From: Mark Webb-Johnson <mark@webb-johnson.net>
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Date: Thu, 9 Nov 2017 13:38:09 +0800
To: OVMS Developers <OvmsDev@lists.teslaclub.hk>
Subject: [Ovmsdev] A promiscous wifi client
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I=E2=80=99ve committed a change to the esp32wifi component, to try to =
support a promiscuous mode for the wifi client. This should make it work =
the way it does on cellphones, computers, and pretty much all equipment. =
Rather than specifying a specific wifi AP to connect to, it just =
connects to whichever it can (based on where it has connected to in the =
past).

Up until now, we=E2=80=99ve supported the wifi client mode as follows:

config set wifi.ssid <SSID> <password>
wifi mode client <SSID>

That seems to work well, and reconnection now seems pretty robust.

What I=E2=80=99ve committed today supports this variant:

config set wifi.ssid <SSID1> <password>
config set wifi.ssid <SSID2> <password>
=E2=80=A6 etc
wifi mode client

The module should then connect to either SSID1 or SSID2, whichever comes =
into range.

I=E2=80=99ve got no idea how phones, laptops, etc, actually implement =
it, and can=E2=80=99t find much information on the ESP32 resources or =
forums. There is certainly no magic =E2=80=98here is a list of SSIDs - =
connect to whichever comes close=E2=80=99 function in the wifi =
libraries. So, I ended up implementing the following logic:

Bring up the wifi as a client, in station mode.
Every 30 seconds or so, do a wifi scan of available SSIDs.
If we find a SSID within range, that has a matching name in config =
wifi.ssid, we try to actively connect to it. For this, we pick the first =
SSID we find that matches.
If we don=E2=80=99t manage to connect (get disconnected), or there is no =
SSID in range that matches anything in config wifi.ssid, wait for 30 =
seconds, then go back and scan again.

It=E2=80=99s not elegant, but seems to work. Change is isolated in =
esp32wifi.{h,cpp}, which is pretty small and manageable at the moment. =
Please give it a go, and let me know how it works out for you.

Regards, Mark.

P.S. Also found (and cleaned up) a big stonking memory leak in =E2=80=98wi=
fi scan=E2=80=99.


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<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html =
charset=3Dutf-8"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" =
class=3D""><div class=3D""><br class=3D""></div><div class=3D"">I=E2=80=99=
ve committed a change to the esp32wifi component, to try to support a =
promiscuous mode for the wifi client. This should make it work the way =
it does on cellphones, computers, and pretty much all equipment. Rather =
than specifying a specific wifi AP to connect to, it just connects to =
whichever it can (based on where it has connected to in the =
past).</div><div class=3D""><br class=3D""></div><div class=3D"">Up =
until now, we=E2=80=99ve supported the wifi client mode as =
follows:</div><div class=3D""><br class=3D""></div><div class=3D""><ul =
class=3D"MailOutline"><li class=3D"">config set wifi.ssid &lt;SSID&gt; =
&lt;password&gt;</li><li class=3D"">wifi mode client =
&lt;SSID&gt;</li></ul></div><div class=3D""><br class=3D""></div><div =
class=3D"">That seems to work well, and reconnection now seems pretty =
robust.</div><div class=3D""><br class=3D""></div><div class=3D"">What =
I=E2=80=99ve committed today supports this variant:</div><div =
class=3D""><br class=3D""></div><div class=3D""><ul =
class=3D"MailOutline"><li class=3D"">config set wifi.ssid &lt;SSID1&gt; =
&lt;password&gt;</li><li class=3D"">config set wifi.ssid &lt;SSID2&gt; =
&lt;password&gt;</li><li class=3D"">=E2=80=A6 etc</li><li class=3D"">wifi =
mode client</li></ul></div><div class=3D""><br class=3D""></div><div =
class=3D"">The module should then connect to either SSID1 or SSID2, =
whichever comes into range.</div><div class=3D""><br class=3D""></div><div=
 class=3D"">I=E2=80=99ve got no idea how phones, laptops, etc, actually =
implement it, and can=E2=80=99t find much information on the ESP32 =
resources or forums. There is certainly no magic =E2=80=98here is a list =
of SSIDs - connect to whichever comes close=E2=80=99 function in the =
wifi libraries. So, I ended up implementing the following =
logic:</div><div class=3D""><br class=3D""></div><div class=3D""><ul =
class=3D"MailOutline"><li class=3D"">Bring up the wifi as a client, in =
station mode.</li><li class=3D"">Every 30 seconds or so, do a wifi scan =
of available SSIDs.</li><li class=3D"">If we find a SSID within range, =
that has a matching name in config wifi.ssid, we try to actively connect =
to it. For this, we pick the first SSID we find that matches.</li><li =
class=3D"">If we don=E2=80=99t manage to connect (get disconnected), or =
there is no SSID in range that matches anything in config wifi.ssid, =
wait for 30 seconds, then go back and scan again.</li></ul></div><div =
class=3D""><br class=3D""></div><div class=3D"">It=E2=80=99s not =
elegant, but seems to work. Change is isolated in esp32wifi.{h,cpp}, =
which is pretty small and manageable at the moment. Please give it a go, =
and let me know how it works out for you.</div><div class=3D""><br =
class=3D""></div><div class=3D"">Regards, Mark.</div><div class=3D""><br =
class=3D""></div><div class=3D"">P.S. Also found (and cleaned up) a big =
stonking memory leak in =E2=80=98wifi scan=E2=80=99.</div><div =
class=3D""><br class=3D""></div></body></html>=

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