query cancellation

Author: Christophe Macabiau

lib/client.js

@@ -21,6 +21,8 @@ var Client = function(config) {
   this.queryQueue = [];
   this.password = config.password || defaults.password;
   this.encoding = 'utf8';
+  this.processID = null;
+  this.secretKey = null;
   var self = this;
 };
 
@@ -59,6 +61,11 @@ p.connect = function(callback) {
     con.password(md5password);
   });
 
+  con.once('backendKeyData', function(msg) {
+  	self.processID = msg.processID;
+  	self.secretKey = msg.secretKey;
+	});
+
   //hook up query handling events to connection
   //after the connection initially becomes ready for queries
   con.once('readyForQuery', function() {
@@ -130,6 +137,25 @@ p.connect = function(callback) {
 
 };
 
+p.cancel = function(client, query) {
+	if (client.activeQuery == query) {
+		var con = this.connection;
+
+		if(this.host && this.host.indexOf('/') === 0) {
+			con.connect(this.host + '/.s.PGSQL.' + this.port);
+		} else {
+			con.connect(this.port, this.host);
+		}
+
+		//once connection is established send cancel message
+		con.on('connect', function() {
+			con.cancel(client.processID, client.secretKey);
+		});
+	}
+	else if (client.queryQueue.indexOf(query) != -1)
+		client.queryQueue.splice(client.queryQueue.indexOf(query), 1);
+};
+
 p._pulseQueryQueue = function() {
   if(this.readyForQuery===true) {
     this.activeQuery = this.queryQueue.shift();

lib/connection.js

@@ -73,6 +73,23 @@ p.startup = function(config) {
   this.stream.write(buffer);
 };
 
+p.cancel = function(processID, secretKey) {
+  var bodyBuffer = this.writer
+    .addInt16(1234)
+    .addInt16(5678)
+    .addInt32(processID)
+    .addInt32(secretKey)
+    .addCString('').flush();
+
+  var length = bodyBuffer.length + 4;
+
+  var buffer = new Writer()
+    .addInt32(length)
+    .add(bodyBuffer)
+    .join();
+  this.stream.write(buffer);
+};
+
 p.password = function(password) {
   //0x70 = 'p'
   this._send(0x70, this.writer.addCString(password));

lib/index.js

@@ -81,6 +81,16 @@ PG.prototype.connect = function(config, callback) {
   return pool.acquire(cb);
 }
 
+// cancel the query runned by the given client
+PG.prototype.cancel = function(config, client, query) {
+  var c = config;
+  //allow for no config to be passed
+  if(typeof c === 'function')
+    c = defaults;
+  var cancellingClient = new this.Client(c);
+  cancellingClient.cancel(client, query);
+}
+
 module.exports = new PG(Client);
 
 //lazy require native module...the native module may not have installed