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How to handle HTTP POSTs with a changing number of name-value pairs

December 22nd, 2008 Posted by Stuart Moncrieff 7 Comments »

Occasionally you will find that you need to create a VuGen script for a web application which changes the number of name-value pairs which are sent with a POST request. This tech tip shows you how to handle this situation by dynamically constructing a POST body.

In the example below, you can see that the web_submit_data function for the updateItemsFromSearch request (which adds items to a shopping cart) has six item IDs and six item quantities. The web_subit_data function presents the name-value pairs of the POST request in an easy to read format, but doesn’t give too many clues as to how you might handle the case of submitting a varying numbers of item IDs, without writing an if statement and having separate web_submit_data functions for every possible number of items.

Fortunately, there is an easy way to do this. Read on…

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web_submit_data("updateItemsFromSearch.do", 
	"Action=http://www.example.com.au/catalog/updateItemsFromSearch.do", 
	"Method=POST", 
	"TargetFrame=", 
	"RecContentType=text/html", 
	"Referer=http://www.example.com.au/catalog/search.do?key=0/46EF7F373045033002000000AC193D36", 
	"Snapshot=t10.inf", 
	"Mode=HTML", 
	ITEMDATA, 
	"Name=sortOption", "Value=PRICE_ASCENDING", ENDITEM, 
	"Name=pageselect", "Value=10", ENDITEM, 
	"Name=page", "Value=", ENDITEM, 
	"Name=itemPageSize", "Value=10", ENDITEM, 
	"Name=next", "Value=addToBasket", ENDITEM, 
	"Name=itemkey", "Value=46EF7F373045033002000000AC193D364785F195AFD7401600000000AC193D51", ENDITEM, 
	"Name=order", "Value=", ENDITEM, 
	"Name=itemquantity", "Value=1", ENDITEM, 
	"Name=isExtendedResult", "Value=null", ENDITEM, 
	"Name=display_scenario", "Value=products", ENDITEM, 
	"Name=contractkey", "Value=", ENDITEM, 
	"Name=contractitemkey", "Value=", ENDITEM, 
	"Name=item[0].itemID", "Value=46EF7F373045033002000000AC193D364785F195AFD7401600000000AC193D51", ENDITEM, 
	"Name=item[0].quantity", "Value=1", ENDITEM, 
	"Name=item[1].itemID", "Value=46EF7F373045033002000000AC193D3640EBE620771F00A500000000AC193D52", ENDITEM, 
	"Name=item[1].quantity", "Value=1", ENDITEM, 
	"Name=item[2].itemID", "Value=46EF7F373045033002000000AC193D363F4191CB824400F3E1000000AC193D38", ENDITEM, 
	"Name=item[2].quantity", "Value=1", ENDITEM, 
	"Name=item[3].itemID", "Value=46EF7F373045033002000000AC193D36464DB497A33B005602000000AC193D51", ENDITEM, 
	"Name=item[3].quantity", "Value=1", ENDITEM, 
	"Name=item[4].itemID", "Value=46EF7F373045033002000000AC193D36484A7C7E995A8034E1008000AC193D51", ENDITEM, 
	"Name=item[4].quantity", "Value=1", ENDITEM, 
	"Name=item[5].itemID", "Value=46EF7F373045033002000000AC193D36484E990F2564C27EE1008000AC193D35", ENDITEM, 
	"Name=item[5].quantity", "Value=1", ENDITEM, 
	LAST);

