DataUrlDecoder

/*
 * Copyright (c) 2002-2025 Gargoyle Software Inc.
 *
 * Licensed 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
 * https://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.htmlunit.protocol.data;

import static java.nio.charset.StandardCharsets.US_ASCII;
import static org.htmlunit.protocol.data.DataURLConnection.DATA_PREFIX;

import java.io.UnsupportedEncodingException;
import java.net.URL;
import java.nio.charset.Charset;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException;
import java.util.Base64;

import org.apache.commons.lang3.StringUtils;
import org.htmlunit.util.MimeType;
import org.htmlunit.util.UrlUtils;

/**
 * Helper to work with data URLs.
 * @see <a href="http://www.ietf.org/rfc/rfc2397.txt">RFC2397</a>
 * @author Marc Guillemot
 * @author Ronald Brill
 * @author Carsten Steul
 */
public class DataUrlDecoder {
    private static final Charset DEFAULT_CHARSET = US_ASCII;
    private static final String DEFAULT_MEDIA_TYPE = MimeType.TEXT_PLAIN;
    private final String mediaType_;
    private final Charset charset_;
    private final byte[] content_;

    /**
     * C'tor.
     * @param data the data
     * @param mediaType the media type
     * @param charset the charset
     */
    protected DataUrlDecoder(final byte[] data, final String mediaType, final Charset charset) {
        content_ = data;
        mediaType_ = mediaType;
        charset_ = charset;
    }

    /**
     * Decodes a data URL providing simple access to the information contained by the URL.
     * @param url the URL to decode
     * @return the {@link DataUrlDecoder} holding decoded information
     * @throws UnsupportedEncodingException if the encoding specified by the data URL is invalid or not
     */
    public static DataUrlDecoder decode(final URL url) throws UnsupportedEncodingException {
        return decodeDataURL(url.toExternalForm());
    }

    /**
     * Decodes a data URL providing simple access to the information contained by the URL.
     * @param url the string representation of the URL to decode
     * @return the {@link DataUrlDecoder} holding decoded information
     * @throws UnsupportedEncodingException if the encoding specified by the data URL is invalid or not
     *         available on the JVM
     */
    public static DataUrlDecoder decodeDataURL(final String url) throws UnsupportedEncodingException {
        if (!url.startsWith(DATA_PREFIX)) {
            throw new UnsupportedEncodingException("Invalid data url: '" + url + "' (wrong prefix)");
        }
        final int comma = url.indexOf(',');
        if (comma < 0) {
            throw new UnsupportedEncodingException("Invalid data url: '" + url + "' (no data)");
        }

        String beforeData = url.substring(DATA_PREFIX.length(), comma);
        final boolean base64 = beforeData.endsWith(";base64");
        if (base64) {
            beforeData = beforeData.substring(0, beforeData.length() - 7);
        }
        final String mediaType = extractMediaType(beforeData);
        final Charset charset = extractCharset(beforeData);

        try {
            byte[] data = url.substring(comma + 1).getBytes(charset);
            data = UrlUtils.decodeDataUrl(data, base64);
            if (base64) {
                data = Base64.getDecoder().decode(data);
            }
            return new DataUrlDecoder(data, mediaType, charset);
        }
        catch (final IllegalArgumentException e) {
            final UnsupportedEncodingException ex =
                    new UnsupportedEncodingException("Invalid data url: '" + url + "' (data decoding failed)");
            ex.initCause(e);
            throw ex;
        }
    }

    private static Charset extractCharset(final String beforeData) {
        if (beforeData.contains(";")) {
            String charsetName = StringUtils.substringAfter(beforeData, ";");
            charsetName = charsetName.trim();
            if (charsetName.startsWith("charset=")) {
                charsetName = charsetName.substring(8);
            }
            try {
                return Charset.forName(charsetName);
            }
            catch (final UnsupportedCharsetException | IllegalCharsetNameException e) {
                return DEFAULT_CHARSET;
            }
        }
        return DEFAULT_CHARSET;
    }

    private static String extractMediaType(final String beforeData) {
        if (beforeData.contains("/")) {
            if (beforeData.contains(";")) {
                return StringUtils.substringBefore(beforeData, ";");
            }
            return beforeData;
        }
        return DEFAULT_MEDIA_TYPE;
    }

    /**
     * Gets the media type information contained in the data URL.
     * @return "text/plain" if the URL didn't contain any media type information
     */
    public String getMediaType() {
        return mediaType_;
    }

    /**
     * Gets the charset information specified in the data URL.
     * @return "US-ASCII" if the URL didn't contain any charset information
     */
    public String getCharset() {
        return charset_.name();
    }

    /**
     * Gets the bytes contained in the data URL.
     * @return the content
     */
    public byte[] getBytes() {
        return content_;
    }

    /**
     * Gets the text content of the data URL. This makes sense only for data URL that
     * represents some text.
     * @return the text content
     * @throws UnsupportedEncodingException if decoding failed using the specified charset
     */
    public String getDataAsString() throws UnsupportedEncodingException {
        return new String(content_, charset_);
    }
}