# Unsure of how to pass Map\[String, String\] headers from session feeder into request **URL:** \ **Category:** Gatling (Open-Source)\ **Created:** [July 28, 2022, 5:45pm UTC](https://community.gatling.io/t/unsure-of-how-to-pass-map-string-string-headers-from-session-feeder-into-request/6991 "2022-07-28T17:45:54Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![AlbinoTheMouse](https://dub1.discourse-cdn.com/flex013/user_avatar/community.gatling.io/albinothemouse/32/961_2.png) [@AlbinoTheMouse](https://community.gatling.io/u/AlbinoTheMouse)\ **Post date:** [July 28, 2022, 5:45pm UTC](https://community.gatling.io/t/unsure-of-how-to-pass-map-string-string-headers-from-session-feeder-into-request/6991/1 "2022-07-28T17:45:54Z")
I have a json feeder that is generated from live traffic which contains headers and request urls. I cannot figure out how to get the headers to be picked up from the session and placed into the request. My first approach was: ```auto scenario(name) .feed(feeder) .exec( http("API call") .get("#{Url}") .headers("#{Header}") .check(status.is(200)) ) .inject( rampUsersPerSec(usersPerSec) to maxUsers during(rampSec seconds), constantUsersPerSec(maxUsers) during(constSec seconds)) .protocols(httpConf) ``` However, I quickly saw that the session ETL will not work for `Headers()`. I have not seen a way to access the `session` while inside the call to `headers`, so I haven’t been able to do `.headers(session("Header")`. Then I tried ```auto scenario(name) .feed(feeder) .exec{session => val url = session("Url").as[String] val headers = session("Header").as[Map[String, String]] http("API call") .get(url) .headers(headers) .check(status.is(200)) session } .inject( rampUsersPerSec(usersPerSec) to maxUsers during(rampSec seconds), constantUsersPerSec(maxUsers) during(constSec seconds)) .protocols(httpConf) ``` However this results in no requests being sent. I assume it’s because I return the original `session` from the `exec` call instead of a new session modified by the call to `http` (I’m new to scala, not sure of the terminology here). I have not figured out how to return a new `session` with the http request instead of the old one. Is there a modification I can make to either of these approaches that will work? Is there something else that I’ve not considered? I’d appreciate any advice on how to achieve this. Thanks! ---
**Author:** ![shoaib42](https://dub1.discourse-cdn.com/flex013/user_avatar/community.gatling.io/shoaib42/32/844_2.png) [@shoaib42](https://community.gatling.io/u/shoaib42)\ **Post date:** [July 28, 2022, 6:11pm UTC](https://community.gatling.io/t/unsure-of-how-to-pass-map-string-string-headers-from-session-feeder-into-request/6991/2 "2022-07-28T18:11:39Z")
What you did in the second try is return a session, the http().get().header… will just create a HttpRequestBuilder and do nothing with it. If you really want to go down the rabbit hole and end up shooting yourself in the foot you can try TrieMap [Scala Standard Library 2.12.8 - scala.collection.concurrent.TrieMap](https://www.scala-lang.org/api/2.12.8/scala/collection/concurrent/TrieMap.html) , your milage will definitely vary. Simplest is to have the headers set like the following ```auto .header("foo", "#{fooval}") .header("bar", "#{barval}") ``` ---
**Author:** ![AlbinoTheMouse](https://dub1.discourse-cdn.com/flex013/user_avatar/community.gatling.io/albinothemouse/32/961_2.png) [@AlbinoTheMouse](https://community.gatling.io/u/AlbinoTheMouse)\ **Post date:** [July 28, 2022, 8:09pm UTC](https://community.gatling.io/t/unsure-of-how-to-pass-map-string-string-headers-from-session-feeder-into-request/6991/3 "2022-07-28T20:09:51Z")
Thanks for the reply! Do you know what I can do for header values that may or may not be present? This code fails if `sometimes-header` is not present. ```auto .header("sometimes-header", "#{Header.sometimes-header}") ``` It seems like I cannot do this either ```auto .header("sometimes-header", session("Header").as[Map[String,String]].getOrElse("sometimes-header", "default-value")) ``` The map is also immutable, so I cannot insert an item into it either. ---