First, let’s take a look at what VuGen actually sends to the web server…

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POST /catalog/updateItemsFromSearch.do HTTP/1.1\r\n
Content-Type: application/x-www-form-urlencoded\r\n
Cache-Control: no-cache\r\n
Referer: http://www.example.com.au/catalog/search.do?key=0/46EF7F373045033002000000AC193D36\r\n
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)\r\n
Accept-Encoding: gzip, deflate\r\n
Accept-Language: en-us\r\n
Accept: */*\r\n
Connection: Keep-Alive\r\n
Host: www.example.com.au\r\n
Cookie: JSESSIONID=(J2EE5934700)ID1010337953DB11208117568232223992End; saplb_*=(J2EE5934700)5934753\r\n
Content-Length: 896\r\n
\r\n
sortOption=PRICE_ASCENDING&pageselect=10&page=&itemPageSize=10&next=addToBasket&itemkey=46
EF7F373045033002000000AC193D364785F195AFD7401600000000AC193D51&order=&itemquantity=1&isExt
endedResult=null&display_scenario=products&contractkey=&contractitemkey=&item%5B0%5D.itemI
D=46EF7F373045033002000000AC193D364785F195AFD7401600000000AC193D51&item%5B0%5D.quantity=1&
item%5B1%5D.itemID=46EF7F373045033002000000AC193D3640EBE620771F00A500000000AC193D52&item%5
B1%5D.quantity=1&item%5B2%5D.itemID=46EF7F373045033002000000AC193D363F4191CB824400F3E10000
00AC193D38&item%5B2%5D.quantity=1&item%5B3%5D.itemID=46EF7F373045033002000000AC193D36464DB
497A33B005602000000AC193D51&item%5B3%5D.quantity=1&item%5B4%5D.itemID=46EF7F37304503300200
0000AC193D36484A7C7E995A8034E1008000AC193D51&item%5B4%5D.quantity=1&item%5B5%5D.itemID=46
EF7F373045033002000000AC193D36484E990F2564C27EE1008000AC193D35&item%5B5%5D.quantity=1

As you can see, the name-value pairs that were so easy to read in the web_submit_data function are really just sent as a big blob of text, with each name-value pair separated by an ampersand (&) and some characters URL-encoded (e.g. “[” becomes “%5B”).

We can make our VuGen script look more like the actual HTTP request by regenerating the script with web_custom_request selected. Select Tools > Regenerate Script, then select the recording option of URL-based script. Under URL Advanced, select Use web_custom_request only.

You script will now look something like this…

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web_custom_request("updateItemsFromSearch.do", 
	"URL=http://www.example.com.au/catalog/updateItemsFromSearch.do", 
	"Method=POST", 
	"Resource=0", 
	"RecContentType=text/html", 
	"Referer=http://www.example.com.au/catalog/search.do?key=0/46EF7F373045033002000000AC193D36", 
	"Snapshot=t207.inf", 
	"Mode=HTTP", 
	"Body=sortOption=PRICE_ASCENDING&pageselect=10&page=&itemPageSize=10&next=addToBasket&itemkey=46EF7F373045033002000000AC193D364785F195AFD7401600000000AC193D51&order=&itemquantity=1&isExtendedResult=null&display_scenario=products&contractkey=&contractitemkey=&item%5B0%5D.itemID=46EF7F373045033002000000AC193D364785F195AFD7401600000000AC193D51&item%5B0%5D.quantity=1&item%5B1%5D.itemID=46EF7F373045033002000000AC193D3640EBE620771F00A500000000AC193D52&item%5B1%5D.quantity=1&item%5B2%5D.itemID="
	"46EF7F373045033002000000AC193D363F4191CB824400F3E1000000AC193D38&item%5B2%5D.quantity=1&item%5B3%5D.itemID=46EF7F373045033002000000AC193D36464DB497A33B005602000000AC193D51&item%5B3%5D.quantity=1&item%5B4%5D.itemID=46EF7F373045033002000000AC193D36484A7C7E995A8034E1008000AC193D51&item%5B4%5D.quantity=1&item%5B5%5D.itemID=46EF7F373045033002000000AC193D36484E990F2564C27EE1008000AC193D35&item%5B5%5D.quantity=1", 
	LAST);

The next step is to dynamically construct the string that will be sent as the body argument of the web_custom_request function. Do this by

  • Correlate your values using ORD=All (line 4) from the response to your search request (line 15).
  • Write a for loop to build a parameter containing your POST body (line 31). Save time by using lr_paramarr functions to extract the values from the parameter array you created with web_reg_save_param(”Ord=All”, …).
  • Use web_custom_request to send your POST body.
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lr_start_transaction("search for product");
 
