001/*
002 * Copyright (C) 2022 - 2023, the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *    http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016package io.github.ascopes.jct.diagnostics;
017
018import static java.util.Objects.requireNonNull;
019
020import java.io.IOException;
021import java.io.OutputStream;
022import java.io.OutputStreamWriter;
023import java.io.Writer;
024import java.nio.charset.Charset;
025import org.apiguardian.api.API;
026import org.apiguardian.api.API.Status;
027
028/**
029 * A writer that wraps an output stream and also writes any content to an in-memory buffer.
030 *
031 * <p>This is thread-safe.
032 *
033 * @author Ashley Scopes
034 * @since 0.0.1
035 */
036@API(since = "0.0.1", status = Status.STABLE)
037public final class TeeWriter extends Writer {
038
039  private final Object lock;
040
041  private volatile boolean closed;
042
043  private final Writer writer;
044
045  // We use a StringBuilder and manually synchronise it rather than
046  // a string buffer, as we want to manually synchronise the builder
047  // and the delegated output writer at the same time.
048  private final StringBuilder builder;
049
050  /**
051   * Initialise the writer.
052   *
053   * @param writer the underlying writer to "tee" to.
054   */
055  public TeeWriter(Writer writer) {
056    lock = new Object();
057    closed = false;
058
059    this.writer = requireNonNull(writer, "writer");
060    builder = new StringBuilder();
061    builder.ensureCapacity(512);
062  }
063
064  @Override
065  public void close() throws IOException {
066    // release to set and acquire to check ensures in-order operations to prevent
067    // a very minute chance of a race condition.
068    synchronized (lock) {
069      if (!closed) {
070        closed = true;
071        builder.trimToSize();
072        writer.flush();
073        writer.close();
074      }
075    }
076  }
077
078  @Override
079  public void flush() throws IOException {
080    synchronized (lock) {
081      ensureOpen();
082      writer.flush();
083    }
084  }
085
086  /**
087   * Get the content of the internal buffer.
088   *
089   * @return the content.
090   * @since 0.2.1
091   */
092  @API(since = "0.2.1", status = Status.STABLE)
093  public String getContent() {
094    synchronized (lock) {
095      return builder.toString();
096    }
097  }
098
099  /**
100   * Get the content of the internal buffer.
101   *
102   * <p>This calls {@link #getContent()} internally as of 0.2.1.
103   *
104   * @return the content.
105   */
106  @Override
107  public String toString() {
108    return getContent();
109  }
110
111  @Override
112  public void write(char[] cbuf, int off, int len) throws IOException {
113    synchronized (lock) {
114      ensureOpen();
115
116      writer.write(cbuf, off, len);
117      // Only append to the buffer once we know that the writing
118      // operation has completed.
119      builder.append(cbuf, off, len);
120    }
121  }
122
123  private void ensureOpen() {
124    if (closed) {
125      throw new IllegalStateException("TeeWriter is closed");
126    }
127  }
128
129  /**
130   * Create a tee writer for the given output stream.
131   *
132   * <p>Remember you may need to manually flush the tee writer for all contents to be committed to
133   * the output stream.
134   *
135   * @param outputStream the output stream.
136   * @param charset the charset.
137   * @return the Tee Writer.
138   * @since 0.2.1
139   */
140  @API(since = "0.2.1", status = Status.STABLE)
141  public static TeeWriter wrapOutputStream(OutputStream outputStream, Charset charset) {
142    requireNonNull(outputStream, "outputStream");
143    requireNonNull(charset, "charset");
144    var writer = new OutputStreamWriter(outputStream, charset);
145    return new TeeWriter(writer);
146  }
147}