoader for entity resolution
5. Monitor Metrics - Track query performance and batch sizes

Security

1. Validate Inputs - Use field-level validation
2. Omit Sensitive Fields - Use omit: true for internal data
3. Implement Auth Middleware - Centralize authentication
4. Rate Limiting - Protect against abuse
5. TLS/SSL - Secure gRPC connections in production

🧪 Testing

# Run all tests
cargo test

# Run with logging
RUST_LOG=debug cargo test

# Run specific test
cargo test test_federation_config

📦 Project Structure

grpc-graphql-gateway-rs/
├── src/
│   ├── lib.rs              # Public API
│   ├── gateway.rs          # Gateway implementation
│   ├── schema.rs           # Schema builder
│   ├── federation.rs       # Federation support
│   ├── dataloader.rs       # DataLoader for batching
│   ├── grpc_client.rs      # gRPC client management
│   ├── middleware.rs       # Middleware system
│   └── runtime.rs          # HTTP/WebSocket server
├── proto/
│   ├── graphql.proto       # GraphQL annotations
│   └── *.proto            # Your service definitions
├── examples/
│   ├── greeter/           # Basic example
│   └── federation/        # Federation example
└── tests/                 # Integration tests

🤝 Contributing

Contributions are welcome! Please feel free to submit a Pull Request. For major changes, please open an issue first to discuss what you would like to change.

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🙏 Acknowledgments

• Inspired by grpc-graphql-gateway (Go)
• Built with async-graphql
• Powered by tonic
• Federation based on Apollo Federation v2

🔗 Links

• Documentation
• Crates.io
• Repository
• Examples
• Federation Guide
• Entity Resolution Guide

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