Metacat

/**

 *  '$RCSfile$'

 *  Copyright: 2000 Regents of the University of California and the

 *              National Center for Ecological Analysis and Synthesis

 *

 *   '$Author: tao $'

 *     '$Date: 2003-08-11 18:30:18 -0700 (Mon, 11 Aug 2003) $'

 * '$Revision: 1786 $'

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * 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 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

package edu.ucsb.nceas.metacat.client;

import java.io.BufferedReader;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.PushbackReader;

import java.io.IOException;

import java.io.StringWriter;

import java.io.Reader;

import java.net.URL;

import java.util.Properties;

import edu.ucsb.nceas.utilities.HttpMessage;

/**

 *  This interface provides methods for initializing and logging in to a 

 *  Metacat server, and then querying, reading, transforming, inserting, 

 *  updating and deleting documents from that server.

 */

public class MetacatClient implements Metacat

{

    /** The URL string for the metacat server */

    private String metacatUrl;

    /**

     * Constructor to create a new instance. Protected because instances

     * should only be created by the factory MetacatFactory.

     */

    protected MetacatClient()

    {

    }

    /**

     *  Method used to log in to a metacat server. Implementations will need

     *  to cache a cookie value to make the session persistent.  Each time a

     *  call is made to one of the other methods (e.g., read), the cookie will

     *  need to be passed back to the metacat server along with the request.

     *

     *  @param username   the username of the user, like an LDAP DN

     *  @param password   the password for that user for authentication

     *  @throws MetacatAuthException when the username/password could

     *                    not be authenticated

     */

    public void login(String username, String password) 

           throws MetacatAuthException, MetacatInaccessibleException

    {

        Properties prop = new Properties();

        prop.put("action", "login");

        prop.put("qformat", "xml");

        prop.put("username", username);

        prop.put("password", password);

        String response = null;

        try {

            response = sendDataForString(prop);

        } catch (Exception e) {

            throw new MetacatInaccessibleException(e.getMessage());

        }

        if (response.indexOf("<login>") == -1) {

            HttpMessage.setCookie(null);

            throw new MetacatAuthException(response);

        }

    }

    /**

     * Read an XML document from the metacat server session, accessed by docid,

     * and returned as a Reader.

     *

     * @param docid the identifier of the document to be read

     * @return a Reader for accessing the document

     * @throws InsufficientKarmaException when the user has insufficent rights 

     *                                    for the operation

     * @throws MetacatInaccessibleException when the metacat server can not be

     *                                    reached or does not respond

     * @throws MetacatException when the metacat server generates another error

     */

    public Reader read(String docid) throws InsufficientKarmaException,

        MetacatInaccessibleException, MetacatException

    {

        PushbackReader pbr = null;

        Properties prop = new Properties();

        prop.put("action", "read");

        prop.put("qformat", "xml");

        prop.put("docid", docid);

        InputStream response = null;

        try {

            response = sendData(prop);

        } catch (Exception e) {

            throw new MetacatInaccessibleException(e.getMessage());

        }

        pbr = new PushbackReader(new InputStreamReader(response), 512);

        try {

            char[] characters = new char[512];

            int len = pbr.read(characters, 0, 512);

            StringWriter sw = new StringWriter();

            sw.write(characters, 0, len);

            String message = sw.toString();

            sw.close();

            pbr.unread(characters, 0, len);

            if (message.indexOf("<error>") != -1) {

                if (message.indexOf("does not have permission") != -1) {

                    throw new InsufficientKarmaException(message);

                } else {

                    throw new MetacatException(message);

                }

            }

        } catch (IOException ioe) {

            throw new MetacatException(

                    "MetacatClient: Error converting Reader to String." 

                    + ioe.getMessage());

        }

        return pbr;

    }

    /**

     * Query the metacat document store with the given metacat-compatible 

     * query document, and return the result set as a Reader.

     *

     * @param xmlQuery a Reader for accessing the XML version of the query

     * @return a Reader for accessing the result set

     */

    public Reader query(Reader xmlQuery) throws MetacatInaccessibleException,

                                                IOException

    {

        Reader reader = null;

        String query = null;

        try

        {

          query = readerToString(xmlQuery);

        }

        catch (IOException ioE)

        {

          throw ioE;

        }

        //set up properties

        Properties prop = new Properties();

        prop.put("action", "squery");

        prop.put("qformat", "xml");

        prop.put("query", query);

        InputStream response = null;

        try {

            response = sendData(prop);

        } catch (Exception e) {

            throw new MetacatInaccessibleException(e.getMessage());

        }

        reader = new InputStreamReader(response);

        return reader;

    }

    /**

     * Insert an XML document into the repository.

