Code snippets:Downloading Files

From MDC

Contents 1 Downloading Files 1.1 Downloading Files that require credentials 2 Downloading Images 3 Download Observers 4 See Also

[edit] Downloading Files

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

var persist = Components.classes["@mozilla.org/embedding/browser/nsWebBrowserPersist;1"].
    createInstance(Components.interfaces.nsIWebBrowserPersist);
persist.saveURI(urlToFile, null, null, null, "", nsFileInstance);

[edit] 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.

TODO: This code needs testing

var persist = Components.classes["@mozilla.org/embedding/browser/nsWebBrowserPersist;1"].
    createInstance(Components.interfaces.nsIWebBrowserPersist);
var hardCodedUserName = "ericjung";
var hardCodedPassword = "foobar";
persist.progressListener = {
  // implements nsIAuthPrompt
  prompt: function(dialogTitle, text, passwordRealm, savePassword, defaultText, result) {
    result.value = hardCodedPassword;
    return true;
  },
  promptPassword: function(dialogTitle, text, passwordRealm, savePassword, pwd) {
    pwd.value = hardCodedPassword;
    return true;
  },
  promptUsernameAndPassword: function(dialogTitle, text, passwordRealm, savePassword, user, pwd) {
    user.value = hardCodedUserName;
    pwd.value = hardCodedPassword;    
    return true;
  }
};
persist.saveURI(urlToFile, null, null, null, "", nsFileInstance);

[edit] Downloading Images

Sample function for fetching an image file from a URL.

// This function is for fetching an image file from a URL. 
// Accepts a URL and returns the file. 
// Returns empty if the file is not found (with an 404 error for instance). 
// Tried with .jpg, .ico, .gif (even .html).

function GetImageFromURL(url) { 
  var ioserv = Components.classes["@mozilla.org/network/io-service;1"] 
    .getService(Components.interfaces.nsIIOService); 
  var channel = ioserv.newChannel(url, 0, null); 
  var stream = channel.open(); 

  if (channel instanceof Components.interfaces.nsIHttpChannel && channel.responseStatus != 200) { 
    return ""; 
  }

  var bstream = Components.classes["@mozilla.org/binaryinputstream;1"] 
    .createInstance(Components.interfaces.nsIBinaryInputStream); 
  bstream.setInputStream(stream); 

  var size = 0; 
  var file_data = ""; 
  while(size = bstream.available()) { 
    file_data += bstream.readBytes(size); 
  } 

  return file_data; 
}

[edit] Download Observers

Sample download observer for Firefox 2 Download manager.

// ******************************
// DownloadObserver
// ******************************
function sampleDownload_init(){
  //**** Add download observer
  var observerService = Components.classes["@mozilla.org/observer-service;1"]
                                  .getService(Components.interfaces.nsIObserverService);
  observerService.addObserver(sampleDownloadObserver, "dl-start", false);
  observerService.addObserver(sampleDownloadObserver, "dl-done", false);
  observerService.addObserver(sampleDownloadObserver, "dl-cancel", false);
  observerService.addObserver(sampleDownloadObserver, "dl-failed", false);

  window.addEventListener("unload", function() {
    observerService.removeObserver(sampleDownloadObserver, "dl-start");
    observerService.removeObserver(sampleDownloadObserver, "dl-done");
    observerService.removeObserver(sampleDownloadObserver, "dl-cancel");
    observerService.removeObserver(sampleDownloadObserver, "dl-failed");
  }, false);
}
var sampleDownloadObserver = {
  observe: function (subject, topic, state) {
    var oDownload = subject.QueryInterface(Components.interfaces.nsIDownload);
    //**** Get Download file object
    var oFile = null;
    try{
      oFile = oDownload.targetFile;  // New firefox 0.9+
    } catch (e){
      oFile = oDownload.target;      // Old firefox 0.8
    }
    //**** Download Start
    if (topic == "dl-start"){
      alert('Start download to - '+oFile.path); 
    }
    //**** Download Cancel
    if(topic == "dl-cancel"){ 
      alert('Canceled download to - '+oFile.path); 
    }
    //**** Download Failed
    else if(topic == "dl-failed"){ 
      alert('Failed download to - '+oFile.path);
    }
    //**** Download Successs
    else if(topic == "dl-done"){
      alert('Done download to - '+oFile.path);
    }    
  }
}
window.addEventListener("load", sampleDownload_init, false);

[edit] See Also

nsIDownloadProgressListener

Saving the current web page to a local file

Saving an arbitrary URL to a local file