Improve line folding algorithm

[emersion]

With #29 we no longer generate broken signatures with FWS where they shouldn't be. However we could still improve our folding algorithm. Given these constraints:

• We want to be RFC-conformant (lines < 1000 chars)
• We don't want something too complicated (see Fix DKIM-Signature header flowing, it is not valid to arbitrarily sli… #27)
• Ensuring that lines are <75 chars is not necessary

We may want to fix these:

• We still don't properly fold h= params if they are very long
• We fold b= params at 75 chars, but we don't need to

[ludusrusso]

I can work on it on the next days! :D
My idea is to write two simple functions, one to fold h and one for b (that we already have).

[emersion]

Nice!

I think to fold h, it'll probably be simpler to do it before turning the list into a string, ie. in formatTagList:

go-msgauth/dkim/sign.go

Line 340 in fb07ec9

func formatTagList(l []string) string {

[ludusrusso]

Nice!

I think to fold h, it'll probably be simpler to do it before turning the list into a string, ie. in formatTagList:

go-msgauth/dkim/sign.go

Line 340 in fb07ec9

func formatTagList(l []string) string {

Thats right, but I then need to change some piece of code in the middle, I thinks that it would be simpler by just use Strings.split in

go-msgauth/dkim/header.go

Line 95 in fb07ec9

func formatHeaderParams(headerFieldName string, params map[string]string) string {

[wjywbs]

By the way, #30 fixed the h= wrapping as well.