[GitHub] [johnzon] dblevins commented on a diff in pull request #84: Show a chunk of json when mapping the object fails

[GitBox <gi...@apache.org>]

dblevins commented on code in PR #84:
URL: https://github.com/apache/johnzon/pull/84#discussion_r858050906


##########
johnzon-core/src/main/java/org/apache/johnzon/core/Snippet.java:
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@@ -0,0 +1,435 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.johnzon.core;
+
+import javax.json.JsonArray;
+import javax.json.JsonObject;
+import javax.json.JsonValue;
+import javax.json.stream.JsonGenerator;
+import javax.json.stream.JsonGeneratorFactory;
+import java.io.ByteArrayOutputStream;
+import java.io.Closeable;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.UncheckedIOException;
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.apache.johnzon.core.JsonGeneratorFactoryImpl.GENERATOR_BUFFER_LENGTH;
+
+/**
+ * Constructs short snippets of serialized JSON text representations of
+ * JsonValue instances in a way that is ideal for error messages.
+ *
+ * Instances of Snippet are thread-safe, reusable and memory-safe.  Snippet
+ * serializes only enough of the json to fill the desired snippet size and
+ * is therefore safe to use regardless of the size of the JsonValue.
+ */
+public class Snippet {
+
+    private final int max;
+    private final JsonGeneratorFactory generatorFactory;
+
+    /**
+     * This constructor should be used only in static or other scenarios were
+     * there is no JsonGeneratorFactory instance in scope.
+     *
+     * @param max the maximum length of the serialized json produced via of()
+     */
+    public Snippet(final int max) {
+        this(max, new JsonGeneratorFactoryImpl(new HashMap<String, Object>() {
+            {
+                this.put(GENERATOR_BUFFER_LENGTH, max);
+            }
+        }));
+    }
+
+    /**
+     * This is the preferred approach to using Snippet in any context where
+     * there is an existing JsonGeneratorFactory in scope.
+     *
+     * @param max the maximum length of the serialized json produced via of()
+     * @param generatorFactory the JsonGeneratorFactory created by the user
+     */
+    public Snippet(final int max, final JsonGeneratorFactory generatorFactory) {
+        this.max = max;
+        this.generatorFactory = generatorFactory;
+    }
+
+    /**
+     * Create a serialized json representation of the supplied
+     * JsonValue, truncating the value to the specified max length.
+     * Truncated text appears with a suffix of "..."
+     *
+     * This method is thread safe.
+     * 
+     * @param value the JsonValue to be serialized as json text
+     * @return a potentially truncated json text
+     */
+    public String of(final JsonValue value) {
+        switch (value.getValueType()) {
+            case TRUE: return "true";
+            case FALSE: return "false";
+            case NULL: return "null";
+            default: {
+                try (final Buffer buffer = new Buffer()) {
+                    buffer.write(value);
+                    return buffer.get();
+                }
+            }
+        }
+    }
+
+    /**
+     * Create a serialized json representation of the supplied
+     * JsonValue, truncating the value to the specified max length.
+     * Truncated text appears with a suffix of "..."
+     *
+     * This method is thread safe.
+     *
+     * Avoid using this method in any context where there already
+     * is a JsonGeneratorFactory instance in scope. For those scenarios
+     * use the constructor that accepts a JsonGeneratorFactory instead.
+     *
+     * @param value the JsonValue to be serialized as json text
+     * @param max the maximum length of the serialized json text
+     * @return a potentially truncated json text
+     */
+    public static String of(final JsonValue value, final int max) {
+        return new Snippet(max).of(value);
+    }
+
+    /**
+     * There are several buffers involved in the creation of a json string.
+     * This class carefully manages them all.
+     *
+     * JsonGeneratorImpl with a 64k buffer (by default)
+     * ObjectStreamWriter with an 8k buffer
+     * SnippetOutputStream with a buffer of maxSnippetLength
+     *
+     * As we create json via calling the JsonGenerator it is critical we
+     * flush the work in progress all the way through these buffers and into
+     * the final SnippetOutputStream buffer.
+     *
+     * If we do not, we risk creating up to 64k of json when we may only
+     * need 50 bytes.  We could potentially optimize this code so the
+     * buffer held by JsonGeneratorImpl is also the maxSnippetLength.
+     */
+    class Buffer implements Closeable {
+        private final JsonGenerator generator;
+        private final SnippetOutputStream snippet;
+
+        private Buffer() {
+            this.snippet = new SnippetOutputStream(max);
+            this.generator = generatorFactory.createGenerator(snippet);
+        }
+
