JsonGenerator#close() is not idempotent and may cause data corruption.

impl/src/main/java/org/eclipse/parsson/JsonGeneratorImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2021 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2022 Oracle and/or its affiliates. All rights reserved.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v. 2.0, which is available at
@@ -90,6 +90,7 @@ private static enum Scope {
     // flush the underlying output source
     private final char buf[];     // capacity >= INT_MIN_VALUE_CHARS.length
     private int len = 0;
+    private boolean closed = false;
 
     JsonGeneratorImpl(Writer writer, BufferPool bufferPool) {
         this.writer = writer;
@@ -515,16 +516,19 @@ private static class Context {
 
     @Override
     public void close() {
-        if (currentContext.scope != Scope.IN_NONE || currentContext.first) {
-            throw new JsonGenerationException(JsonMessages.GENERATOR_INCOMPLETE_JSON());
-        }
-        flushBuffer();
-        try {
-            writer.close();
-        } catch (IOException ioe) {
-            throw new JsonException(JsonMessages.GENERATOR_CLOSE_IO_ERR(), ioe);
+        if (!closed) {
+            if (currentContext.scope != Scope.IN_NONE || currentContext.first) {
+                throw new JsonGenerationException(JsonMessages.GENERATOR_INCOMPLETE_JSON());
+            }
+            flushBuffer();
+            try {
+                writer.close();
+            } catch (IOException ioe) {
+                throw new JsonException(JsonMessages.GENERATOR_CLOSE_IO_ERR(), ioe);
+            }
+            bufferPool.recycle(buf);
+            closed = true;
         }
-        bufferPool.recycle(buf);
     }
 
     // begin, end-1 indexes represent characters that need not

impl/src/test/java/org/eclipse/parsson/tests/JsonGeneratorTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2021 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2022 Oracle and/or its affiliates. All rights reserved.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v. 2.0, which is available at
@@ -22,6 +22,7 @@
 import jakarta.json.*;
 import jakarta.json.stream.*;
 import java.io.*;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Random;
@@ -542,4 +543,34 @@ public void testFlush() throws Exception {
         assertEquals("{}", baos.toString("UTF-8"));
     }
 
+    public void testClose() {
+        StringWriter sw = new StringWriter();
+        JsonGeneratorFactory factory = Json.createGeneratorFactory(Collections.emptyMap());
+        try (JsonGenerator generator = factory.createGenerator(sw)) {
+            generator.writeStartObject();
+            generator.writeEnd();
+            // Unnecessary close()
+            generator.close();
+            assertEquals("{}", sw.toString());
+        } 
+        StringWriter sw1 = new StringWriter();
+        StringWriter sw2 = new StringWriter();
+        try (JsonGenerator generator1 = factory.createGenerator(sw1);
+                JsonGenerator generator2 = factory.createGenerator(sw2)) {
+            generator1.writeStartObject();
+            generator1.write("key", "value");
+
+            generator2.writeStartArray();
+            generator2.write("item");
+            generator2.write("item2");
+
+            generator1.write("key2", "value2");
+
+            generator2.writeEnd();
+
+            generator1.writeEnd();
+        }
+        assertEquals("{\"key\":\"value\",\"key2\":\"value2\"}", sw1.toString());
+        assertEquals("[\"item\",\"item2\"]", sw2.toString());
+    }
 }