# Wanting to extract some request variables, hash, insert into header **URL:** \ **Category:** Gatling (Open-Source)\ **Created:** [August 28, 2013, 9:30am UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553 "2013-08-28T09:30:38Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![Dino\_Fancellu](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@Dino\_Fancellu](https://community.gatling.io/u/Dino_Fancellu)\ **Post date:** [August 28, 2013, 9:30am UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/1 "2013-08-28T09:30:38Z")
Using Gatling 2.0.0-M3a I have to set a header value to an encryption hash based on the uri, method, datetime, any body. I can get this all to work if I do it all manually, i.e. call the hashing function with the values I am going to use. However if there a way from my Get/PostHttpRequestBuilder to do a header(“hash”,somefunc), with somefunc getting the above uri, method, body and passing it to the hashing function? i.e. I don’t want to have to have to repeat myself, but easily set the hash value based on what is already in the request Thanks. ---
**Author:** ![Excilys](https://avatars.discourse-cdn.com/v4/letter/e/8797f3/32.png) [@Excilys](https://community.gatling.io/u/Excilys)\ **Post date:** [August 28, 2013, 9:54am UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/2 "2013-08-28T09:54:22Z")
Nope ---
**Author:** ![Dino\_Fancellu](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@Dino\_Fancellu](https://community.gatling.io/u/Dino_Fancellu)\ **Post date:** [August 28, 2013, 10:08am UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/3 "2013-08-28T10:08:26Z")
I suspected as much. What if AbstractHttpRequestBuilder had a getAttributes:HttpAttributes method? Its a case class, immutable. Just would be useful to do some post-processing on a builder as described above. Thanks. Dno. ---
**Author:** ![Excilys](https://avatars.discourse-cdn.com/v4/letter/e/8797f3/32.png) [@Excilys](https://community.gatling.io/u/Excilys)\ **Post date:** [August 28, 2013, 12:32pm UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/4 "2013-08-28T12:32:07Z")
What for? AbstractHttpRequestBuilder.httpAttributes is public. ---
**Author:** ![Dino\_Fancellu1](https://avatars.discourse-cdn.com/v4/letter/d/7cd45c/32.png) [@Dino\_Fancellu1](https://community.gatling.io/u/Dino_Fancellu1)\ **Post date:** [August 28, 2013, 12:40pm UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/5 "2013-08-28T12:40:37Z")
Really? val getOrderDetails=http(“GetOrderDetails”) .get(url) println (getOrderDetails.httpAttributes) won’t compile. ---
**Author:** ![Excilys](https://avatars.discourse-cdn.com/v4/letter/e/8797f3/32.png) [@Excilys](https://community.gatling.io/u/Excilys)\ **Post date:** [August 28, 2013, 12:52pm UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/6 "2013-08-28T12:52:41Z")
Ah, you’re right. Anyway, you can manually create a RequestBuilder, the constructors are public. ---
**Author:** ![Dino\_Fancellu](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@Dino\_Fancellu](https://community.gatling.io/u/Dino_Fancellu)\ **Post date:** [August 29, 2013, 9:24am UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/7 "2013-08-29T09:24:22Z")
I’m not sure how that helps me. I build up a request, the url uses an orderid from a feed, so will be different with each request, and I have to send a hash header value based on that dynamic url, else the receiving url won’t accept my request. Dino. ---
**Author:** ![Dino\_Fancellu](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@Dino\_Fancellu](https://community.gatling.io/u/Dino_Fancellu)\ **Post date:** [August 29, 2013, 9:34am UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/8 "2013-08-29T09:34:48Z")
Linked to this, might be a solution, just wondering. I feed in some values thus: val orderIds = ((1 to 1000) map (x=\>Map(“oid”-\>x)) toArray).circular … .feed(orderIds) So I have a 1000 repeating “oid” values. Now, its easy to simply insert that value into a header like this: .header(“oid”,"${oid}") However, is there a good way I could call some custom function based on that ${oid} ? e.g. .header(“oid”,“myfunc(${oid})”) Thanks. ---
