Validate discovery messages against JSON schema

[bergie]

Now coordinator crashes on malformed discovery messages, as reported in c-base/c-flo#35

May 14 03:31:26 c-flo node[3134]: Participant discovery failed: Discovery message missing .inports
May 14 03:31:26 c-flo node[3134]:  Error: Discovery message missing .inports
May 14 03:31:26 c-flo node[3134]:     at Coordinator.participantDiscovered (/opt/c-flo/node_modules/msgflo/src/coordinator.coffee:168:11)
May 14 03:31:26 c-flo node[3134]:     at Coordinator.handleFbpMessage (/opt/c-flo/node_modules/msgflo/src/coordinator.coffee:160:8)
May 14 03:31:26 c-flo node[3134]:     at /opt/c-flo/node_modules/msgflo/src/coordinator.coffee:135:14
May 14 03:31:26 c-flo node[3134]:     at MessageBroker.Client._onMessage (/opt/c-flo/node_modules/msgflo-nodejs/lib/mqtt.js:165:22)
May 14 03:31:26 c-flo node[3134]:     at MqttClient.<anonymous> (/opt/c-flo/node_modules/msgflo-nodejs/lib/mqtt.js:58:26)
May 14 03:31:26 c-flo node[3134]:     at emitThree (events.js:116:13)
May 14 03:31:26 c-flo node[3134]:     at MqttClient.emit (events.js:197:7)
May 14 03:31:26 c-flo node[3134]:     at MqttClient._handlePublish (/opt/c-flo/node_modules/mqtt/lib/client.js:816:12)
May 14 03:31:26 c-flo node[3134]:     at MqttClient._handlePacket (/opt/c-flo/node_modules/mqtt/lib/client.js:286:12)
May 14 03:31:26 c-flo node[3134]:     at process (/opt/c-flo/node_modules/mqtt/lib/client.js:242:12)
May 14 03:31:26 c-flo node[3134]:     at Writable.writable._write (/opt/c-flo/node_modules/mqtt/lib/client.js:252:5)
May 14 03:31:26 c-flo node[3134]:     at doWrite (/opt/c-flo/node_modules/mqtt/node_modules/readable-stream/lib/_stream_writable.js:338:64)
May 14 03:31:26 c-flo node[3134]:     at writeOrBuffer (/opt/c-flo/node_modules/mqtt/node_modules/readable-stream/lib/_stream_writable.js:327:5)
May 14 03:31:26 c-flo node[3134]:     at Writable.write (/opt/c-flo/node_modules/mqtt/node_modules/readable-stream/lib/_stream_writable.js:264:11)
May 14 03:31:26 c-flo node[3134]:     at Socket.ondata (_stream_readable.js:555:20)
May 14 03:31:26 c-flo node[3134]:     at emitOne (events.js:96:13)
May 14 03:31:26 c-flo node[3134]:     at Socket.emit (events.js:191:7)
May 14 03:31:26 c-flo node[3134]:     at readableAddChunk (_stream_readable.js:176:18)
May 14 03:31:26 c-flo node[3134]:     at Socket.Readable.push (_stream_readable.js:134:10)
May 14 03:31:26 c-flo node[3134]:     at TCP.onread (net.js:563:20)
May 14 03:31:26 c-flo node[3134]:
May 14 03:31:26 c-flo node[3134]:  {"command":"participant","protocol":"discovery","payload":{"component":"c-base/music-player","label":"Show URL on a public screen.","outports":[{"queue":"megablast/current_song","type":"object","description":"JSON object of the current song being played.","id":"current_song"}],"role":"megablast","id":"cdmmpqtt83779605327991","icon":"television"}}

[jonnor]

This is not a crash, but the output of a warning due to the discovery message being malformed. Not a bug.

[jonnor]

But using a JSON schema here instead of basic validation would be nice, since then we would also validate actual values and not just their presence.