Since a few versions Airfoil and Airfoil Satellite work very closely together, allowing to control the Airfoil 'server'-instance from a running Airfoil Satellite App - whether it is running on a computer or mobile device.
This is realized with an (undocumented) protocoll, on which I did a bit of reverse engineering. My goal is to implement a Airfoil-MQTT bridge to controll the speaker volume and source from an OpenHAB home automation system.
node mdns-discovery.js
You'll get a response similar to
$ node mdns-discovery.js
Match: Seims-Lappi.local:25590
Match: Seims-Lappi.local:52563
node tcp-client.js <hosname> <port>
The app will do the protocoll handshake for you and subscribes to a few events. You can execute the command above and try to move a volume slider in Airfoil, the output will look like this:
$ node tcp-client.js Seims-Lappi.local 52563
Connected
Match Version
Match OK
Handshake Done, subscribing
532;{"replyID":"3","data":{"speakers":[{"password":false,"volume":1,"longIdentifier":"com.rogueamoeba.airfoil.LocalSpeaker","name":"Computer","type":"local","connected":false},{"password":false,"volume":0.3247283,"longIdentifier":"Chromecast-Audio","name":"Chromecast-Audio","type":"chromecast","connected":false}],"canRemoteControl":true,"canConnect":true,"notifications":["remoteControlChangedRequest","speakerConnectedChanged","speakerListChanged","speakerNameChanged","speakerPasswordChanged","speakerVolumeChanged"]}}
105;{"request":"speakerVolumeChanged","data":{"longIdentifier":"Chromecast-Audio","volume":0.3241107}}
105;{"request":"speakerVolumeChanged","data":{"longIdentifier":"Chromecast-Audio","volume":0.3251297}}
105;{"request":"speakerVolumeChanged","data":{"longIdentifier":"Chromecast-Audio","volume":0.3261487}}
105;{"request":"speakerVolumeChanged","data":{"longIdentifier":"Chromecast-Audio","volume":0.3271677}}
105;{"request":"speakerVolumeChanged","data":{"longIdentifier":"Chromecast-Audio","volume":0.3281868}}
105;{"request":"speakerVolumeChanged","data":{"longIdentifier":"Chromecast-Audio","volume":0.3292058}}
105;{"request":"speakerVolumeChanged","data":{"longIdentifier":"Chromecast-Audio","volume":0.3302248}}
The best way to further instpect the communitation between Airfoil and Airfoil Satellite is to use Wireshark with the filter tcp.port == <port>.
Connect with the command netcat <hostname> <port>. The port changes every time, but is broadcased via Bonjour/Zeroconf/mDNS using the service identifier _slipstreamrem._tcp.local.
Once connected, Airfoil will send you its protocoll version:
com.rogueamoeba.protocol.slipstreamremote
majorversion=1,minorversion=5
you reply with your own protocol version, so just Copy&Paste the same output into the terminal window:
com.rogueamoeba.protocol.slipstreamremote
majorversion=1,minorversion=5
Send it by pressing [Enter]. You'll receive an
OK
and send an ok back (again with pressing [Enter]):
OK
The previous two messages you sent, were terminated with and endl, \n or 0x0a character at the end. This is because you sent it by pressing [Enter]. Netcat automatically added this character and sent the message.
From now on this character is prohibited in the protocoll. Everytime you send a message by pressing [Enter] the connection will terminate! You can still Copy&Paste messages into the terminal window, but from now on you'll have to send it by pressing [Ctrl+D].
For e.g. try to Copy & Paste this message and send it with [Ctrl+D]:
82;{"request":"getSourceList","requestID":"7","data":{"iconSize":16,"scaleFactor":1}}
The 82 is the message length, excluding the 82; itself. The actual TCP package has a length of 85 then.
You'll get a reply similar to this one (this is the JSON-pretty-printed version):
{
"replyID": "7",
"data": {
"systemAudio": [
{
"friendlyName": "System Audio",
"icon": "...",
"identifier": "com.rogueamoeba.source.systemaudio"
}
],
"audioDevices": [
{
"friendlyName": "Built-in Microphone",
"icon": "...",
"identifier": "AppleHDAEngineInput:1B,0,1,0:1"
},
{
"friendlyName": "Soundflower (2ch)",
"icon": "...",
"identifier": "SoundflowerEngine:0"
},
{
"friendlyName": "Soundflower (64ch)",
"icon": "...",
"identifier": "SoundflowerEngine:1"
}
],
"recentApplications": [
{
"friendlyName": "Spotify",
"icon": "...",
"identifier": "/Applications/Spotify.app"
},
{
"friendlyName": "Safari",
"icon": "...",
"identifier": "/Applications/Safari.app"
}
]
}
}
The icon data is a Base64 encoded image. The requestID can be any number. The original software uses an incremented number starting from 0.
122;{"request":"selectSource","requestID":"5","data":{"type":"recentApplications","identifier":"\/Applications\/Spotify.app"}}
respoonse
45;{"request":"sourceMetadataChanged","data":{}}
100;{"request":"connectToSpeaker","requestID":"5","data":{"longIdentifier":"843835649D9C@Seim's Lappi"}}
You'll get multiple reponses when you subscribed with the command cited earlier:
109;{"request":"speakerConnectedChanged","data":{"longIdentifier":"843835649D9C@Seim's Lappi","connected":false}}
45;{"request":"sourceMetadataChanged","data":{}}
108;{"request":"speakerConnectedChanged","data":{"longIdentifier":"843835649D9C@Seim's Lappi","connected":true}}
39;{"replyID":"5","data":{"success":true}}
This is also what the tcp-client.js does.
212;{"request":"subscribe","requestID":"3","data":{"notifications":["remoteControlChangedRequest","speakerConnectedChanged","speakerListChanged","speakerNameChanged","speakerPasswordChanged","speakerVolumeChanged"]}}
After subcribing, Airfoil will send you updates whenever one of the events you subscribed to is fired. Such a notification message might look like this:
45;{"request":"sourceMetadataChanged","data":{}}
When Airfoil broadcasts a sourceMetadataChanged to all subscribed clients, this message will look like:
45;{"request":"sourceMetadataChanged","data":{}}
You gain no more information from this except "something changed". The Airfoil Satellite App for e.g. sends out a new request, to find out which data was changed (here the pretty-printed communication):
{
"request": "getSourceMetadata",
"requestID": "7",
"data": {
"scaleFactor": 1,
"requestedData": {
"album": true,
"remoteControlAvailable": true,
"machineIconAndScreenshot": 64,
"bundleid": true,
"albumArt": 64,
"sourceName": true,
"title": true,
"icon": 16,
"trackMetadataAvailable": true,
"artist": true,
"machineModel": true,
"machineName": true
}
}
}
Response:
{
"replyID": "7",
"data": {
"metadata": {
"album": "Yours Truly, Angry Mob",
"remoteControlAvailable": true,
"bundleid": "com.spotify.client",
"machineIconAndScreenshot": "...",
"title": "Ruby",
"sourceName": "Spotify",
"albumArt": "...",
"icon": "...",
"trackMetadataAvailable": 1,
"artist": "Kaiser Chiefs",
"machineModel": "MacBookAir6,2",
"machineName": "Seim's Lappi"
}
}
}