istream/dechunk: remove DechunkInputAction::DESTROYED

This eliminates a use-after-free bug in
DechunkIstream::InvokeDechunkEnd() and eliminates an illegal state in
DechunkIstream::_ConsumeBucketList() because that method is not
allowed to destroy the DechunkIstream object.

Author: MaxKellermann

src/istream/DechunkIstream.cxx

@@ -249,10 +249,6 @@ DechunkIstream::InvokeDechunkEnd() noexcept
 		ClearInput();
 		break;
 
-	case DechunkHandler::DechunkInputAction::DESTROYED:
-		ClearInput();
-		break;
-
 	case DechunkHandler::DechunkInputAction::CLOSE:
 		CloseInput();
 		break;
@@ -405,7 +401,6 @@ DechunkIstream::OnData(std::span<const std::byte> src) noexcept
 			   instead of 0 */
 			break;
 
-		case DechunkHandler::DechunkInputAction::DESTROYED:
 		case DechunkHandler::DechunkInputAction::CLOSE:
 			return 0;
 		}

src/istream/DechunkIstream.hxx

@@ -29,11 +29,6 @@ public:
 		 * Close the #DechunkIstream.
 		 */
 		CLOSE,
-
-		/**
-		 * The method has destroyed the #DechunkIstream.
-		 */
-		DESTROYED,
 	};
 
 	/**

test/istream/TestDechunkIstream.cxx

@@ -41,9 +41,6 @@ struct MyDechunkHandler final : DechunkHandler {
 		assert(state == State::END_SEEN);
 		state = State::END;
 
-		if (action == DechunkInputAction::DESTROYED)
-			input->Close();
-
 		return action;
 	}
 };
@@ -146,7 +143,6 @@ TestAction(EventLoop &event_loop, struct pool &pool,
 	MyDechunkHandler dechunk_handler{action};
 
 	switch (action) {
-	case DechunkHandler::DechunkInputAction::DESTROYED:
 	case DechunkHandler::DechunkInputAction::ABANDON:
 		/* this kludge extracts a pointer to the input */
 		dechunk_handler.input = input.Steal();
@@ -236,21 +232,3 @@ TEST(DechunkIstream, CloseActionBuckets2)
 {
 	TestAction(DechunkHandler::DechunkInputAction::CLOSE, true, true);
 }
-
-/**
- * Test DechunkInputAction::DESTROYED.
- */
-TEST(DechunkIstream, DestroyedAction)
-{
-	TestAction(DechunkHandler::DechunkInputAction::DESTROYED, false);
-}
-
-TEST(DechunkIstream, DestroyedActionBuckets)
-{
-	TestAction(DechunkHandler::DechunkInputAction::DESTROYED, true);
-}
-
-TEST(DechunkIstream, DestroyedActionBuckets2)
-{
-	TestAction(DechunkHandler::DechunkInputAction::DESTROYED, true, true);
-}