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/*
* 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.
*/
/* $Id$ */
package org.apache.fop.afp.util;
import java.io.IOException;
import java.io.InputStream;
/**
* A helper class to read structured fields from a MO:DCA document. Each
* component of a mixed object document is explicitly defined and delimited
* in the data. This is accomplished through the use of MO:DCA data structures,
* called structured fields. Structured fields are used to envelop document
* components and to provide commands and information to applications using
* the data. Structured fields may contain one or more parameters. Each
* parameter provides one value from a set of values defined by the architecture.
* <p/>
* MO:DCA structured fields consist of two parts: an introducer that identifies
* the length and type of the structured field, and data that provides the
* structured field's effect. The data is contained in a set of parameters,
* which can consist of other data structures and data elements. The maximum
* length of a structured field is 32767 bytes.
* <p/>
*/
public class StructuredFieldReader {
/**
* The input stream to read
*/
private InputStream inputStream = null;
/**
* The constructor for the StructuredFieldReader
* @param inputStream the input stream to process
*/
public StructuredFieldReader(InputStream inputStream) {
this.inputStream = inputStream;
}
/**
* Get the next structured field as identified by the identifer
* parameter (this must be a valid MO:DCA structured field.
* @param identifier the three byte identifier
* @throws IOException if an I/O exception occurred
* @return the next structured field or null when there are no more
*/
public byte[] getNext(byte[] identifier) throws IOException {
int bufferPointer = 0;
byte[] bufferData = new byte[identifier.length + 2];
for (int x = 0; x < identifier.length; x++) {
bufferData[x] = 0x00;
}
int c;
while ((c = inputStream.read()) > -1) {
bufferData[bufferPointer] = (byte) c;
// Check the last characters in the buffer
int index = 0;
boolean found = true;
for (int i = identifier.length - 1; i > -1; i--) {
int p = bufferPointer - index;
if (p < 0) {
p = bufferData.length + p;
}
index++;
if (identifier[i] != bufferData[p]) {
found = false;
break;
}
}
if (found) {
byte[] length = new byte[2];
int a = bufferPointer - identifier.length;
if (a < 0) {
a = bufferData.length + a;
}
int b = bufferPointer - identifier.length - 1;
if (b < 0) {
b = bufferData.length + b;
}
length[0] = bufferData[b];
length[1] = bufferData[a];
int reclength = ((length[0] & 0xFF) << 8)
+ (length[1] & 0xFF) - identifier.length - 2;
byte[] retval = new byte[reclength];
inputStream.read(retval, 0, reclength);
return retval;
}
bufferPointer++;
if (bufferPointer >= bufferData.length) {
bufferPointer = 0;
}
}
return null;
}
}
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