Fail promise in MessageToByteHandler write error cases (#1096)

* Fail promise in MessageToByteHandler write error cases

* Add test case for MessageToByteHandler failing write promises

Author: wlisac

Sources/NIO/Codec.swift

@@ -767,6 +767,7 @@ extension MessageToByteHandler {
         case .notInChannelYet:
             preconditionFailure("MessageToByteHandler.write called before it was added to a Channel")
         case .error(let error):
+            promise?.fail(error)
             context.fireErrorCaught(error)
             return
         case .done:
@@ -784,6 +785,7 @@ extension MessageToByteHandler {
             context.write(self.wrapOutboundOut(self.buffer!), promise: promise)
         } catch {
             self.state = .error(error)
+            promise?.fail(error)
             context.fireErrorCaught(error)
         }
     }

Tests/LinuxMain.swift

@@ -75,6 +75,7 @@ import XCTest
          testCase(IntegerTypesTest.allTests),
          testCase(MarkedCircularBufferTests.allTests),
          testCase(MessageToByteEncoderTest.allTests),
+         testCase(MessageToByteHandlerTest.allTests),
          testCase(MulticastTest.allTests),
          testCase(NIOAnyDebugTest.allTests),
          testCase(NIOCloseOnErrorHandlerTest.allTests),

Tests/NIOTests/CodecTest+XCTest.swift

@@ -74,3 +74,12 @@ extension MessageToByteEncoderTest {
    }
 }
 
+extension MessageToByteHandlerTest {
+
+   static var allTests : [(String, (MessageToByteHandlerTest) -> () throws -> Void)] {
+      return [
+                ("testThrowingEncoderFailsPromises", testThrowingEncoderFailsPromises),
+           ]
+   }
+}
+

Tests/NIOTests/CodecTest.swift

@@ -1587,3 +1587,31 @@ private class PairOfBytesDecoder: ByteToMessageDecoder {
         return .needMoreData
     }
 }
+
+public final class MessageToByteHandlerTest: XCTestCase {
+    private struct ThrowingMessageToByteEncoder: MessageToByteEncoder {
+        private struct HandlerError: Error { }
+        
+        typealias OutboundIn = Int
+
+        public func encode(data value: Int, out: inout ByteBuffer) throws {
+            if value == 0 {
+                out.writeInteger(value)
+            } else {
+                throw HandlerError()
+            }
+        }
+    }
+    
+    func testThrowingEncoderFailsPromises() {
+        let channel = EmbeddedChannel()
+        
+        XCTAssertNoThrow(try channel.pipeline.addHandler(MessageToByteHandler(ThrowingMessageToByteEncoder())).wait())
+        
+        XCTAssertNoThrow(try channel.writeAndFlush(0).wait())
+        
+        XCTAssertThrowsError(try channel.writeAndFlush(1).wait())
+        
+        XCTAssertThrowsError(try channel.writeAndFlush(0).wait())
+    }
+}