datagram too long!

I get this:

:net(error): Attempt to send TCP datagram of 57127082 bytes--too long!

What is max datagram length? And how could i use a datagram to send a file?

The default max datagram length (through the net system) is 64K bytes, because they are prefixed by a 2-byte length indication.

You can set the config variable:

tcp-header-size 4

to configure Panda to use a 4-byte indication instead, which allows you to go up to 4 GB in one go.

Obviously, you must set this variable on both server and client.