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Situation: I'm trying to replace Flash Socket communication (byte-range) with javascript, to avoid the flash socket security policy file restrictions.

Details: I have binary data from javascript, and I can pass it to flash by base64 encoding/decoding, but this is too slow. Saving to disk and passing the local url is not an option (and not just for speed, but also clients prefer everything in memory, and the swf file may be restricted from loading local files). Furthermore, not using base64 doesn't work, as flash's ExternalInterface uses XML (which isn't designed to carry binary data) to pass the data to AS3.

Question: Is there any way to get binary data from JS to AS3 without writing to disk and not bae64 encoding?

I am aware of Action Message Format (AMF) but it seems to add way to many external dependencies, and may still be slow?

Note: My program needs to be as browser compatible as possible, and it's downloaded by clients (so needs to be small) and it also needs to run as fast as possible...

thanks!

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  • Are you ruling out base64 because of performance? What is the binary data? Is it large? There is no way to send binary data between Flash and Javascript unless you marshal it into a text based format. AMF will not be slower, but it's for client/server communication, not JS <--> AS3. Commented Jul 12, 2012 at 21:38
  • I never heard of ExternalInterface using XML before? You can pass basic JavaScript data types via ExternalInterface. But why not just fix the socket policy crossdomain issues you have instead of hacking a way around it? Commented Jul 12, 2012 at 21:44
  • AMF is the way to go, and it is not slow. In fact, it is faster than using JavaScript to encode/decode. ExternalInterface has limitation of 4K data, so it is a fragile approach. Commented Jul 12, 2012 at 22:05
  • Sunil D. - binary data includes png/jpg and can be in the megabytes, and can there can be dozens/hundreds of these. Commented Jul 12, 2012 at 22:28
  • The_asMan - It seems ExternalInterface always marshals XML, and the format is specified (you have to do it manually when going through as ActiveX control). When you pass binary you get a missing </string> element error. As for the socket policy, there is no issue, it's just extra work for clients (it's a lot more involved then just a crossdomain.xml file for Flash Sockets) Tianzhen Lin - There is no 4k limit, at least on FP 10/11, I've passed 3-4MB in a single call. Commented Jul 12, 2012 at 22:34

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I've modified my thinking slightly about this problem:

There is no straight forward way to send binary data between Flash and Javascript without marshaling it into a text based format first (ie: base64 encoding it).

As noted by the OP, to facilitate communication between Actionscript and Javascript the ExternalInterface class actually marshals objects/data into an XML format. As such the binary data would need to go through this conversion to XML.

New thought: when you use ExternalInterface the Flash application actually modifies the DOM, adding methods that serialize/deserialize the data to/from XML (reference needed, I've read about this but cannot find it now). Technically, it might be possible to re-define these methods in Javascript and fix the XML parsing errors you saw when trying to pass binary data. You'd have to determine the names of the names of these methods (I recall them starting with __Flash__ or something similar).

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Thanks, I see what you're talking about. I'm going to investigate ExternalInterface js methods further, and also how SWFObject embeds the swf binary.
I thought of another means, though I haven't implemented a full test yet. SWF files can handle binary, and using swfobject.js a swf can be injected into the DOM. Then on the flash side the LocalConnection class can pass binary between swf's. However, LocalConnection has a 40kb limit per send() so a bunch of AMF packets have to be sent potentially. Then there is all the overhead of; creating a swf file in memory in pure JS, injecting to the dom, waiting for the new swf to start in flash, and then sending the 40kb amf packets. In the end it may be the same as base64 encoding/decoding..

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