**Author:** ![shoaib42](https://dub1.discourse-cdn.com/flex013/user_avatar/community.gatling.io/shoaib42/32/844_2.png) [@shoaib42](https://community.gatling.io/u/shoaib42)\ **Post date:** [July 28, 2022, 10:04pm UTC](https://community.gatling.io/t/unsure-of-how-to-pass-map-string-string-headers-from-session-feeder-into-request/6991/4 "2022-07-28T22:04:19Z")
Not sure why you you can’t do the #2 option, try this, you are not mutating the Map object, you are getting the Map Object stored at “Header” in the session HashMap, then doing a getOrElse ```auto .header("sometimes-header", session => session("Header").as[Map[String,String]].getOrElse("sometimes-header", "default-value")) ``` ---
**Author:** ![AlbinoTheMouse](https://dub1.discourse-cdn.com/flex013/user_avatar/community.gatling.io/albinothemouse/32/961_2.png) [@AlbinoTheMouse](https://community.gatling.io/u/AlbinoTheMouse)\ **Post date:** [July 29, 2022, 1:35pm UTC](https://community.gatling.io/t/unsure-of-how-to-pass-map-string-string-headers-from-session-feeder-into-request/6991/5 "2022-07-29T13:35:24Z")
Thanks for the suggestion. That gives me the following error: ```auto type mismatch; found : Object required: io.gatling.commons.validation.Validation[String] .header("sometimes-header", session => session("Header").as[Map[String,String]].getOrElse("sometimes-header", "default-value")) ``` Can I perform a cast here to resolve it? Apologies if this is a basic question. ---
**Author:** ![slandelle](https://dub1.discourse-cdn.com/flex013/user_avatar/community.gatling.io/slandelle/32/4_2.png) [@slandelle](https://community.gatling.io/u/slandelle)\ **Post date:** [July 29, 2022, 1:41pm UTC](https://community.gatling.io/t/unsure-of-how-to-pass-map-string-string-headers-from-session-feeder-into-request/6991/6 "2022-07-29T13:41:04Z")
Not `header`. `headers`. ---
**Author:** ![shoaib42](https://dub1.discourse-cdn.com/flex013/user_avatar/community.gatling.io/shoaib42/32/844_2.png) [@shoaib42](https://community.gatling.io/u/shoaib42)\ **Post date:** [July 29, 2022, 1:57pm UTC](https://community.gatling.io/t/unsure-of-how-to-pass-map-string-string-headers-from-session-feeder-into-request/6991/7 "2022-07-29T13:57:37Z")
Finally I got to my workspace. What you had an issue was getOrElse was returning a Success(String). Here is a solution I tested and works ```auto val getBooks = http("getListOfBooks") .get("/list") .header("Authorization", "#{auth}") .queryParam("limit", "#{limit}") .header("sometimes-header", session => session("Header").as[Map[String,String]].getOrElse("sometimes-header", "default-value").toString) // intelliJ sensed that .toString is not necessary but it actually is :/ val scn = scenario("test") .exec(_.setAll(("auth", "foobar"), ("limit", 10), ("Header", Map[String,String]()))) .exec(getBooks) .exec(_.set("Header", Map("sometimes-header" -> "present-value"))) //this sets the value of sometimes-header .exec(getBooks) setUp(scn.inject(atOnceUsers(1))).protocols(httpProtocol) ``` The first execution uses the default value since we have an empty Map, ```auto ========================= HTTP request: GET https://localhost:8443/list?limit=10 headers: accept-language: en-US,en;q=0.5 accept-encoding: gzip, deflate sometimes-header: default-value accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Authorization: foobar user-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:101.0) Gecko/20100101 Firefox/101.0 host: localhost:8443 ========================= ``` The second time we set a value of the `sometimes-header` and vola we use that ```auto ========================= HTTP request: GET https://localhost:8443/list?limit=10 headers: accept-language: en-US,en;q=0.5 accept-encoding: gzip, deflate sometimes-header: present-value accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Authorization: foobar user-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:101.0) Gecko/20100101 Firefox/101.0 host: localhost:8443 ========================= ```