ActionScript 2.0 Language Reference - Adobe Help and Support

The FileReference.upload() and FileReference.download() functions are
nonblocking. These functions return after they are called, before the file transmission is
complete. In addition, if the FileReference object goes out of scope, any upload or download
that has not yet been completed on that object is cancelled upon leaving the scope. So, be sure
that your FileReference object will remain in scope for as long as the upload or download
could be expected to continue.
The file is uploaded to the URL passed in the url parameter. The URL must be a server script
configured to accept uploads. Flash Player uploads files using the HTTP POST method. The
server script that handles the upload should expect a POST request with the following
elements:
■ A Content-Type element of multipart/form-data
■ A Content-Disposition element with a name attribute set to "Filedata" by default and
a filename attribute set to the name of the original file
■ The binary contents of the file
Here is a sample POST request:
Content-Type: multipart/form-data; boundary=AaB03x
--AaB03x
Content-Disposition: form-data; name="Filedata"; filename="example.jpg"
Content-Type: application/octet-stream
... contents of example.jpg ...
--AaB03x--
To send POST parameters to the server, set the value of FileReference.postData to your
parameters. You can send GET parameters to the server with the upload() call by appending
parameters to the URL.
If the file to be uploaded is bigger than approximately 10 KB, Windows Flash Player versions
first send a test upload POST with zero content prior to uploading the actual file in order to
verify that the transmission is likely to be successful. The second POST contains an actual file
content. For smaller files, Flash Player does a single upload POST with the file to be uploaded.
The Macintosh players currently do not do test upload POSTs.
Note: If your server requires user authentication, only SWF files running in a browser—that
is, using the browser plug-in or ActiveX control—can provide a dialog box to prompt the user
for a user name and password for authentication, and only for downloads. For uploads that
use the plug-in or ActiveX control, and for uploads and downloads that use the stand-alone or
external player, the file transfer fails.
590 ActionScript classes