WLprinter Web-to-local print solution Version 0.9

Transcription

1 WLprinter Web-to-local print solution Version 0.9 Tekki October 7, 2010 Contents 1 Introduction What is WLprinter? System requirements Limitations Disclaimer Installation Installation of the WLprinter server Installation of the WLprinter client Integration with SQL-Ledger Installation of the WLprinter modules Edit the menu Working with WLprinter Printing within SQL-Ledger Using the client application Technical details etc/wlprinter.conf bin/fileprinter.pl bin/getlink.pl www/wlprinter.pl sql-ledger/bin/mozilla/wlprinter.pl

2 Figure 1: Application server in the local network 1 Introduction 1.1 What is WLprinter? WLprinter is a web-to-local print solution that allows an web-based application to print PDF and Postscript files to Windows or Linux printers behind a firewall. It was designed primarily for the ERP solution SQL-Ledger (see but can easily be adapted to other applications too. A web application server that runs in the same subnetwork as its clients sends its print jobs to IP addresses that are directly accessible to it, either to network printers or using a share on a client PC (Figure 1). If the server is placed in the web, or if the application runs on a service like Amazon EC2, this procedure fails, because the printers are part of a private network that is hidden behind a firewall (Figure 2). The users have to download files and print them out manually. WLprinter establishes a connection between client and server and allows the latter to print to the client without user interaction, as if both machines were placed in the same 2

3 Figure 2: Server placed outside subnet (Figure 3). A second case where WLprinter may be useful is when the application is accessed by many and often changing clients, so that it would be too complicated to register every printer to the application. Using WLprinter, for example a notebook attached ad-hoc to the network can print immediately to its own USB printer (Figure 4). 1.2 System requirements Server: a web application that produces PDF or Postscript outputs a web server that support Perl Client: Java runtime (JRE) or development kit (JDK) or higher a printer with PDF or Postscript support Adobe Reader for Windows PCs without Postscript printer 1.3 Limitations PDF, PS: At the moment, WLprinter supports only documents in PDF or Postscript format. 3

4 Figure 3: WLprinter connects server and client Figure 4: WLprinter used to connect a big number of clients 4

5 SSL: WLprinter doesn t work on SSL connections with self-signed certificates. If you use a self-signed certificate, you have to move the WLprinter server to an unencrypted connection. In this case, you can t call it directly, but have to use the redirect function described in the technical details. javax.print: WLprinter partially uses the Java Print Service API, that unfortunately isn t very reliable. In some constellations, for example when printing to virtual printers like FreePDF or when printing PDF instead of PS on a Linux client, documents disappear in the nowhere without producing an error message. For this reason, it is recommended either to print PS to printers with native Postscript support, or on Windows to print PDF, so WLprinter can make use of the Adobe Reader s print features. 1.4 Disclaimer THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CON- TRIBUTORS AS IS AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUD- ING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABIL- ITY 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 CONSE- QUENTIAL 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 (IN- CLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 2 Installation 2.1 Installation of the WLprinter server The following instructions assume that you have Opensuse with Apache2 installed on your server. 1. log in to your server as root 2. create the folder /usr/local/wlprinter 1 mkdir /usr/local/wlprinter 3. download the program from to the wlprinter folder 1 If you change the folder names, you have to modify the paths in the configuration file 5

6 cd /usr/local/wlprinter/ wget 4. untar the program tar -xvzf wlprinter.tar.gz 5. create a spool directory mkdir spool 6. restrict the access to the spool directory to the web server process chown «wwwuser».«wwwgroup» spool chmod 700 spool «wwwuser» and «wwwgroup» are placeholders that you have to replace with the correct values 7. copy the web server configuration file cd /etc/apache2/vhosts.d/ cp /usr/local/wlprinter/etc/apache2/wlprinter-httpd.conf. 8. restart the web server /etc/init.d/apache2 restart The user and group names of the web server, indicated with «wwwuser» and «wwwgroup» change from distribution to distribution. If you don t know them, type: ps ax -o user,group,command grep apache2 Or, if you get no result: ps ax -o user,group,command grep httpd On Opensuse, the output will look like this: root root /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf... wwwrun www /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf... wwwrun www /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf... This means you have to use wwwrun as user and www as group name. The location of the config file differs, too. In Ubuntu, where the names to use are the same www-data for the group and the user, you copy the file to sites_available and link it to sites_enabled. cd /etc/apache2/sites_available cp /usr/local/wlprinter/etc/wlprinter-httpd.conf. cd../sites_enabled ln -s../sites_available/wlprinter-httpd.conf. 6

