refactor(read-preference): remove duplicate ReadPreference

There was a ReadPreference defined in mongodb-core as well as in
this driver, which lead to much confusion, unneccesary code
duplication, and most importantly an inability to confidently use
`instanceof` with `ReadPreference`. We now simply use the one from
mongodb-core, and forward that in our exports.

NODE-1187

index.js

@@ -1,3 +1,5 @@
+'use strict';
+
 // Core module
 var core = require('mongodb-core'),
   Instrumentation = require('./lib/apm');
@@ -16,7 +18,7 @@ connect.Collection = require('./lib/collection');
 connect.Server = require('./lib/topologies/server');
 connect.ReplSet = require('./lib/topologies/replset');
 connect.Mongos = require('./lib/topologies/mongos');
-connect.ReadPreference = require('./lib/read_preference');
+connect.ReadPreference = require('mongodb-core').ReadPreference;
 connect.GridStore = require('./lib/gridfs/grid_store');
 connect.Chunk = require('./lib/gridfs/chunk');
 connect.Logger = core.Logger;

lib/collection.js

@@ -14,8 +14,7 @@ var checkCollectionName = require('./utils').checkCollectionName,
   handleCallback = require('./utils').handleCallback,
   decorateCommand = require('./utils').decorateCommand,
   formattedOrderClause = require('./utils').formattedOrderClause,
-  ReadPreference = require('./read_preference'),
-  CoreReadPreference = require('mongodb-core').ReadPreference,
+  ReadPreference = require('mongodb-core').ReadPreference,
   CommandCursor = require('./command_cursor'),
   Define = require('./metadata'),
   Cursor = require('./cursor'),
@@ -297,7 +296,7 @@ Collection.prototype.find = function(query, options, callback) {
   newOptions.slaveOk = options.slaveOk != null ? options.slaveOk : this.s.db.slaveOk;
 
   // Add read preference if needed
-  newOptions = getReadPreference(this, newOptions, this.s.db, this);
+  newOptions = getReadPreference(this, newOptions, this.s.db);
 
   // Set slave ok to true if read preference different from primary
   if (
@@ -3193,28 +3192,28 @@ var writeConcern = function(target, db, col, options) {
 
 // Figure out the read preference
 var getReadPreference = function(self, options, db) {
-  var r = null;
+  let r = null;
   if (options.readPreference) {
     r = options.readPreference;
   } else if (self.s.readPreference) {
     r = self.s.readPreference;
   } else if (db.s.readPreference) {
     r = db.s.readPreference;
+  } else {
+    return options;
   }
 
-  if (r instanceof ReadPreference) {
-    options.readPreference = new CoreReadPreference(r.mode, r.tags, {
-      maxStalenessSeconds: r.maxStalenessSeconds
-    });
-  } else if (typeof r === 'string') {
-    options.readPreference = new CoreReadPreference(r);
+  if (typeof r === 'string') {
+    options.readPreference = new ReadPreference(r);
   } else if (r && !(r instanceof ReadPreference) && typeof r === 'object') {
-    var mode = r.mode || r.preference;
+    const mode = r.mode || r.preference;
     if (mode && typeof mode === 'string') {
-      options.readPreference = new CoreReadPreference(mode, r.tags, {
+      options.readPreference = new ReadPreference(mode, r.tags, {
         maxStalenessSeconds: r.maxStalenessSeconds
       });
     }
+  } else if (!(r instanceof ReadPreference)) {
+    throw new TypeError('Invalid read preference: ' + r);
   }
 
   return options;

lib/command_cursor.js

@@ -1,12 +1,11 @@
 'use strict';
 
 var inherits = require('util').inherits,
-  ReadPreference = require('./read_preference'),
+  ReadPreference = require('mongodb-core').ReadPreference,
   MongoError = require('mongodb-core').MongoError,
   Readable = require('stream').Readable,
   Define = require('./metadata'),
-  CoreCursor = require('./cursor'),
-  CoreReadPreference = require('mongodb-core').ReadPreference;
+  CoreCursor = require('./cursor');
 
