Iot sdk thesis

3.3.2
 
Session API (tinydtls/session.c, tinydtls/session.h) 
tinydtls/session.h
defines the structure 
session_t
which defines variables to 
store socket address, address type, size of the address and interface index. It has been defined 
as shown in the following code snippet. 
(
NOTE:
The variables that depend on UNIX libraries have been shown in in red) 

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55 
typedef
struct
{ 
socklen_t size
;
/**< size of addr > defined in sys/socket.h */
union
{ 
struct
sockaddr sa
; 
//Defined in sys/socket.h to hold address family and 
address string 
struct
sockaddr_storage st
; 
// Defined in sys/socket.h to store the complete 
socket addresses
struct
sockaddr_in sin
; 
// Defined in sys/socket.h to deal with IPv4 socket 
addresses
struct
sockaddr_in6 sin6
; 
// Defined in sys/socket.h to deal with IPv6 socket 
addresses
} addr; 
uint8_t ifindex; 
} session_t; 
 
Resolving the UNIX dependency:
To port this sessions structure on Arduino-like SODAQ 
SARA:
•
The UNIX-specific structures have been deleted. A 32-bit integer to hold the socket 
length, a simple string to hold the IP, and a 16-bit integer to hold the port are defined, 
to compensate for this removal. 
Design Decision
: The reason for adding only three variables is that, the NB-IoT API by 
SODAQ can allow UDP messaging as long as remote IP and port have been defined.
•
IPv6 related structures (
sockaddr_in6
) do not need to be compensated for, so it is only 
removed. 
Design Decision:
SODAQ’s NB-IoT API allows only for IPv4 networking, not IPv6.
After making these changes, the 
session_t
structure looks as shown in following code snippet:
typedef
struct
{ 
// socklen_t size;
uint32_t
size; 
//Added for SODAQ to hold length of the socket
union
{ 
//struct sockaddr sa;
// struct sockaddr_storage st;
//struct sockaddr_in sin;
char
* remoteIpStr; 
//Added for SODAQ to hold remote IP
uint16_t
port; 
//Added for SODAQ to hold remote port
//struct sockaddr_in6 sin6;
} addr; 
uint8_t
ifindex; 
} session_t; 

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56 
‘Sessions’ API defines the following functions. The purpose of the functionalities has 
been described in the comments. 
* Initializes the session_t object to its default values */
void
dtls_session_init(session_t *sess);
/*
Compares the given session objects. /
int
_dtls_address_equals_impl(
const
session_t *a, 
const
session_t *b); 
Between these functions, 
_dtls_address_equals_impl()
depends on structures from 
socket programming API.
int
_dtls_address_equals_impl(
const
session_t *a, 
const
session_t *b)
{ 
/*It starts by checking whether the inequality between session_t a and 
session_t b can be established by checking comparing ifindex, size, 
sa.sa_family variables in each variable */
if
( a->ifindex != b->ifindex ||
a->size != b->size ||
a->addr.
sa.sa_family 
!= b->addr.
sa.sa_family
) 
return
0
; 
/*Then, it proceeds to determine the address family first and later compare 
individual variables and contents to determine whether the sessions are equal 
or not. Again, it uses the variables of UNIX-dependent structures, as 
follows:*/
switch
(a->addr.
sa.sa_family
) { 
case
AF_INET: 
/* Case IPv4*/
return
a->addr.
sin.sin_port 
== b->addr.
sin.sin_port 
/* Compare if ports are 
equal*/
&&
memcmp(&a->addr.sin.
sin_addr
,
&b->addr.sin.
sin_addr
,
sizeof
(
struct
in_addr) 
) == 
0
; 
/* Compare if the addresses are lexicographically equal */
case
AF_INET6: 
/* Case IPv6 */
return
a->addr.
sin6.sin6_port 
== b->addr.
sin6.sin6_port 
/* Compare if ports 
are equal*/
&&
memcmp(&a->addr.
sin6.sin6_addr
, &b->addr.
sin6.sin6_addr
,
sizeof
(
struct
in6_addr)) == 
0
; 
/* Compare if the addresses are
lexicographically equal */
}
return
0
; 
} 

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