Trailers sent on idle streams deserve to be sent too.

Sources/NIOHTTP2/NGHTTP2Session.swift

@@ -693,6 +693,14 @@ class NGHTTP2Session {
             // TODO(cory): Error handling.
             precondition(isEndStream)
             streamData.dataProvider.bufferEOF(trailers: headers)
+
+            if case .pending = streamData.dataProvider.state {
+                // The data provider is currently in the pending state, we need to tell nghttp2 it's active again so
+                // the trailers get emitted.
+                let rc = nghttp2_session_resume_data(self.session, frame.streamID.networkStreamID!)
+                precondition(rc == 0)
+                streamData.dataProvider.didResume()
+            }
             return
         }
 

Tests/NIOHTTP2Tests/SimpleClientServerTests+XCTest.swift

@@ -48,6 +48,7 @@ extension SimpleClientServerTests {
                 ("testFailingUnflushedWritesForGoaway", testFailingUnflushedWritesForGoaway),
                 ("testFailingFlushedWritesForGoaway", testFailingFlushedWritesForGoaway),
                 ("testSendingTrailers", testSendingTrailers),
+                ("testSendingTrailersWhenDataProviderIsIdle", testSendingTrailersWhenDataProviderIsIdle),
                 ("test1XXResponseHeaderFields", test1XXResponseHeaderFields),
                 ("testPriorityFramesAreNotEmitted", testPriorityFramesAreNotEmitted),
                 ("testStreamClosedWithNoError", testStreamClosedWithNoError),

Tests/NIOHTTP2Tests/SimpleClientServerTests.swift

@@ -1006,6 +1006,41 @@ class SimpleClientServerTests: XCTestCase {
         XCTAssertNoThrow(try self.serverChannel.finish())
     }
 
+    func testSendingTrailersWhenDataProviderIsIdle() throws {
+        // Begin by getting the connection up.
+        try self.basicHTTP2Connection()
+
+        // We're now going to try to send a request from the client to the server. This request will be one headers frame, one
+        // data frame, and then another headers frame for trailers. The headers frame for trailers will be sent late, to
+        // reproduce https://github.com/apple/swift-nio-http2/issues/24.
+        let headers = HTTPHeaders([(":path", "/"), (":method", "POST"), (":scheme", "https"), (":authority", "localhost")])
+        let trailers = HTTPHeaders([("x-trailers-field", "true")])
+        var requestBody = self.clientChannel.allocator.buffer(capacity: 128)
+        requestBody.write(staticString: "A simple HTTP/2 request.")
+
+        let clientStreamID = HTTP2StreamID()
+        let reqFrame = HTTP2Frame(streamID: clientStreamID, payload: .headers(headers))
+        let reqBodyFrame = HTTP2Frame(streamID: clientStreamID, payload: .data(.byteBuffer(requestBody)))
+        var trailerFrame = HTTP2Frame(streamID: clientStreamID, payload: .headers(trailers))
+        trailerFrame.flags.insert(.endStream)
+
+        let serverStreamID = try self.assertFramesRoundTrip(frames: [reqFrame, reqBodyFrame], sender: self.clientChannel, receiver: self.serverChannel).first!.streamID
+
+        // Now we can send the next trailers.
+        XCTAssertNoThrow(try self.assertFramesRoundTrip(frames: [trailerFrame], sender: self.clientChannel, receiver: self.serverChannel))
+
+        // Let's send a quick response back. This response should also contain trailers.
+        let responseHeaders = HTTPHeaders([(":status", "200"), ("content-length", "0")])
+        let respFrame = HTTP2Frame(streamID: serverStreamID, payload: .headers(responseHeaders))
+        var respTrailersFrame = HTTP2Frame(streamID: serverStreamID, payload: .headers(trailers))
+        respTrailersFrame.flags.insert(.endStream)
+        XCTAssertNoThrow(try self.assertFramesRoundTrip(frames: [respFrame], sender: self.serverChannel, receiver: self.clientChannel))
+        XCTAssertNoThrow(try self.assertFramesRoundTrip(frames: [respTrailersFrame], sender: self.serverChannel, receiver: self.clientChannel))
+
+        XCTAssertNoThrow(try self.clientChannel.finish())
+        XCTAssertNoThrow(try self.serverChannel.finish())
+    }
+
     func test1XXResponseHeaderFields() throws {
         // Begin by getting the connection up.
         try self.basicHTTP2Connection()

Tests/NIOHTTP2Tests/TestUtilities.swift

@@ -119,7 +119,7 @@ extension XCTestCase {
         var receivedFrames = [HTTP2Frame]()
 
         for frame in frames {
-            let receivedFrame = try receiver.assertReceivedFrame()
+            let receivedFrame = try receiver.assertReceivedFrame(file: file, line: line)
             receivedFrame.assertFrameMatches(this: frame, file: file, line: line)
             receivedFrames.append(receivedFrame)
         }