Postman - how to loop request until I get a specific response?

Question

I'm testing API with Postman and I have a problem: My request goes to sort of middleware, so either I receive a full 1000+ line JSON, or I receive PENDING status and empty array of results:

{
  "meta": {
    "status": "PENDING",
    "missing_connectors_count": 0,
    "xxx_type": "INTERNATIONAL"
  },
  "results": []
}

The question is, how to loop this request in Postman until I will get status SUCCESS and results array > 0? When I'm sending those requests manually one-by-one it's ok, but when I'm running them through Collection Runner, "PENDING" messes up everything.

Latter

Related: https://mcmap.net/q/504005/-postman-get-gmail-email-id-iterate-through-email-ids. – Bone

Answer 1

I found an awesome post about retrying a failed request by Christian Baumann which allowed me to find a suitable approach to the exact same problem of first polling the status of some operation and only when it's complete run the actual tests.

The code I'd end up if I were you is:

const maxNumberOfTries = 3; // your max number of tries
const sleepBetweenTries = 5000; // your interval between attempts

if (!pm.environment.get("tries")) {
    pm.environment.set("tries", 1);
}

const jsonData = pm.response.json();

if ((jsonData.meta.status !== "SUCCESS" && jsonData.results.length === 0) && (pm.environment.get("tries") < maxNumberOfTries)) {
     const tries = parseInt(pm.environment.get("tries"), 10);
     pm.environment.set("tries", tries + 1);
     setTimeout(function() {}, sleepBetweenTries);
     postman.setNextRequest(request.name);
 } else {
     pm.environment.unset("tries");

     // your actual tests go here...
}

What I liked about this approach is that the call postman.setNextRequest(request.name) doesn't have any hardcoded request names. The downside I see with this approach is that if you run such request as a part of the collection, it will be repeated a number of times, which might bloat your logs with unnecessary noise.

The alternative I was considering is writhing a Pre-request Script which will do polling (by sending a request) and spinning until the status is some kind of completion. The downside of this approach is the need for much more code for the same logic.

Assignee

For Postman v6.5.2+, use pm.info.requestName rather than request.name. Ref: - #44690030 - learning.postman.com/docs/writing-scripts/script-references/… – Moravian

Answer 2

When waiting for services to be ready, or when polling for long-running job results, I see 4 basic options:

1. Use Postman collection runner or newman and set a per-step delay. This delay is inserted between every step in the collection. Two challenges here: it can be fragile unless you set the delay to a value the request duration will never exceed, AND, frequently, only a small number of steps need that delay and you are increasing total test run time, creating excessive build times for a common build server delaying other pending builds.
2. Use https://postman-echo.com/delay/10 where the last URI element is number of seconds to wait. This is simple and concise and can be inserted as a single step after the long running request. The challenge is if the request duration varies widely, you may get false failures because you didn't wait long enough.
3. Retry the same step until success with postman.setNextRequest(request.name);. The challenge here is that Postman will execute the request as fast as it can which can DDoS your service, get you black-listed (and cause false failures), and chew up a lot of CPU if run on a common build server - slowing other builds.
4. Use setTimeout() in a Pre-request Script. The only downside I see in this approach is that if you have several steps needing this logic, you end up with some cut & paste code that you need to keep in sync

Note: there are minor variations on these - like setting them on a collection, a collection folder, a step, etc.

I like option 4 because it provides the right level of granularity for most of my cases. Note that this appears to be the only way to "sleep" in a Postman script. Now standard javascript sleep methods like a Promise with async and await are not supported and using the sandbox's lodash _.delay(function() {}, delay, args[...]) does not keep script execution on the Pre-request script.

In Postman standalone app v6.0.10, set your step Pre-request script to:

console.log('Waiting for job completion in step "' + request.name + '"');

// Construct our request URL from environment variables
var url = request['url'].replace('{{host}}', postman.getEnvironmentVariable('host'));
var retryDelay = 1000;
var retryLimit = 3;

function isProcessingComplete(retryCount) {
    pm.sendRequest(url, function (err, response) {
        if(err) {
            // hmmm. Should I keep trying or fail this run? Just log it for now.
            console.log(err);
        } else {
            // I could also check for response.json().results.length > 0, but that
            // would omit SUCCESS with empty results which may be valid
            if(response.json().meta.status !== 'SUCCESS') {
                if (retryCount < retryLimit) {
                    console.log('Job is still PENDING. Retrying in ' + retryDelay + 'ms');
                    setTimeout(function() {
                        isProcessingComplete(++retryCount);
                    }, retryDelay);
                } else {
                    console.log('Retry limit reached, giving up.');
                    postman.setNextRequest(null);
                }
            }
        }
    });
}

isProcessingComplete(1);

And you can do your standard tests in the same step.