// Save all item IDs returned by product search
web_reg_save_param("ItemID_array",
	"LB=<a href=\"javascript:seeSingleItem('",
	"RB='",
	"Ord=All",
	"Search=Body",
	"RelFrameId=1",
	"IgnoreRedirections=Yes",
	LAST);
 
web_reg_find("Text=Search Results for {SearchTerm}", LAST);
 
web_url("Search", 
	"URL=http://www.example.com.au/catalog/search.do?key={SearchTerm}", 
	"TargetFrame=center2", 
	"Resource=0", 
	"RecContentType=text/html", 
	"Referer=http://www.example.com.au/", 
	"Snapshot=t8.inf", 
	"Mode=HTML", 
	LAST);
 
lr_end_transaction("search for product",LR_AUTO);
	lr_think_time(5);
lr_start_transaction("add to basket");
 
// Construct variable length POST body.
lr_save_string(lr_eval_string("sortOption=PRICE_ASCENDING&pageselect=10&page=&itemPageSize=10&next=addToBasket&itemkey={ItemIDarray_1}&order=&itemquantity=1&isExtendedResult=null&display_scenario=products&contractkey=&contractitemkey="), "Body");
for (i=0; i<lr_paramarr_len("ItemIDarray"); i++) {
	lr_save_string(lr_paramarr_idx("ItemIDarray", i+1), "ItemID");
	lr_save_int(i, "ItemIndex");
	lr_save_string(lr_eval_string("{Body}&item%5B{ItemIndex}%5D.itemID={ItemID}&item%5B{ItemIndex}%5D.quantity=1"), "Body");
}
 
web_reg_find("Text=Mini Shopping Basket", LAST);
 
web_custom_request("updateItemsFromSearch.do", 
	"URL=http://www.example.com.au/catalog/updateItemsFromSearch.do", 
	"Method=POST", 
	"Resource=0", 
	"RecContentType=text/html", 
	"Referer=http://www.example.com.au/catalog/search.do?key={SearchTerm}", 
	"Snapshot=t207.inf", 
	"Mode=HTTP", 
	"Body={Body}",  // use dynamically constructed POST body.
	LAST);
 
lr_end_transaction("add to basket",LR_AUTO);

This is a useful technique to add to your repertoire.

 

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7 Responses to “How to handle HTTP POSTs with a changing number of name-value pairs”

  1. Gorakshnath Says:
    April 14th, 2009 at 3:56 am

    Awesome Work !! Thanks Stuart

  2. Stuart Moncrieff Says:
    May 7th, 2009 at 1:23 pm

    Scott Moore has an alternative solution here: http://www.loadtester.com/vugen-dynamic-data-websubmitdata

  3. meey s. Says:
    June 1st, 2009 at 7:19 pm

    Hi,
    Thanks this is a great topic. I have been trying to find a way to get this done without having to change the arguments in the web_submit_data functions whenever the project team asks to change the number of name-value pairs that they want me to run the test with.

    Btw, I would like to ask if the lr_paramarr_idx and lr_paramarr_len is a function found in higher LR versions. I have tried looking for it in LR8.1 function library but these functions do not exist. Is there a work-around for this without having to use C string functions? Thanks!

    [Stuart's Reply: Yes, the lr_paramarr functions are fairly recent. They are definitely not in LoadRunner 8.1.4.]

  4. Aju Says:
    October 21st, 2009 at 9:04 pm

    Scott’s solution is quick n dirty work around and does not scale beyond a predefined limit. I’ve been using web_custom_request for generating dynamic name-value pairs and is a very elegant solution.

    The code above would be complete if you add “convert=HTML_TO_URL” argument to the web_reg_save_param call that builds ItemID_array, so that the reserved characters like &, ?, @ etc. within the captured values (if any) will be converted to percent encoding.

  5. Stuart Moncrieff Says:
    October 28th, 2009 at 12:10 pm

    Thank you for your improvement to my code.

    Cheers,
    Stuart.

  6. Stan Desyatnikov Says:
    November 26th, 2009 at 12:12 am

    Hi,
    Thanks for the very useful tip.

    One note: “Save time by using lr_paramarr functions to extract the values from the parameter array you created with web_reg_find.” likely should end with “… you created with web_reg_save_param(”ItemID_array…” ?

  7. Stuart Moncrieff Says:
    November 26th, 2009 at 10:30 am

    Nice pickup Stan! I have corrected the article.

    Cheers,
    Stu.

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