**Author:** ![Excilys](https://avatars.discourse-cdn.com/v4/letter/e/8797f3/32.png) [@Excilys](https://community.gatling.io/u/Excilys)\ **Post date:** [August 29, 2013, 9:47am UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/9 "2013-08-29T09:47:37Z")
Ah, OK! You have to understand how Gatling works with EL and Expressions. Most DSL methods take Expression[T] parameters. Expression is a type alias for (Session) =\> Validation[T], meaning a function that takes a Session input and return a Validation (something that can either be a Success containing the value or a Failure containing the error message). Then, how is it you can pass Strings to methods taking Expression[String] parameters? There’s a implicit conversion that happens if you pass a String to a method expecting an Expression[String]! It parses the String and resolve whatever ${} EL it might contains. So, the point is, as the documentation states, that you can explicitly pass an Expression[String]. If you do so, you can’t use EL there, as the implicit conversion doesn’t happen. So if you want to use Session attributes, you have to do it programatically. .header(“oid”, session =\> session(“oid”).validate[String].map(myfunc)) where myfunc if a def that takes a String and returns a String. Get it? ---
**Author:** ![Dino\_Fancellu](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@Dino\_Fancellu](https://community.gatling.io/u/Dino_Fancellu)\ **Post date:** [August 29, 2013, 10:25am UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/10 "2013-08-29T10:25:41Z")
Thanks, that made is very clear. Should be able to do some good things with that functionality now. I understand that in using 2.x I’m rather on the bleeding edge. You might want to add the above to the 2.,x wiki page for others. Dino. ---
**Author:** ![Dino\_Fancellu](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@Dino\_Fancellu](https://community.gatling.io/u/Dino_Fancellu)\ **Post date:** [August 29, 2013, 11:11am UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/11 "2013-08-29T11:11:24Z")
Ok, progress: def url:Expression[String]={ _(“oid”).validate[String].map("/myurl//"+_) } later on: .get(url) However I also have another Expression[String] function that uses that url def expectedHmac:Expression[String]={ session=\> hmacgen.generateHmac( url(session).toString. // how do I get the Validation to turn to a string? It comes back as Success(/theurl). I want the url “GET”, x\_date, “”).getHmac() } How do I turn the Validation into a string? ---
**Author:** ![Excilys](https://avatars.discourse-cdn.com/v4/letter/e/8797f3/32.png) [@Excilys](https://community.gatling.io/u/Excilys)\ **Post date:** [August 29, 2013, 11:21am UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/12 "2013-08-29T11:21:04Z")
>      def url:Expression[String]={ >       \_("oid").validate[String].map("/myurl//"+\_) >     } If I may, that's a matter of style, but I personally find the first \_ unreadable. Matter of taste maybe. > later on: > > .get(url) > > However I also have another Expression[String] function that uses that url > > def expectedHmac:Expression[String]={ >       session=\> > >         hmacgen.generateHmac( > url(session).toString. // how do I get the Validation to turn to a string? > It comes back as Success(/theurl). I want the url > "GET", x\_date, > "").getHmac() >     } That's the other way around: you first get a Validation of your url, then map its content: def expectedHmac:Expression[String]= { session =\> url(session).map(url =\> hmacgen.generateHmac(url, "GET", x\_date).getHmac) } ---