7 2.2 Installation of the WLprinter client The WLprinter client needs no installation. It will be downloaded, installed and updated automatically using Java Network Launch Protocol (JNLP) from tekki.ch or, depending on your configuration, from your own server. NOTE: The beta version doesn t include the client code yet, it can only be downloaded from tekki.ch. 2.3 Integration with SQL-Ledger In this section, you see how to use WLprinter together with SQL-Ledger ( Imitating this model, it should be simple to integrate it with other web applications Installation of the WLprinter modules To install in SQL-Ledger the modules required to work with WLprinter, you call the script./sl-install.pl that you find in the base directory of WLprinter. It asks you for the path to your SQL-Ledger installation. If it s /usr/local/sql-ledger, just press ENTER. The script does a lot of work. Here are some details: Instead of printing to a real printer using lpr, SQL-Ledger has to send the print jobs to WLprinter, more exact to its module fileprinter.pl. The command to use is: «some output» /usr/bin/wlprinter/bin/fileprinter.pl «username» WLprinter needs to know the user name to identify which document belongs to which user. In SQL-Ledger, the user name is stored in $form-»{login}, but this field is not available yet at the moment when sql-ledger.conf with the definition of the printers is read in. For this reason, the install script creates a custom_«filename».pl for all the modules in bin/mozilla, that adds WLprinter to the printer list. If it finds already existing custom files, it adds the WLprinter code at the beginning of them and leaves the rest untouched. Next, it creates a gateway script in the SQL-Ledger base directory and copies the WLprinter startup module to bin/mozilla. An existing bin/mozilla/wlprinter.pl will be copied to wlprinter.pl.old. If you have modified it, check the new file for changes and copy your modifications back to it. Now WLprinter is available as a print target Edit the menu To be able to open the WLprinter client, you need a new entry in the SQL-Ledger menu. Edit your custom_menu.ini or create a new one, and add this or a similar text: 7

8 Figure 5: Choose the printer with your user name Figure 6: WLprinter in the SQL-Ledger menu [Tools] [Tools--WLprinter] module=wlprinter.pl action=open After such changes and if you don t use the default English language, don t forget to move to your translation folder and run./locales.pl. 3 Working with WLprinter 3.1 Printing within SQL-Ledger You print to WLprinter in the same way you would print to any other printer. Just choose the printer with your user name and the appropriate file format and click the Print or Print and Post button (Figure 5). If you always use WLprinter, you can set it as your default printer in your Preferences. 3.2 Using the client application It doesn t matter at what moment you start the client application, before you print the first document or later. If it isn t running yet when you print, your jobs will be stored on the server until the WLprinter client connects. You can even create print jobs when you work on your mobile phone and print the documents out later when you are back in your office. To start the client from SQL-Ledger, click on the WLprinter menu entry you created before (Figure 6). 8

9 Figure 7: WLprinter client connected to the server The WLprinter client is downloaded and started automatically. If you open it for the first time or if it was updated, you will be prompted to accept the certificate and with this allow the program to access your computer. The WLprinter client first searches your PC for available printers and displays them on a list. Besides the names of the printers, you see what kind of documents they accept. If you run a Windows computer, WLprinter looks for an Adobe Reader that can be used to print PDF files. Finally, it connects to the WLprinter server (Figure 7). Now you have 10 seconds 2 to change the printer, if necessary. You will see virtual printers like Fax, FreePDF or Windows XPS Document Writer on the list, but as it was said in the introduction, the Java Print API doesn t work with them, so you can t send a Postscript file to FreePDF, even if the list tells you that it supports it. For PDF, these printers are available, because PDF format uses the WLprinter s own driver that calls the Adobe Reader on your PC. 3 This means for example that you can print a fax from SQL-Ledger, if the fax service of your PC is configured properly. After the waiting time is over, the client asks the server for open printing jobs, receives them and sends them to the selected printer (Figure 8). If the format of the document isn t supported by the selected printer, WLprinter displays an error message that gives you the possibility either to change the printer, or to delete this or all the pending jobs (Figure 9). Normally, you always print to your default printer, so the WLprinter client doesn t need any interaction at all. 2 or the time you have set in wlprinter.conf 3 The problem is known that Adobe Reader keeps jumping to the foreground while printing to a nondefault printer. 9

