# Set a session variable before the performance test runs

**URL:** <https://community.gatling.io/t/set-a-session-variable-before-the-performance-test-runs/8825>\
**Category:** Gatling (Open-Source)\
**Created:** [March 20, 2024, 6:55pm UTC](https://community.gatling.io/t/set-a-session-variable-before-the-performance-test-runs/8825 "2024-03-20T18:55:57Z")\
**Posts on this page:** 9\
**Page:** 1

<div class="post-metadata">

**Author:** ![gkandale](https://avatars.discourse-cdn.com/v4/letter/g/c2a13f/32.png) [@gkandale](https://community.gatling.io/u/gkandale)\
**Post date:** [March 20, 2024, 6:55pm UTC](https://community.gatling.io/t/set-a-session-variable-before-the-performance-test-runs/8825/1 "2024-03-20T18:55:57Z")

</div>

Hi All, my application has known cookie in the test environment that I can use to start my performance test but part of that cookie changes in subsequent requests. Each virtual user I start can use that cookie the first time but then I have to change dynamically for the 2,3,4,nth time that vUser sends a request. In other words if I start with 10 vUsers I will get 10 passed requests but then All other requests will fail with a 401. This is my code, and I guess I am not setting the AWSALB after the first time through per vUser. Any suggestions? Will setting a flag at start time to false and using a doIfOrElse statement work?

This is the header stuff

```auto
public class BaseSimulation extends Simulation {
    public static Map<String, String> getSessionHeadersWithAWSALB(){
        Map<String, String> sessionHeaders = new HashMap<String, String>();
        sessionHeaders.put("Content-Type", "application/json");
        sessionHeaders.put("accept", "application/json");
        sessionHeaders.put("x-requested-with", "XMLHttpRequest" );
        sessionHeaders.put("pragma", "no-cache");
        return sessionHeaders;
    }
}

```

This is the API call

```auto
public class Metrics extends BaseSimulation {
    public static final ChainBuilder requestSomeMetricsHours =
            feed(jsonFile("cda/somemanager/zones.json").random())
                    .doIfEquals("#{accessible}", true).then(
                            feed(dateHourFeeder)
                                    .exec(http("Some Metrics Request")
                                                            .post("/api/v1/some/Metrics")
                                                            .headers(getSessionHeadersWithAWSALB())
                                                            .header("COOKIE", "X-Token=fdbcac451beba3c93e2f8b08a7919e210081f1813e4d6dddf83777cb3347e0f9; AWSALB=#{awsalb}; AWSALBCORS=#{awsalb}")
                                                            .body(ElFileBody("payloads/getSomeManagerMetrics.json")).asJson()
                                                            .check(status().is(200))
                                                            .check(status().saveAs("status"))
                                                            .check(bodyString().saveAs("responseBody"))
                                                            .check(headerRegex("Set-Cookie", "AWSALB=(.*?);").saveAs("awsalb"))
                                                            .check(jsonPath("$.endTime").exists().saveAs("endTime"))
                                                            .check(jsonPath("$.startTime").exists().saveAs("startTime"))
                                            ).exec(session -> {
                                                System.out.println(session.getString("awsalb"));
                                                return session;
                                            })
                                    );
}

```

```auto
public class SomeMetricsRequestsScenarios {
    public static final ScenarioBuilder scnSomeMetricsRequestsHoursScenario = SomeMetricsRequestsScenariosChains("Request Some Metrics Hourly",
            Metrics.requestSomeMetricsHours
    );

    public static ScenarioBuilder SomeMetricsRequestsScenariosChains(String name, ChainBuilder... chains) {
        return scenario(name).forever().on(
                exec(session -> {
                    Session awsalb = session.set("awsalb", "w5rhjuzJtx55UIcWx0jkmJHqXQrXavnXMma/XcR4WbZJofhSCo4aPbtNAmDIAhwGyuE9s0Y61s85D6qQOiAnZxqI6iOW3z6iqvBVPjoIeI+6UwuomNkz5xVs0aMT");
                    return awsalb;
                })
                        .exec(List.of(chains))
                .pause(2)
        );
    }
}

```

Simulation Code

```auto
public class EnergyMetricsRequestsSimulation {

    HashMap<String, List<PopulationBuilder>> scenario = new HashMap<>();

    {
        scenario.put("EnergyMetricsRequestHours",
                List.of(SomeMetricsRequestsScenarios.scnSomeMetricsRequestsHoursScenario.injectOpen(rampUsers(PerformanceProperties.userCount())
                                .during(PerformanceProperties.rampDuration()))
                        .protocols(httpProtocol))
        );
    }

    {
        setUp(scenario.get(PerformanceProperties.testScenario()))
                .maxDuration(Duration.ofSeconds(PerformanceProperties.testDuration()))
                .protocols(httpProtocol);
    }

