Printing from Android devices

As many of you may know, Android supports native printing since Android 4.4. This means, that there is new api handling communication between application from which user prints and application that later sends the job to the printer.

So how it works? First lets have a look at applications from which user prints.

Main responsibility of these applications is to prepare output for print in pdf format. This includes for example paging or updating image to landscape or portrait mode.

Application from which user prints uses then system PrintManager service.

PrintManager printManager = (PrintManager) getSystemService(Context.PRINT_SERVICE);

Document output is prepared with PrintDocumentAdapter which is passed as second parameter of PrintManagers print function.

printManager.print(jobName, new PrintDocumentAdapter(...), printAttributes);

Now we are heading to the second part of job printing, where we have to discover printers and send them our job. This is responsibility of PrintService.

Printer discovery

We can either add printers manually. Set their ip address and port, or we can look for network printers in the local network.

Let’s have a look on how to find printers which support Zeroconf discovery in local network. Implementations of Zeroconf are for example Avahi daemon or Bonjour.

When printer discovery in Android is started, onCreatePrinterDiscoverySession() method in PrintService is called. Here we have to create our PrinterDiscoverySession.

Responsibilities of PrinterDiscoverySession are pretty straightforward.

• find and add discovered printers
• remove previously added printers that disappeared
• update already added printers

In this example we will use NsdManager. NsdManager is native Android solution for finding zeroconf services. On the other hand its functionality is very limited, but for purpose of this demo it’s satisfactory. There exist other and better solutions, for example JmDNS. Current limitation of NsdManager is not being able to load txt records of mDNS messages.

In order to use NsdManager we have to implement two interfaces. DiscoveryLisener (handles discovery callbacks) and ResolveListener (handles resolving callbacks). I will call them OurDiscoveryListener and OurResolveListener.

First in onStartPrinterDiscovery() method we create new instance of DiscoveryListener and start the actual discovery.

discoveryListener = new OurDiscoveryListener(nsdManager);
nsdManager.discoverServices(SERVICE_TYPE, NsdManager.PROTOCOL_DNS_SD, discoveryListener);

This is pretty self-explanatory. We specify discovery service type, which is either “_ipps_.tcp.” or “_ipp_.tcp”, depending on the fact if we want to encrypt ipp messages or don’t.

And when service is found, then OurDiscoveryListener will handle what happens in individual states of discovery.

In the following code we can see that for example when service is found we try to resolve it with NsdManager.

public void onServiceFound(NsdServiceInfo service) {
    nsdManager.resolveService(service, new OurResolveListener());
}

Resolving service means, that we try to get more information about the service. This includes host ip and port. OurPrinterResolveListener then handles states what should happen when resolving succeeds or fails. When resolving succeeds, we process gained data and save it for future use.

Last part of printer discovery is to find more details about selected printer and checking whether is this printer still available. This is handled in onStartPrinterStateTracking() method.

Discovering details about printer can be done for examaple with ipp operation Get-Printer-Attributes and according to received data, set the printer information. Second function is to keep tracking of the printer state.

The following code sample just shows how to set few printer capabilities, which should be set according to the printer attributes. This doesn’t contain  tracking of printer state.

@Override
public void onStartPrinterStateTracking(PrinterId printerId) {
    // check for info we found when printer was discovered
    PrinterInfo printerInfo = findPrinterInfo(printerId);

    if (printerInfo != null) {
        PrinterCapabilitiesInfo capabilities = new PrinterCapabilitiesInfo.Builder(printerId)
                .setMinMargins(new PrintAttributes.Margins(200, 200, 200, 200))
                .addMediaSize(PrintAttributes.MediaSize.ISO_A4, true)
                .addMediaSize(PrintAttributes.MediaSize.ISO_A5, false)
                .addResolution(new PrintAttributes.Resolution("R1", "200x200", 200, 200), false)
                .addResolution(new PrintAttributes.Resolution("R2", "200x300", 200, 300), true)
                .setColorModes(PrintAttributes.COLOR_MODE_COLOR |
                        PrintAttributes.COLOR_MODE_MONOCHROME, PrintAttributes.COLOR_MODE_COLOR)
                .build();

        printerInfo = new PrinterInfo.Builder(printerInfo)
                .setCapabilities(capabilities).build();

        // We add printer info to system service
        List<PrinterInfo> printers = new ArrayList();
        printers.add(printerInfo);
        addPrinters(printers);
    }
}

When different printer is selected, then onStopPrinterStateTracking is called and onStartPrinterStateTracking again.

Printing:

Android itself doesn’t contain implementation of any printing protocol. Because of this I created small IPP parser. But that’s topic for another day.

Here I will only show example of handling queued print job.

In the following code we pick one job according to id from saved processed jobs and set his state to printing. Class PrintTask in the following example is just Android AsyncTask which in background creates IPP request and appends job data.

public void handleQueuedPrintJob(PrintJobId printJobId, PrinterId printerId) {
    final PrintJob printJob = mProcessedPrintJobs.get(printJobId);
    if (printJob == null) {
        return;
    }

    if (printJob.isQueued()) {
        printJob.start();
    }

    OurPrinter ourPrinter = ourDiscoverySession.getPrinter(printerId);

    if (ourPrinter != null) {
        AsyncTask <Void, Void, Void> printTask =
                new PrintTask(printJob, ourPrinter);
        printTask.execute();
    }
}

In case that we have decided to use ipps, we also have to set correct certificate. Next step is to create new HttpURLConnection. (or HttpsURLConnection for secure transfer).

The last thing we have to do is to write into the output stream our IPP message, send it and wait for response from server.

Android manifest file

We have to set necessary permissions in the Android manifest file, in order to be able to run the PrintService.
Add android.permission.BIND_PRINT_SERVICE when creating the service. Example:

...
<service android:name=".OurPrintService" 
    android:permission="android.permission.BIND_PRINT_SERVICE">

    <intent-filter>
        <action android:name="android.printservice.PrintService" />
    </intent-filter>
</service>
...

This allows system to bind to the PrintService. Otherwise the service wouldn’t be shown in the system.

Also

<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.START_PRINT_SERVICE_CONFIG_ACTIVITY" />

permissions are needed for printer discovery and to access files in external storage.