10 Figure 8: WLprinter client printing Figure 9: Error message for unsupported file format 10

11 4 Technical details 4.1 etc/wlprinter.conf wlprinter.conf is the configuration file. It contains the following keys: $version The version of the server software. Don t change this, it is used by the client to check its compatibility with the server. $spooldir The directory where the print jobs are stored before they are sent to the clients. You can change it to another value, but make sure the new directory is available and the web server has exclusive access to it. $tokenfile The file where the access keys are stored. You can move it somewhere else, but consider the precautions mentioned above. $alias The alias name of the wlprinter/www/ directory on the web server. It has to correspond with the Alias value in wlprinter-httpd.conf, without leading and trailing slashes. $interval The time in seconds between the attempts of the client to download printing jobs. Values smaller than 10 are ignored. $headlength The number of bytes that are sent to the client to identify the format of the document. $codebase The URL from where the client code can be downloaded. For the Beta version, the code is only available on tekki.ch, later it will be possible to install it on your own server. 4.2 bin/fileprinter.pl fileprinter.pl is the virtual printer that accepts jobs sent from the web application. It stores the documents in the spool folder until they are forwarded to the clients. The way to call it is: «some output» /usr/bin/wlprinter/bin/fileprinter.pl «username» The user name is necessary for the program to identify the owner of the print job. 4.3 bin/getlink.pl getlink.pl is called from the web application with: /usr/bin/wlprinter/bin/getlink.pl «username» 11

12 and returns a link that can be sent to the user to connect to the WLprinter server. The link contains the path to the server application, starting with the directory alias defined in wlprinter.conf, and an access key that identifies the user. The web application, in our case SQL-Ledger, is responsible to control that only authenticated users are supplied with this key. 4.4 www/wlprinter.pl wlprinter.pl is the web frontend that communicates with the WLprinter client. always accessed in the following way: It is «your server»/«wlprinter alias»/wlprinter.pl?id=... where id is the access key created with getlink.pl. Without an id or a wrong one, you will get an error messages that you are not authenticated. Additional arguments are: action=main or no argument, will return the JNLP page that invokes the client application. action=redirect redirects to main. This function has to be used when the WLprinter server isn t immediately able to find out its own address when called from the web application, for example when the latter runs on and the first on action=version returns the version number of the WLprinter server. action=list creates a list with the id numbers of the pending jobs. These numbers are used as docid for the following commands. action=head&docid=... returns the n first bytes of the document identified by docid, where n is the number set in $headlength. action=get&docid=... downloads the content of the job as an application/octet-stream. action=delete&docid=... deletes the specified document from the spool directory. action=deleteall cancels all pending jobs for this user. action=logout invalidates the access key. After calling this function, the user can t connect to the server anymore until the web application asks getlink.pl to create a new key for him. 4.5 sql-ledger/bin/mozilla/wlprinter.pl This is the module that redirects from SQL-Ledger to WLprinter. The first important command is where it calls getlink.pl to create the link and the access key for the user: my $wllink = qx /usr/local/wlprinter/bin/getlink.pl $form-»{login} ; 12

13 Later it uses this value to replace the frame in the browser with WLprinter: «script type="text/javascript"» window.location.href="../$wllink"; «/script» This code works when your SQL-Ledger runs in «yourserver»/sql-ledger and WLprinter in «yourserver»/wlprinter. If you have an other configuration, you may have to tune this script until it produces the desired result. 13