UnionInputStream: combines sequential InputStreams into one

The UnionInputStream utility class combines multiple sequential
InputStreams so they appear to the caller as a single stream with
no gaps.  This can be used to concentate streams coming from multiple
independent HTTP connections (for example).

The companion unit test covers the class's full functionality.

Change-Id: I0676c7b5e082a5886bf0e8f43f9fd6c46a666228
Signed-off-by: Shawn O. Pearce <sop@google.com>

1 files changed, 208 insertions, 0 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/io/UnionInputStream.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/io/UnionInputStream.java
new file mode 100644
index 0000000000..f0183717a7
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/io/UnionInputStream.java
@@ -0,0 +1,208 @@
+/*
+ * Copyright (C) 2009, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.util.io;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Iterator;
+import java.util.LinkedList;
+
+/**
+ * An InputStream which reads from one or more InputStreams.
+ * <p>
+ * This stream may enter into an EOF state, returning -1 from any of the read
+ * methods, and then later successfully read additional bytes if a new
+ * InputStream is added after reaching EOF.
+ * <p>
+ * Currently this stream does not support the mark/reset APIs. If mark and later
+ * reset functionality is needed the caller should wrap this stream with a
+ * {@link java.io.BufferedInputStream}.
+ * */
+public class UnionInputStream extends InputStream {
+	private static final InputStream EOF = new InputStream() {
+		@Override
+		public int read() throws IOException {
+			return -1;
+		}
+	};
+
+	private final LinkedList<InputStream> streams = new LinkedList<InputStream>();
+
+	/** Create an empty InputStream that is currently at EOF state. */
+	public UnionInputStream() {
+		// Do nothing.
+	}
+
+	/**
+	 * Create an InputStream that is a union of the individual streams.
+	 * <p>
+	 * As each stream reaches EOF, it will be automatically closed before bytes
+	 * from the next stream are read.
+	 *
+	 * @param inputStreams
+	 *            streams to be pushed onto this stream.
+	 */
+	public UnionInputStream(InputStream... inputStreams) {
+		for (InputStream i : inputStreams)
+			add(i);
+	}
+
+	private InputStream head() {
+		return streams.isEmpty() ? EOF : streams.getFirst();
+	}
+
+	private void pop() throws IOException {
+		if (!streams.isEmpty())
+			streams.removeFirst().close();
+	}
+
+	/**
+	 * Add the given InputStream onto the end of the stream queue.
+	 * <p>
+	 * When the stream reaches EOF it will be automatically closed.
+	 *
+	 * @param in
+	 *            the stream to add; must not be null.
+	 */
+	public void add(final InputStream in) {
+		streams.add(in);
+	}
+
+	/**
+	 * Returns true if there are no more InputStreams in the stream queue.
+	 * <p>
+	 * If this method returns {@code true} then all read methods will signal EOF
+	 * by returning -1, until another InputStream has been pushed into the queue
+	 * with {@link #add(InputStream)}.
+	 *
+	 * @return true if there are no more streams to read from.
+	 */
+	public boolean isEmpty() {
+		return streams.isEmpty();
+	}
+
+	@Override
+	public int read() throws IOException {
+		for (;;) {
+			final InputStream in = head();
+			final int r = in.read();
+			if (0 <= r)
+				return r;
+			else if (in == EOF)
+				return -1;
+			else
+				pop();
+		}
+	}
+
+	@Override
+	public int read(byte[] b, int off, int len) throws IOException {
+		int cnt = 0;
+		while (0 < len) {
+			final InputStream in = head();
+			final int n = in.read(b, off, len);
+			if (0 < n) {
+				cnt += n;
+				off += n;
+				len -= n;
+			} else if (in == EOF)
+				return 0 < cnt ? cnt : -1;
+			else
+				pop();
+		}
+		return cnt;
+	}
+
+	@Override
+	public int available() throws IOException {
+		return head().available();
+	}
+
+	@Override
+	public long skip(long len) throws IOException {
+		long cnt = 0;
+		while (0 < len) {
+			final InputStream in = head();
+			final long n = in.skip(len);
+			if (0 < n) {
+				cnt += n;
+				len -= n;
+
+			} else if (in == EOF) {
+				return cnt;
+
+			} else {
+				// Is this stream at EOF? We can't tell from skip alone.
+				// Read one byte to test for EOF, discard it if we aren't
+				// yet at EOF.
+				//
+				final int r = in.read();
+				if (r < 0) {
+					pop();
+				} else {
+					cnt += 1;
+					len -= 1;
+				}
+			}
+		}
+		return cnt;
+	}
+
+	@Override
+	public void close() throws IOException {
+		IOException err = null;
+
+		for (Iterator<InputStream> i = streams.iterator(); i.hasNext();) {
+			try {
+				i.next().close();
+			} catch (IOException closeError) {
+				err = closeError;
+			}
+			i.remove();
+		}
+
+		if (err != null)
+			throw err;
+	}
+}