TCP: Actually invoke SendQueued when the window widens.

IMMEDIATE_ACKNOWLEDGE invokes SendQueued ... but with
a send window size forced to 0, so it just generates an
ACK (or a duplicate ACK as the case may be), and doesn't
actually trigger sending of data.

So, adjust the check, introduce a new action flag, and
invoke it properly.

Fixes traffic stalls caused by waiting for the
persist timeout to occur.

This amends hrev51540 (yes, from 2017.)

Change-Id: I6344463938cfaa0134bb8cf3e224789cded0987c
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7285
Reviewed-by: waddlesplash <[email protected]>

src/add-ons/kernel/network/protocols/tcp/TCPEndpoint.cpp

@@ -1737,8 +1737,12 @@ TCPEndpoint::_Receive(tcp_segment_header& segment, net_buffer* buffer)
 	}
 #endif
 
-	if (advertisedWindow > fSendWindow)
-		action |= IMMEDIATE_ACKNOWLEDGE;
+	if (fSendWindow < fSendMaxSegmentSize
+			&& advertisedWindow >= fSendMaxSegmentSize) {
+		// Our current send window is less than a segment wide, and the new one
+		// is larger, so trigger a send in case there's anything to be sent.
+		action |= SEND_QUEUED;
+	}
 
 	fSendWindow = advertisedWindow;
 	if (advertisedWindow > fSendMaxWindow)
@@ -1824,7 +1828,7 @@ TCPEndpoint::_Receive(tcp_segment_header& segment, net_buffer* buffer)
 
 	// The buffer may be freed if its data is added to the queue, so cache
 	// the size as we still need it later.
-	uint32 bufferSize = buffer->size;
+	const uint32 bufferSize = buffer->size;
 
 	if ((bufferSize > 0 || (segment.flags & TCP_FLAG_FINISH) != 0)
 		&& _ShouldReceive())
@@ -1934,6 +1938,9 @@ TCPEndpoint::SegmentReceived(tcp_segment_header& segment, net_buffer* buffer)
 	else if (segmentAction & ACKNOWLEDGE)
 		DelayedAcknowledge();
 
+	if (segmentAction & SEND_QUEUED)
+		_SendQueued();
+
 	if ((fFlags & (FLAG_CLOSED | FLAG_DELETE_ON_CLOSE))
 			== (FLAG_CLOSED | FLAG_DELETE_ON_CLOSE)) {
 

src/add-ons/kernel/network/protocols/tcp/tcp.h

@@ -269,12 +269,13 @@ struct tcp_segment_header {
 };
 
 enum tcp_segment_action {
-	KEEP					= 0x00,
-	DROP					= 0x01,
-	RESET					= 0x02,
-	ACKNOWLEDGE				= 0x04,
-	IMMEDIATE_ACKNOWLEDGE	= 0x08,
-	DELETED_ENDPOINT		= 0x10,
+	KEEP					= 0,
+	DROP					= (1 << 0),
+	RESET					= (1 << 1),
+	ACKNOWLEDGE				= (1 << 2),
+	IMMEDIATE_ACKNOWLEDGE	= (1 << 3),
+	SEND_QUEUED				= (1 << 4),
+	DELETED_ENDPOINT		= (1 << 5),
 };