Erlang：crypo的问题：sha（）

Question

This works in my erlang shell:

1> U = default_user_name().
2> crypto:start().
3> crypto:sha(U).
4> crypto:stop().

But when I compile this:

default_pw() ->
    U = default_user_name(),
    crypto:start(),
    crypto:sha(U),
    crypto:stop().

And execute it in the erlang shell, I get this:

1> person:default_pw().

** exception error: bad argument

 in function  port_control/3

    called as port_control(crypto_drv04,5,<<"jDoe">>)

 in call from crypto:control/2

Two questions:

1) What am I doing wrong?

2) It seems that I need to start and stop the crypto server. But is there a better place to start and stop it in my application?

Many thanks,

LRP

Answer 1

The error you are getting indicates that the crypto application was not started. An easy way to start it is just to add it as a parameter to erl like so:

$ erl -s crypto

I had a look at the current implementation of crypto and the past release notes for erlang and I came to the following conclusions (someone please correct me if I'm wrong):

1. Erlang releases <14A require crypto to be started prior to calling any functions because the library used a port driver. This makes sense because I got the error you described with 13B04 after not starting crypto.
2. Erlang releases >=14A don't require crypto to be started as the implementation now uses NIFs. This makes sense because the current implementation of crypto_server.erl is just a gen_server template, and on 14B03 I don't need to start the application in order to make crypto:sha/1 work.