Enforce request cardinality for unary-request calls also for the case of zero request messages being sent.

Sources/SwiftGRPCNIO/CallHandlers/BaseCallHandler.swift

@@ -19,7 +19,7 @@ public class BaseCallHandler<RequestMessage: Message, ResponseMessage: Message>:
   /// Called when the client has half-closed the stream, indicating that they won't send any further data.
   ///
   /// Overridden by subclasses if the "end-of-stream" event is relevant.
-  public func endOfStreamReceived() { }
+  public func endOfStreamReceived() throws { }
 
   /// Whether this handler can still write messages to the client.
   private var serverCanWrite = true
@@ -30,6 +30,12 @@ public class BaseCallHandler<RequestMessage: Message, ResponseMessage: Message>:
   public init(errorDelegate: ServerErrorDelegate?) {
     self.errorDelegate = errorDelegate
   }
+
+  /// Sends an error status to the client while ensuring that all call context promises are fulfilled.
+  /// Because only the concrete call subclass knows which promises need to be fulfilled, this method needs to be overridden.
+  func sendErrorStatus(_ status: GRPCStatus) {
+    fatalError("needs to be overridden")
+  }
 }
 
 extension BaseCallHandler: ChannelInboundHandler {
@@ -40,10 +46,10 @@ extension BaseCallHandler: ChannelInboundHandler {
   /// return a status with code `.internalError`.
   public func errorCaught(ctx: ChannelHandlerContext, error: Error) {
     errorDelegate?.observe(error)
-
+    
     let transformed = errorDelegate?.transform(error) ?? error
     let status = (transformed as? GRPCStatusTransformable)?.asGRPCStatus() ?? GRPCStatus.processingError
-    self.write(ctx: ctx, data: NIOAny(GRPCServerResponsePart<ResponseMessage>.status(status)), promise: nil)
+    sendErrorStatus(status)
   }
 
   public func channelRead(ctx: ChannelHandlerContext, data: NIOAny) {
@@ -60,7 +66,11 @@ extension BaseCallHandler: ChannelInboundHandler {
       }
 
     case .end:
-      endOfStreamReceived()
+      do {
+        try endOfStreamReceived()
+      } catch {
+        self.errorCaught(ctx: ctx, error: error)
+      }
     }
   }
 }

Sources/SwiftGRPCNIO/CallHandlers/BidirectionalStreamingCallHandler.swift

@@ -36,9 +36,13 @@ public class BidirectionalStreamingCallHandler<RequestMessage: Message, Response
     }
   }
 
-  public override func endOfStreamReceived() {
+  public override func endOfStreamReceived() throws {
     eventObserver?.whenSuccess { observer in
       observer(.end)
     }
   }
+
+  override func sendErrorStatus(_ status: GRPCStatus) {
+    context?.statusPromise.fail(error: status)
+  }
 }

Sources/SwiftGRPCNIO/CallHandlers/ClientStreamingCallHandler.swift

@@ -35,9 +35,13 @@ public class ClientStreamingCallHandler<RequestMessage: Message, ResponseMessage
     }
   }
 
-  public override func endOfStreamReceived() {
+  public override func endOfStreamReceived() throws {
     eventObserver?.whenSuccess { observer in
       observer(.end)
     }
   }
+
+  override func sendErrorStatus(_ status: GRPCStatus) {
+    context?.responsePromise.fail(error: status)
+  }
 }

Sources/SwiftGRPCNIO/CallHandlers/ServerStreamingCallHandler.swift

@@ -28,7 +28,7 @@ public class ServerStreamingCallHandler<RequestMessage: Message, ResponseMessage
   public override func processMessage(_ message: RequestMessage) throws {
     guard let eventObserver = self.eventObserver,
       let context = self.context else {
-        throw GRPCError.server(.requestCardinalityViolation)
+        throw GRPCError.server(.requestCardinalityViolationTooManyRequests)
     }
 
     let resultFuture = eventObserver(message)
@@ -37,4 +37,14 @@ public class ServerStreamingCallHandler<RequestMessage: Message, ResponseMessage
       .cascade(promise: context.statusPromise)
     self.eventObserver = nil
   }
+
+  public override func endOfStreamReceived() throws {
+    if self.eventObserver != nil {
+      throw GRPCError.server(.requestCardinalityViolationTooFewRequests)
+    }
+  }
+
+  override func sendErrorStatus(_ status: GRPCStatus) {
+    context?.statusPromise.fail(error: status)
+  }
 }

