Unknown AMF type & other errors when transfering files from flash to java

Question

I'm using a Flash tool to transfer data to Java. I'm having problems when it comes to sending multiple objects at once. The objects being sent are just generic Object objects, so it's not a case of needed to register a class alias or anything.

Sending one object works fine. Once I start sending multiple objects (putting the same Objects in an Array and sending that), it starts getting weird. Up to three objects in an Array seems to work fine. More than that I get different errors in the readObject() function, such as:

Unknown AMF type '47'
Unknown AMF type '40'
Unknown AMF type '20'
OutOfBoundsExceptions index 23, size 0
NullPointerException
etc.

Sending 3 objects will work, sending 4 gives me the error. If I delete one of the previous 3 that worked (while keeping the fourth that was added), it'll work again. Anyone know what's going on?

Some more info:

Communication goes through a Socket class on the Flash side. This is pure AS3, no flex.
Messages are compressed before being sent and decompressed on the server, so I'm pretty sure it's not a buffer size issue (unless I'm missing something)
BlazeDS version seems to be 4.0.0.14931 on the jar
Flash version is 10.1 (it's an AIR app)

Update with rough code

Examples of the objects being sent:

var o:Object    = { };
o._key          = this._key.toString();
o.someParam     = someString;
o.someParam2    = someInt;
o.someParam3    = [someString1, someString2, someString3];
...

It's added to our event object (which we use to determine the event to call, the data etc to pass). The event object is been registered as a class alias

That object is sent to the server through a Socket like so:

myByteArray.writeObject( eventObj );
myByteArray.compress();
mySocket.writeBytes( myByteArray );
mySocket.flush();

On the server side, we receive the bytes, and decompress them. We create a Amf3Input object and set the input stream, then read it:

Amf3Input amf3Input = new Amf3Input( mySerializationContext );
amf3Input.setInputStream( new ByteArrayInputStream( buffer ) ); // buffer is a byte[]
MyEventObj eventObj = (MyEventObj)amf3Input.readObject(); // MyEventObj is the server version of the client event object

If it's going to crash with an "unknown AMF type error", it does so immediately i.e. when we try to read the object, and not when it's trying to read a subobject.

In stepping through the read code, it seems when I pass an array of objects, if the length is <= 4, it reads the length right. If the length is bigger than that, it reads it's length as 4.

I've added some rough code - it's a bit hard to take out the relevant bits without posting a huge source dump (which I can't do anyway). There's nothing special going on. Plus it works when sending single objects, or small arrays of objects. Go above 3 and it goes crazy — divillysausages

warhammerkid warhammerkid · Accepted Answer · 2011-11-03T16:27:06

If you're getting AMF deserialization errors, there are several possible issues that could be contributing to the problem. Here are several techniques for doing further diagnostics:

Use a network traffic sniffer to make sure that what you are sending matches what you are receiving. On the Mac I'll use CocoaPacketAnalyzer, or you can try Charles, which can actually decode AMF packets that it notices.
Feed the data to a different AMF library, like PyAMF or RocketAMF to see if it's a problem with BlazeDS or with how you're calling it. It's also possible that you may get a different error message that will give you a better idea of where it's failing.
Check the format of the AMF packet. AMF server calls have some additional wrapping around them that would throw off a deserializer if it's not expecting to encounter that wrapping, and vice versa for purely serialized objects. Server call packets always start off with a 0x00, followed by the AMF version (0x00, 0x03, or in rare cases 0x02).

Unknown AMF type & other errors when transfering files from flash to java

2 Answers