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<chapter>
  <header>
    <copyright>
      <year>2001</year><year>2009</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
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    <title>Using the File Transfer Service</title>
    <prepared></prepared>
    <docno></docno>
    <date>2001-08-07</date>
    <rev></rev>
    <file>ch_system.xml</file>
  </header>

  <section>
    <title>Overview</title>
    <p>This chapter describes how two File Transfer Service applications interact.</p>

    <section>
      <title>Components</title>
      <p>There are several ways the OMG File Transfer Service can be used. 
        Below one scenario is visualized: </p>
      <marker id="CosFileTransfer"></marker>
      <image file="CosFileTransfer.gif">
        <icaption>Figure 1: The File Transfer Service Components.</icaption>
      </image>
      <list type="bulleted">
        <item><em>Source ORB:</em> this is the ORB we want to transfer a file from/via and it holds 
         an object reference to a 
        <seealso marker="CosFileTransfer_VirtualFileSystem">Virtual File System (VFS)</seealso> which, 
         in this example, represents an FTP server.</item>
        <item><em>Target ORB:</em> the goal may be, for example, to transfer a new file or append to an 
         existing file placed at the location that this ORB's <c>VFS</c> represents.
         In this scenario it is the local disk or the NFS.</item>
        <item><em>Transport Protocol:</em> initially the ORB's, i.e., target and source, communicate via
         normal <c>CORBA</c> requests to determine whether or not they can communicate. If the 
         File Transfer Service's have one, or more, <c>Transport Protocol</c> in common the data
         will be streamed using this protocol. The cosFileTransfer application currently supports 
        <c>TCP/IP</c> and <c>SSL</c>.</item>
      </list>
      <p>Which type of file system the <c>VFS</c> is supposed to represent is determined
        by the options given when creating it, which is also how one determine which 
        <c>Transport Protocol</c> to use. Hence, the source and target <c>VFS</c> described above
        can be started by invoking, respectively, the following operations:</p>
      <code type="none">
1> SVFS = cosFileTransferApp:create_VFS('FTP', [], Host, 21, [{protocol, tcp}]),
2> TVFS = cosFileTransferApp:create_VFS({'NATIVE', 'cosFileTransferNATIVE_file'}, 
                                        [], OtherHost, 0, [{protocol, tcp}]),
      </code>
      <p>Naturally can any combination of <c>VFS</c>-types be used and it is also possible
        to use own drivers, i.e., <c>{'NATIVE', 'MyDriver'}</c>.</p>
      <p>After creating necessary <c>VFS's</c> we can login in and perform operations
        on files and directories residing on each file system.</p>
    </section>

    <section>
      <title>How To Use SSL</title>
      <p>To be able to use <c>SSL</c> as transport protocol a few configuration
        parameters must be set. The required parameters depend on if Orber is
        the target or/and the source ORB. However, the SSL_CERT_FILE variable
        must be defined in both cases.</p>
      <p>Setting of a CA certificate file with an option does not work due to 
        weaknesses in the SSLeay package. A work-around in the ssl application is 
        to set the OS environment variable SSL_CERT_FILE before SSL is started. 
        However, then the CA certificate file will be global for all connections 
        (both incoming and outgoing calls).</p>

      <section>
        <title>Configurations when cosFileTransfer is Used as Target</title>
        <p>The following three configuration variables can be used to configure
          cosFileTransfer's SSL target behavior.</p>
        <list type="bulleted">
          <item><em>ssl_server_certfile</em> which is a path to a file containing a
           chain of PEM encoded certificates for cosFileTransfer as target.</item>
          <item><em>ssl_server_verify</em> which specifies type of verification: 
           0 = do not verify peer; 1 = verify peer, verify client once, 2 = 
           verify peer, verify client once, fail if no peer certificate. 
           The default value is 0.</item>
          <item><em>ssl_server_depth</em> which specifies verification depth, i.e.
           how far in a chain of certificates the verification process shall 
           proceed before the verification is considered successful. The
           default value is 1. </item>
        </list>
        <p>There also exist a number of API functions for accessing the values of 
          these variables:</p>
        <list type="bulleted">
          <item>cosFileTransferApp:ssl_server_certfile/0</item>
          <item>cosFileTransferApp:ssl_server_verify/0</item>
          <item>cosFileTransferApp:ssl_server_depth/0</item>
        </list>
      </section>

      <section>
        <title>Configurations when cosFileTransfer is used as Source</title>
        <p>Below is the list of configuration variables used when cosFileTransfer
          act as the source application.</p>
        <list type="bulleted">
          <item><em>ssl_client_certfile</em> which is a path to a file containing a
           chain of PEM encoded certificates used in outgoing calls.</item>
          <item><em>ssl_client_verify</em> which specifies type of verification: 
           0 = do not verify peer; 1 = verify peer, verify client once, 2 = 
           verify peer, verify client once, fail if no peer certificate. 
           The default value is 0.</item>
          <item><em>ssl_client_depth</em> which specifies verification depth, i.e. 
           how far in a chain of certificates the verification process shall
           proceed before the verification is considered successful. The
           default value is 1. </item>
        </list>
        <p>There also exist a number of API functions for accessing the values of
          these variables in the client processes:</p>
        <list type="bulleted">
          <item>cosFileTransferApp:ssl_client_certfile/0</item>
          <item>cosFileTransferApp:ssl_client_verify/0</item>
          <item>cosFileTransferApp:ssl_client_depth/0</item>
        </list>
      </section>
    </section>
  </section>
</chapter>

