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_tcp.h"
30
31
32 /**************************************************************************/
33 /* */
34 /* FUNCTION RELEASE */
35 /* */
36 /* _nx_tcp_mss_option_get PORTABLE C */
37 /* 6.1 */
38 /* AUTHOR */
39 /* */
40 /* Yuxin Zhou, Microsoft Corporation */
41 /* */
42 /* DESCRIPTION */
43 /* */
44 /* This function searches for the Maximum Segment Size (MSS) option. */
45 /* If found, first check the option length, if option length is not */
46 /* valid, it returns NX_FALSE to the caller, else it set the mss value */
47 /* and returns NX_TRUE to the caller. Otherwise, NX_TRUE is returned. */
48 /* */
49 /* INPUT */
50 /* */
51 /* option_ptr Pointer to option area */
52 /* option_area_size Size of option area */
53 /* mss Max segment size */
54 /* */
55 /* OUTPUT */
56 /* */
57 /* NX_FALSE TCP option is invalid */
58 /* NX_TRUE TCP option is valid */
59 /* */
60 /* CALLS */
61 /* */
62 /* None */
63 /* */
64 /* CALLED BY */
65 /* */
66 /* _nx_tcp_packet_process TCP packet processing */
67 /* _nx_tcp_server_socket_relisten Socket relisten processing */
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_mss_option_get(UCHAR * option_ptr,ULONG option_area_size,ULONG * mss)78 UINT _nx_tcp_mss_option_get(UCHAR *option_ptr, ULONG option_area_size, ULONG *mss)
79 {
80
81 ULONG option_length;
82
83 /* Initialize the value. */
84 *mss = 0;
85
86 /* Loop through the option area looking for the MSS. */
87 while (option_area_size >= 4)
88 {
89
90 /* Is the current character the MSS type? */
91 if (*option_ptr == NX_TCP_MSS_KIND)
92 {
93
94 /* Yes, we found it! */
95
96 /* Move the pointer forward by one. */
97 option_ptr++;
98
99 /* Check the option length, if option length is not equal to 4, return NX_FALSE. */
100 if (*option_ptr++ != 4)
101 {
102 return(NX_FALSE);
103 }
104
105 /* Build the mss size. */
106 *mss = (ULONG)*option_ptr++;
107
108 /* Get the LSB of the MSS. */
109 *mss = (*mss << 8) | (ULONG)*option_ptr;
110
111 /* Finished, get out of the loop! */
112 break;
113 }
114
115 /* Otherwise, process relative to the option type. */
116
117 /* Check for end of list. */
118 if (*option_ptr == NX_TCP_EOL_KIND)
119 {
120
121 /* Yes, end of list, get out! */
122 break;
123 }
124
125 /* Check for NOP. */
126 if (*option_ptr++ == NX_TCP_NOP_KIND)
127 {
128
129 /* One character option! */
130 option_area_size--;
131 }
132 else
133 {
134
135 /* Derive the option length. */
136 option_length = ((ULONG)*option_ptr);
137
138 /* Return when option length is invalid. */
139 if (option_length == 0)
140 {
141 return(NX_FALSE);
142 }
143
144 /* Move the option pointer forward. */
145 option_ptr = option_ptr + (option_length - 1);
146
147 /* Determine if this is greater than the option area size. */
148 if (option_length > option_area_size)
149 {
150 return(NX_FALSE);
151 }
152 else
153 {
154 option_area_size = option_area_size - option_length;
155 }
156 }
157 }
158
159 /* Return. */
160 return(NX_TRUE);
161 }
162
163
