add wrappers to enable/disable Padding for encryption contexts

[rameshrv]

We needed to disable and use customized padding in our product. This code change enables us (and others who need it) to have custom padding.

[hasit]

I need this as well. We need to turn off the default padding and do it our way because we need to comply with our clients.

[zeebo]

Thanks for this contribution. I have some changes I'd like to request in order to get it merged:

• Can you change the method to be SetPadding(bool) rather than two methods?
• We can't add methods to an exported interface due to back-compat concerns. Your local code can still type assert to get access to the new method.

Let me know if you're willing to make these changes. Be sure to add yourself to the AUTHORS file as well. Thanks!

[rameshrv]

@zeebo , thanks ! I will do the changes as you suggested and update the PR.

[hasit]

@zeebo, can you please expand on what you meant here?

We can't add methods to an exported interface due to back-compat concerns. Your local code can still type assert to get access to the new method.

[zeebo]

A package depending on this package may have a local implementation of the interface on some type and adding methods to it would cause that package to no longer compile because the local implementation would not have that method.

I try to be really careful about back compat. That's why https://godoc.org/github.com/spacemonkeygo/openssl#LoadPrivateKeyFromPEMWidthPassword still exists. :)

[rameshrv]

@zeebo just pushed the changes. However, I am still unclear of this: SetPadding will still be not accessible outside (as of my current changes) but you say we could type assert and access it from applications ? Can you please elaborate on that ? I have tried to type assert it as EncryptionCipherCtx or CipherCtx, it never works. I will need to put it in one of the external structs/interfaces to access it right ?

[zeebo]

Here's what I mean: https://play.golang.org/p/bqyEPtjsWB3

[rameshrv]

@zeebo , thank you for the reference ! It works like a charm..I have never used an exported method in that way !

I have now changed the AUTHORS file, as well as squashed my previous commits into one single commit. Do you think the current changes are good enough to merge into the main line ?

[zeebo]

Perfect! Thanks for the work.