Commodore Maze Generator on AWS Lambda via API Gateway

The Commodore Maze Generator Program

I needed something “useful” to output from my Commodore VICE Lambda Custom Runtime that also didn’t require much input (if any) from the requester. Otherwise, I’d have to sanitize the input that is being passed to a shell script and potentially validate it if I didn’t want unpredictable behavior. I settled on a Commodore 128 version of the Commodore Maze Generator (the fast and slow will be unnecessary once we launch from the Lambda with the -warp option on VICE, but I never changed the program so it’s left in here. The fast and slow and everything before line 50 is Commodore 128 BASIC 7.0-specific, but the Commodore 64 version just requires substitution of POKE commands instead. (See vice-lambda repo on GitHub for latest version)

5 fast
10 scnclr
20 color 0,2
30 color 4,2
40 color 5,1
50 for y=1 to 25
60 for x=1 to 40
70 print chr$(205.5+rnd(1));
80 next x
90 next y
95 slow
100 goto 100

Making sure that the Lambda returns an image for Lambda

I want to be able to use Lambda Proxy Integration when setting up the API Gateway, so I need to return a format that maps the information properly. The response JSON needs to have:

  • isBase64Encoded set to true (necessary for the translation of the PNG back from base64)
  • headers with "Content-type" and "content-disposition" set (image/png and inline for this example)
  • statusCode of 200 (right now, if we have an error it’s either not caught or happens at the Lambda invocation level)
  • body containing the base64 data. Note the -w 0 argument to turn off line breaks when wrapping… Lambda Proxy Integration doesn’t handle that well.
function handler() {
  cd vice
  SEED=$((0 - `od -An -N2 -i /dev/random`))
  ./x128 -silent -sound -keybuf "
  3 i=rnd($SEED)
  `cat ../maze.bas`
  " -warp -limitcycles 20000000 -exitscreenshotvicii /tmp/$1.png 2>&1 >/dev/null
  cd ..

  RESPONSE="{\"isBase64Encoded\": true, \"headers\": {\"Content-type\": \"image/png\", \"content-disposition\":\"inline\"}, \"statusCode\":200, \"body\":\"`base64 -w 0 /tmp/$1.png`\"}"

  echo $RESPONSE

Also note that we’re passing in a SEED value because, otherwise, the Commodore 128 will generate the same maze every time.

Repackage the Lambda and upload as in the Commodore VICE Lambda Custom Runtime blog post.

Setting up the API Gateway

Go to API Gateway in the AWS Console and select [Create API]

APIs Create API

Choose [Build] under “REST API” (we won’t be using OIDC/OAuth2/CORS…)

REST API -> Build

Choose REST, New API, and name your API:


Create a GET Method and check the checkmark

Create Method
API Method verb selection -> GET
Check the checkmark to commit
  • Choose “Lambda Function” for your Integration Type
  • Check “Use Lambda Proxy Integration”
  • Type the name of the Lambda that you’ve calling and select it and [Save] and confirm that you want to add role/permission for the Lambda.
GET API configuration

Deploy the API

Back on your API view, select the [Actions] dropdown and [Deploy API]

API Actions "Deploy API"

Just create a new dev stage… we’re not going to “production” with this experiment

Create new dev stage

and [Deploy]

It’s broken

If you click the Invoke URL presented, you will get a broken image

Invoke URL
Broken image from the API

Since we’re only sending back PNG files, we can just tell the API that */* is a Binary Media Type by going to Settings on the left sidebar for the API and [(+) Add Binary Media Type]

Add Binary Media Type

Be sure to save the settings, redeploy the API and be sure to use the Invoke URL for the correct API! (I had two identical and was “fixing” the wrong one… hence the different API URL snapshots)

Commodore Maze Generator PNG 1

If you refresh, you should get a new maze from the Commodore maze generator program:

Commodore Maze Generator run 2

Some Troubleshooting

  • Be sure to save your settings
  • Test your API call to Lambda in the Method Execution view (Resources -> GET -> Test [lightning bolt])
  • Be sure to redeploy your API after settings change.

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