AS3 multipart form data request generator
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A multipart form data request generator

Demo :

The JPEGEncoder used in this demo can be found here:

Restrictions :

In Flash Player 10 and later, if you use a multipart Content-Type (for example "multipart/form-data") that contains an upload (indicated by a "filename" parameter in a "content-disposition" header within the POST body), the POST operation is subject to the security rules applied to uploads:

  • The POST operation must be performed in response to a user-initiated action, such as a mouse click or key press. [adobe outdated documentation ?]

  • If the POST operation is cross-domain (the POST target is not on the same server as the SWF file that is sending the POST request), the target server must provide a URL policy file that permits cross-domain access.

Source :

How to use it

Create a new Multipart object giving it the url you're asking for. The method will be automatically set at POST.

Then you can use the following methods agains your object:

  • addField(string fieldName, string value)
  • addFile(string fieldName, ByteArray file, string mimeType, string fileName)

Then you can retrieve the request at yourObject.request and load it with the native urlloader of actionscript.

Extracted from the Demo, here is a basic example:

// Instanciate Multipart with url
var form:Multipart = new Multipart(url);

// Add fields
form.addField("field1", "hello");
form.addField("field2", "world");

// Add files
form.addFile("file1", text, "text/plain", "test.txt");
form.addFile("file2", image, "image/jpeg", "test.jpg");

// Load request
var loader:URLLoader = new URLLoader();
loader.addEventListener(Event.COMPLETE, onComplete);
try {
} catch (error: Error) {
	textField.text = "Unable to load request : "+error.message;