[BUG] State Transition from eCONNECT_SYN to eCLOSE_WAIT?

Describe the bug
The TCP state machine incorrectly transitions from eCONNECT_SYN (SYN-SENT) to eCLOSE_WAIT in error scenarios. Per RFC 793, connections that fail during establishment should transition to eCLOSED, not eCLOSE_WAIT.

FreeRTOS-Plus-TCP/source/FreeRTOS_TCP_Transmission.c

Lines 115 to 139 in 22c095e

    
                   if( pxSocket->u.xTCP.eTCPState != eCONNECT_SYN ) 
        
                   { 
        
                       /* The connection is in a state other than SYN. */ 
        
                       pxNetworkBuffer = NULL; 
        
                       /* prvTCPSendRepeated() will only create a network buffer if necessary, 
        
                        * i.e. when data must be sent to the peer. */ 
        
                       lResult = prvTCPSendRepeated( pxSocket, &pxNetworkBuffer ); 
        
                       if( pxNetworkBuffer != NULL ) 
        
                       { 
        
                           vReleaseNetworkBufferAndDescriptor( pxNetworkBuffer ); 
        
                       } 
        
                   } 
        
                   else 
        
                   { 
        
                       if( pxSocket->u.xTCP.ucRepCount >= 3U ) 
        
                       { 
        
                           /* The connection is in the SYN status. The packet will be repeated 
        
                            * to most 3 times.  When there is no response, the socket get the 
        
                            * status 'eCLOSE_WAIT'. */ 
        
                           FreeRTOS_debug_printf( ( "Connect: giving up %xip:%u\n", 
        
                                                    ( unsigned ) pxSocket->u.xTCP.xRemoteIP.ulIP_IPv4, /* IP address of remote machine. */ 
        
                                                    pxSocket->u.xTCP.usRemotePort ) );                 /* Port on remote machine. */ 
        
                           vTCPStateChange( pxSocket, eCLOSE_WAIT );

RFC 793 Compliance Issue

RFC 793 specifies that SYN-SENT state errors/timeouts should transition to CLOSED, not CLOSE-WAIT.

@Fr3ya

HI @Fr3ya,

I agree with your assessment. Would you like to open a PR to resolve this?

Best,

Jason Carroll

You're quick, Jason. I'm still studying the effects of the change and simulate it on a LAN.

So please hold on a second.

Thanks, Hein

@Fr3ya

To be honest, I just looked at the code path and it appears to go from SYN to CLOSED_WAIT, which is against RFC 793 (figure 6 under 3.2 shows the state machine) as @Fr3ya pointed out.

I tested the proposed change in hardware: I could not find any different behaviour.
Do you want to create a PR your self? If not, we can do it as well.

I guess this is the only change FreeRTOS_TCP_Transmission.c:

-    vTCPStateChange( pxSocket, eCLOSE_WAIT );
+    vTCPStateChange( pxSocket, eCLOSED );

Thank you

@htibosch

Thanks @htibosch @jasonpcarroll for heading up, I just opened the PR.

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[BUG] State Transition from eCONNECT_SYN to eCLOSE_WAIT? #1301

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	if( pxSocket->u.xTCP.eTCPState != eCONNECT_SYN )
	{
	/* The connection is in a state other than SYN. */
	pxNetworkBuffer = NULL;

	/* prvTCPSendRepeated() will only create a network buffer if necessary,
	* i.e. when data must be sent to the peer. */
	lResult = prvTCPSendRepeated( pxSocket, &pxNetworkBuffer );

	if( pxNetworkBuffer != NULL )
	{
	vReleaseNetworkBufferAndDescriptor( pxNetworkBuffer );
	}
	}
	else
	{
	if( pxSocket->u.xTCP.ucRepCount >= 3U )
	{
	/* The connection is in the SYN status. The packet will be repeated
	* to most 3 times. When there is no response, the socket get the
	* status 'eCLOSE_WAIT'. */
	FreeRTOS_debug_printf( ( "Connect: giving up %xip:%u\n",
	( unsigned ) pxSocket->u.xTCP.xRemoteIP.ulIP_IPv4, /* IP address of remote machine. */
	pxSocket->u.xTCP.usRemotePort ) ); /* Port on remote machine. */
	vTCPStateChange( pxSocket, eCLOSE_WAIT );

[BUG] State Transition from eCONNECT_SYN to eCLOSE_WAIT? #1301

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jasonpcarroll commented on Nov 20, 2025

htibosch commented on Nov 20, 2025

jasonpcarroll commented on Nov 20, 2025

htibosch commented on Nov 21, 2025

Fr3ya commented on Nov 21, 2025

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