google cloud print from android without dialog

Question

Can someone tell me if it is possible to silently print using google cloud print from an android device? The goal is that my app grabs a file from a URL or from the SD card and then sends it to a specific printer - all without interaction from anyone looking at the screen or touching anything. It will actually be triggered by a barcode scan on a blue tooth connected device.

Thanks

Answer 1

Well, it is possible but I don't know why there's not too much information about it in the documentation...

The tricky part is connecting to the google cloud print API using only the android device (with no third party servers as the documentation explains here: https://developers.google.com/cloud-print/docs/appDevGuide ), so that's what I'm going to explain.

First, you have to include in your app the Google sign-in API, I recommend firebase API https://firebase.google.com/docs/auth/android/google-signin

Then you have to go to your Google API console: https://console.developers.google.com in the menu, go to Credentials scroll to OAuth 2.0 client IDs select Web client (auto created by Google Service) and save into your project the Client ID and Client secret keys... In my project, I saved them as "gg_client_web_id" and "gg_client_web_secret" as you will see below in the code.

Next, I'm going to paste all the code and then I'll explain it:

public class MainActivity extends AppCompatActivity
    implements GoogleApiClient.OnConnectionFailedListener {
private GoogleApiClient mGoogleApiClient;
private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthListener;
private static final int REQUEST_SINGIN = 1;
private TextView txt;
public static final String TAG = "mysupertag";
public static final String URLBASE = "https://www.google.com/cloudprint/";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    txt = (TextView) findViewById(R.id.txt);
    mAuth = FirebaseAuth.getInstance();
    // Configure Google Sign In
    GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
            .requestIdToken(getString(R.string.gg_client_web_id))
            .requestEmail()
            .requestServerAuthCode(getString(R.string.gg_client_web_id))
            .requestScopes(new Scope("https://www.googleapis.com/auth/cloudprint"))
            .build();
    mGoogleApiClient = new GoogleApiClient.Builder(this)
            .enableAutoManage(this /* FragmentActivity */, this /* OnConnectionFailedListener */)
            .addApi(Auth.GOOGLE_SIGN_IN_API, gso)
            .build();

    findViewById(R.id.sign_in_button).setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            signIn();
        }
    });

    mAuthListener = new FirebaseAuth.AuthStateListener() {
        @Override
        public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            FirebaseUser user = firebaseAuth.getCurrentUser();
            if (user != null) {
                // User is signed in
                Log.d(TAG, "onAuthStateChanged:signed_in:" + user.getUid());
            } else {
                // User is signed out
                Log.d(TAG, "onAuthStateChanged:signed_out");
            }
            // ...
        }
    };
}

@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
    Log.d(TAG, "error connecting: " + connectionResult.getErrorMessage());
    Toast.makeText(this, "error CONN", Toast.LENGTH_LONG).show();
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...);
    if (requestCode == REQUEST_SINGIN) {
        GoogleSignInResult result = Auth.GoogleSignInApi.getSignInResultFromIntent(data);
        if (result.isSuccess()) {
            // Google Sign In was successful, authenticate with Firebase
            GoogleSignInAccount account = result.getSignInAccount();
            firebaseAuthWithGoogle(account);
        } else {
            // Google Sign In failed, update UI appropriately
            // ...
            Toast.makeText(this, "error ", Toast.LENGTH_LONG).show();
        }
    }
}

private void signIn() {
    Intent signInIntent = Auth.GoogleSignInApi.getSignInIntent(mGoogleApiClient);
    startActivityForResult(signInIntent, REQUEST_SINGIN);
}

@Override
public void onStart() {
    super.onStart();
    mAuth.addAuthStateListener(mAuthListener);
}

@Override
public void onStop() {
    super.onStop();
    if (mAuthListener != null) {
        mAuth.removeAuthStateListener(mAuthListener);
    }
}

private void firebaseAuthWithGoogle(final GoogleSignInAccount acct) {
    Log.d(TAG, "firebaseAuthWithGoogle:" + acct.getId());

    AuthCredential credential = GoogleAuthProvider.getCredential(acct.getIdToken(), null);
    mAuth.signInWithCredential(credential)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    Log.d(TAG, "signInWithCredential:onComplete:" + task.isSuccessful());

                    // If sign in fails, display a message to the user. If sign in succeeds
                    // the auth state listener will be notified and logic to handle the
                    // signed in user can be handled in the listener.
                    FirebaseUser user = task.getResult().getUser();
                    txt.setText(user.getDisplayName() + "\n" + user.getEmail());//todo
                    if (!task.isSuccessful()) {
                        Log.w(TAG, "signInWithCredential", task.getException());
                        Toast.makeText(MainActivity.this, "Authentication failed.",
                                Toast.LENGTH_SHORT).show();
                    }
                    getAccess(acct.getServerAuthCode());
                }
            });
}

private void getPrinters(String token) {
    Log.d(TAG, "TOKEN: " + token);
    String url = URLBASE + "search";
    Ion.with(this)
            .load("GET", url)
            .addHeader("Authorization", "Bearer " + token)
            .asString()
            .withResponse()
            .setCallback(new FutureCallback<Response<String>>() {
                @Override
                public void onCompleted(Exception e, Response<String> result) {
                    Log.d(TAG, "finished " + result.getHeaders().code() + ": " +
                            result.getResult());
                    if (e == null) {
                        Log.d(TAG, "nice");
                    } else {
                        Log.d(TAG, "error");
                    }
                }
            });
}

