lambda-qr

QR Code Generator for AWS Lambda

Will take the request body that is POSTed to the endpoint, and generate a QR code from it.

This is a Serverless app, written in Go (Golang), running in AWS Lambda, with API Gateway in front of it, and AWS CloudFront in front of that (for caching).

This is an experiment. Uptime is not guaranteed, and there is no SLA. But all-in-all, it should be reasonably reliable.

NOTE: I've tried to build this in a way that is very cheap to run. But if you find yourself using this more than just occasionally, consider kicking me down a few bucks to offset the cost of running this service. https://cash.me/$rparman

Usage

The https://qr.ryanparman.com hostname is a CloudFront caching distribution, in front of API Gateway, in front of a Lambda function.

There are two endpoints:

• qr.png — This will return a (bitmap) PNG file.
• qr.svg — This will return a (vector) SVG file.

Additionally, it accepts 2 query-string parameters.

NOTE: Different browsers support different maximum lengths for URLs, with a generally-accepted answer of 2083 characters end-to-end. Some browsers support longer URLs, but in practice, trying to pack that much data into a little QR code results in a barely-usable QR code. As such, it is recommended that you stick to less verbose data structures.

Response Bodies

The bodies of the responses contain PNG-formatted binary data, or SVG-formatted XML data. Both could be written directly to disk as a file.

Example Data

You can find examples of data formats which are broadly supported, in the wiki.

Developing/Deploying

Golang

Go (when spoken) or Golang (when written) is a strongly-typed language from Google that "blends the simplicity of Python with the performance of C". Static binaries can be compiled for all major platforms, and many minor ones.

It is recommended that you install Golang using your system's package manager. If you don't have one (or if the version is too old), you can install Golang from its website. Reading the Getting Started documentation is a valuable exercise.

brew update && brew install golang

Glide

Golang dependencies are managed with Glide. You should install them before compiling this project.

curl https://glide.sh/get | sh
glide install

GoMetaLinter

GoMetaLinter pulls together many popular linting tools, and can run them on a project.

gometalinter.v2 --install

Serverless

Serverless is a platform that wraps AWS Lambda and AWS CloudFormation, simplifying the deployment of Lambda apps. Serverless is written in Node.js, so you need to install that first.

I recommend you install the Node Version Manager, and use that to install the latest Node.js and npm. Once that's complete, install serverless.

npm i -g serverless

Developing

This app is small, and is self-contained in main.go.

By default, it expects to be running in AWS Lambda, receiving HTTP requests coming from API Gateway.

If you are performing local development/testing, run make build to build for the local platform, then bin/qr -mock to run it. The local build reads from mock.json and treats it as an incoming request from API Gateway. You can change the query-string parameters to have the app respond to the documented query string parameters.

make build

# PNG
bin/qr -mock

# SVG
QR_SVG=true bin/qr -mock

Make sure that you run the linter to catch any issues.

make lint

You can test some QR code data by reviewing github:zxing/zxing.

Deployment

serverless uses the same local credentials that the AWS CLI tools and the AWS SDKs use. If you haven't configured those yet, do that first.

Run make package to build a binary for AWS Lambda. Then, serverless deploy to deploy the app to your environment.

make package
serverless deploy