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Jackson is a high-performance JSON processor (parser, generator)
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package main;

import java.io.*;

import org.codehaus.jackson.*;

import java.util.Random;

/**
 * Set of basic unit tests for verifying that the string
 * generation, including character escaping, works as expected.
 */
public class TestStringGeneration
    extends BaseTest
{
    final static String[] SAMPLES = new String[] {
        "\"test\"",
        "\n", "\\n", "\r\n", "a\\b", "tab:\nok?",
        "a\tb\tc\n\fdef\t \tg\"\"\"h\"\\ijklmn\b",
        "\"\"\"", "\\r)'\"",
        "Longer text & other stuff:\twith some\r\n\r\n random linefeeds etc added in to cause some \"special\" handling \\\\ to occur...\n"
    };

    public void testBasicEscaping()
        throws Exception
    {
        doTestBasicEscaping(false);
        doTestBasicEscaping(true);
    }

    public void testLongerRandomSingleChunk()
        throws Exception
    {
        /* Let's first generate 100k of pseudo-random characters, favoring
         * 7-bit ascii range
         */
        for (int round = 0; round < 80; ++round) {
            String content = generateRandom(75000+round);
            doTestLongerRandom(content, false);
            doTestLongerRandom(content, true);
        }
    }

    public void testLongerRandomMultiChunk()
        throws Exception
    {
        /* Let's first generate 100k of pseudo-random characters, favoring
         * 7-bit ascii range
         */
        for (int round = 0; round < 70; ++round) {
            String content = generateRandom(73000+round);
            doTestLongerRandomMulti(content, false, round);
            doTestLongerRandomMulti(content, true, round);
        }
    }

    /*
    ///////////////////////////////////////////////////////////////
    // Internal methods
    ///////////////////////////////////////////////////////////////
     */

    private String generateRandom(int len)
    {
        StringBuilder sb = new StringBuilder(len+1000); // pad for surrogates
        Random r = new Random(len);
        for (int i = 0; i < len; ++i) {
            if (r.nextBoolean()) { // non-ascii
                int value = r.nextInt() & 0xFFFF;
                // Otherwise easy, except that need to ensure that
                // surrogates are properly paired: and, also
                // their values do not exceed 0x10FFFF
                if (value >= 0xD800 && value <= 0xDFFF) {
                    // Let's discard first value, then, and produce valid pair
                    int fullValue = (r.nextInt() & 0xFFFFF);
                    sb.append((char) (0xD800 + (fullValue >> 10)));
                    value = 0xDC00 + (fullValue & 0x3FF);
                }
                sb.append((char) value);
            } else { // ascii
                sb.append((char) (r.nextInt() & 0x7F));
            }
        }
        return sb.toString();
    }   

    private void doTestBasicEscaping(boolean charArray)
        throws Exception
    {
        for (int i = 0; i < SAMPLES.length; ++i) {
            String VALUE = SAMPLES[i];
            StringWriter sw = new StringWriter();
            JsonGenerator gen = new JsonFactory().createJsonGenerator(sw);
            gen.writeStartArray();
            if (charArray) {
                char[] buf = new char[VALUE.length() + i];
                VALUE.getChars(0, VALUE.length(), buf, i);
                gen.writeString(buf, i, VALUE.length());
            } else {
                gen.writeString(VALUE);
            }
            gen.writeEndArray();
            gen.close();
            String docStr = sw.toString();
            JsonParser jp = createParserUsingReader(docStr);
            assertEquals(JsonToken.START_ARRAY, jp.nextToken());
            JsonToken t = jp.nextToken();
            assertEquals(JsonToken.VALUE_STRING, t);
            assertEquals(VALUE, jp.getText());
            assertEquals(JsonToken.END_ARRAY, jp.nextToken());
            assertEquals(null, jp.nextToken());
            jp.close();
        }
    }

    private void doTestLongerRandom(String text, boolean charArray)
        throws Exception
    {
        ByteArrayOutputStream bow = new ByteArrayOutputStream(text.length());
        JsonGenerator gen = new JsonFactory().createJsonGenerator(bow, JsonEncoding.UTF8);
        gen.writeStartArray();
        if (charArray) {
            char[] buf = new char[text.length()];
            text.getChars(0, text.length(), buf, 0);
            gen.writeString(buf, 0, text.length());
        } else {
            gen.writeString(text);
        }
        gen.writeEndArray();
        gen.close();
        byte[] docData = bow.toByteArray();
        JsonParser jp = new JsonFactory().createJsonParser(new ByteArrayInputStream(docData));
        assertEquals(JsonToken.START_ARRAY, jp.nextToken());
        JsonToken t = jp.nextToken();
        assertEquals(JsonToken.VALUE_STRING, t);
        String act = jp.getText();
        if (!text.equals(act)) {
            if (text.length() != act.length()) {
                fail("Expected string length "+text.length()+", actual "+act.length());
            }
            int i = 0;
            for (int len = text.length(); i < len; ++i) {
                if (text.charAt(i) != act.charAt(i)) {
                    break;
                }
            }
            fail("Strings differ at position #"+i+" (len "+text.length()+"): expected char 0x"+Integer.toHexString(text.charAt(i))+", actual 0x"+Integer.toHexString(act.charAt(i)));
        }
        assertEquals(JsonToken.END_ARRAY, jp.nextToken());
        assertEquals(null, jp.nextToken());
        jp.close();
    }

    private void doTestLongerRandomMulti(String text, boolean charArray, int round)
        throws Exception
    {
        ByteArrayOutputStream bow = new ByteArrayOutputStream(text.length());
        JsonGenerator gen = new JsonFactory().createJsonGenerator(bow, JsonEncoding.UTF8);
        gen.writeStartArray();

        gen.writeString(text);
        gen.writeEndArray();
        gen.close();
        
        gen = new JsonFactory().createJsonGenerator(bow, JsonEncoding.UTF8);
        gen.writeStartArray();
        gen.writeStartArray();

        Random rnd = new Random(text.length());
        int offset = 0;

        while (offset < text.length()) {
            int shift = 1 + ((rnd.nextInt() & 0xFFFFF) % 12); // 1 - 12
            int len = (1 << shift) + shift; // up to 4k
            if ((offset + len) >= text.length()) {
                len = text.length() - offset;
            } else {
            	// Need to avoid splitting surrogates though
            	char c = text.charAt(offset+len-1);
            	if (c >= 0xD800 && c < 0xDC00) {
            		++len;
            	}
            }
            if (charArray) {
                char[] buf = new char[len];
                text.getChars(offset, offset+len, buf, 0);
                gen.writeString(buf, 0, len);
            } else {
                gen.writeString(text.substring(offset, offset+len));
            }
            offset += len;
        }

        gen.writeEndArray();
        gen.close();
        byte[] docData = bow.toByteArray();
        JsonParser jp = new JsonFactory().createJsonParser(new ByteArrayInputStream(docData));
        assertEquals(JsonToken.START_ARRAY, jp.nextToken());

        offset = 0;
        while (jp.nextToken() == JsonToken.VALUE_STRING) {
        	// Let's verify, piece by piece
        	String act = jp.getText();
        	String exp = text.substring(offset, offset+act.length());
        	if (!act.equals(exp)) {
        		fail("String segment ["+offset+" - "+(offset+act.length())+"[ different");
        	}
        	offset += act.length();
        }
        assertEquals(JsonToken.END_ARRAY, jp.getCurrentToken());
        jp.close();
    }

}