meecrowave-proxy/src/main/java/org/apache/meecrowave/proxy/servlet/service/SimpleSubstitutor.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF 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 org.apache.meecrowave.proxy.servlet.service;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

// duplicated to not depend on core if this module is deployed in another servlet container
public class SimpleSubstitutor {
    private final char[] prefix = "${".toCharArray();
    private final char[] suffix = "}".toCharArray();
    private final char[] valueDelimiter = ":-".toCharArray();
    private final Map<String, String> valueMap;

    public SimpleSubstitutor(final Map<String, String> valueMap) {
        this.valueMap = valueMap;
    }

    public String replace(final String source) {
        if (source == null) {
            return null;
        }
        final StringBuilder builder = new StringBuilder(source);
        if (substitute(builder, 0, source.length(), null) <= 0) {
            return source;
        }
        return replace(builder.toString());
    }

    private int substitute(final StringBuilder buf, final int offset, final int length, List<String> priorVariables) {
        final boolean top = priorVariables == null;
        boolean altered = false;
        int lengthChange = 0;
        char[] chars = buf.toString().toCharArray();
        int bufEnd = offset + length;
        int pos = offset;
        while (pos < bufEnd) {
            final int startMatchLen = isMatch(prefix, chars, pos, bufEnd);
            if (startMatchLen == 0) {
                pos++;
            } else {
                if (pos > offset && chars[pos - 1] == '$') {
                    buf.deleteCharAt(pos - 1);
                    chars = buf.toString().toCharArray();
                    lengthChange--;
                    altered = true;
                    bufEnd--;
                } else {
                    final int startPos = pos;
                    pos += startMatchLen;
                    int endMatchLen;
                    while (pos < bufEnd) {
                        endMatchLen = isMatch(suffix, chars, pos, bufEnd);
                        if (endMatchLen == 0) {
                            pos++;
                        } else {
                            String varNameExpr = new String(chars, startPos
                                    + startMatchLen, pos - startPos
                                    - startMatchLen);
                            pos += endMatchLen;
                            final int endPos = pos;

                            String varName = varNameExpr;
                            String varDefaultValue = null;

                            final char[] varNameExprChars = varNameExpr.toCharArray();
                            for (int i = 0; i < varNameExprChars.length; i++) {
                                if (isMatch(prefix, varNameExprChars, i, varNameExprChars.length) != 0) {
                                    break;
                                }
                                final int match = isMatch(valueDelimiter, varNameExprChars, i, varNameExprChars.length);
                                if (match != 0) {
                                    varName = varNameExpr.substring(0, i);
                                    varDefaultValue = varNameExpr.substring(i + match);
                                    break;
                                }
                            }

                            if (priorVariables == null) {
                                priorVariables = new ArrayList<>();
                                priorVariables.add(new String(chars,
                                        offset, length));
                            }

                            checkCyclicSubstitution(varName, priorVariables);
                            priorVariables.add(varName);

                            final String varValue = getOrDefault(varName, varDefaultValue);
                            if (varValue != null) {
                                final int varLen = varValue.length();
                                buf.replace(startPos, endPos, varValue);
                                altered = true;
                                int change = substitute(buf, startPos, varLen, priorVariables);
                                change = change + varLen - (endPos - startPos);
                                pos += change;
                                bufEnd += change;
                                lengthChange += change;
                                chars = buf.toString().toCharArray();
                            }

                            priorVariables.remove(priorVariables.size() - 1);
                            break;
                        }
                    }
                }
            }
        }
        if (top) {
            return altered ? 1 : 0;
        }
        return lengthChange;
    }

    protected String getOrDefault(final String varName, final String varDefaultValue) {
        return valueMap.getOrDefault(varName, varDefaultValue);
    }

    private int isMatch(final char[] chars, final char[] buffer, int pos,
                        final int bufferEnd) {
        final int len = chars.length;
        if (pos + len > bufferEnd) {
            return 0;
        }
        for (int i = 0; i < chars.length; i++, pos++) {
            if (chars[i] != buffer[pos]) {
                return 0;
            }
        }
        return len;
    }

    private void checkCyclicSubstitution(final String varName, final List<String> priorVariables) {
        if (!priorVariables.contains(varName)) {
            return;
        }
        final StringBuilder buf = new StringBuilder(256);
        buf.append("Infinite loop in property interpolation of ");
        buf.append(priorVariables.remove(0));
        buf.append(": ");
        appendWithSeparators(buf, priorVariables);
        throw new IllegalStateException(buf.toString());
    }

    private void appendWithSeparators(final StringBuilder builder, final Collection<String> iterable) {
        if (iterable != null && !iterable.isEmpty()) {
            final Iterator<?> it = iterable.iterator();
            while (it.hasNext()) {
                builder.append(it.next());
                if (it.hasNext()) {
                    builder.append("->");
                }
            }
        }
    }
}