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/*
 * Copyright (c) 2011-2017 The original author or authors
 * ------------------------------------------------------
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Apache License v2.0 which accompanies this distribution.
 *
 *     The Eclipse Public License is available at
 *     http://www.eclipse.org/legal/epl-v10.html
 *
 *     The Apache License v2.0 is available at
 *     http://www.opensource.org/licenses/apache2.0.php
 *
 * You may elect to redistribute this code under either of these licenses.
 */

package org.atmosphere.sockjs;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.io.CharTypes;
import com.fasterxml.jackson.core.json.JsonWriteContext;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.module.SimpleModule;

import java.io.IOException;

/**
 * SockJS requires a special JSON codec - it requires that many other characters,
 * over and above what is required by the JSON spec are escaped.
 * To satisfy this we escape any character that escapable with short escapes and
 * any other non ASCII character we unicode escape it
 *
 * @author Tim Fox
 */
public class JsonCodec {

    private final static ObjectMapper mapper;

    static {
        mapper = new ObjectMapper();

        // By default, Jackson does not escape unicode characters in JSON strings
        // This should be ok, since a valid JSON string can contain unescaped JSON
        // characters.
        // However, SockJS requires that many unicode chars are escaped. This may
        // be due to browsers barfing over certain unescaped characters
        // So... when encoding strings we make sure all unicode chars are escaped

        // This code adapted from http://wiki.fasterxml.com/JacksonSampleQuoteChars
        SimpleModule simpleModule = new SimpleModule();

        simpleModule.addSerializer(String.class, new JsonSerializer() {
            final char[] HEX_CHARS = "0123456789abcdef".toCharArray();
            final int[] ESCAPE_CODES = CharTypes.get7BitOutputEscapes();

            private void writeUnicodeEscape(JsonGenerator gen, char c) throws IOException {
                gen.writeRaw('\\');
                gen.writeRaw('u');
                gen.writeRaw(HEX_CHARS[(c >> 12) & 0xF]);
                gen.writeRaw(HEX_CHARS[(c >> 8) & 0xF]);
                gen.writeRaw(HEX_CHARS[(c >> 4) & 0xF]);
                gen.writeRaw(HEX_CHARS[c & 0xF]);
            }

            private void writeShortEscape(JsonGenerator gen, char c) throws IOException {
                gen.writeRaw('\\');
                gen.writeRaw(c);
            }

            @Override
            public void serialize(String str, JsonGenerator gen, SerializerProvider provider) throws IOException {
                int status = ((JsonWriteContext) gen.getOutputContext()).writeValue();
                switch (status) {
                    case JsonWriteContext.STATUS_OK_AFTER_COLON:
                        gen.writeRaw(':');
                        break;
                    case JsonWriteContext.STATUS_OK_AFTER_COMMA:
                        gen.writeRaw(',');
                        break;
                    case JsonWriteContext.STATUS_EXPECT_NAME:
                        throw new JsonGenerationException("Can not write string value here");
                }
                gen.writeRaw('"');
                for (char c : str.toCharArray()) {
                    if (c >= 0x80) writeUnicodeEscape(gen, c); // use generic escaping for all non US-ASCII characters
                    else {
                        // use escape table for first 128 characters
                        int code = (c < ESCAPE_CODES.length ? ESCAPE_CODES[c] : 0);
                        if (code == 0) gen.writeRaw(c); // no escaping
                        else if (code == -1) writeUnicodeEscape(gen, c); // generic escaping
                        else writeShortEscape(gen, (char) code); // short escaping (\n \t ...)
                    }
                }
                gen.writeRaw('"');
            }
        });
        mapper.registerModule(simpleModule);
    }

    public static String encode(Object obj) {
        try {
            return mapper.writeValueAsString(obj);
        } catch (JsonProcessingException e) {
            return null;
        }
    }

    public static Object decodeValue(String str, Class clazz) {
        try {
            return mapper.readValue(str, clazz);
        } catch (IOException e) {
            return null;
        }
    }
}