How to split a large query parameter whose value contains a question mark

Is it possible to split a large query parameter into 2 smaller query parameters when the value contains a question mark character?

Examples:

URL received:

http://<HOST>:8000/path?apikey=123123?key1=value1

Query parameter:

"?apikey=123123?key1=value1"

Current response:

"args": {
    "apikey": "123123?key1=value1"
}

Desired result:

"?apikey=123123&AppID=value1"

This can be done through the Request Transformer Advanced plugin.

The query parameter for apikey is coming into kong as a long string. To split this up we will use the advanced templates inside the Request Transformer Advanced plugin. This will allow us to grab the value of apikey and split the string into 2 query parameters.

Important: Request Transformer Advanced applies its transformations in a fixed order (remove, rename, replace, add, append). If config.replace.querystring rewrites a parameter’s value, any config.add.querystring template that runs afterwards no longer sees that parameter’s original value — it only sees the already-replaced one. Since both steps in this recipe need to read from the original, unmodified apikey value, the add step must read it via kong.request.get_raw_query() (the raw, untouched querystring) rather than via query_params.apikey, which will already reflect the replace step’s output by the time add runs.

1. We need to create a function for config.replace.querystring. This will replace the value for apikey to just the data before the ?key1value. In the function we find the location of the ? and then create a substring of the starting point up until the ?.

   Doing this created the first query parameter of just apikey=123123.

   Save the file as test.lua.

   Sample Snippet:

   apikey:$((function() 
       local s=query_params.apikey:find("?") 
       local first=query_params.apikey:sub(1,s-1)
       return first
   end)())

   Copied!

2. Next we need to create a function for config.add.querystring. This will create a 2nd query parameter AppID with the value of value1. In this function we read the raw, original querystring (not query_params, which by this point has already been rewritten by Step 1’s replace transformation) via kong.request.get_raw_query(), find the location of the = after key1, and then create a substring of the remaining value.

   Doing this created the second query parameter of just AppID=value1.

   Save this file as test2.lua.

   Sample Snippet:

   AppID:$((function() 
       local raw = kong.request.get_raw_query()
       local s = raw:find("?")
       local second = raw:sub(s+1,#raw)
       local third = second:find("=")
       local secvalue = second:sub(third+1,#second)
       return secvalue
   end)())

   Copied!

3. Create the plugin via curl parsing in the 2 files.

   curl --location --request POST 'http://<HOST>:8001/plugins' \
   --header 'Kong-Admin-Token: <TOKEN>' \
   --form 'config.replace.querystring=@"/<pathToFile>/test.lua"' \
   --form 'config.add.querystring=@"/<pathToFile>/test2.lua"' \
   --form 'name="request-transformer-advanced"'

   Copied!

   Initial Request:

   
   http://<HOST>:8000/path?apikey=123123?key1=value1

   Copied!

   Final Response:

   
   "args": 
   {
   	"AppID": "value1",
   	"apikey": "123123"
   }

   Copied!

At this point the query parameters are split into 2 separate parameters.