Sending (some) functions between OTP versions fails with 'badfun'
Did you know that you can send Erlang functions between Erlang nodes? You can. Did you know that the OTP versions need to match?
Start Erlang distribution
We’ll start two Erlang nodes, running different major versions of OTP:
$ source ~/.kerl/erlangs/OTP-26.2.5.3/activate
$ erl -sname otp26
Erlang/OTP 26 [erts-14.2.5.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit]
Eshell V14.2.5.3 (press Ctrl+G to abort, type help(). for help)
(otp26@roger-m1)1>
$ source ~/.kerl/erlangs/OTP-27.3.3/activate
$ erl -sname otp27
Erlang/OTP 27 [erts-15.2.6] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit]
Eshell V15.2.6 (press Ctrl+G to abort, type help(). for help)
(otp27@roger-m1)1>
Then we’ll connect them into a cluster; run this on the OTP-26 node:
(otp26@roger-m1)1> net_kernel:connect_node('otp27@roger-m1').
true
(otp26@roger-m1)2> nodes().
['otp27@roger-m1']
Register shell processes
To communicate between the two nodes, we’ll need a registered process; we’ll register the shell:
(otp26@roger-m1)3> register(shell, self()).
true
(otp27@roger-m1)1> register(shell, self()).
true
We don’t need to register both, since we’ll only send messages in one direction, but I like the symmetry.
Send a simple message
(otp26@roger-m1)5> {shell, 'otp27@roger-m1'} ! hello.
hello
(otp27@roger-m1)3> flush().
Shell got hello
ok
That works.
Send a simple function
Now to send a function:
(otp26@roger-m1)7> {shell, 'otp27@roger-m1'} ! fun() -> hello end.
#Fun<erl_eval.43.105768164>
(otp27@roger-m1)3> F = receive F -> F end.
#Fun<erl_eval.43.105768164>
(otp27@roger-m1)4> F().
hello
Send a more complex function
That works. What if we send something slightly more complicated?
(otp26@roger-m1)6> {shell, 'otp27@roger-m1'} ! fun(M) -> maps:size(M) end.
#Fun<erl_eval.42.105768164>
(otp27@roger-m1)5> G = receive G -> G end.
#Fun<erl_eval.42.105768164>
(otp27@roger-m1)6> G(#{}).
** exception error: bad function #Fun<shell.5.18354929>
It fails with “bad function” (or badfun), because the serialized function depends on OTP-26, and we’re running OTP-27.