Add IPv6 support for Espressif

[jepler]

What works:

• Getting a v6 address
• Resolving v6 addresses
• Connecting to v6 addresses
• sending to v6 addresses (UDP)
• Pinging a v6 address

presently you have to start_dhcp to get v6 addresses

Addresses & ping:

>>> import wifi, socketpool
>>> wifi.radio.ping("1.1.1.1")
0.021
>>> wifi.radio.start_dhcp()
>>> wifi.radio.addresses
('FE80::7EDF:A1FF:FE00:518C', 'FD5F:3F5C:FE50:0:7EDF:A1FF:FE00:518C', '10.0.3.96')
>>> wifi.radio.dns
'FD5F:3F5C:FE50::1'
>>> wifi.radio.ping(_)
0.014
>>> socket = socketpool.SocketPool(wifi.radio)
>>> socket.getaddrinfo("google.com", 80)
[(2, 0, 0, 'google.com', ('209.85.145.139', 80))]
>>> socket.getaddrinfo("ipv6.google.com", 80)
[(10, 0, 0, 'ipv6.google.com', ('2607:F8B0:4001:C06::64', 80, 0, 0))]

I added name resolution to wifi ping (espressif only):

>>> wifi.radio.ping("google.com")
0.043
>>> wifi.radio.ping("ipv6.google.com")
0.048

NTP manually:

>>> ntp_addr = ("fd5f:3f5c:fe50::20e", 123)
>>> PACKET_SIZE = 48
>>> 
>>> buf = bytearray(PACKET_SIZE)
>>> with socket.socket(socket.AF_INET6, socket.SOCK_DGRAM) as s:
...     s.settimeout(1)
...     buf[0] = 0b0010_0011
...     s.sendto(buf, ntp_addr)
...     print(s.recvfrom_into(buf))
...     print(buf)
... 
48
(48, ('0.0.0.0', 123))
bytearray(b'$\x01\x03\xeb\x00\x00\x00\x00\x00\x00\x00GGPS\x00\xeaA0h\x07s;\xc0\x00\x00\x00\x00\x00\x00\x00\x00\xeaA0n\xeb4\x82-\xeaA0n\xebAU\xb1')

http manually:

>>> s = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
>>> s.connect(("fd5f:3f5c:fe50::1", 80))
>>> s.send("GET / HTTP/1.0\r\n\r\n")
18
>>> b = bytearray(100)
>>> s.recv_into(b)
100
>>> b
bytearray(b'HTTP/1.0 200 OK\r\nConnection: close\r\nETag: "31e-346-65e90ba6"\r\nLast-Modified: Thu, 07 Mar 2024 00:34:')
>>> s.close()

Todo (some may end up as subsequent PRs):

• enable generally on espressif (right now only on metro esp32s2)
• determine when to start dhcp6. right now starts on wifi.radio.start_dhcp() but not on wifi workflow. not sure where dhcp4 is started
• fix return values of recvfrom & accept (needs C API changes)
• fix build errors on raspberrypi
• enable v4 & v6 by default
  • {start,stop}_dhcp_client to gain 2 kwarg-only arguments, defaulting to true
  • v6 to be started automatically
• support v6 addresses in bind, sendto

Future PRs:

• add ping-by-name on raspberrypi
• set & remove v6 addresses
• access to v6 gateway & netmask-equivalent
• add support for all v6 properties on AP
• support v6-only networks (where dhcp4 never assigns an address)?
• ipaddress.IPv6Address

[jepler]

• I didn't find the esp-idf API for v6 netmask & route equivalent, so not adding it at this time
• adding & removing addresses is unclear as well (there's esp_netif_add_ip6_address but it is defined as an event handler) and there's not currently a use case
  • though ipv6 AP would need .. something
• v6-only networks also left for future
• need to test raspberrypi & add ping-by-string there

[jepler]

Other modules & libraries may need to be updated in order to support v6. For instance, do adafruit_requests & adafruit_ntp work properly with v6 addresses & names? Since our focus is on v6 for matter support, I did not investigate this or file issues.

[jepler]

good news! this does seem to set ipv6 mdns records:

$ avahi-resolve -6 -n cpy-00518c.local
cpy-00518c.local	fe80::7edf:a1ff:fe00:518c

[tannewt]

A few questions. It all looks pretty good. Thanks for figuring this out!

[tannewt]

Why not use this all of the time?

[jepler]

good point. will revise.

[tannewt]

How would you determine this in CPython? Should it be on Radio or SocketPool (if CPython's socket has a way to detect it.) I'm thinking ahead to having a thread network interface that is ipv6-only (I think.)

[jepler]

good question. I don't think there's a look-before-you-leap "is there working ipv6" check in CPython.. However, in CPython with no ipv6 global connectivity, a v6 connect() to an internet address will promptly fail:

>>> s.connect(("ipv6.google.com", 80))
OSError: [Errno 101] Network is unreachable

If the OS lacked even support compile-time for V6 sockets at all then the socket module can lack the AF_INET6 definition:

#ifdef AF_INET6
    ADD_INT_MACRO(m, AF_INET6); /* IP version 6 */
#endif

and creating a socket with an unsupported family will raise an exception:

>>> socket.socket(socket.AF_UNSPEC, socket.SOCK_STREAM)
OSError: [Errno 97] Address family not supported by protocol

[jepler]

I can drop these properties if they're not useful. I really only added them so that the documentation could show a "correct" default parameter for start_dhcp_server, by showing the constant supports_ipv6 instead of a literal True or False which would be incorrect

[anecdata]

I don't have an in-depth understanding of IPv6, so I could be off-base on this. Do we know if the espressif (and eventually, the raspberrypi) implementation uses the RFC 4941 IPv6 privacy extensions? If not, I'd suggest not starting IPv6 by default. Some users may be concerned if their microcontrollers are globally identifiable.

It could be that the DHCP server will take care of this, but's that's dependent on the DHCP server implementation (https://media.defense.gov/2023/Jan/18/2003145994/-1/-1/1/CSI_IPv6_security_guidance_.PDF, p.2).

[jepler]

I'm happy to change this to default v6 off until we understand the ramifications better. @tannewt say the word

[anecdata]

Found this:

DHCPv6 in lwIP is very simple and supports only stateless configuration

This is probably the original SLAAC mechanism, and may be a permanent address embedding the hardware MAC address (could be verified with testing).