content: /*
   * Copyright (c) 2021, Oracle and/or its affiliates.
   *
   * This program is free software; you can redistribute it and/or modify it under
   * the terms of the GNU General Public License, version 2.0, as published by the
   * Free Software Foundation.
   *
   * This program is also distributed with certain software (including but not
   * limited to OpenSSL) that is licensed under separate terms, as designated in a
   * particular file or component or in included license documentation. The
   * authors of MySQL hereby grant you an additional permission to link the
   * program and your derivative works with the separately licensed software that
   * they have included with MySQL.
   *
   * Without limiting anything contained in the foregoing, this file, which is
   * part of MySQL Connector/J, is also subject to the Universal FOSS Exception,
   * version 1.0, a copy of which can be found at
   * http://oss.oracle.com/licenses/universal-foss-exception.
   *
   * This program is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
   * FOR A PARTICULAR PURPOSE. See the GNU General Public License, version 2.0,
   * for more details.
   *
   * You should have received a copy of the GNU General Public License along with
   * this program; if not, write to the Free Software Foundation, Inc.,
   * 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA
   */
  
  package com.mysql.cj.protocol.x;
  
  import java.io.FilterInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.util.LinkedList;
  import java.util.Queue;
  
  /**
   * An {@link InputStream} wrapper that reads from a queue of underlying {@link InputStream}s, giving the impression that all data is coming from a single,
   * continuous, source.
   */
  public class ContinuousInputStream extends FilterInputStream {
      private Queue<InputStream> inputStreams = new LinkedList<>();
  
      private boolean closed = false;
  
      protected ContinuousInputStream(InputStream in) {
          super(in);
      }
  
      /**
       * Returns the number of bytes available in the active underlying {@link InputStream}.
       * 
       * @return the number of bytes available.
       * @see FilterInputStream#available()
       */
      @Override
      public int available() throws IOException {
          ensureOpen();
          int available = super.available();
          if (available == 0 && nextInLine()) {
              return available();
          }
          return available;
      }
  
      /**
       * Closes this stream and all underlying {@link InputStream}s.
       * 
       * @see FilterInputStream#close()
       */
      @Override
      public void close() throws IOException {
          if (!this.closed) {
              this.closed = true;
              super.close();
              for (InputStream is : this.inputStreams) {
                  is.close();
              }
          }
      }
  
      /**
       * Reads one byte from the underlying {@link InputStream}. When EOF is reached, then reads from the next {@link InputStream} in the queue.
       * 
       * @see FilterInputStream#read()
       */
      @Override
      public int read() throws IOException {
          ensureOpen();
          int read = super.read();
          if (read >= 0) {
              return read;
          }
          if (nextInLine()) {
              return read();
          }
          return read;
      }
  
      /**
       * Forwards the read to {@link #read(byte[], int, int)}.
       * 
       * @see FilterInputStream#read(byte[])
       */
      @Override
      public int read(byte[] b) throws IOException {
          ensureOpen();
          return read(b, 0, b.length);
      }
  
      /**
       * Reads bytes from the underlying {@link InputStream}. When EOF is reached, then reads from the next {@link InputStream} in the queue.
       * 
       * @see FilterInputStream#read(byte[], int, int)
       */
      @Override
      public int read(byte[] b, int off, int len) throws IOException {
          ensureOpen();
          int toRead = Math.min(len, available());
          int read = super.read(b, off, toRead);
          if (read > 0) {
              return read;
          }
          if (nextInLine()) {
              return read(b, off, len);
          }
          return read;
      }
  
      /**
       * Adds another {@link InputStream} to the {@link InputStream}s queue.
       * 
       * @param newIn
       *            the {@link InputStream} to add.
       * @return
       *         <code>true</code> if the element was added to the {@link InputStream}s queue.
       */
      protected boolean addInputStream(InputStream newIn) {
          return this.inputStreams.offer(newIn);
      }
  
      /**
       * Closes the currently active {@link InputStream} and replaces it by the the head of the {@link InputStream}s queue.
       * 
       * @return
       *         <code>true</code> if the currently active {@link InputStream} was replaced by a new one.
       * @throws IOException
       *             if errors occur while closing the currently active {@link InputStream}.
       */
      private boolean nextInLine() throws IOException {
          InputStream nextInputStream = this.inputStreams.poll();
          if (nextInputStream != null) {
              super.close();
              this.in = nextInputStream;
              return true;
          }
          return false;
      }
  
      /**
       * Ensures that this {@link InputStream} wasn't closed yet.
       * 
       * @throws IOException
       *             if this {@link InputStream} was closed.
       */
      private void ensureOpen() throws IOException {
          if (this.closed) {
              throw new IOException("Stream closed");
          }
      }
  }
  