Add support for JsonGenerator.Key

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

@@ -150,6 +150,18 @@ private JsonGenerator writeName(String name) {
         return this;
     }
 
+    private void writeName(Key name) {
+        writeComma();
+        final char[] escaped = name.toCharArray();
+        final int required = escaped.length;
+        if (len + required >= buf.length) {
+            flushBuffer();
+        }
+        System.arraycopy(escaped, 0, buf, len, required);
+        len += required;
+        writeColon();
+    }
+
     @Override
     public JsonGenerator write(String name, String fieldValue) {
         write(name, (CharSequence) fieldValue);
@@ -464,6 +476,19 @@ public JsonGenerator writeKey(String name) {
         return this;
     }
 
+    @Override
+    public JsonGenerator writeKey(JsonGenerator.Key name) {
+        if (currentContext.scope != Scope.IN_OBJECT) {
+            throw new JsonGenerationException(
+                    JsonMessages.GENERATOR_ILLEGAL_METHOD(currentContext.scope));
+        }
+        writeName(name);
+        stack.push(currentContext);
+        currentContext = new Context(Scope.IN_FIELD);
+        currentContext.first = false;
+        return this;
+    }
+
     @Override
     public JsonGenerator writeEnd() {
         if (currentContext.scope == Scope.IN_NONE) {

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

@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2012, 2021 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
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the
+ * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
+ * version 2 with the GNU Classpath Exception, which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ */
+
+package org.eclipse.parsson;
+
+import jakarta.json.stream.JsonGenerator;
+
+final class JsonGeneratorKeyImpl {
+
+    static JsonGenerator.Key createKey(String name) {
+        return new Key(quoteEscape(name));
+    }
+
+    /**
+     * A key that is already escaped so then can just be written directly.
+     */
+    private static class Key implements JsonGenerator.Key {
+
+        private final char[] escapedName;
+
+        Key(String escapedName) {
+            this.escapedName = escapedName.toCharArray();
+        }
+
+        @Override
+        public char[] toCharArray() {
+            return escapedName;
+        }
+    }
+
+    private static String quoteEscape(CharSequence string) {
+        StringBuilder builder = new StringBuilder();
+        builder.append('"');
+        int len = string.length();
+        for (int i = 0; i < len; i++) {
+            int begin = i, end = i;
+            char c = string.charAt(i);
+            // find all the characters that need not be escaped
+            // unescaped = %x20-21 | %x23-5B | %x5D-10FFFF
+            while (c >= 0x20 && c <= 0x10ffff && c != 0x22 && c != 0x5c) {
+                i++;
+                end = i;
+                if (i < len) {
+                    c = string.charAt(i);
+                } else {
+                    break;
+                }
+            }
+            // Write characters without escaping
+            if (begin < end) {
+                builder.append(string, begin, end);
+                if (i == len) {
+                    break;
+                }
+            }
+
+            switch (c) {
+                case '"':
+                case '\\':
+                    builder.append('\\');
+                    builder.append(c);
+                    break;
+                case '\b':
+                    builder.append('\\');
+                    builder.append('b');
+                    break;
+                case '\f':
+                    builder.append('\\');
+                    builder.append('f');
+                    break;
+                case '\n':
+                    builder.append('\\');
+                    builder.append('n');
+                    break;
+                case '\r':
+                    builder.append('\\');
+                    builder.append('r');
+                    break;
+                case '\t':
+                    builder.append('\\');
+                    builder.append('t');
+                    break;
+                default:
+                    String hex = "000" + Integer.toHexString(c);
+                    builder.append("\\u" + hex.substring(hex.length() - 4));
+            }
+        }
+        return builder.append('"').toString();
+    }
+}

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

@@ -44,6 +44,11 @@
 public class JsonProviderImpl extends JsonProvider {
     private final BufferPool bufferPool = new BufferPoolImpl();
 
+    @Override
+    public JsonGenerator.Key createGeneratorKey(String name) {
+        return JsonGeneratorKeyImpl.createKey(name);
+    }
+
     @Override
     public JsonGenerator createGenerator(Writer writer) {
         return new JsonGeneratorImpl(writer, bufferPool);

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

@@ -16,13 +16,12 @@
 
 package org.eclipse.parsson.tests;
 
+import jakarta.json.spi.JsonProvider;
 import junit.framework.TestCase;
 
 import jakarta.json.Json;
-import jakarta.json.JsonBuilderFactory;
 import jakarta.json.JsonObject;
 import jakarta.json.JsonObjectBuilder;
-import jakarta.json.JsonValue;
 import jakarta.json.stream.JsonGenerationException;
 import jakarta.json.stream.JsonGenerator;
 import java.io.StringWriter;
@@ -37,6 +36,46 @@
  */
 public class JsonFieldTest extends TestCase {
 
+    public void testKeyFieldObject() {
+        StringWriter sw = new StringWriter();
+        JsonProvider provider = JsonProvider.provider();
+
+        JsonGenerator.Key f1Name = provider.createGeneratorKey("f1Name");
+        JsonGenerator.Key innerFieldName = provider.createGeneratorKey("innerFieldName");
+        JsonGenerator.Key f2Name = provider.createGeneratorKey("f2Name");
+
+        JsonGenerator generator = provider.createGenerator(sw);
+
+        generator.writeStartObject();
+        generator.writeKey(f1Name);
+        generator.writeStartObject();
+        generator.writeKey(innerFieldName).write("innerFieldValue");
+        generator.writeEnd();
+        generator.writeKey(f2Name).write("f2Value");
+        generator.writeEnd();
+
+        generator.close();
+        assertEquals("{\"f1Name\":{\"innerFieldName\":\"innerFieldValue\"},\"f2Name\":\"f2Value\"}", sw.toString());
+    }
+
+    public void testKeyFieldEscaped() {
+        StringWriter sw = new StringWriter();
+        JsonProvider provider = JsonProvider.provider();
+
+        JsonGenerator.Key f1Name = provider.createGeneratorKey("\"f1Name\"");
+        JsonGenerator.Key f2Name = provider.createGeneratorKey("f2-name");
+
+        JsonGenerator generator = provider.createGenerator(sw);
+
+        generator.writeStartObject();
+        generator.writeKey(f1Name).write("a");
+        generator.writeKey(f2Name).write("b");
+        generator.writeEnd();
+
+        generator.close();
+        assertEquals("{\"\\\"f1Name\\\"\":\"a\",\"f2-name\":\"b\"}", sw.toString());
+    }
+
     public void testFieldAsOnlyMember() {
         StringWriter sw = new StringWriter();
         JsonGenerator generator = Json.createGenerator(sw);