src/java/org/codehaus/jackson/Base64Variants.java

/* Jackson JSON-processor.
 *
 * Copyright (c) 2007- Tatu Saloranta, tatu.saloranta@iki.fi
 *
 * Licensed under the License specified in file LICENSE, included with
 * the source code and binary code bundles.
 * You may not use this file except in compliance with the License.
 *
 * 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.codehaus.jackson;

/**
 * Container for commonly used Base64 variants.
 * 
 * @author Tatu Saloranta
 */
public final class Base64Variants
{
    final static String STD_BASE64_ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    /**
     * This variant is what most people would think of "the standard"
     * Base64 encoding.
     *<p>
     * See <a href="">wikipedia Base64 entry</a> for details.
     *<p>
     * Note that although this can be thought of as the standard variant,
     * it is <b>not</b> the default for Jackson: no-linefeeds alternative
     * is because of JSON requirement of escaping all linefeeds.
     */
    public final static Base64Variant MIME;
    static {
        MIME = new Base64Variant("MIME", STD_BASE64_ALPHABET, true, '=', 76);
    }

    /**
     * Slightly non-standard modification of {@link #MIME} which does not
     * use linefeeds (max line length set to infinite). Useful when linefeeds
     * wouldn't work well (possibly in attributes), or for minor space savings
     * (save 1 linefeed per 76 data chars, ie. ~1.4% savings).
     */
    public final static Base64Variant MIME_NO_LINEFEEDS;
    static {
        MIME_NO_LINEFEEDS = new Base64Variant(MIME, "MIME-NO-LINEFEEDS", Integer.MAX_VALUE);
    }

    /**
     * This variant is the one that predates {@link #MIME}: it is otherwise
     * identical, except that it mandates shorter line length.
     */
    public final static Base64Variant PEM = new Base64Variant(MIME, "PEM", true, '=', 64);

    /**
     * This non-standard variant is usually used when encoded data needs to be
     * passed via URLs (such as part of GET request). It differs from the
     * base {@link #MIME} variant in multiple ways.
     * First, no padding is used: this also means that it generally can not
     * be written in multiple separate but adjacent chunks (which would not
     * be the usual use case in any case). Also, no linefeeds are used (max
     * line length set to infinite). And finally, two characters (plus and
     * slash) that would need quoting in URLs are replaced with more
     * optimal alternatives (hyphen and underscore, respectively).
     */
    public final static Base64Variant MODIFIED_FOR_URL;
    static {
        StringBuffer sb = new StringBuffer(STD_BASE64_ALPHABET);
        // Replace plus with hyphen, slash with underscore (and no padding)
        sb.setCharAt(sb.indexOf("+"), '-');
        sb.setCharAt(sb.indexOf("/"), '_');
        /* And finally, let's not split lines either, wouldn't work too
         * well with URLs
         */
        MODIFIED_FOR_URL = new Base64Variant("MODIFIED-FOR-URL", sb.toString(), false, Base64Variant.PADDING_CHAR_NONE, Integer.MAX_VALUE);
    }

    /**
     * Method used to get the default variant ("MIME_NO_LINEFEEDS") for cases
     * where caller does not explicitly specify the variant.
     * We will prefer no-linefeed version because linefeeds in JSON values
     * must be escaped, making linefeed-containing variants sub-optimal.
     */
    public static Base64Variant getDefaultVariant() {
        return MIME_NO_LINEFEEDS;
    }
}