Extract a header value or return default

[zettelmj]

I some situation it would be handy to for the headerValue* directives to allow to specify a default value that is used if the header is not present.

for headerValueByName this could look like this:

def headerValueByName(headerName: String, default: String): Directive1[String] = headerValue(optionalValue(headerName.toLowerCase)) | provide(default)

[jrudolph]

Hi @zettelmj, thanks for the suggestion.

I wonder if the new directive would be general enough to warrant adding it to the library of directives. Using

(headerValue(headerName) | provide(default))

directly, instead, seems to be more explicit to me.

[zettelmj]

Hi @jrudolph,

that looks way better than what i tried over the weekend. Passing a function down through the directives makes all of the look very convoluted. Additionally it changes a bunch of signatures.
I'll give the "provide" directive a try.

Cheers
Jens

[ktoso]

Would you have some time to add this pattern to our documentation, in

• http://doc.akka.io/docs/akka-http/current/scala/http/routing-dsl/directives/header-directives/headerValue.html
• https://github.com/akka/akka-http/blob/master/docs/src/main/paradox/java/http/routing-dsl/directives/header-directives/headerValue.md

That would be very nice of you :) A way of saying thanks in a way :-)

[jlprat]

I would say for the Java DSL is not that straight forward, unless #620 is done

[jrudolph]

@jlprat agreed.

[zettelmj]

@ktoso just putting it into headerValue feels a bit strange cause it is effectively just an application of http://doc.akka.io/docs/akka-http/current/scala/http/routing-dsl/directives/index.html#composing-directives.

There are some examples in composing-directives but they aren't covering this scenario.
Maybe a sub page of examples what can be done by composing patterns would be good?!

Thank you
Jens

[ktoso]

Page with patterns would also be good, but this one I think is basically a headerValue "or else..." which is why I think it makes sense to add to its page. We have examples of directives which have such additional documentation (simply as section inside their docs) :)

[jrudolph]

In #666, @zettelmj added the example to the Scala documentation. Would make sense to add something similar to the Java documented, not least for consistency.