 /**
  * @fileOverview The **CommandCursor** class is an internal class that embodies a
@@ -162,23 +161,24 @@ var define = (CommandCursor.define = new Define('CommandCursor', CommandCursor,
  * @throws {MongoError}
  * @return {Cursor}
  */
-CommandCursor.prototype.setReadPreference = function(r) {
-  if (this.s.state === CommandCursor.CLOSED || this.isDead())
+CommandCursor.prototype.setReadPreference = function(readPreference) {
+  if (this.s.state === CommandCursor.CLOSED || this.isDead()) {
     throw MongoError.create({ message: 'Cursor is closed', driver: true });
-  if (this.s.state !== CommandCursor.INIT)
+  }
+
+  if (this.s.state !== CommandCursor.INIT) {
     throw MongoError.create({
       message: 'cannot change cursor readPreference after cursor has been accessed',
       driver: true
     });
+  }
 
-  if (r instanceof ReadPreference) {
-    this.s.options.readPreference = new CoreReadPreference(r.mode, r.tags, {
-      maxStalenessSeconds: r.maxStalenessSeconds
-    });
-  } else if (typeof r === 'string') {
-    this.s.options.readPreference = new CoreReadPreference(r);
-  } else if (r instanceof CoreReadPreference) {
-    this.s.options.readPreference = r;
+  if (readPreference instanceof ReadPreference) {
+    this.s.options.readPreference = readPreference;
+  } else if (typeof readPreference === 'string') {
+    this.s.options.readPreference = new ReadPreference(readPreference);
+  } else {
+    throw new TypeError('Invalid read preference: ' + readPreference);
   }
 
   return this;

lib/cursor.js

@@ -4,13 +4,12 @@ var inherits = require('util').inherits,
   f = require('util').format,
   formattedOrderClause = require('./utils').formattedOrderClause,
   handleCallback = require('./utils').handleCallback,
-  ReadPreference = require('./read_preference'),
+  ReadPreference = require('mongodb-core').ReadPreference,
   MongoError = require('mongodb-core').MongoError,
   Readable = require('stream').Readable,
   Define = require('./metadata'),
   CoreCursor = require('mongodb-core').Cursor,
   Map = require('mongodb-core').BSON.Map,
-  CoreReadPreference = require('mongodb-core').ReadPreference,
   executeOperation = require('./utils').executeOperation;
 
 /**
@@ -867,20 +866,20 @@ define.classMethod('forEach', { callback: true, promise: false });
  * @throws {MongoError}
  * @return {Cursor}
  */
-Cursor.prototype.setReadPreference = function(r) {
-  if (this.s.state !== Cursor.INIT)
+Cursor.prototype.setReadPreference = function(readPreference) {
+  if (this.s.state !== Cursor.INIT) {
     throw MongoError.create({
       message: 'cannot change cursor readPreference after cursor has been accessed',
       driver: true
     });
-  if (r instanceof ReadPreference) {
-    this.s.options.readPreference = new CoreReadPreference(r.mode, r.tags, {
-      maxStalenessSeconds: r.maxStalenessSeconds
-    });
-  } else if (typeof r === 'string') {
-    this.s.options.readPreference = new CoreReadPreference(r);
-  } else if (r instanceof CoreReadPreference) {
-    this.s.options.readPreference = r;
+  }
+
+  if (readPreference instanceof ReadPreference) {
+    this.s.options.readPreference = readPreference;
+  } else if (typeof readPreference === 'string') {
+    this.s.options.readPreference = new ReadPreference(readPreference);
+  } else {
+    throw new TypeError('Invalid read preference: ' + readPreference);
   }
 
   return this;

lib/db.js

@@ -10,11 +10,10 @@ var EventEmitter = require('events').EventEmitter,
   handleCallback = require('./utils').handleCallback,
   filterOptions = require('./utils').filterOptions,
   toError = require('./utils').toError,
-  ReadPreference = require('./read_preference'),
+  ReadPreference = require('mongodb-core').ReadPreference,
   f = require('util').format,
   Admin = require('./admin'),
   Code = require('mongodb-core').BSON.Code,
-  CoreReadPreference = require('mongodb-core').ReadPreference,
   MongoError = require('mongodb-core').MongoError,
   ObjectID = require('mongodb-core').ObjectID,
   Define = require('./metadata'),
@@ -270,25 +269,30 @@ Object.defineProperty(Db.prototype, 'writeConcern', {
 });
 
