Fixes a bug

Author: fabianfett

Sources/AsyncHTTPClient/ConnectionPool/HTTPRequestStateMachine+Demand.swift

@@ -61,13 +61,18 @@ extension HTTPRequestStateMachine {
             }
         }
 
-        mutating func channelReadComplete() -> CircularBuffer<ByteBuffer> {
+        mutating func channelReadComplete() -> CircularBuffer<ByteBuffer>? {
             switch self.state {
             case .waitingForBytes(let buffer):
-                var newBuffer = buffer
-                newBuffer.removeAll(keepingCapacity: true)
-                self.state = .waitingForReadOrDemand(newBuffer)
-                return buffer
+                if buffer.isEmpty {
+                    self.state = .waitingForRead(buffer)
+                    return nil
+                } else {
+                    var newBuffer = buffer
+                    newBuffer.removeAll(keepingCapacity: true)
+                    self.state = .waitingForReadOrDemand(newBuffer)
+                    return buffer
+                }
 
             case .waitingForRead,
                  .waitingForDemand,

Sources/AsyncHTTPClient/ConnectionPool/HTTPRequestStateMachine.swift

@@ -426,7 +426,11 @@ struct HTTPRequestStateMachine {
             return self.avoidingStateMachineCoW { (state) -> Action in
                 let buffer = streamState.channelReadComplete()
                 state = .running(requestState, .receivingBody(head, streamState))
-                return .forwardResponseBodyParts(buffer)
+                if let buffer = buffer {
+                    return .forwardResponseBodyParts(buffer)
+                } else {
+                    return .wait
+                }
             }
 
         case .modifying:

Tests/AsyncHTTPClientTests/HTTPRequestStateMachineTests+XCTest.swift

@@ -38,6 +38,7 @@ extension HTTPRequestStateMachineTests {
             ("testRequestIsNotSendUntilChannelIsWritable", testRequestIsNotSendUntilChannelIsWritable),
             ("testConnectionBecomesInactiveWhileWaitingForWritable", testConnectionBecomesInactiveWhileWaitingForWritable),
             ("testResponseReadingWithBackpressure", testResponseReadingWithBackpressure),
+            ("testChannelReadCompleteTriggersButNoBodyDataWasReceivedSoFar", testChannelReadCompleteTriggersButNoBodyDataWasReceivedSoFar),
             ("testResponseReadingWithBackpressureEndOfResponseAllowsReadEventsToTriggerDirectly", testResponseReadingWithBackpressureEndOfResponseAllowsReadEventsToTriggerDirectly),
             ("testCancellingARequestInStateInitializedKeepsTheConnectionAlive", testCancellingARequestInStateInitializedKeepsTheConnectionAlive),
             ("testCancellingARequestBeforeBeingSendKeepsTheConnectionAlive", testCancellingARequestBeforeBeingSendKeepsTheConnectionAlive),

Tests/AsyncHTTPClientTests/HTTPRequestStateMachineTests.swift

@@ -279,6 +279,33 @@ class HTTPRequestStateMachineTests: XCTestCase {
         XCTAssertEqual(state.demandMoreResponseBodyParts(), .wait)
     }
 
+    func testChannelReadCompleteTriggersButNoBodyDataWasReceivedSoFar() {
+        var state = HTTPRequestStateMachine(isChannelWritable: true)
+        let requestHead = HTTPRequestHead(version: .http1_1, method: .GET, uri: "/")
+        let metadata = RequestFramingMetadata(connectionClose: false, body: .none)
+        XCTAssertEqual(state.startRequest(head: requestHead, metadata: metadata), .sendRequestHead(requestHead, startBody: false))
+
+        let responseHead = HTTPResponseHead(version: .http1_1, status: .ok, headers: HTTPHeaders([("content-length", "12")]))
+        XCTAssertEqual(state.channelRead(.head(responseHead)), .forwardResponseHead(responseHead, pauseRequestBodyStream: false))
+        let part0 = ByteBuffer(bytes: 0...3)
+        let part1 = ByteBuffer(bytes: 4...7)
+        let part2 = ByteBuffer(bytes: 8...11)
+        XCTAssertEqual(state.channelReadComplete(), .wait)
+        XCTAssertEqual(state.read(), .read)
+        XCTAssertEqual(state.channelRead(.body(part0)), .wait)
+        XCTAssertEqual(state.channelRead(.body(part1)), .wait)
+        XCTAssertEqual(state.channelReadComplete(), .forwardResponseBodyParts(.init([part0, part1])))
+        XCTAssertEqual(state.read(), .wait)
+        XCTAssertEqual(state.demandMoreResponseBodyParts(), .read)
+        XCTAssertEqual(state.channelReadComplete(), .wait)
+        XCTAssertEqual(state.read(), .read)
+        XCTAssertEqual(state.channelRead(.body(part2)), .wait)
+        XCTAssertEqual(state.channelRead(.end(nil)), .succeedRequest(.none, .init([part2])))
+        XCTAssertEqual(state.channelReadComplete(), .wait)
+        XCTAssertEqual(state.read(), .read)
+        XCTAssertEqual(state.demandMoreResponseBodyParts(), .wait)
+    }
+
     func testResponseReadingWithBackpressureEndOfResponseAllowsReadEventsToTriggerDirectly() {
         var state = HTTPRequestStateMachine(isChannelWritable: true)
         let requestHead = HTTPRequestHead(version: .http1_1, method: .GET, uri: "/")