Correct use of close event in queryStream() samples and doc

Author: cjbj

CHANGELOG.md

@@ -20,13 +20,22 @@
   records ([ODPI-C
   change](https://github.com/oracle/odpi/commit/4e80a81257ce6e1066f4f6242fed533eaed45753)).
 
+- Corrected `queryStream()` documentation and examples to show the `'close'`
+  event should be received before closing connections.  If connections are
+  closed on the `'end'` event, then significant C layer memory may be [held
+  open](https://github.com/oracle/node-oracledb/issues/1173) until the garbage
+  collector frees the associated JavaScript resource.
+
 - Reverted the
   [`events`](https://oracle.github.io/node-oracledb/doc/api.html#propdbevents)
   default back to pre-4.0 behavior due to connection creation timeouts in some
   environments.  It is now *false* again.
 
 - Error changes:
 
+    - Ensured that `queryStream()` errors raised during close are emitted in the
+      `'error'` event.
+
     - Enforce only one of `connectString` or `connectionString` being used for
       connection.
 

doc/api.md

@@ -3703,11 +3703,11 @@ This function provides query streaming support.  The parameters are
 the same as [`execute()`](#execute) except a callback is not used.
 Instead this function returns a stream used to fetch data.
 
-Each row is returned as a `data` event.  Query metadata is available
-via a `metadata` event.  The `end` event indicates the end of the
-query results.
-
-The connection must remain open until the stream is completely read.
+Each row is returned as a `data` event.  Query metadata is available via a
+`metadata` event.  The `end` event indicates the end of the query results. The
+connection must remain open until the stream is completely read and the `close`
+event received.  Alternatively the Stream [`destroy()`][92] method can be used
+to terminate a stream early.
 
 For tuning, adjust the value of
 [`oracledb.fetchArraySize`](#propdbfetcharraysize) or the
@@ -8841,22 +8841,23 @@ await rs.close();
 Streaming of query results allows data to be piped to other streams,
 for example when dealing with HTTP responses.
 
-Use [`connection.queryStream()`](#querystream) to create a stream from
-a top level query and listen for events.  You can also call
-[`connection.execute()`](#execute) and use
-[`toQueryStream()`](#toquerystream) to return a stream from the
-returned [ResultSet](#resultsetclass), an OUT bind REF CURSOR
-ResultSet, or [Implicit Results](#implicitresults) ResultSet.
+Use [`connection.queryStream()`](#querystream) to create a stream from a top
+level query and listen for events.  You can also call
+[`connection.execute()`](#execute) and use [`toQueryStream()`](#toquerystream)
+to return a stream from the returned [ResultSet](#resultsetclass), from an OUT
+bind REF CURSOR ResultSet, or from [Implicit Results](#implicitresults)
+ResultSets.
 
-With streaming, each row is returned as a `data` event.  Query
-metadata is available via a `metadata` event.  The `end` event
-indicates the end of the query results.
+With streaming, each row is returned as a `data` event.  Query metadata is
+available via a `metadata` event.  The `end` event indicates the end of the
+query results, however it is generally best to put end-of-fetch logic in the
+`close` event.
 
 Query results should be fetched to completion to avoid resource leaks, or the
-Stream [`destroy()`][92] method can be used to terminate a stream early.
-
-The connection must remain open until the stream is completely read
-and any returned [Lob](#lobclass) objects have been processed.
+Stream [`destroy()`][92] method can be used to terminate a stream early.  When
+fetching, the connection must remain open until the stream is completely read
+and the `close` event received.  Any returned [Lob](#lobclass) objects should
+also be processed first.
 
 The query stream implementation is a wrapper over the [ResultSet
 Class](#resultsetclass).  In particular, successive calls to
@@ -8879,7 +8880,11 @@ stream.on('data', function (data) {
 });
 
 stream.on('end', function () {
-  // release connection...
+  // all data has been fetched...
+});
+
+stream.on('close', function () {
+  // can now close connection...  (Note: do not close connections on 'end')
 });
 
 stream.on('metadata', function (metadata) {

examples/selectstream.js

@@ -69,7 +69,13 @@ async function run() {
       });
 
       stream.on('end', function() {
-        // console.log("stream 'end' event");
+        // console.log("stream 'end' event"); // all data has been fetched
+      });
+
+      stream.on('close', function() {
+        // console.log("stream 'close' event");
+        // The underlying ResultSet has been closed, so the connection can now
+        // be closed, if desired.  Note: do not close connections on 'end'.
         resolve(rowcount);
       });
     });

lib/querystream.js

@@ -67,7 +67,11 @@ function QueryStream(resultSet) {
     // Using setImmediate to ensure that end event handlers are processed
     // before the destroy logic is invoked.
     setImmediate(function() {
-      self._destroy(null, function() {});
+      self._destroy(null, function(err) {
+        if (err) {
+          self.emit('error', err);
+        }
+      });
     });
   });
 }