Note: Standard caveats apply to making retryLimit large.

Desex

Excellent explanation; however, I notice that the setTimeout() does not get honored in Collection runs. Doesn't matter if it's a 10 or 20 second wait, it still just runs the step and moves on. – Toothbrush

@Guy, did you find a workaround for running Collections? – Catfish

@Catfish wow, this is almost a year old! I've since moved on; I don't even use postman that much these days. Not bc I don't like it, just that I have different tasks. But thank you kindly. – Toothbrush

For others, Instead of using setTimeOut(), I'm using a combination of postman.setNextRequest() to control which endpoints are called next and posting to postman-echo.com/delay{int} to do my wait. – Catfish

Answer 3

Try this:

var body = JSON.parse(responseBody);

if (body.meta.status !== "SUCCESS" && body.results.length === 0){
  postman.setNextRequest("This_same_request_title");
} else {
  postman.setNextRequest("Next_request_title"); 
  /* you can also try postman.setNextRequest(null); */  
}

Uboat

You could end up in an infinite loop if your API is not working correctly. Ideally you should have a finite retry counter where the counter is also on the if condition. Once the counter reaches a limit you should exit to "Next_request_title" with appropriate error/warning. – Cracow

Answer 4

I was searching for an answer to the same question and thought of a possible solution as I was reading your question. Use postman workflow to rerun your request every time you don't get the response you're looking for. Anyway, that's what I'm gonna try.

postman.setNextRequest("request_name");

https://www.getpostman.com/docs/workflows

Tonicity

Answer 5

I didn't succeed to find the complete guidelines for this issue that's why I decided to invest some time and to describe all steps of the process from A to Z. I will be observing an example where we will need to pass through transaction ids and in each iteration to change query param for next transaction id from the list.

Step 1. Prepare your request

https://some url/{{queryParam}}

1. Add {{queryParam}} variable for changing it from pre-request script.
2. If you need a token for request you should add it here, in Authorization tab.
3. Save request to collection (Save button in the right corner). For demonstration purpose I will use "Transactions Request" name. We will need to use this name later on.

Step 2. Prepare pre-request script

In postman use tab Pre-request Script to change transactionId variable from query param to actual transaction id.

let ids = pm.collectionVariables.get("TransactionIds");
ids = JSON.parse(ids);

const id = ids.shift();
console.log('id', id)

postman.setEnvironmentVariable("transactionId", id);
pm.collectionVariables.set("TransactionIds", JSON.stringify(ids));

pm.collectionVariables.get - gets array of transaction ids from collection variables. We will set it up in Step 4.

ids.shift() - we use it to remove id that we will use from our ids list (to prevent running twice on the same id)

postman.setEnvironmentVariable("transactionId", id) - change transaction id from query param to actual transaction id

pm.collectionVariables.set("TransactionIds", JSON.stringify(ids)) - we are setting up a new collection of variables that now does not include the id that was handled.

Step 3. Prepare Tests

In postman use tab Tests to create a loop logic. Tests will be executed after the request execution, so we can use it to make next request.

let ids = pm.collectionVariables.get("TransactionIds");
ids = JSON.parse(ids);

if (ids && ids.length > 0){
    console.log('length', ids.length);
    postman.setNextRequest("Transactions Request");
} else {
    postman.setNextRequest(null);
}

postman.setNextRequest("Transactions Request") - calls a new request, in this case it will call the "Transactions Request" request

Step 4. Run Collections

In Postman from the left side bar you should choose Collections (click on it) and then choose a tab Variables.

This is the collection variables. In our example we used TransactionIds as a variable, so put in Current Value the array of transaction ids on which you want to loop.

Now you can click on Run (the button from right corner, near Save button) to run our loop requests.

You will be proposed to choose on which request you want to perform an action. Choose the request that we’ve created "Transactions Request".

It will run our request with pre-request script and with logic that we’ve set in Tests. In the end postman will open a new window with summary of our run.

Duggan