+        private void write(final JsonValue value) {
+            if (snippet.terminate()) {
+                return;
+            }
+
+            switch (value.getValueType()) {
+                case ARRAY: {
+                    write(value.asJsonArray());
+                    break;
+                }
+                case OBJECT: {
+                    write(value.asJsonObject());
+                    break;
+                }
+                default: {
+                    generator.write(value);
+                    generator.flush();
+                }
+            }
+        }
+
+        private void write(final JsonArray array) {
+            if (snippet.terminate()) {
+                return;
+            }
+
+            if (array.isEmpty()) {
+                generator.write(array);
+                generator.flush();
+                return;
+            }
+
+            generator.writeStartArray();
+            generator.flush();
+            for (final JsonValue jsonValue : array) {
+                if (snippet.terminate()) {
+                    break;
+                }
+                write(jsonValue);
+            }
+            generator.writeEnd();
+            generator.flush();
+        }
+
+        private void write(final JsonObject object) {
+            if (snippet.terminate()) {
+                return;
+            }
+
+            if (object.isEmpty()) {
+                generator.write(object);
+                generator.flush();
+                return;
+            }
+
+            generator.writeStartObject();
+            generator.flush();
+            for (final Map.Entry<String, JsonValue> entry : object.entrySet()) {
+                if (snippet.terminate()) {
+                    break;
+                }
+                write(entry.getKey(), entry.getValue());
+            }
+            generator.writeEnd();
+            generator.flush();
+        }
+
+        private void write(final String name, final JsonValue value) {
+            if (snippet.terminate()) {
+                return;
+            }
+
+            switch (value.getValueType()) {
+                case ARRAY:
+                    generator.writeStartArray(name);
+                    generator.flush();
+                    final JsonArray array = value.asJsonArray();
+                    for (final JsonValue jsonValue : array) {
+                        if (snippet.terminate()) {
+                            break;
+                        }
+                        write(jsonValue);
+                    }
+                    generator.writeEnd();
+                    generator.flush();
+
+                    break;
+                case OBJECT:
+                    generator.writeStartObject(name);
+                    generator.flush();
+                    final JsonObject object = value.asJsonObject();
+                    for (final Map.Entry<String, JsonValue> keyval : object.entrySet()) {
+                        if (snippet.terminate()) {
+                            break;
+                        }
+                        write(keyval.getKey(), keyval.getValue());
+                    }
+                    generator.writeEnd();
+                    generator.flush();
+
+                    break;
+                default: {
+                    generator.write(name, value);
+                    generator.flush();
+                }
+            }
+        }
+
+        private String get() {
+            generator.flush();
+            return snippet.isTruncated() ? snippet.get() + "..." : snippet.get();
+        }
+
+        @Override
+        public void close() {
+            generator.close();
+        }
+    }
+
+    /**
+     * Specialized OutputStream with three internal states:
+     * Writing, Completed, Truncated.
+     *
+     * When there is still space left for more json, the
+     * state will be Writing
+     *
+     * If the last write brought is exactly to the end of
+     * the max length, the state will be Completed.
+     *
+     * If the last write brought us over the max length, the
+     * state will be Truncated.
+     */
+    static class SnippetOutputStream extends OutputStream {
+
+        private final ByteArrayOutputStream buffer;
+        private OutputStream mode;
+
+        public SnippetOutputStream(final int max) {
+            this.buffer = new ByteArrayOutputStream(Math.min(max, 8192));
+            this.mode = new Writing(max, buffer);
+        }
+
+        public String get() {
+            return buffer.toString();
+        }
+
+        /**
+         * Calling this method implies the need to continue
+         * writing and a question on if that is ok.
+         *
+         * It impacts internal state in the same way as
+         * calling a write method.
+         *
+         * @return true if no more writes are possible
+         */
+        public boolean terminate() {

Review Comment:
   Took a lot of renaming till I found something just right :)



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