third-party/java/aosp/src/com/android/common/utils/XmlUtils.java

/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * 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
 *
 *      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.android.common.utils;

import static com.android.common.SdkConstants.AMP_ENTITY;
import static com.android.common.SdkConstants.ANDROID_NS_NAME;
import static com.android.common.SdkConstants.ANDROID_URI;
import static com.android.common.SdkConstants.APOS_ENTITY;
import static com.android.common.SdkConstants.APP_PREFIX;
import static com.android.common.SdkConstants.LT_ENTITY;
import static com.android.common.SdkConstants.QUOT_ENTITY;
import static com.android.common.SdkConstants.XMLNS;
import static com.android.common.SdkConstants.XMLNS_PREFIX;
import static com.android.common.SdkConstants.XMLNS_URI;

import com.android.common.SdkConstants;
import com.android.common.annotations.NonNull;
import com.android.common.annotations.Nullable;

import org.w3c.dom.Attr;
import org.w3c.dom.Document;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;

import java.util.HashSet;

/** XML Utilities */
public class XmlUtils {
    /**
     * Returns the namespace prefix matching the requested namespace URI.
     * If no such declaration is found, returns the default "android" prefix for
     * the Android URI, and "app" for other URI's.
     *
     * @param node The current node. Must not be null.
     * @param nsUri The namespace URI of which the prefix is to be found,
     *              e.g. {@link SdkConstants#ANDROID_URI}
     * @return The first prefix declared or the default "android" prefix
     *              (or "app" for non-Android URIs)
     */
    @NonNull
    public static String lookupNamespacePrefix(@NonNull Node node, @NonNull String nsUri) {
        String defaultPrefix = ANDROID_URI.equals(nsUri) ? ANDROID_NS_NAME : APP_PREFIX;
        return lookupNamespacePrefix(node, nsUri, defaultPrefix);
    }

    /**
     * Returns the namespace prefix matching the requested namespace URI.
     * If no such declaration is found, returns the default "android" prefix.
     *
     * @param node The current node. Must not be null.
     * @param nsUri The namespace URI of which the prefix is to be found,
     *              e.g. {@link SdkConstants#ANDROID_URI}
     * @param defaultPrefix The default prefix (root) to use if the namespace
     *              is not found. If null, do not create a new namespace
     *              if this URI is not defined for the document.
     * @return The first prefix declared or the provided prefix (possibly with
     *              a number appended to avoid conflicts with existing prefixes.
     */
    public static String lookupNamespacePrefix(
            @Nullable Node node, @Nullable String nsUri, @Nullable String defaultPrefix) {
        // Note: Node.lookupPrefix is not implemented in wst/xml/core NodeImpl.java
        // The following code emulates this simple call:
        //   String prefix = node.lookupPrefix(NS_RESOURCES);

        // if the requested URI is null, it denotes an attribute with no namespace.
        if (nsUri == null) {
            return null;
        }

        // per XML specification, the "xmlns" URI is reserved
        if (XMLNS_URI.equals(nsUri)) {
            return XMLNS;
        }

        HashSet<String> visited = new HashSet<String>();
        Document doc = node == null ? null : node.getOwnerDocument();

        // Ask the document about it. This method may not be implemented by the Document.
        String nsPrefix = null;
        try {
            nsPrefix = doc != null ? doc.lookupPrefix(nsUri) : null;
            if (nsPrefix != null) {
                return nsPrefix;
            }
        } catch (Throwable t) {
            // ignore
        }

        // If that failed, try to look it up manually.
        // This also gathers prefixed in use in the case we want to generate a new one below.
        for (; node != null && node.getNodeType() == Node.ELEMENT_NODE;
               node = node.getParentNode()) {
            NamedNodeMap attrs = node.getAttributes();
            for (int n = attrs.getLength() - 1; n >= 0; --n) {
                Node attr = attrs.item(n);
                if (XMLNS.equals(attr.getPrefix())) {
                    String uri = attr.getNodeValue();
                    nsPrefix = attr.getLocalName();
                    // Is this the URI we are looking for? If yes, we found its prefix.
                    if (nsUri.equals(uri)) {
                        return nsPrefix;
                    }
                    visited.add(nsPrefix);
                }
            }
        }