Sources/SwiftGRPCNIO/CallHandlers/UnaryCallHandler.swift

@@ -29,7 +29,7 @@ public class UnaryCallHandler<RequestMessage: Message, ResponseMessage: Message>
   public override func processMessage(_ message: RequestMessage) throws {
     guard let eventObserver = self.eventObserver,
       let context = self.context else {
-      throw GRPCError.server(.requestCardinalityViolation)
+      throw GRPCError.server(.requestCardinalityViolationTooManyRequests)
     }
 
     let resultFuture = eventObserver(message)
@@ -38,4 +38,14 @@ public class UnaryCallHandler<RequestMessage: Message, ResponseMessage: Message>
       .cascade(promise: context.responsePromise)
     self.eventObserver = nil
   }
+
+  public override func endOfStreamReceived() throws {
+    if self.eventObserver != nil {
+      throw GRPCError.server(.requestCardinalityViolationTooFewRequests)
+    }
+  }
+
+  override func sendErrorStatus(_ status: GRPCStatus) {
+    context?.responsePromise.fail(error: status)
+  }
 }

Sources/SwiftGRPCNIO/GRPCError.swift

@@ -87,8 +87,11 @@ public enum GRPCServerError: Error, Equatable {
   /// It was not possible to serialize the response protobuf.
   case responseProtoSerializationFailure
 
+  /// Zero requests were sent for a unary-request call.
+  case requestCardinalityViolationTooFewRequests
+
   /// More than one request was sent for a unary-request call.
-  case requestCardinalityViolation
+  case requestCardinalityViolationTooManyRequests
 
   /// The server received a message when it was not in a writable state.
   case serverNotWritable
@@ -143,7 +146,10 @@ extension GRPCServerError: GRPCStatusTransformable {
     case .responseProtoSerializationFailure:
       return GRPCStatus(code: .internalError, message: "could not serialize response proto")
 
-    case .requestCardinalityViolation:
+    case .requestCardinalityViolationTooFewRequests:
+      return GRPCStatus(code: .unimplemented, message: "request cardinality violation; method requires exactly one request but client sent none")
+
+    case .requestCardinalityViolationTooManyRequests:
       return GRPCStatus(code: .unimplemented, message: "request cardinality violation; method requires exactly one request but client sent more")
 
     case .serverNotWritable:

Tests/SwiftGRPCNIOTests/NIOServerWebTests.swift

@@ -42,24 +42,30 @@ class NIOServerWebTests: NIOBasicEchoTestCase {
     data.insert(UInt8(0), at: 0)
     return data
   }
-
-  private func gRPCWebOKTrailers() -> Data {
-    var data = "grpc-status: 0\r\ngrpc-message: OK".data(using: .utf8)!
+  
+  private func gRPCWebTrailers(status: Int, message: String) -> Data {
+    var data = "grpc-status: \(status)\r\ngrpc-message: \(message)".data(using: .utf8)!
     // Add the gRPC prefix with the compression byte and the 4 length bytes.
     for i in 0..<4 {
       data.insert(UInt8((data.count >> (i * 8)) & 0xFF), at: 0)
     }
     data.insert(UInt8(0x80), at: 0)
     return data
   }
+
+  private func gRPCWebOKTrailers() -> Data {
+    return gRPCWebTrailers(status: 0, message: "OK")
+  }
 
-  private func sendOverHTTP1(rpcMethod: String, message: String, handler: @escaping (Data?, Error?) -> Void) {
+  private func sendOverHTTP1(rpcMethod: String, message: String?, handler: @escaping (Data?, Error?) -> Void) {
     let serverURL = URL(string: "http://localhost:5050/echo.Echo/\(rpcMethod)")!
     var request = URLRequest(url: serverURL)
     request.httpMethod = "POST"
     request.setValue("application/grpc-web-text", forHTTPHeaderField: "content-type")
 
-    request.httpBody = gRPCEncodedEchoRequest(message).base64EncodedData()
+    if let message = message {
+      request.httpBody = gRPCEncodedEchoRequest(message).base64EncodedData()
+    }
 
     let sem = DispatchSemaphore(value: 0)
     URLSession.shared.dataTask(with: request) { (data, response, error) in
@@ -85,7 +91,25 @@ extension NIOServerWebTests {
         completionHandlerExpectation.fulfill()
       }
     }
-
+
+    waitForExpectations(timeout: defaultTestTimeout)
+  }
+
+  func testUnaryWithoutRequestMessage() {
+    let expectedData = gRPCWebTrailers(
+      status: 12, message: "request cardinality violation; method requires exactly one request but client sent none")
+    let expectedResponse = expectedData.base64EncodedString()
+
+    let completionHandlerExpectation = expectation(description: "completion handler called")
+
+    sendOverHTTP1(rpcMethod: "Get", message: nil) { data, error in
+      XCTAssertNil(error)
+      if let data = data {
+        XCTAssertEqual(String(data: data, encoding: .utf8), expectedResponse)
+        completionHandlerExpectation.fulfill()
+      }
+    }
+
     waitForExpectations(timeout: defaultTestTimeout)
   }