Inspect Connection (#784)

Handles `console.log` and `utils.inspect` invocations for a better debugging experience.

`agent` and `ssl` are hidden since they made the logs very hard to read.
The user can still access them with `instance.agent` and `instance.ssl`.

lib/Connection.js

@@ -20,6 +20,7 @@
 'use strict'
 
 const assert = require('assert')
+const { inspect } = require('util')
 const http = require('http')
 const https = require('https')
 const debug = require('debug')('elasticsearch')
@@ -54,7 +55,7 @@ class Connection {
       maxSockets: keepAliveFalse ? Infinity : 256,
       maxFreeSockets: 256
     }, opts.agent)
-    this._agent = this.url.protocol === 'http:'
+    this.agent = this.url.protocol === 'http:'
       ? new http.Agent(agentOptions)
       : new https.Agent(Object.assign({}, agentOptions, this.ssl))
 
@@ -146,7 +147,7 @@ class Connection {
     if (this._openRequests > 0) {
       setTimeout(() => this.close(callback), 1000)
     } else {
-      this._agent.destroy()
+      this.agent.destroy()
       callback()
     }
   }
@@ -193,7 +194,7 @@ class Connection {
       auth: !!url.username === true || !!url.password === true
         ? `${url.username}:${url.password}`
         : undefined,
-      agent: this._agent
+      agent: this.agent
     }
 
     const paramsKeys = Object.keys(params)
@@ -218,6 +219,23 @@ class Connection {
 
     return request
   }
+
+  // Handles console.log and utils.inspect invocations.
+  // We want to hide `agent` and `ssl` since they made
+  // the logs very hard to read. The user can still
+  // access them with `instance.agent` and `instance.ssl`.
+  [inspect.custom] (depth, options) {
+    return {
+      url: this.url,
+      id: this.id,
+      headers: this.headers,
+      deadCount: this.deadCount,
+      resurrectTimeout: this.resurrectTimeout,
+      _openRequests: this._openRequests,
+      status: this.status,
+      roles: this.roles
+    }
+  }
 }
 
 Connection.statuses = {