@nolim1t

This has taken me some time to figure out. But I guess one of my new initiatives is to build microservices without running server infrastructure because its much more cost efficient to do so. (Yes it’s centralized, blahblah… but blockchain tech is still very new. Eventually I want to be able to read identity information off my blog onto the public blockchain).

Why am I pushing AWS lambda? Because it takes time and resources to set up a server farm properly. Or you are locked into a platform such as heroku (which I still think is great if you’re deploying standard web apps). Or parse/firebase/backendless if you’re into mobile app development. Those backend as a service platforms are great however, look whats happening with parse its good to have many options available. I don’t evangelize lots of technologies. For me, hackers are like painters/artists - they focus on the best way to get the job done given tools available.

I’ve figured out the GET part easily enough, but the POST part through API gateway requires the format into application/json and not application/x-www-form-urlencoded

This is ok if you’re building your own APIs, however if you want to be a good internet citizen and stick with the usual standards - most APIs actually use application/x-www-form-urlencoded for POST requests.

But I finally found a solution (and it seems to work out quite well. Almost too well in fact.

The Steps

1. Amazon API Gateway -> Click “Create API”.
2. Enter in the API details. Something descriptive will do
3. Click “Create API”.
4. Click “Create Resource”.
5. Enter in details of the resource (this is how you would access the API)
6. Click “Create Resource”.
7. Click “Create Method”.
8. Select “POST” or “GET” (this is how you would request the resource)
9. Integration type = “Lambda function”, pick region as appropriate, write code as appropriate to action / store form data.
10. Click “Save”, click “Ok” to grant permission.
11. Click “Integration Request”.
12. Click “Mapping Templates”.
13. Click “Add mapping template”.
14. Content-Type is “application/x-www-form-urlencoded” and click the tick.
15. Click “application/x-www-form-urlencoded”.
16. Click the pencil icon next to “Input passthrough”.
17. Select “Mapping template”.
18. Paste the following into the template box. Don’t forget to include any stage variables! Refer to my post about stage variables and why you should use them.

## convert HTML POST data or HTTP GET query string to JSON
 
## get the raw post data from the AWS built-in variable and give it a nicer name
#if ($context.httpMethod == "POST")
 #set($rawAPIData = $input.path('$'))
#elseif ($context.httpMethod == "GET")
 #set($rawAPIData = $input.params().querystring)
 #set($rawAPIData = $rawAPIData.toString())
 #set($rawAPIDataLength = $rawAPIData.length() - 1)
 #set($rawAPIData = $rawAPIData.substring(1, $rawAPIDataLength))
 #set($rawAPIData = $rawAPIData.replace(", ", "&"))
#else
 #set($rawAPIData = "")
#end
 
## first we get the number of "&" in the string, this tells us if there is more than one key value pair
#set($countAmpersands = $rawAPIData.length() - $rawAPIData.replace("&", "").length())
 
## if there are no "&" at all then we have only one key value pair.
## we append an ampersand to the string so that we can tokenise it the same way as multiple kv pairs.
## the "empty" kv pair to the right of the ampersand will be ignored anyway.
#if ($countAmpersands == 0)
 #set($rawPostData = $rawAPIData + "&")
#end
 
## now we tokenise using the ampersand(s)
#set($tokenisedAmpersand = $rawAPIData.split("&"))
 
## we set up a variable to hold the valid key value pairs
#set($tokenisedEquals = [])
 
## now we set up a loop to find the valid key value pairs, which must contain only one "="
#foreach( $kvPair in $tokenisedAmpersand )
 #set($countEquals = $kvPair.length() - $kvPair.replace("=", "").length())
 #if ($countEquals == 1)
  #set($kvTokenised = $kvPair.split("="))
  #if ($kvTokenised[0].length() > 0)
   ## we found a valid key value pair. add it to the list.
   #set($devNull = $tokenisedEquals.add($kvPair))
  #end
 #end
#end
 
## We now populate the key value stuff.
## Including any stage variables too because 'tis bad to check in configuration variables
{
 "version": "$stageVariables.get('version')",
 "tablename": "$stageVariables.get('tablename')",
#foreach( $kvPair in $tokenisedEquals )
  ## finally we output the JSON for this pair and append a comma if this isn't the last pair
  #set($kvTokenised = $kvPair.split("="))
 "$util.urlDecode($kvTokenised[0])" : #if($kvTokenised[1].length() > 0)"$util.urlDecode($kvTokenised[1])"#{else}""#end#if( $foreach.hasNext ),#end
#end
}

1. Click the tick next to the “Mapping template” dropdown.
2. Click “<- Method Execution”.
3. Click “Deploy API”.
4. Set a deployment stage type (eg. Prod , with a description of the deployment). Please note this is saved as part of the deployment history so you want to make this descriptive eventually so later you will know what you did 6 months ago.
5. Click “Deploy”.

Credit: AWS Forums