```

I run the code with following mvn command

```auto
mvn gatling:test -Dgatling.simulationClass=com.cisco.performance.simulations.SomeMetricsRequestsSimulation -DvUsers="10" -DrampDuration="1" -DtestDuration="300" -DtestScenario="SomeMetricsRequestHours" -DmetricsHours="1"

```

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<div class="post-metadata">

**Author:** ![sbrevet](https://dub1.discourse-cdn.com/flex013/user_avatar/community.gatling.io/sbrevet/32/830_2.png) [@sbrevet](https://community.gatling.io/u/sbrevet)\
**Post date:** [March 20, 2024, 7:34pm UTC](https://community.gatling.io/t/set-a-session-variable-before-the-performance-test-runs/8825/2 "2024-03-20T19:34:07Z")

</div>

Hi @gkandale!

Cookies are a wild beast over there!

Did you consult the [documentation about them](https://docs.gatling.io/reference/script/protocols/http/helpers/#dealing-with-cookies)?

Cookie are naturally managed by gatling. In another word, the virtual user will send the cookie that the server ask in the `Set-Cookie` header of previous responses.

What I see is that your scenario management feel over-complicated (especially for a reproducer)

If I take your scenario:

```java
  ScenarioBuilder scn = scenario("My scenario").forever().on(
    exec(session -> session.set("awsalb", "w5rhjuzJtx55UIcWx0jkmJHqXQrXavnXMma/XcR4WbZJofhSCo4aPbtNAmDIAhwGyuE9s0Y61s85D6qQOiAnZxqI6iOW3z6iqvBVPjoIeI+6UwuomNkz5xVs0aMT")), // <- this will reset the value at each loop
    feed(jsonFile("cda/somemanager/zones.json").random()),
    doIf("#{accessible}").then(
      feed(dateHourFeeder),
      http("Some Metrics Request")
        .post("/api/v1/some/Metrics")
        .headers(getSessionHeadersWithAWSALB())
        .header("COOKIE", "X-Token=fdbcac451beba3c93e2f8b08a7919e210081f1813e4d6dddf83777cb3347e0f9; AWSALB=#{awsalb}; AWSALBCORS=#{awsalb}")
        .body(ElFileBody("payloads/getSomeManagerMetrics.json")).asJson()
        .check(status().is(200))
        .check(status().saveAs("status"))
        .check(bodyString().saveAs("responseBody"))
        .check(headerRegex("Set-Cookie", "AWSALB=(.*?);").saveAs("awsalb")) // <- this won't work
        .check(jsonPath("$.endTime").exists().saveAs("endTime"))
        .check(jsonPath("$.startTime").exists().saveAs("startTime"))
      ),
      exec(session -> {
        System.out.println(session.getString("awsalb"));
        return session;
      })
   )
  );

```

This code reset the awsalb session variable in each loop.  
And the headerRegex won’t capture the cookie

I hope that helps.

Cheers!

---

<div class="post-metadata">

**Author:** ![gkandale](https://avatars.discourse-cdn.com/v4/letter/g/c2a13f/32.png) [@gkandale](https://community.gatling.io/u/gkandale)\
**Post date:** [March 20, 2024, 7:56pm UTC](https://community.gatling.io/t/set-a-session-variable-before-the-performance-test-runs/8825/3 "2024-03-20T19:56:06Z")

</div>

Hey Sébastien, yes it is a beast ☹ Not happy about this…  
Do you have any suggestions on how I can set session variable awsalb with the known cookie before the scenario starts for each vUser and then set with the result of the headerRegex the subsequent times?

---

<div class="post-metadata">

**Author:** ![gkandale](https://avatars.discourse-cdn.com/v4/letter/g/c2a13f/32.png) [@gkandale](https://community.gatling.io/u/gkandale)\
**Post date:** [March 20, 2024, 8:01pm UTC](https://community.gatling.io/t/set-a-session-variable-before-the-performance-test-runs/8825/4 "2024-03-20T20:01:42Z")

</div>

BTW, the cookie is used to authenticate the api call

---

<div class="post-metadata">

**Author:** ![gkandale](https://avatars.discourse-cdn.com/v4/letter/g/c2a13f/32.png) [@gkandale](https://community.gatling.io/u/gkandale)\
**Post date:** [March 21, 2024, 8:13pm UTC](https://community.gatling.io/t/set-a-session-variable-before-the-performance-test-runs/8825/5 "2024-03-21T20:13:39Z")

</div>

I figured it out. I just flush the Cookies at the end of each transaction using **flushCookieJar()**, essentially disabling Gatling’s automatic Cookie handling. I guess whatever cookie management Gatling does is not compatible with the application and throws errors.

Oh and I had to set Accept-Encoding to None because gzip kept giving me “ **j.u.z.DataFormatException: invalid stored block lengths** ” errors.

