Downloading Files

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2012-06 ( 77)
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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
);

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最新评论

Downloading Files

Downloading files

Downloading Binary Files with a Progress Listener

Downloading files that require credentials

Downloading Images

Download observers

See also

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博主相关

文章分类

社区版块

存档分类

最新评论

Downloading Files

Downloading files

Downloading Binary Files with a Progress Listener

Downloading files that require credentials

Downloading Images

Download observers

See also

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发表评论

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