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/***************************************************************************
* Copyright (c) 2024 Microsoft Corporation
* Copyright (c) 2025-present Eclipse ThreadX Contributors
*
* This program and the accompanying materials are made available under the
* terms of the MIT License which is available at
* https://opensource.org/licenses/MIT.
*
* SPDX-License-Identifier: MIT
**************************************************************************/
/**************************************************************************/
/**************************************************************************/
/** */
/** NetX Component */
/** */
/** Transmission Control Protocol (TCP) */
/** */
/**************************************************************************/
/**************************************************************************/
#define NX_SOURCE_CODE
/* Include necessary system files. */
#include "nx_api.h"
#include "nx_tcp.h"
/**************************************************************************/
/* */
/* FUNCTION RELEASE */
/* */
/* _nx_tcp_mss_option_get PORTABLE C */
/* 6.4.3 */
/* AUTHOR */
/* */
/* Yuxin Zhou, Microsoft Corporation */
/* */
/* DESCRIPTION */
/* */
/* This function searches for the Maximum Segment Size (MSS) option. */
/* If found, first check the option length, if option length is not */
/* valid, it returns NX_FALSE to the caller, else it set the mss value */
/* and returns NX_TRUE to the caller. Otherwise, NX_TRUE is returned. */
/* */
/* INPUT */
/* */
/* option_ptr Pointer to option area */
/* option_area_size Size of option area */
/* mss Max segment size */
/* */
/* OUTPUT */
/* */
/* NX_FALSE TCP option is invalid */
/* NX_TRUE TCP option is valid */
/* */
/* CALLS */
/* */
/* None */
/* */
/* CALLED BY */
/* */
/* _nx_tcp_packet_process TCP packet processing */
/* _nx_tcp_server_socket_relisten Socket relisten processing */
/* */
/**************************************************************************/
UINT _nx_tcp_mss_option_get(UCHAR *option_ptr, ULONG option_area_size, ULONG *mss)
{
ULONG option_length;
/* Initialize the value. */
*mss = 0;
/* Loop through the option area looking for the MSS. */
while (option_area_size >= 4)
{
/* Is the current character the MSS type? */
if (*option_ptr == NX_TCP_MSS_KIND)
{
/* Yes, we found it! */
/* Move the pointer forward by one. */
option_ptr++;
/* Check the option length, if option length is not equal to 4, return NX_FALSE. */
if (*option_ptr++ != 4)
{
return(NX_FALSE);
}
/* Build the mss size. */
*mss = (ULONG)*option_ptr++;
/* Get the LSB of the MSS. */
*mss = (*mss << 8) | (ULONG)*option_ptr;
/* Finished, get out of the loop! */
break;
}
/* Otherwise, process relative to the option type. */
/* Check for end of list. */
if (*option_ptr == NX_TCP_EOL_KIND)
{
/* Yes, end of list, get out! */
break;
}
/* Check for NOP. */
if (*option_ptr++ == NX_TCP_NOP_KIND)
{
/* One character option! */
option_area_size--;
}
else
{
/* Derive the option length. */
option_length = ((ULONG)*option_ptr);
/* Return when option length is invalid. */
if (option_length == 0)
{
return(NX_FALSE);
}
/* Move the option pointer forward. */
option_ptr = option_ptr + (option_length - 1);
/* Determine if this is greater than the option area size. */
if (option_length > option_area_size)
{
return(NX_FALSE);
}
else
{
option_area_size = option_area_size - option_length;
}
}
}
/* Return. */
return(NX_TRUE);
}
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