1 /**************************************************************************/
2 /*                                                                        */
3 /*       Copyright (c) Microsoft Corporation. All rights reserved.        */
4 /*                                                                        */
5 /*       This software is licensed under the Microsoft Software License   */
6 /*       Terms for Microsoft Azure RTOS. Full text of the license can be  */
7 /*       found in the LICENSE file at https://aka.ms/AzureRTOS_EULA       */
8 /*       and in the root directory of this software.                      */
9 /*                                                                        */
10 /**************************************************************************/
11 
12 
13 /**************************************************************************/
14 /**************************************************************************/
15 /**                                                                       */
16 /** NetX Component                                                        */
17 /**                                                                       */
18 /**   Transmission Control Protocol (TCP)                                 */
19 /**                                                                       */
20 /**************************************************************************/
21 /**************************************************************************/
22 
23 #define NX_SOURCE_CODE
24 
25 
26 /* Include necessary system files.  */
27 
28 #include "nx_api.h"
29 #include "nx_ip.h"
30 #include "nx_tcp.h"
31 
32 
33 /**************************************************************************/
34 /*                                                                        */
35 /*  FUNCTION                                               RELEASE        */
36 /*                                                                        */
37 /*    _nx_tcp_socket_state_syn_received                   PORTABLE C      */
38 /*                                                           6.1          */
39 /*  AUTHOR                                                                */
40 /*                                                                        */
41 /*    Yuxin Zhou, Microsoft Corporation                                   */
42 /*                                                                        */
43 /*  DESCRIPTION                                                           */
44 /*                                                                        */
45 /*    This function processes packets during the SYN RECEIVED state,      */
46 /*    which is the state after the initial SYN message was responded to   */
47 /*    with an SYN/ACK message.  The expected value here is an ACK, which  */
48 /*    will move us into an ESTABLISHED state ready for sending and        */
49 /*    receiving of TCP data.                                              */
50 /*                                                                        */
51 /*  INPUT                                                                 */
52 /*                                                                        */
53 /*    socket_ptr                            Pointer to owning socket      */
54 /*    tcp_header_ptr                        Pointer to packet header      */
55 /*                                                                        */
56 /*  OUTPUT                                                                */
57 /*                                                                        */
58 /*    None                                                                */
59 /*                                                                        */
60 /*  CALLS                                                                 */
61 /*                                                                        */
62 /*    _nx_tcp_socket_thread_resume          Resume suspended thread       */
63 /*    _nx_tcp_packet_send_rst               Send RST packet               */
64 /*                                                                        */
65 /*  CALLED BY                                                             */
66 /*                                                                        */
67 /*    _nx_tcp_socket_packet_process         Process TCP packet for socket */
68 /*                                                                        */
69 /*  RELEASE HISTORY                                                       */
70 /*                                                                        */
71 /*    DATE              NAME                      DESCRIPTION             */
72 /*                                                                        */
73 /*  05-19-2020     Yuxin Zhou               Initial Version 6.0           */
74 /*  09-30-2020     Yuxin Zhou               Modified comment(s),          */
75 /*                                            resulting in version 6.1    */
76 /*                                                                        */
77 /**************************************************************************/
_nx_tcp_socket_state_syn_received(NX_TCP_SOCKET * socket_ptr,NX_TCP_HEADER * tcp_header_ptr)78 VOID  _nx_tcp_socket_state_syn_received(NX_TCP_SOCKET *socket_ptr, NX_TCP_HEADER *tcp_header_ptr)
79 {
80 
81 
