Downloading Files

Downloading files

To download a file, create an instance of nsIWebBrowserPersist and call its nsIWebBrowserPersist.saveURI() method, passing it a URL to download and an nsIFile instance representing the local file name/path.

01 // create a persist
02 var persist = Components.classes[ "@mozilla.org/embedding/browser/nsWebBrowserPersist;1" ]
03 .createInstance(Components.interfaces.nsIWebBrowserPersist);
04
05 // with persist flags if desired See nsIWebBrowserPersist page for more PERSIST_FLAGS.
06 const nsIWBP = Components.interfaces.nsIWebBrowserPersist;
07 const flags = nsIWBP.PERSIST_FLAGS_REPLACE_EXISTING_FILES;
08 persist.persistFlags = flags | nsIWBP.PERSIST_FLAGS_FROM_CACHE;
09
10 // do the save
11 persist.saveURI(uriToFile, null , null , null , "" , nsIFile);

If you don't need detailed progress information, you might be happier with nsIDownloader .

Downloading Binary Files with a Progress Listener

To download a binary file with custom progress listener:

01 var persist = Components.classes[ "@mozilla.org/embedding/browser/nsWebBrowserPersist;1" ]
02 .createInstance(Components.interfaces.nsIWebBrowserPersist);
03 var file = Components.classes[ "@mozilla.org/file/local;1" ]
04 .createInstance(Components.interfaces.nsILocalFile);
05 file.initWithPath( "C:\\a\\path\\file.bin" ); // download destination
06 var obj_URI = Components.classes[ "@mozilla.org/network/io-service;1" ]
07 .getService(Components.interfaces.nsIIOService)
08 .newURI(aURLToDownload, null , null );
09 persist.progressListener = {
10 onProgressChange: function (aWebProgress, aRequest, aCurSelfProgress, aMaxSelfProgress, aCurTotalProgress, aMaxTotalProgress) {
11 var percentComplete = (aCurTotalProgress/aMaxTotalProgress)*100;
12 var ele = document.getElementById( "progress_element" );
13 ele.innerHTML = percentComplete + "%" ;
14 },
15 onStateChange: function (aWebProgress, aRequest, aStateFlags, aStatus) {
16 // do something
17 }
18 }
19 persist.saveURI(obj_URI, null , null , null , "" , file);

Downloading files that require credentials

Before calling nsIWebBrowserPersist.saveURI() , you need to set the progressListener property of the nsIWebBrowserPersist instance to an object that implements nsIAuthPrompt . Normally, nsIAuthPrompt expects a prompt to be displayed so the user can enter credentials, but you can return a username and password credentials directly without prompting the user. If you want to open a login prompt, you can use the default prompt by calling the window watcher's getNewAuthPrompter() method.

01 var persist = Components.classes[ "@mozilla.org/embedding/browser/nsWebBrowserPersist;1" ]
02 .createInstance(Components.interfaces.nsIWebBrowserPersist);
03 var hardCodedUserName = "ericjung" ;
04 var hardCodedPassword = "foobar" ;
05 persist.progressListener = {
06
07 QueryInterface: function (iid) {
08 if (iid.equals(Components.interfaces.nsIAuthPrompt) ||
09 iid.equals(Components.interfaces.nsISupports))
10 return this ;
11 throw Components.results.NS_ERROR_NO_INTERFACE;
12 },
13
14 // implements nsIAuthPrompt
15 prompt: function (dialogTitle, text, passwordRealm, savePassword, defaultText, result) {
16 result.value = hardCodedPassword;
17 return true ;
18 },
19 promptPassword: function (dialogTitle, text, passwordRealm, savePassword, pwd) {
20 pwd.value = hardCodedPassword;
21 return true ;
22 },
23 promptUsernameAndPassword: function (dialogTitle, text, passwordRealm, savePassword, user, pwd) {
24 user.value = hardCodedUserName;
25 pwd.value = hardCodedPassword;
26 return true ;
27 }
28 };
29 persist.saveURI(urlToFile, null , null , null , "" , nsFileInstance);

The above is going to give you errors about missing nsIDownloadProgressListener methods, so you should implement that as well. For example, with empty dummy methods if you are not interested about the progress.

Instead of using QI like above, you can also implement nsIInterfaceRequestor and return nsIAuthPrompt from there, like nsIWebBrowserPersist .progressListener documentation suggests.

Downloading Images

Sample function for fetching an image file from a URL.

01 // This function is for fetching an image file from a URL.
02 // Accepts a URL and returns the file.
03 // Returns empty if the file is not found (with an 404 error for instance).
04 // Tried with .jpg, .ico, .gif (even .html).
05
06 function GetImageFromURL(url) {
07 var ioserv = Components.classes[ "@mozilla.org/network/io-service;1" ]
08 .getService(Components.interfaces.nsIIOService);
09 var channel = ioserv.newChannel(url, 0, null );
10 var stream = channel.open();
11
12 if (channel instanceof Components.interfaces.nsIHttpChannel && channel.responseStatus != 200) {
13 return "" ;
14 }
15
16 var bstream = Components.classes[ "@mozilla.org/binaryinputstream;1" ]
17 .createInstance(Components.interfaces.nsIBinaryInputStream);
18 bstream.setInputStream(stream);
19
20 var size = 0;
21 var file_data = "" ;
22 while (size = bstream.available()) {
23 file_data += bstream.readBytes(size);
24 }
25
26 return file_data;
27 }

Download observers

Sample download observer for Firefox 2 Download manager.

01 // ******************************
02 // DownloadObserver
03 // ******************************
04 function sampleDownload_init(){
05 //**** Add download observer
06 var observerService = Components.classes[ "@mozilla.org/observer-service;1" ]
07 .getService(Components.interfaces.nsIObserverService);
08 observerService.addObserver(sampleDownloadObserver, "dl-start" , false );
09 observerService.addObserver(sampleDownloadObserver, "dl-done" , false );
10 observerService.addObserver(sampleDownloadObserver, "dl-cancel" , false );
11 observerService.addObserver(sampleDownloadObserver, "dl-failed" , false );
12
13 window.addEventListener( "unload" , function () {
14 observerService.removeObserver(sampleDownloadObserver, "dl-start" );
15 observerService.removeObserver(sampleDownloadObserver, "dl-done" );
16 observerService.removeObserver(sampleDownloadObserver, "dl-cancel" );
17 observerService.removeObserver(sampleDownloadObserver, "dl-failed" );
18 }, false );
19 }
20 var sampleDownloadObserver = {
21 observe: function (subject, topic, state) {
22 var oDownload = subject.QueryInterface(Components.interfaces.nsIDownload);
23 //**** Get Download file object
24 var oFile = null ;
25 try {
26 oFile = oDownload.targetFile; // New firefox 0.9+
27 } catch (e){
28 oFile = oDownload.target; // Old firefox 0.8
29 }
30 //**** Download Start
31 if (topic == "dl-start" ){
32 alert( 'Start download to - ' +oFile.path);
33 }
34 //**** Download Cancel
35 if (topic == "dl-cancel" ){
36 alert( 'Canceled download to - ' +oFile.path);
37 }
38 //**** Download Failed
39 else if (topic == "dl-failed" ){
40 alert( 'Failed download to - ' +oFile.path);
41 }
42 //**** Download Successs
43 else if (topic == "dl-done" ){
44 alert( 'Done download to - ' +oFile.path);
45 }
46 }
47 }
48 window.addEventListener( "load" , sampleDownload_init, false );

See also

• nsIDownloadProgressListener
• Saving the current web page to a local file
• Saving an arbitrary URL to a local file
• Customizing the download progress bar appearance