 /**
- * Converts provided read preference to CoreReadPreference
+ * Ensures provided read preference is properly converted into an object
  * @param {(ReadPreference|string|object)} readPreference the user provided read preference
- * @return {CoreReadPreference}
+ * @return {ReadPreference}
  */
-var convertReadPreference = function(readPreference) {
-  if (readPreference && typeof readPreference === 'string') {
-    return new CoreReadPreference(readPreference);
-  } else if (readPreference instanceof ReadPreference) {
-    return new CoreReadPreference(readPreference.mode, readPreference.tags, {
-      maxStalenessSeconds: readPreference.maxStalenessSeconds
-    });
-  } else if (readPreference && typeof readPreference === 'object') {
-    var mode = readPreference.mode || readPreference.preference;
-    if (mode && typeof mode === 'string') {
-      readPreference = new CoreReadPreference(mode, readPreference.tags, {
-        maxStalenessSeconds: readPreference.maxStalenessSeconds
-      });
+const convertReadPreference = function(readPreference) {
+  if (readPreference) {
+    if (typeof readPreference === 'string') {
+      return new ReadPreference(readPreference);
+    } else if (
+      readPreference &&
+      !(readPreference instanceof ReadPreference) &&
+      typeof readPreference === 'object'
+    ) {
+      const mode = readPreference.mode || readPreference.preference;
+      if (mode && typeof mode === 'string') {
+        return new ReadPreference(mode, readPreference.tags, {
+          maxStalenessSeconds: readPreference.maxStalenessSeconds
+        });
+      }
+    } else if (!(readPreference instanceof ReadPreference)) {
+      throw new TypeError('Invalid read preference: ' + readPreference);
     }
   }
+
   return readPreference;
 };
 
@@ -314,7 +318,7 @@ var executeCommand = function(self, command, options, callback) {
   if (options.readPreference) {
     options.readPreference = convertReadPreference(options.readPreference);
   } else {
-    options.readPreference = CoreReadPreference.primary;
+    options.readPreference = ReadPreference.primary;
   }
 
   // Debug information
@@ -770,7 +774,7 @@ var evaluate = function(self, code, parameters, options, callback) {
   }
 
   // Set primary read preference
-  options.readPreference = new CoreReadPreference(ReadPreference.PRIMARY);
+  options.readPreference = new ReadPreference(ReadPreference.PRIMARY);
 
   // Execute the command
   self.command(cmd, options, function(err, result) {

lib/gridfs/grid_store.js

@@ -36,7 +36,7 @@
  */
 var Chunk = require('./chunk'),
   ObjectID = require('mongodb-core').BSON.ObjectID,
-  ReadPreference = require('../read_preference'),
+  ReadPreference = require('mongodb-core').ReadPreference,
   Buffer = require('buffer').Buffer,
   Collection = require('../collection'),
   fs = require('fs'),
@@ -130,7 +130,7 @@ var GridStore = function GridStore(db, id, filename, mode, options) {
     this.options['root'] == null ? GridStore.DEFAULT_ROOT_COLLECTION : this.options['root'];
   this.position = 0;
   this.readPreference =
-    this.options.readPreference || db.options.readPreference || ReadPreference.PRIMARY;
+    this.options.readPreference || db.options.readPreference || ReadPreference.primary;
   this.writeConcern = _getWriteConcern(db, this.options);
   // Set default chunk size
   this.internalChunkSize =
@@ -1396,7 +1396,7 @@ var list = function(db, rootCollection, options, callback) {
   }
 
   // Establish read preference
-  var readPreference = options.readPreference || ReadPreference.PRIMARY;
+  var readPreference = options.readPreference || ReadPreference.primary;
   // Check if we are returning by id not filename
   var byId = options['id'] != null ? options['id'] : false;
   // Fetch item

lib/mongo_client.js

@@ -7,7 +7,7 @@ var parse = require('./url_parser'),
   EventEmitter = require('events').EventEmitter,
   inherits = require('util').inherits,
   Define = require('./metadata'),
-  ReadPreference = require('./read_preference'),
+  ReadPreference = require('mongodb-core').ReadPreference,
   Logger = require('mongodb-core').Logger,
   MongoError = require('mongodb-core').MongoError,
   handleCallback = require('./utils').handleCallback,