From 00fa448587532cc219977679bb8c573a1dcae11c Mon Sep 17 00:00:00 2001
From: Dave Cramer <davecramer@gmail.com>
Date: Mon, 18 Nov 2019 10:29:22 -0500
Subject: [PATCH] fix: NPE as a result of calling executeQuery twice on a
 statement fixes issue #684 (#1610)

---
 .../java/org/postgresql/jdbc/PgResultSet.java | 22 ++++++++++++++-----
 .../java/org/postgresql/jdbc/PgStatement.java |  6 ++---
 .../jdbc4/jdbc41/CloseOnCompletionTest.java   |  9 ++++++++
 3 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/pgjdbc/src/main/java/org/postgresql/jdbc/PgResultSet.java b/pgjdbc/src/main/java/org/postgresql/jdbc/PgResultSet.java
index 9cc490a00e..14a9195ca5 100644
--- a/pgjdbc/src/main/java/org/postgresql/jdbc/PgResultSet.java
+++ b/pgjdbc/src/main/java/org/postgresql/jdbc/PgResultSet.java
@@ -1852,17 +1852,27 @@ public boolean next() throws SQLException {
 
   public void close() throws SQLException {
     try {
-      // release resources held (memory for tuples)
-      rows = null;
-      if (cursor != null) {
-        cursor.close();
-        cursor = null;
-      }
+      closeInternally();
     } finally {
       ((PgStatement) statement).checkCompletion();
     }
   }
 
+  /*
+  used by PgStatement.closeForNextExecution to avoid
+  closing the firstUnclosedResult twice.
+  checkCompletion above modifies firstUnclosedResult
+  fixes issue #684
+   */
+  protected void closeInternally() throws SQLException {
+    // release resources held (memory for tuples)
+    rows = null;
+    if (cursor != null) {
+      cursor.close();
+      cursor = null;
+    }
+  }
+
   public boolean wasNull() throws SQLException {
     checkClosed();
     return wasNullFlag;
diff --git a/pgjdbc/src/main/java/org/postgresql/jdbc/PgStatement.java b/pgjdbc/src/main/java/org/postgresql/jdbc/PgStatement.java
index 3940e7a2c7..efc0e3364b 100644
--- a/pgjdbc/src/main/java/org/postgresql/jdbc/PgStatement.java
+++ b/pgjdbc/src/main/java/org/postgresql/jdbc/PgStatement.java
@@ -125,7 +125,7 @@ public class PgStatement implements Statement, BaseStatement {
   /**
    * The first unclosed result.
    */
-  protected ResultWrapper firstUnclosedResult = null;
+  protected volatile ResultWrapper firstUnclosedResult = null;
 
   /**
    * Results returned by a statement that wants generated keys.
@@ -327,9 +327,9 @@ protected void closeForNextExecution() throws SQLException {
     // Close any existing resultsets associated with this statement.
     synchronized (this) {
       while (firstUnclosedResult != null) {
-        ResultSet rs = firstUnclosedResult.getResultSet();
+        PgResultSet rs = (PgResultSet)firstUnclosedResult.getResultSet();
         if (rs != null) {
-          rs.close();
+          rs.closeInternally();
         }
         firstUnclosedResult = firstUnclosedResult.getNext();
       }
diff --git a/pgjdbc/src/test/java/org/postgresql/test/jdbc4/jdbc41/CloseOnCompletionTest.java b/pgjdbc/src/test/java/org/postgresql/test/jdbc4/jdbc41/CloseOnCompletionTest.java
index 801d1503a1..5eac284cb0 100644
--- a/pgjdbc/src/test/java/org/postgresql/test/jdbc4/jdbc41/CloseOnCompletionTest.java
+++ b/pgjdbc/src/test/java/org/postgresql/test/jdbc4/jdbc41/CloseOnCompletionTest.java
@@ -15,6 +15,7 @@
 import org.junit.Test;
 
 import java.sql.Connection;
+import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;
@@ -89,4 +90,12 @@ public void testNoResultSet() throws SQLException {
     stmt.executeUpdate(TestUtil.insertSQL("table1", "1"));
     assertFalse(stmt.isClosed());
   }
+
+  @Test
+  public void testExecuteTwice() throws SQLException {
+    PreparedStatement s = conn.prepareStatement("SELECT 1");
+    s.closeOnCompletion();
+    s.executeQuery();
+    s.executeQuery();
+  }
 }