gRPC

gRPC im Überblick

gRPC ist ein Framework für Remote Procedure Calls – du rufst Funktionen auf einem anderen Server auf, als wären sie lokal. Es kann effizienter als JSON-basierte REST-Kommunikation sein, weil es Protocol Buffers und HTTP/2 nutzt.

REST vs. gRPC:

Beispiel – User-Service:

// user.proto
syntax = "proto3";

service UserService {
  rpc GetUser(GetUserRequest) returns (User);
  rpc ListUsers(ListUsersRequest) returns (stream User);
}

message GetUserRequest {
  int32 id = 1;
}

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

Aufruf (Python):

response = stub.GetUser(GetUserRequest(id=user_id))
print(response.name)

Technisch betrachtet

Protocol Buffers

Schema definieren:

syntax = "proto3";

package myapp;

message Product {
  int32 id = 1;
  string name = 2;
  double price = 3;
  repeated string tags = 4;  // Array
  optional string description = 5;
  
  enum Status {
    UNKNOWN = 0;
    ACTIVE = 1;
    DISCONTINUED = 2;
  }
  Status status = 6;
}

Code generieren:

protoc --python_out=. --grpc_python_out=. product.proto

Generiert typsichere Klassen für unterstützte Programmiersprachen.

Streaming-Patterns

1. Unary (Standard):

rpc GetUser(Request) returns (Response);

Ein Request → Eine Response

2. Server Streaming:

rpc ListUsers(Request) returns (stream User);

Ein Request → Viele Responses

3. Client Streaming:

rpc UploadChunks(stream Chunk) returns (Response);

Viele Requests → Eine Response

4. Bidirectional Streaming:

rpc Chat(stream Message) returns (stream Message);

Viele Requests ↔ Viele Responses (gleichzeitig)

Server-Implementierung (Python)

import grpc
from concurrent import futures
import user_pb2
import user_pb2_grpc

class UserServicer(user_pb2_grpc.UserServiceServicer):
    def GetUser(self, request, context):
        user = db.get_user(request.id)
        if not user:
            context.set_code(grpc.StatusCode.NOT_FOUND)
            context.set_details('User not found')
            return user_pb2.User()
        return user_pb2.User(
            id=user.id,
            name=user.name,
            email=user.email
        )

def serve():
    server = grpc.server(futures.ThreadPoolExecutor(max_workers=max_workers))
    user_pb2_grpc.add_UserServiceServicer_to_server(UserServicer(), server)
    server.add_insecure_port(server_address)
    server.start()
    server.wait_for_termination()

Client-Implementierung

import grpc
import user_pb2
import user_pb2_grpc

channel = grpc.insecure_channel(server_address)
stub = user_pb2_grpc.UserServiceStub(channel)

# Unary Call
response = stub.GetUser(user_pb2.GetUserRequest(id=user_id))

# Server Streaming
for user in stub.ListUsers(user_pb2.ListUsersRequest()):
    print(user.name)

Error Handling

try:
    response = stub.GetUser(request)
except grpc.RpcError as e:
    if e.code() == grpc.StatusCode.NOT_FOUND:
        print("User not found")
    elif e.code() == grpc.StatusCode.DEADLINE_EXCEEDED:
        print("Timeout")
    else:
        print(f"Error: {e.details()}")

gRPC vs. REST – Wann was?