82     /* Determine if the incoming message is an ACK message.  If it is and
83        if it is proper, move into the ESTABLISHED state.  */
84     if (tcp_header_ptr -> nx_tcp_header_word_3 & NX_TCP_ACK_BIT)
85     {
86 
87         if (tcp_header_ptr -> nx_tcp_acknowledgment_number == socket_ptr -> nx_tcp_socket_tx_sequence)
88         {
89 
90             /* If trace is enabled, insert this event into the trace buffer.  */
91             NX_TRACE_IN_LINE_INSERT(NX_TRACE_INTERNAL_TCP_STATE_CHANGE, socket_ptr -> nx_tcp_socket_ip_ptr, socket_ptr, socket_ptr -> nx_tcp_socket_state, NX_TCP_ESTABLISHED, NX_TRACE_INTERNAL_EVENTS, 0, 0);
92 
93             /* Save the window size.  */
94             socket_ptr -> nx_tcp_socket_tx_window_advertised =
95                 tcp_header_ptr -> nx_tcp_header_word_3 & NX_LOWER_16_MASK;
96 
97 #ifdef NX_ENABLE_TCP_WINDOW_SCALING
98 
99             /* The window size advertised in the SYN packet is NEVER scaled. Therefore there is no
100                need to apply the scale shift.  However validate snd_win_scale  and rcv_win_scale. */
101             if (socket_ptr -> nx_tcp_snd_win_scale_value == 0xFF)
102             {
103 
104                 /* Peer does not support window scale option. */
105                 socket_ptr -> nx_tcp_snd_win_scale_value = 0;
106                 socket_ptr -> nx_tcp_rcv_win_scale_value = 0;
107 
108                 /* Since peer does not offer window scaling feature, make sure
109                    our default window size for this connection does not exceed 65535 bytes. */
110                 if (socket_ptr -> nx_tcp_socket_rx_window_maximum > 65535)
111                 {
112                     socket_ptr -> nx_tcp_socket_rx_window_default = 65535;
113                     socket_ptr -> nx_tcp_socket_rx_window_current = 65535;
114                 }
115             }
116 
117             /* Updated the window size.  */
118             socket_ptr -> nx_tcp_socket_tx_window_advertised <<= socket_ptr -> nx_tcp_snd_win_scale_value;
119 
120 #endif /* NX_ENABLE_TCP_WINDOW_SCALING  */
121 
122             /* Set the initial slow start threshold to be the advertised window size. */
123             socket_ptr -> nx_tcp_socket_tx_slow_start_threshold = socket_ptr -> nx_tcp_socket_tx_window_advertised;
124 
125             /* Set the initial congestion control window size. */
126             /* Section 3.1, Page 5, RFC5681. */
127             if (socket_ptr -> nx_tcp_socket_timeout_retries > 0)
128             {
129 
130                 /* Set the initial congestion control window size to be the mss. */
131                 socket_ptr -> nx_tcp_socket_tx_window_congestion = socket_ptr -> nx_tcp_socket_connect_mss;
132             }
133             else
134             {
135                 socket_ptr -> nx_tcp_socket_tx_window_congestion = (socket_ptr -> nx_tcp_socket_connect_mss << 2);
136                 if (socket_ptr -> nx_tcp_socket_connect_mss > 1095)
137                 {
138                     socket_ptr -> nx_tcp_socket_tx_window_congestion -= socket_ptr -> nx_tcp_socket_connect_mss;
139                 }
140                 if (socket_ptr -> nx_tcp_socket_connect_mss > 2190)
141                 {
142                     socket_ptr -> nx_tcp_socket_tx_window_congestion -= socket_ptr -> nx_tcp_socket_connect_mss;
143                 }
144             }
145 
146             /* Move into the ESTABLISHED state.  */
147             socket_ptr -> nx_tcp_socket_state =  NX_TCP_ESTABLISHED;
148 #ifndef NX_DISABLE_EXTENDED_NOTIFY_SUPPORT
149 
150             /* If registered with the TCP socket, call the application's connection completion callback function.  */
151             if (socket_ptr -> nx_tcp_establish_notify)
152             {
153 
154                 /* Call the application's establish callback function.    */
155                 (socket_ptr -> nx_tcp_establish_notify)(socket_ptr);
156             }
157 #endif
158 
159 
160 #ifdef NX_ENABLE_TCP_KEEPALIVE
161             /* Is the keepalive feature enabled on this socket? */
162             if (socket_ptr -> nx_tcp_socket_keepalive_enabled)
163             {
164                 /* Setup the TCP Keepalive timer to initial values.  */
165                 socket_ptr -> nx_tcp_socket_keepalive_timeout =  NX_TCP_KEEPALIVE_INITIAL;
166                 socket_ptr -> nx_tcp_socket_keepalive_retries =  0;
167             }
168 #endif
169             /* Update the value of nx_tcp_socket_rx_sequence_acked */
170             socket_ptr -> nx_tcp_socket_rx_sequence_acked =    socket_ptr -> nx_tcp_socket_rx_sequence;
171 
172             /* Determine if we need to wake a thread suspended on the connection.  */
173             if (socket_ptr -> nx_tcp_socket_connect_suspended_thread)
174             {
175 
176                 /* Resume the suspended thread.  */
177                 _nx_tcp_socket_thread_resume(&(socket_ptr -> nx_tcp_socket_connect_suspended_thread), NX_SUCCESS);
178             }
179         }
180         /* Check for an invalid ACK message that signals an error on the other side.  */
181         else
182         {
183 
184             /* Invalid response was received, it is likely that the other side still
185                thinks a previous connection is active.  Send a reset (RST) message to
186                the other side to clear any previous connection.  */
187 
188             /* Send the RST packet.  */
189             _nx_tcp_packet_send_rst(socket_ptr, tcp_header_ptr);
190         }
191     }
192 }
193 
194