private void getAccess(String code) {
    String url = "https://www.googleapis.com/oauth2/v4/token";
    Ion.with(this)
            .load("POST", url)
            .setBodyParameter("client_id", getString(R.string.gg_client_web_id))
            .setBodyParameter("client_secret", getString(R.string.gg_client_web_secret))
            .setBodyParameter("code", code)
            .setBodyParameter("grant_type", "authorization_code")
            .asString()
            .withResponse()
            .setCallback(new FutureCallback<Response<String>>() {
                @Override
                public void onCompleted(Exception e, Response<String> result) {
                    Log.d(TAG, "result: " + result.getResult());
                    if (e == null) {
                        try {
                            JSONObject json = new JSONObject(result.getResult());
                            getPrinters(json.getString("access_token"));
                        } catch (JSONException e1) {
                            e1.printStackTrace();
                        }
                    } else {
                        Log.d(TAG, "error");
                    }
                }
            });
}}

As you can see, in the onCreate the important part is creating the GoogleSignInOptions WITH the google cloud print scope AND calling the requestIdToken/requestServerAuthCode methods.

Then in the firebaseAuthWithGoogle method call the getAccess method in order to get the OAuth access token, for making all requests I'm using Ion library: https://github.com/koush/ion

Next with the access_token you can now do requests to the google cloud print API, in this case I call the getPrinters method, in this method I call the "search" method (from google cloud print API) to get all the printers associated to the google account that has signed in.. (to associate a printer to a google account visit this: https://support.google.com/cloudprint/answer/1686197?hl=en&p=mgmt_classic ) Note the .addHeader("Authorization", "Bearer " + token), this is the important part of the request, the "token" var is the access_token, you NEED add this Authorization header in order to use the API and don't forget to refresh when it expires, as explained here : https://developers.google.com/identity/protocols/OAuth2ForDevices in the "Using a refresh token" part.

And that's it, you can now print something sending a POST request to the "submit" method of the google cloud print API, I recommend to go here: https://developers.google.com/cloud-print/docs/appInterfaces and see all the methods available and how to use them (wich parameters send to them, etc). Of course in that link explains the "submit" method too.

EDIT:

EXAMPLE OF HOW TO SEND A REQUEST TO "/submit" FOR PRINTING USING ION LIBRARY AND MJSON LIBRARY (https://bolerio.github.io/mjson/) THE MJSON IS FOR CREATING A JSON OBJECT, YOU CAN CREATE IT THE WAY YOU PREFER

private void printPdf(String pdfPath, String printerId) {
    String url = URLBASE + "submit";
    Ion.with(this)
            .load("POST", url)
            .addHeader("Authorization", "Bearer " + YOUR_ACCESS_TOKEN)
            .setMultipartParameter("printerid", printerId)
            .setMultipartParameter("title", "print test")
            .setMultipartParameter("ticket", getTicket())
            .setMultipartFile("content", "application/pdf", new File(pdfPath))
            .asString()
            .withResponse()
            .setCallback(new FutureCallback<Response<String>>() {
                @Override
                public void onCompleted(Exception e, Response<String> result) {
                    if (e == null) {
                        Log.d(TAG, "PRINTTT CODE: " + result.getHeaders().code() +
                                ", RESPONSE: " + result.getResult());
                        Json j = Json.read(result.getResult());
                        if (j.at("success").asBoolean()) {
                            Toast.makeText(MainActivity.this, "Success", Toast.LENGTH_LONG).show();
                        } else {
                            Toast.makeText(MainActivity.this, "ERROR", Toast.LENGTH_LONG).show();
                        }
                    } else {
                        Toast.makeText(MainActivity.this, "ERROR", Toast.LENGTH_LONG).show();
                        Log.d(TAG, e.toString());
                    }
                }
            });
}

private String getTicket() {
    Json ticket = Json.object();
    Json print = Json.object();
    ticket.set("version", "1.0");

    print.set("vendor_ticket_item", Json.array());
    print.set("color", Json.object("type", "STANDARD_MONOCHROME"));
    print.set("copies", Json.object("copies", 1));

    ticket.set("print", print);
    return ticket.toString();
}

Answer 2

Yes, You can achieve silent print using this REST API(https://www.google.com/cloudprint/submit) ,I have done it using WCF Service. you need to download contents from url as base64 content, then add

contentType=dataUrl

in the request. Here is the code..

                postData = "printerid=" + PrinterId;
                postData += "&title=" + JobTitle;
                postData += "&ticket=" + ticket;
                postData += "&content=data:" + documentContent.ContentType + ";base64," + documentContent.Base64Content;
                postData += "&contentType=dataUrl";
                postData += "&tag=test";

Then , please make a request to submit REST API in this way.

     var request = (HttpWebRequest)WebRequest.Create("https://www.google.com/cloudprint/submit");
     var data = Encoding.ASCII.GetBytes(postData);
            request.Headers.Add("Authorization: Bearer " + Token);
            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.ContentLength = data.Length;
            request.UseDefaultCredentials = true;

            using (var stream = request.GetRequestStream())
            {
                stream.Write(data, 0, data.Length);
            }
            var response = (HttpWebResponse)request.GetResponse();
            string responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();
            JavaScriptSerializer json_serializer = new JavaScriptSerializer();
            PrintJobResponse printInfo = json_serializer.Deserialize<PrintJobResponse>(responseString);
            return printInfo;

Thanks.