     *

     * @param docid the docid to insert the document

     * @param xmlDocument a Reader for accessing the XML document to be inserted

     * @param schema a Reader for accessing the DTD or XML Schema for 

     *               the document

     * @throws InsufficientKarmaException when the user has insufficent rights 

     *                                    for the operation

     */

    public void insert(String docid, Reader xmlDocument, Reader schema)

        throws InsufficientKarmaException

    {

    }

    /**

     * Update an XML document in the repository.

     *

     * @param docid the docid to update

     * @param xmlDocument a Reader for accessing the XML text to be updated

     * @param schema a Reader for accessing the DTD or XML Schema for 

     *               the document

     * @throws InsufficientKarmaException when the user has insufficent rights 

     *                                    for the operation

     */

    public void update(String docid, Reader xmlDocument, Reader schema)

        throws InsufficientKarmaException

    {

    }

    /**

     * Delete an XML document in the repository.

     *

     * @param docid the docid to delete

     * @throws InsufficientKarmaException when the user has insufficent rights 

     *                                    for the operation

     */

    public void delete(String docid)

        throws InsufficientKarmaException

    {

    }

    /**

     * When the MetacatFactory creates an instance it needs to set the

     * MetacatUrl to which connections should be made.

     *

     * @param metacatUrl the URL for the metacat server

     */

    public void setMetacatUrl(String metacatUrl)

    {

        this.metacatUrl = metacatUrl;

    }

    /************************************************************************

     * PRIVATE METHODS

     ************************************************************************/

    /**

     * Send a request to metacat.

     *

     * @param prop the properties to be URL encoded and sent

     */

    synchronized private InputStream sendDataOnce(Properties prop) 

        throws Exception

    {

        InputStream returnStream = null;

        URL url = new URL(metacatUrl);

        HttpMessage msg = new HttpMessage(url);

        returnStream = msg.sendPostData(prop);

        return returnStream;

    }

    /**

     * Send a request to Metacat

     *

     * @param prop  the properties to be sent to Metacat

     * @return      InputStream as returned by Metacat

     */

    synchronized private InputStream sendData(Properties prop) throws Exception

    {   

        InputStream returnStream = null;

        /*

            Note:  The reason that there are three try statements all executing

            the same code is that there is a problem with the initial connection

            using the HTTPClient protocol handler.  These try statements make 

            sure that a connection is made because it gives each connection a 

            2nd and 3rd chance to work before throwing an error.

            THIS IS A TOTAL HACK.  THIS NEEDS TO BE LOOKED INTO AFTER THE BETA1

            RELEASE OF MORPHO!!!  cwb (7/24/01)

          */

        try {

           return sendDataOnce(prop);

        } catch (Exception e) {

            try {

                return sendDataOnce(prop);

            } catch (Exception e2) {

                try {

                    return sendDataOnce(prop);

                } catch (Exception e3) {

                    System.err.println(

                            "Failed to send data to metacat 3 times.");

                    throw e3;

                }

            }

        }

    }

    /**

     * Send a request to Metacat

     *

     * @param prop  the properties to be sent to Metacat

     * @return      a string as returned by Metacat

     */

    synchronized private String sendDataForString(Properties prop) 

        throws Exception

    {

        String response = null;

        try {

            InputStreamReader returnStream =

                    new InputStreamReader(sendData(prop));

            StringWriter sw = new StringWriter();

            int len;

            char[] characters = new char[512];

            while ((len = returnStream.read(characters, 0, 512)) != -1) {

                sw.write(characters, 0, len);

            }

            returnStream.close();

            response = sw.toString();

            sw.close();

        } catch (Exception e) {

            throw e;

        }

        return response;

    }

    /**

     * Utility method to convert a reader to a String.

     *

     * @param reader the Reader to be converted

     * @return a String representation fo the data read

     */

    private String readerToString(Reader reader) throws IOException

    {

        String response = null;

        try {

            StringWriter sw = new StringWriter();

            int len;

            char[] characters = new char[512];

            while ((len = reader.read(characters, 0, 512)) != -1) {

                sw.write(characters, 0, len);

            }

            response = sw.toString();

            sw.close();

            reader.close();

        } catch (IOException e) {

            throw e;

        }

        return response;

    }

}