Get an IP_ADDRESS_STRING from GetAdaptersAddresses()? - c

Question

GetAdaptersAddresses() will get you addresses in IP_ADAPTER_UNICAST_ADDRESS format, which is defined as:
typedef struct _IP_ADAPTER_UNICAST_ADDRESS {
union {
struct {
ULONG Length;
DWORD Flags;
} ;
} ;
struct _IP_ADAPTER_UNICAST_ADDRESS *Next;
SOCKET_ADDRESS Address;
IP_PREFIX_ORIGIN PrefixOrigin;
IP_SUFFIX_ORIGIN SuffixOrigin;
IP_DAD_STATE DadState;
ULONG ValidLifetime;
ULONG PreferredLifetime;
ULONG LeaseLifetime;
UINT8 OnLinkPrefixLength;
} IP_ADAPTER_UNICAST_ADDRESS, *PIP_ADAPTER_UNICAST_ADDRESS;
The only field that seems to suggest the human-readable IP address string is Address, which is a SOCKET_ADDRESS structure defined as:
typedef struct _SOCKET_ADDRESS {
LPSOCKADDR lpSockaddr;
INT iSockaddrLength;
} SOCKET_ADDRESS, *PSOCKET_ADDRESS;
Which, in turn, uses another structure, SOCKADDR, defined as:
Sorry, it's way to complex to post here, as it varies depending on IPv4 vs. IPv6 and the Windows edition... so here is a link to the definition:
http://msdn.microsoft.com/en-us/library/ms740496%28v=VS.85%29.aspx
If you haven't gotten dizzy yet like I did and followed through this maze of definitions, you probably noticed that it's a nightmare to retrieve the good old dotted string style of an IP address, as it used to be much easier using GetAdaptersInfo().
My question is: Is there a truly IP Helper function that can convert IP_ADAPTER_UNICAST_ADDRESS to an IPv4 dotted string (or an IPv6 string)?

Answer 1

You can use GetIpAddrTable - the returned data structure contains a DWORD dwAddr that is the IPv4 address. The sample code on that first link should show you what you want. Brief excerpt to show you what I mean:
if ( (dwRetVal = GetIpAddrTable( pIPAddrTable, &dwSize, 0 )) != NO_ERROR ) {
printf("GetIpAddrTable failed with error %d\n", dwRetVal);
if (FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL, dwRetVal, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // Default language
(LPTSTR) & lpMsgBuf, 0, NULL)) {
printf("\tError: %s", lpMsgBuf);
LocalFree(lpMsgBuf);
}
exit(1);
}
printf("\tNum Entries: %ld\n", pIPAddrTable->dwNumEntries);
for (i=0; i < (int) pIPAddrTable->dwNumEntries; i++) {
printf("\n\tInterface Index[%d]:\t%ld\n", i, pIPAddrTable->table[i].dwIndex);
IPAddr.S_un.S_addr = (u_long) pIPAddrTable->table[i].dwAddr;
printf("\tIP Address[%d]: \t%s\n", i, inet_ntoa(IPAddr) );
The IP_ADAPTER_UNICAST_ADDRESS contains a SOCKET_ADDRESS in Address, which in turn contains a LPSOCKADDR in lpSockAddr - you can convert this to the ipv4 string form using WSAAddressToString.

Answer 2

Take a look at the documentation for SOCKADDR. That leads us to the documentation for SOCKADDR_STORAGE, which is a helper struct for both IPv4 and IPv6.
Quote from the sockaddr documentation:
Winsock functions using sockaddr are not strictly interpreted to be
pointers to a sockaddr structure. The structure is interpreted
differently in the context of different address families.
For ipv4, you can cast a sockaddr pointer to a sockaddr_in pointer and then access the IPv4 address information from there. Then you can use your favorite string builder to produce a dotted-quad formatted string.
sockaddr_in* address = (sockaddr_in*) temp->Address.lpSockaddr;
uint32_t ipv4 = address->sin_addr.S_un.S_addr;
// First octet: address->sin_addr.S_un.S_un_b.s_b1
// Second octet: address->sin_addr.S_un.S_un_b.s_b2
// Third octet: address->sin_addr.S_un.S_un_b.s_b3
// Fourth octet: address->sin_addr.S_un.S_un_b.s_b4
I would imagine that you can also cast the address for ipv6 in a similar way given the struct definitions (copied below).
struct sockaddr {
ushort sa_family;
char sa_data[14];
};
struct sockaddr_in {
short sin_family;
u_short sin_port;
struct in_addr sin_addr;
char sin_zero[8];
};
struct sockaddr_in6 {
short sin6_family;
u_short sin6_port;
u_long sin6_flowinfo;
struct in6_addr sin6_addr;
u_long sin6_scope_id;
};

Answer 3

You can simply pass _SOCKET_ADDRESS.lpSockaddr and _SOCKET_ADDRESS.iSockaddrLength as lpsaAddress and dwAddressLength arguments to WSAAddressToString function. WSAAddressToString will do necessary conversion for you, no need to dig deeper.
function SOCKET_ADDRESS_ToString(const Addr: SOCKET_ADDRESS): String;
var
Len: DWORD;
begin
if (Addr.lpSockaddr = nil) or (Addr.iSockaddrLength <= 0) then
begin
Result := '';
Exit;
end;
Len := 0;
WSAAddressToString(Addr.lpSockaddr, Addr.iSockaddrLength, nil, nil, Len);
SetLength(Result, Len);
if WSAAddressToString(Addr.lpSockaddr, Addr.iSockaddrLength, nil, PChar(Result), Len) = 0 then
SetLength(Result, Len - 1)
else
Result := '';
end;