Passing an ActionScript JPG Byte Array to Javscript (and eventually to PHP)

Question

Our web application has a feature which uses Flash (AS3) to take photos using the user's web cam, then passes the resulting byte array to PHP where it is reconstructed and saved on the server.

However, we need to be able to take this web application offline, and we have chosen Gears to do so. The user takes the app offline, performs his tasks, then when he's reconnected to the server, we "sync" the data back with our central database.

We don't have PHP to interact with Flash anymore, but we still need to allow users to take and save photos. We don't know how to save a JPG that Flash creates in a local database. Our hope was that we could save the byte array, a serialized string, or somehow actually persist the object itself, then pass it back to either PHP or Flash (and then PHP) to recreate the JPG.

We have tried: - passing the byte array to Javascript instead of PHP, but javascript doesn't seem to be able to do anything with it (the object seems to be stripped of its methods) - stringifying the byte array in Flash, and then passing it to Javascript, but we always get the same string:

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Now we are thinking of serializing the string in Flash, passing it to Javascript, then on the return route, passing that string back to Flash which will then pass it to PHP to be reconstructed as a JPG. (whew). Since no one on our team has extensive Flash background, we're a bit lost.

Is serialization the way to go? Is there a more realistic way to do this? Does anyone have any experience with this sort of thing? Perhaps we can build a javascript class that is the same as the byte array class in AS?

Answer 1

I'm not sure why you would want to use Javascript here. Anyway, the string you pasted looks like the beginning of a JPG header. The problem is that a JPG will for sure contain NULs (characters with 0 as its value). This will most likely truncate the string (as it seems to be the case with the sample you posted). If you want to "stringify" the JPG, the standard approach is encoding it as Base 64.

If you want to persist data locally, however, there's a way to do it in Flash. It's simple, but it has some limitations.

You can use a local Shared Object for this. By default, there's a 100 Kb limit, which is rather inadequate for image files; you could ask the user to allot more space to your app, though. In any case, I'd try to store the image as JPG, not the raw pixels, since the difference in size is very significative.

Shared Objects will handle serialization / deserialization for you transparently. There are some caveats: not every object can really be serialized; for starters, it has to have a parameterless constructor; DisplayObjects such as Sprites, MovieClips, etc, won't work. It's possible to serialize a ByteArray, however, so you could save your JPGs locally (if the user allows for the extra space). You should use AMF3 as the encoding scheme (which is the default, I think); also, you should map the class you're serializing with registerClassAlias to preserve the type of serialized the object (otherwise it will be treated as an Object object). You only need to do it once in the app life cycle, but it must be done before any read / write to the Shared Object.

Something along the lines of:

registerClassAlias("flash.utils.ByteArray",ByteArray);

I'd use Shared Objects rather than Javascript. Just keep in mind that you'll most likely have to ask the user to give you more space for storing the images (which seems reasonable enough if you're allowing them to work offline), and that the user could delete the data at any time (just like he could delete their browser's cookies).

Edit

I realize I didn't really pay much attention the "we have chosen Gears to do so" part of your question.

In that case, you could give the base 64 approach a try to pass the data to JS. From the Actionscript side it's easy (grab one of the many available Base64 encoders/decoders out there), and I assume the Gear's API must have an encoder / decoder available already (or at least it shouldn't be hard to find one). At that point you'll probably have to turn that into a Blob and store it to disk (maybe using the BlobAPI, but I'm not sure as I don't have experience with Gears).