refactor(collation): utility function for checking collation support

Created a function collationNotSupported in utils that returns 
whether or not collation is supported by the server.

Fixes NODE-1522

Author: rweinberger

lib/cursor.js

@@ -6,6 +6,7 @@ const MongoError = require('./error').MongoError;
 const MongoNetworkError = require('./error').MongoNetworkError;
 const mongoErrorContextSymbol = require('./error').mongoErrorContextSymbol;
 const f = require('util').format;
+const collationNotSupported = require('./utils').collationNotSupported;
 
 var BSON = retrieveBSON(),
   Long = BSON.Long;
@@ -634,9 +635,9 @@ var nextFunction = function(self, callback) {
     // Set as init
     self.cursorState.init = true;
 
-    // Server does not support server
-    if (self.cmd && self.cmd.collation && self.server.ismaster.maxWireVersion < 5) {
-      return callback(new MongoError(f('server %s does not support collation', self.server.name)));
+    // error if collation not supported
+    if (collationNotSupported(self.server, self.cmd)) {
+      return callback(new MongoError(`server ${self.server.name} does not support collation`));
     }
 
     try {

lib/topologies/server.js

@@ -21,6 +21,8 @@ var inherits = require('util').inherits,
   SessionMixins = require('./shared').SessionMixins,
   relayEvents = require('../utils').relayEvents;
 
+const collationNotSupported = require('../utils').collationNotSupported;
+
 function getSaslSupportedMechs(options) {
   if (!options) {
     return {};
@@ -748,9 +750,9 @@ Server.prototype.command = function(ns, cmd, options, callback) {
   // If we are not connected or have a disconnectHandler specified
   if (disconnectHandler(self, 'command', ns, cmd, options, callback)) return;
 
-  // Check if we have collation support
-  if (this.ismaster && this.ismaster.maxWireVersion < 5 && cmd.collation) {
-    return callback(new MongoError(f('server %s does not support collation', this.name)));
+  // error if collation not supported
+  if (collationNotSupported(this, cmd)) {
+    return callback(new MongoError(`server ${this.name} does not support collation`));
   }
 
   // Are we executing against a specific topology
@@ -837,9 +839,9 @@ Server.prototype.update = function(ns, ops, options, callback) {
   // If we are not connected or have a disconnectHandler specified
   if (disconnectHandler(self, 'update', ns, ops, options, callback)) return;
 
-  // Check if we have collation support
-  if (this.ismaster && this.ismaster.maxWireVersion < 5 && options.collation) {
-    return callback(new MongoError(f('server %s does not support collation', this.name)));
+  // error if collation not supported
+  if (collationNotSupported(this, options)) {
+    return callback(new MongoError(`server ${this.name} does not support collation`));
   }
 
   // Setup the docs as an array
@@ -872,9 +874,9 @@ Server.prototype.remove = function(ns, ops, options, callback) {
   // If we are not connected or have a disconnectHandler specified
   if (disconnectHandler(self, 'remove', ns, ops, options, callback)) return;
 
-  // Check if we have collation support
-  if (this.ismaster && this.ismaster.maxWireVersion < 5 && options.collation) {
-    return callback(new MongoError(f('server %s does not support collation', this.name)));
+  // error if collation not supported
+  if (collationNotSupported(this, options)) {
+    return callback(new MongoError(`server ${this.name} does not support collation`));
   }
 
   // Setup the docs as an array

lib/utils.js

@@ -48,10 +48,23 @@ try {
   console.warn(err.message);
 }
 
+/*
+ * Checks that collation is supported by server.
+ *
+ * @param {Server} [server] to check against
+ * @param {object} [cmd] object where collation may be specified
+ * @param {function} [callback] callback function
+ * @return true if server does not support collation
+ */
+function collationNotSupported(server, cmd) {
+  return cmd && cmd.collation && server.ismaster && server.ismaster.maxWireVersion < 5;
+}
+
 module.exports = {
   uuidV4,
   calculateDurationInMs,
   relayEvents,
   Kerberos,
-  MongoAuthProcess
+  MongoAuthProcess,
+  collationNotSupported
 };