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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.geometry.io.euclidean.threed.stl;
18  
19  import java.io.BufferedReader;
20  import java.io.InputStream;
21  import java.io.InputStreamReader;
22  import java.io.PushbackInputStream;
23  import java.nio.charset.Charset;
24  import java.text.MessageFormat;
25  import java.util.Arrays;
26  
27  import org.apache.commons.geometry.io.core.internal.GeometryIOUtils;
28  import org.apache.commons.geometry.io.euclidean.threed.FacetDefinitionReader;
29  
30  /** Utility class with factory methods for constructing {@link FacetDefinitionReader}
31   * instances for STL content.
32   */
33  public final class StlFacetDefinitionReaders {
34  
35      /** Utility class; no instantiation. */
36      private StlFacetDefinitionReaders() { }
37  
38      /** Construct a {@link FacetDefinitionReader} for reading STL content from the
39       * given input. The format of the input is checked to determine if it is a binary
40       * or text file and an appropriate reader is returned.
41       * @param in input to read from
42       * @param charset charset to use when checking the input for text content;
43       *      if null, the input is assumed to use the UTF-8 charset
44       * @return facet definition reader
45       * @throws IllegalStateException if a parsing error occurs
46       * @throws java.io.UncheckedIOException if an I/O error occurs
47       */
48      public static FacetDefinitionReader create(final InputStream in, final Charset charset) {
49          final Charset inputCharset = charset != null ?
50                  charset :
51                  StlConstants.DEFAULT_CHARSET;
52  
53          final byte[] testBytes = StlConstants.SOLID_START_KEYWORD.getBytes(inputCharset);
54          final byte[] actualBytes = new byte[testBytes.length];
55  
56          final int read = GeometryIOUtils.applyAsIntUnchecked(in::read, actualBytes);
57          if (read < actualBytes.length) {
58              throw GeometryIOUtils.parseError(MessageFormat.format(
59                      "Cannot determine STL format: attempted to read {0} bytes but found only {1} available",
60                      actualBytes.length, read));
61          }
62  
63          // "unread" the test bytes so that the created readers can start from the
64          // beginning of the content
65          final PushbackInputStream pushbackInput = new PushbackInputStream(in, actualBytes.length);
66          GeometryIOUtils.acceptUnchecked(pushbackInput::unread, actualBytes);
67  
68          if (Arrays.equals(testBytes, actualBytes)) {
69              // this is a text file
70              return new TextStlFacetDefinitionReader(
71                      new BufferedReader(new InputStreamReader(pushbackInput, inputCharset)));
72          } else {
73              // this is a binary file
74              return new BinaryStlFacetDefinitionReader(pushbackInput);
75          }
76      }
77  }