Implement WiFi.getCredentials

[monkbroc]

• User provides an array of WiFiAccessPoint that get filled with the APs saved on the device
• Returns number of APs on device
• Photon only. Returns 0 on the Core since it cannot read APs back from the CC3000 😞

Changes

• Implement wlan_get_credentials in HAL
• Implement WiFi.getCredentials with array arguments
• Add API test

Fixes #453

Usage:

    WiFiAccessPoint ap[5];
    int found = WiFi.getCredentials(ap, 5);
    for (int i=0; i<found; i++) {
        Serial.print("ssid: ");
        Serial.println(ap[i].ssid);
        Serial.println(ap[i].security);
        Serial.println(ap[i].channel);
        Serial.println(ap[i].rssi);
    }

For discussion: my first cut of this was to return a vector<WiFiAccessPoint> (typedefed to WiFiAccessPointList) from WiFi.getCredentials. This made for very nice application code:

WiFiAccessPointList list = WiFi.getCredentials();
for(WiFiAccessPoint ap : list) {
  Serial.println(ap.ssid);
}

But I noticed that WiFi.scan is currently implemented to accept an array allocated on the stack by the caller, so I went with that solution in the end.

Any strong reasons why not create a vector that allocates a few WiFiAccessPoint on the heap whenever WiFi.scan or WiFi.getCredentials is called? It is simple to make a version of WiFi.scan that returns a WiFiAccessPointList too.

Another point of discussion:
Printing the list of available networks on one of my Photon gives me this:

Listing stored access points
Count=5
SSID=TechBreweryNew, security=3
SSID=TechBreweryNew, security=3
SSID=TechBreweryNew, security=3
SSID=TechBreweryNew, security=3
SSID=TechBreweryNew, security=3
End listing

Is it OK that there are 5 copies of the same network? Now that people will be able to read this list out it might cause confusion.

Would it be better to overwrite existing credentials if the SSID is the same rather than make multiple copies?

[m-mcgowan]

Outstanding! 👍 How about we call it WiFi.getCredentials() to mirror WiFi.setCredentials()?

[monkbroc]

Sure. You have write access to my fork if you want to make small changes like that before merging.

[monkbroc]

I renamed this API to WiFi.getCredentials()

[jmaxxz]

I don't see how this gets the configured credentials. It appears to get the everything about the configured wifi networks besides the credentials. Am I misreading this? Or is does this api exposes the preshared keys of previously configured networks.

[monkbroc]

I think what you're saying is it would be best described as "get connections" rather than "get credentials" since it doesn't actually return the passwords, but the connection information for which passwords are available, but cannot be retrieved. I can update the docs to that effect.

[jmaxxz]

@monkbroc yes that is exactly what I am saying. Thanks!