Tech Note 0015
Methods for integrating ExpeDat with other applications, scripts, and work-flows
The ExpeDat file transfer application can be used to do much more than transfer files under end-user control. The light-weight command-line client and server applications are designed to easily interact with other software. This not only allows ExpeDat operations to be automated by other processes, but enables complex interactions between ExpeDat and other programs. All of this can be achieved without source-code level integration, allowing for fast, modular deployment.
Below are the most common examples of how ExpeDat has been embedded and integrated with other software. Please note that many of these examples are fragmentary, so a strong familiarity with your operating system and general programming techniques is assumed. In particular, be aware of the varying need to escape or quote special characters which may have significance for the shell.
For Windows and Mac OS X systems, ExpeDat transfers can be started from web pages, emails, PDFs, or anywhere else you can click a link. Transfers are initiated using the "expedat://" URL scheme. See the Web Integration chapter of the ExpeDat documentation for details.
The servedat server can send or retrieve data using external programs without touching disk. This allows it to act as a gateway to any back-end data system such as cloud storage or databases, and perform real-time processing such as transcoding. Tasks such as listings, deletion, rename, and folder creation can be performed by an Object Handler, allowing you to create fully functional virtual filesystems out of any back-end data system. Object Handlers can execute automation scripts and perform such tasks as email notification, file relocation, or any other function.
Access is defined by the server administrtor. Clients choose amongst available handlers and provide inputs such as query strings, supplemental credentials, or object names. Exit codes are passed all the way back to the client to ensure reliable automation and storage.
See the servedat Object Handlers chapter of the ExpeDat documentation for details and examples.
Just as the server can stream files to and from object handlers, the movedat client can be used to "pipe" data to or from client-side programs. For example, the following shell command would create a tar archive on the fly and upload it to a server:
tar -zcf - /path/dir/ | movedat - user@server:dir.tgz
The next example shows how incoming data can be unpacked as it is downloaded:
movedat user@server:dir.tgz | tar -zxf -
The simplest way to automate ExpeDat operations is to wrap them in a shell script (or a batch script in Windows). For example:
#!/bin/sh # Take argument $1 as the root of two files to download. movedat "server:$1.part1" /local/stagingdir/ movedat "server:$1.part2" /local/stagingdir/
Many of the techniques described below show more complex ways that ExpeDat can interact with scripts.
You can use the unix cron service or the Windows AT service to automate execution of ExpeDat commands at regular intervals. The following cron job would download a particular file every weekday at 5:00am:
00 05 * * 1-5 movedat server:/path/file.jpg /home/me/pictures/
The following AT command could achieve the same thing in Windows:
AT 05:00 /every:m,t,w,th,f C:\ExpeDat\movedat.exe server:/path/file.jpg "C:\Pictures\"
In addition to shell scripts, native programs can also call on movedat. In unix, this is often done with the exec() or popen() system calls. In Windows, this may be done with the CreateProcess() call. For example:
pipefd = popen("movedat server:/pathname/file /local/dir/","r+");
When calling movedat from a script or program, it will be unable to prompt a user to input a password. Therefore there are two methods that you can use to supply a password programatically. The simplest method is to include the password on the command line:
movedat user:password@server:/pathname/file /local/dir/
Alternatively, movedat can store passwords in an encrypted cache for later use. For example:
movedat -A user@server:
movedat -A user:password@server:
The first example will prompt you to enter a password, while the second will take it from the command line. Both examples will encrypt the password and store it. If a command later refers to "user@server:", the encrypted password will be used automatically. See the movedat Authentication chapter of the ExpeDat documentation for more details.
The movedat client returns a numerical exit code which follows the unix convention of 0 for success, and non-zero error codes for failures. Many error codes are supported, allowing a script or parent software to differentiate between problems. For example, code 70 indicates a network problem and so it may be desirable to try again later. Code 10 indicates a bad username or password, and so it may be desirable to query a human user for the correct credentials. See the movedat Exit Codes documentation for details.
When movedat is run underneath another program, the "-s" option will cause it to display machine parseable logs for each operation. This allows the parent software to monitor progress and errors, and provide user feedback. See the movedat Logging documentation for details.
When movedat requests a directory listing, the server sends the results as a series of structured records which movedat then interprets and displays. You can directly access these records, allowing another application to interpret and display them.
The following command signals movedat to list the files in the named directory, and output the raw records:
These are just some simple examples of how ExpeDat can be integrated with other software. Please refer to the documentation referenced in each section for more details.
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