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Async Http Client library purpose is to allow Java applications to easily execute HTTP requests and asynchronously process the HTTP responses.
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/*
 * Copyright 2010 Ning, Inc.
 *
 * Ning 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 com.ning.http.util;

/**
 * Convenience class that encapsulates details of "percent encoding"
 * (as per RFC-3986, see [http://www.ietf.org/rfc/rfc3986.txt]).
 */
public final class UTF8UrlEncoder {

    private static final boolean encodeSpaceUsingPlus = MiscUtils.getBoolean("com.ning.http.util.UTF8UrlEncoder.encodeSpaceUsingPlus", false);

    /**
     * Encoding table used for figuring out ascii characters that must be escaped
     * (all non-Ascii characters need to be encoded anyway)
     */
    private final static boolean[] SAFE_ASCII = new boolean[128];

    static {
        for (int i = 'a'; i <= 'z'; ++i) {
            SAFE_ASCII[i] = true;
        }
        for (int i = 'A'; i <= 'Z'; ++i) {
            SAFE_ASCII[i] = true;
        }
        for (int i = '0'; i <= '9'; ++i) {
            SAFE_ASCII[i] = true;
        }
        SAFE_ASCII['-'] = true;
        SAFE_ASCII['.'] = true;
        SAFE_ASCII['_'] = true;
        SAFE_ASCII['~'] = true;
    }

    private static final char[] HEX = "0123456789ABCDEF".toCharArray();

    private UTF8UrlEncoder() {
    }

    public static String encode(String input) {
        StringBuilder sb = new StringBuilder(input.length() + 16);
        appendEncoded(sb, input);
        return sb.toString();
    }

    public static StringBuilder appendEncoded(StringBuilder sb, CharSequence input) {
        int c;
        for (int i = 0; i < input.length(); i+= Character.charCount(c)) {
            c = Character.codePointAt(input, i);
            if (c <= 127)
                if (SAFE_ASCII[c])
                    sb.append((char) c);
                else
                    appendSingleByteEncoded(sb, c);
            else
                appendMultiByteEncoded(sb, c);
        }
        return sb;
    }

    private final static void appendSingleByteEncoded(StringBuilder sb, int value) {

        if (encodeSpaceUsingPlus && value == 32) {
            sb.append('+');
            return;
        }

        sb.append('%');
        sb.append(HEX[value >> 4]);
        sb.append(HEX[value & 0xF]);
    }

    private final static void appendMultiByteEncoded(StringBuilder sb, int value) {
        if (value < 0x800) {
            appendSingleByteEncoded(sb, (0xc0 | (value >> 6)));
            appendSingleByteEncoded(sb, (0x80 | (value & 0x3f)));
        } else if (value < 0x10000) {
            appendSingleByteEncoded(sb, (0xe0 | (value >> 12)));
            appendSingleByteEncoded(sb, (0x80 | ((value >> 6) & 0x3f)));
            appendSingleByteEncoded(sb, (0x80 | (value & 0x3f)));
        } else {
            appendSingleByteEncoded(sb, (0xf0 | (value >> 18)));
            appendSingleByteEncoded(sb, (0x80 | (value >> 12) & 0x3f));
            appendSingleByteEncoded(sb, (0x80 | (value >> 6) & 0x3f));
            appendSingleByteEncoded(sb, (0x80 | (value & 0x3f)));
        }
    }
}