feat(lnd): show error message if lnd exits

If lnd unexpectedly exits, show the user the last error message
reported by lnd in order to help diagnose issues.

See #674

app/lib/lnd/neutrino.js

@@ -35,6 +35,7 @@ class Neutrino extends EventEmitter {
   currentBlockHeight: number
   lndBlockHeight: number
   lndCfilterHeight: number
+  lastError: ?string
 
   constructor(lndConfig: LndConfig) {
     super()
@@ -46,6 +47,7 @@ class Neutrino extends EventEmitter {
     this.currentBlockHeight = 0
     this.lndBlockHeight = 0
     this.lndCfilterHeight = 0
+    this.lastError = null
   }
 
   static incrementIfHigher = (context: any, property: string, newVal: any): boolean => {
@@ -91,21 +93,29 @@ class Neutrino extends EventEmitter {
     this.process = spawn(this.lndConfig.binaryPath, neutrinoArgs)
       .on('error', error => this.emit(ERROR, error))
       .on('close', code => {
-        this.emit(CLOSE, code)
+        this.emit(CLOSE, code, this.lastError)
         this.process = null
       })
 
-    // Listen for when neutrino prints odata to stderr.
+    // Listen for when neutrino prints data to stderr.
     this.process.stderr.pipe(split2()).on('data', line => {
       if (process.env.NODE_ENV === 'development') {
-        lndLog[lndLogGetLevel(line)](line)
+        const level = lndLogGetLevel(line)
+        lndLog[level](line)
+        if (level === 'error') {
+          this.lastError = line.split('[ERR] LTND:')[1]
+        }
       }
     })
 
     // Listen for when neutrino prints data to stdout.
     this.process.stdout.pipe(split2()).on('data', line => {
       if (process.env.NODE_ENV === 'development') {
-        lndLog[lndLogGetLevel(line)](line)
+        const level = lndLogGetLevel(line)
+        lndLog[level](line)
+        if (level === 'error') {
+          this.lastError = line.split('[ERR] LTND:')[1]
+        }
       }
 
       // password RPC server listening (wallet unlocker started).

app/lib/zap/controller.js

@@ -312,12 +312,12 @@ class ZapController {
       })
     })
 
-    this.neutrino.on('close', code => {
+    this.neutrino.on('close', (code, lastError) => {
       mainLog.info(`Lnd process has shut down (code ${code})`)
       if (this.is('running') || this.is('connected')) {
         dialog.showMessageBox({
           type: 'error',
-          message: `Lnd has unexpectadly quit`
+          message: `Lnd has unexpectadly quit: ${lastError}`
         })
         this.terminate()
       }

test/unit/lnd/neutrino.spec.js

@@ -37,6 +37,9 @@ describe('Neutrino', function() {
       it('should set the "lndCfilterHeight" property to 0', () => {
         expect(this.neutrino.lndCfilterHeight).toEqual(0)
       })
+      it('should set the "lastError" property to be null', () => {
+        expect(this.neutrino.lastError).toEqual(null)
+      })
     })
   })