This implements support for SO_BINDTODEVICE, which allows telling a socket
to use a specific interface instead of lwIP automatically selecting one.
This allows devices that have multiple connections (for example cellular
over PPP in addition to WLAN) to explicitly choose which data is send over
which connection, which may have different reliability and or (mobile data)
costs associated with using them.
The used lwIP network stack already has support for this, so all that was
needed was to expose this functionality in MicroPython. This commit
exposes a new constant SO_BINDTODEVICE which can be set as an socket
option. As a value it expects the name of the interface to bind to. These
names can be retrieved using `.config('ifname')` implemented on each
interface type (including adding in this commit a `.config()` method to
PPP, which it didn't have before), which returns a string with the
interface name:
>>> import machine
>>> import network
>>> network.WLAN(network.AP_IF).config('ifname')
'lo0'
>>> wlan = network.WLAN(network.AP_IF)
>>> wlan.active(True) and wlan.config('ifname')
'ap1'
>>> wlan = network.WLAN(network.STA_IF)
>>> wlan.active(True) and wlan.config('ifname')
'st1'
>>> ppp = network.PPP(machine.UART(0))
>>> ppp.active(True) and ppp.config('ifname')
'pp1'
>>> ppp = network.PPP(machine.UART(0))
>>> ppp.active(True) and ppp.config('ifname')
'pp2'
>>> ppp = network.PPP(machine.UART(0))
>>> ppp.active(True) and ppp.config('ifname')
'pp3'
Note that lo0 seems to be returned by lwIP if the interface is not yet
active. The method can also return None in the case of PPP where the
entire lwIP interface doesn't yet exist before being activated. Currently
no effort is made to unify those cases; it is expected that whatever we
receive from lwIP is valid.
When the socket option is set, this forces using a specific device:
import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_BINDTODEVICE, 'st1')
setsockopt will throw (OSError: [Errno 19] ENODEV) if the specified
interface does not exist.
Tested with LAN, WLAN, and PPP; can specify which interface should be used
and when testing with, for example, HTTP requests to ifconfig.co the
returned IP address confirms a specific interface was used.
Signed-off-by: Daniël van de Giessen <daniel@dvdgiessen.nl>
ba8aad3d1d