This moves the write_offset variable from struct netconn to struct api_msg
This optimizes the storage by only having the space claimed when it is
needed (during a netconn_write_partly() call) and not throughout the
lifetime of the netconn
This also reduces code space/execution by not having to separately manage
clearing/checking write_offset from the current_msg pointer
Lastly, we also save execution by using msg.w.offset as the output
rather than marshaling the result to msg.w.len. Previously, len was used
as input length of dataptr and output for the write operation.
netconn_write_partly() also has access to msg.w.offset, so we can use
that
The forward declaration was added in commit
e2c2afbbe0 for use in struct
lwip_setgetsockopt_data, but became dead after commit
5d2e93e5f0 where the sock pointer was
removed from lwip_setgetsockopt_data
The patch simply copies the relevant bits from the UDP implementation.
Perhaps most notably, the patch does *not* copy the IPv4-only UDP
support for IP_MULTICAST_IF, because that option can also be
implemented using the interface index based approach. Largely thanks
to this omission, at least on 32-bit platforms, this patch does not
increase the RAW PCB size at all.
So far, the UDP core module implemented only IPv4 multicast support.
This patch extends the module with the features necessary for socket
layers on top to implement IPv6 multicast support as well:
o If a UDP PCB is bound to an IPv6 multicast address, a unicast source
address is selected and used to send the packet instead, as is
required (and was the case for IPv4 multicast already).
o Unlike IPv4's IP_MULTICAST_IF socket option, which takes a source
IPv4 address, the IPV6_MULTICAST_IF socket option (from RFC 3493)
takes an interface identifier to denote the interface to use for
outgoing multicast-destined packets. A new pair of UDP PCB API
calls, udp_[gs]et_multicast_netif_index(), are added to support
this. The new definition "NETIF_NO_INDEX" may be used to indicate
that lwIP should pick an interface instead.
IPv4 socket implementations may now also choose to map the given
source address to an interface index immediately and use the new
facility instead of the old udp_[gs]et_multicast_netif_addr() one.
A side effect of limiting the old facility to IPv4 is that for dual-
stack configurations with multicast support, the UDP PCB size is
reduced by (up to) 16 bytes.
o For configurations that enable loopback interface support, the IPv6
code now also supports multicast loopback (IPV6_MULTICAST_LOOP).
o The LWIP_MULTICAST_TX_OPTIONS opt.h setting now covers both IPv4
and IPv6, and as such is no longer strictly linked to IGMP. It is
therefore placed in its own lwIP options subgroup in opt.h.
The IPV6_MULTICAST_HOPS socket option can already be implemented using
the existing IP_MULTICAST_TTL support, and thus requires no additional
changes. Overall, this patch should not break any existing code.
If LWIP_CALLBACK_API is not defined, but TCP_LISTEN_BACKLOG is, then
the LWIP_EVENT_ACCEPT TCP event may be triggered for closed listening
sockets. This case is just as disastrous for the event API as it is
for the callback API, as there is no way for the event hook to tell
whether the listening PCB is still around. Add the same protection
against this case for TCP_LISTEN_BACKLOG as was already in place for
LWIP_CALLBACK_API.
Also remove one NULL check for LWIP_CALLBACK_API that had already
become redundant for all callers, making the TCP_EVENT_ACCEPT code
for that callback wrapper more in line with the rest of the wrappers.