**Author:** ![Dino\_Fancellu](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@Dino\_Fancellu](https://community.gatling.io/u/Dino_Fancellu)\ **Post date:** [August 29, 2013, 12:11pm UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/13 "2013-08-29T12:11:58Z")
Ok, thought as much, that just struck me as a bit odd, having to do a map just to get the value. Would be nice to have a method to get the content. A get/getOrElse in the Option style? If I have to get several values from a bag of session attributes then it gets a bit abstruse. BTW, first url could be even shorter def url:Expression[String]=_(“oid”).map("/myurl/"+_) Ha! Anyway, got my stuff working this way: def urlString:(Session=\>String)={ “/myurl/orderid\_”+\_(“oid”).as[Integer] } def url:Expression[String]=urlString(\_) def expectedHmac:Expression[String]={ session=\> hmacgen.generateHmac( urlString(session), “GET”, x\_date, “”).getHmac() } then .get(url) .header(“Authorization”,expectedHmac) Thanks so much for all your help. Dino. ---
**Author:** ![Excilys](https://avatars.discourse-cdn.com/v4/letter/e/8797f3/32.png) [@Excilys](https://community.gatling.io/u/Excilys)\ **Post date:** [August 29, 2013, 12:34pm UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/14 "2013-08-29T12:34:34Z")
> Ok, thought as much, that just struck me as a bit odd, having to do a map > just to get the value. That's because you still think imperative style and not functional. With map, You didn't just "get the value", you converted a Validation of the url into a Validation of hmac without having to think about the Validation being a Success or a Failure and got the potential error message automatically conveyed for you. > Would be nice to have a method to get the content. A get/getOrElse in the > Option style? get is a big No way! It's just a dangerous stuff that might produce a NPE, being there for imperative developers. getOrElse is a no too, as you'd lose the potential error message if the Validation is a Failure. You can pattern match on Success and Failure if you want. You have to realize that Validation potentially contains more information than just the success object. > If I have to get several values from a bag of session attributes then it > gets a bit abstruse. Nope, that's actually very neat: for {   a \<- session("a").validation[A]   b \<- session("b").validation[B]   c \<- session("c").validation[C] } yield doSomething(a, b, c) > BTW, first url could be even shorter > > def url:Expression[String]=\_("oid").map("/myurl/"+\_) Shorter doesn't mean more readable, coding is no character typing race 😉 > Ha! > > Anyway, got my stuff working this way: > >     def urlString:(Session=\>String)={ >       "/myurl/orderid\_"+\_("oid").as[Integer] >     } > > def url:Expression[String]=urlString(\_) > >      def expectedHmac:Expression[String]={ >       session=\> > >         hmacgen.generateHmac( > urlString(session), > "GET", x\_date, > "").getHmac() >     } > > then > > .get(url) > .header("Authorization",expectedHmac) Well, as[Integer] might throw exceptions (for example, if oid is missing for whatever reason), which would harm performance. You're used to imperative style, and starting this way is fine, but I advice at some point you try to wrap your mind around functional style and use validate instead of as. ---
**Author:** ![Dino\_Fancellu](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@Dino\_Fancellu](https://community.gatling.io/u/Dino_Fancellu)\ **Post date:** [August 29, 2013, 2:16pm UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/15 "2013-08-29T14:16:52Z")
Ok, more idiomatic: def url:Expression[String]={ sess=\> sess(“oid”).validate[Int].map("/myurl/orderid\_"+\_) } def expectedHmac:Expression[String]={ sess=\> url(sess).map(hmacgen.generateHmac(\_,“GET”, x\_date,"").getHmac()) } ---
**Author:** ![Excilys](https://avatars.discourse-cdn.com/v4/letter/e/8797f3/32.png) [@Excilys](https://community.gatling.io/u/Excilys)\ **Post date:** [August 29, 2013, 2:21pm UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/16 "2013-08-29T14:21:24Z")
Much better IMHO 🙂 Just make them val instead of def so you don’t create a new function instance every time and you’ll be good. ---
**Author:** ![Dino\_Fancellu](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@Dino\_Fancellu](https://community.gatling.io/u/Dino_Fancellu)\ **Post date:** [August 29, 2013, 2:25pm UTC](https://community.gatling.io/t/wanting-to-extract-some-request-variables-hash-insert-into-header/553/17 "2013-08-29T14:25:19Z")
Doh! Dino.