const NetifUnicastAddress *Netif::SelectSourceAddress(MessageInfo &aMessageInfo)
{
Address *destination = &aMessageInfo.GetPeerAddr();
int interfaceId = aMessageInfo.mInterfaceId;
const NetifUnicastAddress *rvalAddr = NULL;
const Address *candidateAddr;
uint8_t candidateId;
uint8_t rvalIface = 0;
for (Netif *netif = GetNetifList(); netif; netif = netif->mNext)
{
candidateId = netif->GetInterfaceId();
for (const NetifUnicastAddress *addr = netif->GetUnicastAddresses(); addr; addr = addr->GetNext())
{
candidateAddr = &addr->GetAddress();
if (destination->IsLinkLocal() || destination->IsMulticast())
{
if (interfaceId != candidateId)
{
continue;
}
}
if (rvalAddr == NULL)
{
// Rule 0: Prefer any address
rvalAddr = addr;
rvalIface = candidateId;
}
else if (*candidateAddr == *destination)
{
// Rule 1: Prefer same address
rvalAddr = addr;
rvalIface = candidateId;
goto exit;
}
else if (candidateAddr->GetScope() < rvalAddr->GetAddress().GetScope())
{
// Rule 2: Prefer appropriate scope
if (candidateAddr->GetScope() >= destination->GetScope())
{
rvalAddr = addr;
rvalIface = candidateId;
}
}
else if (candidateAddr->GetScope() > rvalAddr->GetAddress().GetScope())
{
if (rvalAddr->GetAddress().GetScope() < destination->GetScope())
{
rvalAddr = addr;
rvalIface = candidateId;
}
}
else if (addr->mPreferredLifetime != 0 && rvalAddr->mPreferredLifetime == 0)
{
// Rule 3: Avoid deprecated addresses
rvalAddr = addr;
rvalIface = candidateId;
}
else if (aMessageInfo.mInterfaceId != 0 && aMessageInfo.mInterfaceId == candidateId &&
rvalIface != candidateId)
{
// Rule 4: Prefer home address
// Rule 5: Prefer outgoing interface
rvalAddr = addr;
rvalIface = candidateId;
}
else if (destination->PrefixMatch(*candidateAddr) > destination->PrefixMatch(rvalAddr->GetAddress()))
{
// Rule 6: Prefer matching label
// Rule 7: Prefer public address
// Rule 8: Use longest prefix matching
rvalAddr = addr;
rvalIface = candidateId;
}
}
}
exit:
aMessageInfo.mInterfaceId = rvalIface;
return rvalAddr;
}
