Client-Side Streaming gRPC : A Real-World File Upload Example

This project demonstrates client-side streaming using gRPC with a Spring Boot application. It includes:

• A gRPC server that receives file chunks via stream and reconstructs them.

• A REST client that accepts multipart/form-data uploads and streams the file to the server over gRPC.

🔧 Technologies Used

• Java 11
• Spring Boot 2.7.x
• gRPC (1.54.0)
• Protocol Buffers (proto3)
• Maven
• WebFlux + Server-Sent Events (SSE) for REST integration

✅Code Repository Link 

Link - grpc-client-streaming

1. Start gRPC Server

• cd grpc-client-streaming-upload-server mvn spring-boot:run

2. Start REST Client

• cd grpc-client-streaming-upload-client mvn spring-boot:run

3. Upload a File via REST

• curl -X POST http://localhost:8080/upload
  -H "Content-Type: multipart/form-data"
  -F "file=@/path/to/your/file.txt"

✅ Project Structure

Server: grpc-client-streaming-upload

---

• grpc-client-streaming-upload/
  ├── src/
  │   └── main/
  │       ├── java/com/example/grpc/
  │       │   ├── GrpcApplication.java         # Spring Boot main class
  │       │   └── FileUploadService.java       # gRPC service implementation
  │       ├── proto/upload.proto               # gRPC service and message definitions
  │       └── resources/application.properties # gRPC + HTTP port config
  └── pom.xml                                  # Maven config with protobuf plugin

Client: grpc-client-streaming-upload-client

---

• grpc-client-streaming-upload-client/
  ├── src/
  │   └── main/
  │       ├── java/com/example/grpc/
  │       │   ├── GrpcClientApplication.java    # Spring Boot main class
  │       │   └── FileUploadController.java     # REST endpoint that calls gRPC client
  │       ├── proto/upload.proto                # Same proto for stub generation
  │       └── resources/application.properties  # gRPC target address config
  └── pom.xml                                   # Maven config with protobuf plugin

🔍 Quick Explanation of Key Classes

---

🧬 Proto File 

---

• syntax = "proto3";
  option java_multiple_files = true;
  option java_package = "com.example.grpc";
  option java_outer_classname = "FileUploadProto";
  service FileUploader {
    rpc UploadFile (stream FileChunk) returns (UploadStatus);
  }
  message FileChunk {
    string filename = 1;
    bytes content = 2;
  }
  message UploadStatus {
    bool success = 1;
    string message = 2;
  }

🔁 Diagram: REST → gRPC Flowe

---

• [User/Client] ──HTTP/POST──> REST Controller (Spring Boot)
                           └──▶ Reads multipart file
                                └──▶ Opens gRPC stream
                                     └──▶ Sends file chunks
                                          └──▶ gRPC Server handles each chunk
                                               └──▶ On complete, sends UploadStatus

✅ When to Use gRPC Client-Side Streaming

🚫 Anti-Patterns / When Not to Use It

🚫 gRPC Anti-Patterns & When Not to Use It

 🚀 gRPC Streaming Performance Comparison