Implement connection.isConnected(), don't segfault when doing work on…

… closed connection

We need to be able to detect closed connections so that we can more easily integrate with generic-pool.  That module
has a validate() hook which pairs nicely with the connection.isConnected() change I'm proposing here.

Test scenario for reproing segfault issue:
* Open connection
* Set timer for closing connection with connection.close() after 10 seconds
* Wait for timer to activate and close connection
* Try to run connection.execute('SELECT 1 FROM DUAL')
* Segfault occurs
* After this change, it will throw an error instead of segfaulting

README.md

@@ -94,6 +94,13 @@ oracle.connect(connData, function(err, connection) {
 });
 ```
 
+To validate whether the connection is still established after some time:
+
+```javascript
+if (! connection.isConnected()) {
+  // retire this connection from a pool
+}
+```
 
 
 ## Out Params

src/connection.cpp

@@ -22,6 +22,7 @@ void Connection::Init(Handle<Object> target) {
 
   NODE_SET_PROTOTYPE_METHOD(constructorTemplate, "execute", Execute);
   NODE_SET_PROTOTYPE_METHOD(constructorTemplate, "close", Close);
+  NODE_SET_PROTOTYPE_METHOD(constructorTemplate, "isConnected", IsConnected);
   NODE_SET_PROTOTYPE_METHOD(constructorTemplate, "setAutoCommit", SetAutoCommit);
   NODE_SET_PROTOTYPE_METHOD(constructorTemplate, "commit", Commit);
   NODE_SET_PROTOTYPE_METHOD(constructorTemplate, "rollback", Rollback);
@@ -85,6 +86,16 @@ Handle<Value> Connection::Close(const Arguments& args) {
   }
 }
 
+Handle<Value> Connection::IsConnected(const Arguments& args) {
+  Connection* connection = ObjectWrap::Unwrap<Connection>(args.This());
+
+  if(connection && connection->m_connection) {
+    return Boolean::New(true);
+  } else {
+    return Boolean::New(false);
+  }
+}
+
 Handle<Value> Connection::Commit(const Arguments& args) {
   Connection* connection = ObjectWrap::Unwrap<Connection>(args.This());
 
@@ -368,6 +379,9 @@ void Connection::EIO_Execute(uv_work_t* req) {
   oracle::occi::Statement* stmt = NULL;
   oracle::occi::ResultSet* rs = NULL;
   try {
+    if(! baton->connection->m_connection) {
+      throw NodeOracleException("Connection already closed");
+    }
     stmt = baton->connection->m_connection->createStatement(baton->sql);
     stmt->setAutoCommit(baton->connection->m_autoCommit);
     int outputParam = SetValuesOnStatement(stmt, baton->values);
@@ -444,7 +458,9 @@ void Connection::EIO_Execute(uv_work_t* req) {
     rs = NULL;
   }
   if(stmt) {
-    baton->connection->m_connection->terminateStatement(stmt);
+    if(baton->connection->m_connection) {
+      baton->connection->m_connection->terminateStatement(stmt);
+    }
     stmt = NULL;
   }
 }

src/connection.h

@@ -22,6 +22,7 @@ class Connection : ObjectWrap {
   static Handle<Value> New(const Arguments& args);
   static Handle<Value> Execute(const Arguments& args);
   static Handle<Value> Close(const Arguments& args);
+  static Handle<Value> IsConnected(const Arguments& args);
   static Handle<Value> Commit(const Arguments& args);
   static Handle<Value> Rollback(const Arguments& args);
   static Handle<Value> SetAutoCommit(const Arguments& args);