Windows Script Host (jscript): how do i download a binary file?

Question

i'm trying to automate a file download with Windows Script Host (JScript). i see ADODB.Stream has an Open method whose documentation makes it seem like it should be possible to open a HTTP URL and stream the response body:

var url = 'http://example.com/example.tar.gz';
var path = 'example.tar.gz';

var input = WScript.CreateObject('ADODB.Stream');

input.Open(url);
input.SaveToFile(path);
input.Close();

But it bombs on the Open call with

(null): Object or data matching the name, range, or selection criteria was not found within the scope of this operation.

Phenetidine

kids, the only correct answer to any question starting with "How do I use WSH to..." is DON'T. this question was just a tip of the iceberg of problems i had back then, decided to go with python and its win32api, and while it wasn't stellar (docs), i was able to automate quite a bit in windows without losing my sanity. – Phenetidine

Answer 1

Here is the download code in JScript. Also added some references to API information.

var Source = WScript.Arguments.Item(0);
var Target = WScript.Arguments.Item(1);
var Object = WScript.CreateObject('MSXML2.XMLHTTP');

Object.Open('GET', Source, false);
Object.Send();

if (Object.Status == 200)
{
    // Create the Data Stream
    var Stream = WScript.CreateObject('ADODB.Stream');

    // Establish the Stream
    Stream.Open();
    Stream.Type = 1; // adTypeBinary
    Stream.Write(Object.ResponseBody);
    Stream.Position = 0;

    // Create an Empty Target File
    var File = WScript.CreateObject('Scripting.FileSystemObject');
    if (File.FileExists(Target))
    {
        File.DeleteFile(Target);
    }

    // Write the Data Stream to the File
    Stream.SaveToFile(Target, 2); // adSaveCreateOverWrite
    Stream.Close();
}

ADODB Stream:

• http://www.w3schools.com/ado/ado_ref_stream.asp
• http://msdn.microsoft.com/en-us/library/windows/desktop/ms675032.aspx
• http://msdn.microsoft.com/en-us/library/windows/desktop/ms680846.aspx

Scripting.FileSystemObject:

• http://www.w3schools.com/asp/asp_ref_filesystem.asp

Artima

i can't confirm that this actually works as i don't work with windows anymore (hurray!) and in the end i used python anyway. it does look sane and it is jScript, so i'm accepting it. – Phenetidine

Answer 2

You're on the right track.

You should be using the XMLHTTPRequest Object to communicate with the server. It's sort of like "curl" for Windows Script. Once the data is read from the remote server, you can write it into an ADODB stream and manipulate it within your script. In your case, writing to a file using the FileSystemObject seems like the most logical course of action.

So your script might look something like this:

' Set your settings
strFileURL = "http://www.domain.com/file.zip"
strSavePath = "C:\somefolder\"

' Send an HTTP request for the file
Set objXMLHTTP = CreateObject("MSXML2.XMLHTTP")

objXMLHTTP.open "GET", strFileURL, false
objXMLHTTP.send()

' If the server responds with "OK"...
If objXMLHTTP.Status = 200 Then
    ' Create a stream object to write downloaded data to
    Set objADOStream = CreateObject("ADODB.Stream")
    objADOStream.Open
    objADOStream.Type = 1 'adTypeBinary

    objADOStream.Write objXMLHTTP.ResponseBody
    objADOStream.Position = 0

    ' Create an empty file on disk
    Set objFso = Createobject("Scripting.FileSystemObject")
    ' Make sure we don't have any name collision...
    If objFso.Fileexists(strSavePath) Then objFSO.DeleteFile strSavePath
    Set objFso = Nothing

    ' Write the stream data to file
    objADOStream.SaveToFile strSavePath
    objADOStream.Close
    Set objADOStream = Nothing
End if

Set objXMLHTTP = Nothing

Yulma

That's VBscript, not JScript – Blindage

Answer 3

Converted the above code to JavaScript. This appears to work for me. Recommend adding a try catch block to the caller. Also, converted to async. I've used this code to save some 90 files at the same time. Since the delete file (necessary as the overwrite fails) is synchronous, it is better moved to a separate function for multiple files.

function saveFile(sSourceUrl, sDestFile) {
    var objXMLHTTP = new ActiveXObject("MSXML2.XMLHTTP");
    objXMLHTTP.onreadystatechange=function() {
        if (objXMLHTTP.readyState === 4) {
            var objADOStream = new ActiveXObject("ADODB.Stream");
            objADOStream.open();
            objADOStream.type = 1; // Binary
            objADOStream.write(objXMLHTTP.ResponseBody);
            objADOStream.position = 0;
            objADOStream.saveToFile(sDestFile, 2);
            objADOStream.close();
        }
    };

    objXMLHTTP.open("GET", sSourceUrl, false);
    objXMLHTTP.send();
}

Hardnosed

Use objADOStream.saveToFile(sDestFile, 2); // adSaveCreateOverWrite to get rid of the need for file deletion. – Testee

Answer 4

Your URL needs to be in this format:

URL=scheme://server/folder

Oubliette

Would you care to explain why? – Thursday

See MSDN Open Method (ADO Stream). This is saying that the source should be a string formatted like var url = 'URL=http://example.com/example.tar.gz'; – Artima