stream.urls.FIFOConnection Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of streams-api Show documentation
The newest version!
/*
 *  streams library
 *
 *  Copyright (C) 2011-2014 by Christian Bockermann, Hendrik Blom
 * 
 *  streams is a library, API and runtime environment for processing high
 *  volume data streams. It is composed of three submodules "stream-api",
 *  "stream-core" and "stream-runtime".
 *
 *  The streams library (and its submodules) is free software: you can 
 *  redistribute it and/or modify it under the terms of the 
 *  GNU Affero General Public License as published by the Free Software 
 *  Foundation, either version 3 of the License, or (at your option) any 
 *  later version.
 *
 *  The stream.ai library (and its submodules) 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 Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with this program.  If not, see http://www.gnu.org/licenses/.
 */
package stream.urls;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import stream.io.SourceURL;

/**
 * 
 * This class provides an implementation for fifo:// URLs. Such a
 * URL points to a file that is expected to be a named pipe (Unix). Thus, this
 * implementation is not portable and can only be used on Unix systems.
 * 
 * 
 * If the file denoted by the URL does not exist, a new named pipe is created
 * using the mkfifo system command, that is expected to exist on
 * the system.
 * 
 * 
 * @author Christian Bockermann
 * 
 */
public class FIFOConnection extends Connection {

	static Logger log = LoggerFactory.getLogger(FIFOConnection.class);

	protected InputStream inputStream;

	/**
	 * @param url
	 */
	public FIFOConnection(SourceURL url) {
		super(url);
	}

	/**
	 * @see stream.urls.Connection#getSupportedProtocols()
	 */
	@Override
	public String[] getSupportedProtocols() {
		return new String[] { "fifo" };
	}

	/**
	 * @see stream.urls.Connection#connect()
	 */
	@Override
	public InputStream connect() throws IOException {

		try {
			String theUrl = url.toString();

			log.debug("Handling FIFO URL pattern...");
			theUrl = theUrl.replace("fifo:", "file:");
			File file = new File(theUrl.replace("file:", ""));
			if (!file.exists()) {
				log.debug("Creating new fifo file '{}' with mkfifo", file);
				Process p = Runtime.getRuntime().exec(
						"mkfifo " + file.getAbsolutePath());
				log.debug("Waiting for mkfifo to return...");
				int ret = p.waitFor();
				log.debug("mkfifo finished: {}", ret);
			} else {
				log.debug("Using existing fifo-file '{}'", file);
			}

			if (!file.exists()) {
				throw new IOException("Failed to create/acquire FIFO file '"
						+ file.getAbsolutePath() + "'!");
			}

			log.debug("Returning FileInputStream for FIFO {}", file);
			inputStream = new FileInputStream(file);
			return inputStream;

		} catch (Exception e) {
			throw new IOException("Failed to open fifo-queue: "
					+ e.getMessage());
		}
	}

	/**
	 * @see stream.urls.Connection#disconnect()
	 */
	@Override
	public void disconnect() throws IOException {
		if (inputStream != null)
			inputStream.close();
	}
}