New code:

```auto
feed(jsonFile("cda/somemanager/zones.json").random())
        .doIfEquals("#{accessible}", true).then(
                 feed(dateHourFeeder)
                        .exec(http("Some Metrics #{numberOfHours} hour(s) Request")
                                  .post("/some/Metrics")
                                  .headers(getSessionHeaders)
                                  .body(ElFileBody("performancepayload/getSomeManagerMetrics.json")).asJson()
                                  .check(status().is(200))
                                  .check(jsonPath("$.endTime").exists().saveAs("endTime"))
                                  .check(jsonPath("$.startTime").exists().saveAs("startTime"))
                        ).exec(flushCookieJar())
        );
}

```

**Accept Encoding Header:**

```auto
sessionHeaders.put("Accept-Encoding", "None");

```

---

<div class="post-metadata">

**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:** [March 21, 2024, 9:39pm UTC](https://community.gatling.io/t/set-a-session-variable-before-the-performance-test-runs/8825/6 "2024-03-21T21:39:23Z")

</div>

> I guess whatever cookie management Gatling does is not compatible with the application and throws errors

I kind of doubt that there’s something wrong on the Gatling side if you’re using a recent version.

> I had to set Accept-Encoding to None because gzip kept giving me “ **j.u.z.DataFormatException: invalid stored block lengths** ” errors.

Same. I’d say your zipped data is somehow corrupted. If there was a regression there, I think it would have been massively reported.

---

<div class="post-metadata">

**Author:** ![gkandale](https://avatars.discourse-cdn.com/v4/letter/g/c2a13f/32.png) [@gkandale](https://community.gatling.io/u/gkandale)\
**Post date:** [March 22, 2024, 1:19pm UTC](https://community.gatling.io/t/set-a-session-variable-before-the-performance-test-runs/8825/7 "2024-03-22T13:19:11Z")

</div>

> [@slandelle](#):
>
> I kind of doubt that there’s something wrong on the Gatling side if you’re using a recent version.

I didn’t say that there is something wrong with Gatling. I said something is not compatible with cookie management in Gatling and the application I am testing. Sorry if it sounded like I blamed Gatling.

> [@slandelle](#):
>
> Same. I’d say your zipped data is somehow corrupted. If there was a regression there, I think it would have been massively reported.

Again I did not blame Gatling for any issues. I am just telling people that if they see such an error message, check if Accept-Encoding: “gzip” is the issue and set to none to see if it is where the issue is coming from. It is a known issue in Java that gzip sometimes fails decompression (but on the other hand I only see this issue in Gatling and not in Chrome or Firefox)

> Here are some of the known issues with gzip in Java:  
> Gzip:  
> **High CPU utilization:** Gzip compression can cause high CPU utilization on the server side, especially when compressing large files.  
> **Performance degradation:** Gzip compression can cause performance degradation on the server side, especially when handling many requests simultaneously.  
> **Incorrect decompression** : Gzip decompression can sometimes fail, resulting in incorrect data being returned to the client.

Sorry for any offence I caused 😃 , I should stop sending responses late into the evening so I can word properly.

-GK

---

<div class="post-metadata">

**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:** [March 22, 2024, 8:31pm UTC](https://community.gatling.io/t/set-a-session-variable-before-the-performance-test-runs/8825/8 "2024-03-22T20:31:37Z")

</div>

No offense taken.

Both regarding cookies and gzip, I’d be very curious to see what you’re actually doing. Would you be able to provide a reproducer?

> but on the other hand I only see this issue in Gatling and not in Chrome or Firefox

Something I’d like to check for myself.

> Here are some of the known issues with gzip in Java:  
> Gzip:  
> **High CPU utilization:** Gzip compression can cause high CPU utilization on the server side, especially when compressing large files.  
> **Performance degradation:** Gzip compression can cause performance degradation on the server side, especially when handling many requests simultaneously.  
> **Incorrect decompression** : Gzip decompression can sometimes fail, resulting in incorrect data being returned to the client.

This is FUD, I don’t know where you found this.

> **High CPU utilization** / **Performance degradation**

This is the whole point of compression: you’re trading CPU usage for bandwidth, both on the client-side and the server-side (unless you store the content already compressed). The performance of the implementation in the JVM (it ships a version of the standard gzip library) is decent.

> **Incorrect decompression** : Gzip decompression can sometimes fail, resulting in incorrect data being returned to the client.

Gzip decompression fails:

- if the HTTP payload is corrupted
- if the client is buggy

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<div class="post-metadata">

**Author:** ![system](https://europe1.discourse-cdn.com/flex013/uploads/gatling2/original/2X/b/b148e0742de35c6280726cabf3ecd3de2d320f63.png) [@system](https://community.gatling.io/u/system)\
**Post date:** [April 21, 2024, 8:31pm UTC](https://community.gatling.io/t/set-a-session-variable-before-the-performance-test-runs/8825/9 "2024-04-21T20:31:45Z")

</div>

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