Wrapping a executable in a function

Lets look at how to wrap a command line program into a function. We'll assume that you already have an OpenFaaS service running somewhere.

First create the template

1
faas new --lang dockerfile myfunction

Calling the function

I'm going to write a command in ruby so I'll include things from the ruby:3.0.1 base image.

The main thing here is that I'm copying the script into /usr/local/bin and I'm changing the fprocess ENV variable to be xargs gitinfo.rb which will pass in the standard input as command line arguments.

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
  FROM ghcr.io/openfaas/classic-watchdog:0.1.5 as watchdog

  FROM ruby:3.0.1

  RUN apt-get update && apt-get install -y cloc libsqlite3-dev

  COPY --from=watchdog /fwatchdog /usr/bin/fwatchdog
  RUN chmod +x /usr/bin/fwatchdog

  WORKDIR /home/app

  # Add non root user
  RUN useradd app
  RUN chown app /home/app

  COPY Gemfile* ./
  RUN bundle install
  COPY *rb /usr/local/bin/
  RUN chmod +x /usr/local/bin/*rb

  USER app

  # Populate example here - i.e. "cat", "sha512sum" or "node index.js"
  ENV fprocess="xargs gitinfo.rb"
  # Set to true to see request in function logs
  ENV write_debug="false"

  EXPOSE 8080

  HEALTHCHECK --interval=3s CMD [ -e /tmp/.lock ] || exit 1

  CMD ["fwatchdog"]

The script looks like this:

1
2
3
4
5
6
7
  #!/usr/bin/env ruby

  puts "This is the info file"

  ARGV.each do |v,i|
    puts "#{i}: #{v}"
  end

Running without an argument

1
curl https://api.gitgratitude.com/function/gitinfo

This is the info file

Passing in arguments

Here we can pass in data to the function:

1
echo Hello world | curl -X POST --data @- https://api.gitgratitude.com/function/gitinfo

This is the info file
: Hello
: world

Async test

I'm going to use pipedream.com as a way to collect a response. Go there and sign up for it if you haven't, and then set the CALLBACK_URL to be resulting address.

In order to have a function run asyncronously, you need the change the url to start with /async-function/ and pass in an X-Callback-URL header where the result is posted.

1
2
3
4
5
  CALLBACK_URL=https://eno35z9ue0i7ffz.m.pipedream.net
  echo Hello world | curl -X POST \
                          -H "X-Callback-Url: ${CALLBACK_URL}" \
                          --data @- \
                          https://api.gitgratitude.com/async-function/gitinfo

Conclustion

Very simple, very little was changed from the below posts below.

Wrapping a executable in a function

Easy function wrapping

Contents

First create the template

Calling the function

Running without an argument

Passing in arguments

Async test

Conclustion

References

Uploading to S3 on the command line

throwing data into a bucket

Getting emacs working on OSX Monterey

security and permissions