        // Failed the find a prefix. Generate a new sensible default prefix, unless
        // defaultPrefix was null in which case the caller does not want the document
        // modified.
        if (defaultPrefix == null) {
            return null;
        }

        //
        // We need to make sure the prefix is not one that was declared in the scope
        // visited above. Pick a unique prefix from the provided default prefix.
        String prefix = defaultPrefix;
        String base = prefix;
        for (int i = 1; visited.contains(prefix); i++) {
            prefix = base + Integer.toString(i);
        }
        // Also create & define this prefix/URI in the XML document as an attribute in the
        // first element of the document.
        if (doc != null) {
            node = doc.getFirstChild();
            while (node != null && node.getNodeType() != Node.ELEMENT_NODE) {
                node = node.getNextSibling();
            }
            if (node != null) {
                // This doesn't work:
                //Attr attr = doc.createAttributeNS(XMLNS_URI, prefix);
                //attr.setPrefix(XMLNS);
                //
                // Xerces throws
                //org.w3c.dom.DOMException: NAMESPACE_ERR: An attempt is made to create or
                // change an object in a way which is incorrect with regard to namespaces.
                //
                // Instead pass in the concatenated prefix. (This is covered by
                // the UiElementNodeTest#testCreateNameSpace() test.)
                Attr attr = doc.createAttributeNS(XMLNS_URI, XMLNS_PREFIX + prefix);
                attr.setValue(nsUri);
                node.getAttributes().setNamedItemNS(attr);
            }
        }

        return prefix;
    }

    /**
     * Converts the given attribute value to an XML-attribute-safe value, meaning that
     * single and double quotes are replaced with their corresponding XML entities.
     *
     * @param attrValue the value to be escaped
     * @return the escaped value
     */
    @NonNull
    public static String toXmlAttributeValue(@NonNull String attrValue) {
        for (int i = 0, n = attrValue.length(); i < n; i++) {
            char c = attrValue.charAt(i);
            if (c == '"' || c == '\'' || c == '<' || c == '&') {
                StringBuilder sb = new StringBuilder(2 * attrValue.length());
                appendXmlAttributeValue(sb, attrValue);
                return sb.toString();
            }
        }

        return attrValue;
    }

    /**
     * Converts the given attribute value to an XML-text-safe value, meaning that
     * less than and ampersand characters are escaped.
     *
     * @param textValue the text value to be escaped
     * @return the escaped value
     */
    @NonNull
    public static String toXmlTextValue(@NonNull String textValue) {
        for (int i = 0, n = textValue.length(); i < n; i++) {
            char c = textValue.charAt(i);
            if (c == '<' || c == '&') {
                StringBuilder sb = new StringBuilder(2 * textValue.length());
                appendXmlTextValue(sb, textValue);
                return sb.toString();
            }
        }

        return textValue;
    }

    /**
     * Appends text to the given {@link StringBuilder} and escapes it as required for a
     * DOM attribute node.
     *
     * @param sb the string builder
     * @param attrValue the attribute value to be appended and escaped
     */
    public static void appendXmlAttributeValue(@NonNull StringBuilder sb,
            @NonNull String attrValue) {
        int n = attrValue.length();
        // &, ", ' and < are illegal in attributes; see http://www.w3.org/TR/REC-xml/#NT-AttValue
        // (' legal in a " string and " is legal in a ' string but here we'll stay on the safe
        // side)
        for (int i = 0; i < n; i++) {
            char c = attrValue.charAt(i);
            if (c == '"') {
                sb.append(QUOT_ENTITY);
            } else if (c == '<') {
                sb.append(LT_ENTITY);
            } else if (c == '\'') {
                sb.append(APOS_ENTITY);
            } else if (c == '&') {
                sb.append(AMP_ENTITY);
            } else {
                sb.append(c);
            }
        }
    }

    /**
     * Appends text to the given {@link StringBuilder} and escapes it as required for a
     * DOM text node.
     *
     * @param sb the string builder
     * @param textValue the text value to be appended and escaped
     */
    public static void appendXmlTextValue(@NonNull StringBuilder sb, @NonNull String textValue) {
        for (int i = 0, n = textValue.length(); i < n; i++) {
            char c = textValue.charAt(i);
            if (c == '<') {
                sb.append(LT_ENTITY);
            } else if (c == '&') {
                sb.append(AMP_ENTITY);
            } else {
                sb.append(c);
            }
        }
    }
}