container to pipe to an executable and out again

Question

I need a Docker image which contains a Linux executable where I can pipe an input file into when running it like this (in cmd on Windows or bash on Linux):

docker run --rm -i myContainer < myInputFile > myOutputFile

In my case it is the executable cucumber-json-formatter-linux-386 which converts NDJSON Cucumber messages into a JSON file (to be used e.g. for Xray).

Why Docker?

There is also a Windows executable available, but our security software says it contains a virus.
So I can’t download it, but to be honest, I also don’t trust it.
I need something OS indepedent, also running in CI, etc.

Why convert?

Cucumber can output JSON directly. But I am using @badeball/cypress-cucumber-preprocessor which only can output NDJSON and needs me to use that binary to convert it into JSON. @badeball wrote “I've refactored my implementation to output messages, because that was significantly easier implementation wise”. So it’s not Cucumber writing those NDJSON messages here.

If the project already publishes runnable binaries built for your architecture, do you actually need it in a Docker image? It seems like directly running `./cucumber-json-formatter-linux-amd64` (maybe renaming the executable to be shorter) would be more convenient than trying to invoke `docker run` to do the same thing. — David Maze, Jul 05 '22 at 13:13
I just added some of the reasons. Hopefully it will be clear now. — Marcus, Jul 05 '22 at 13:34

Marcus · Accepted Answer · 2022-07-08T13:28:10.593

Assuming you already have installed Docker, create a folder containing the following file called “Dockerfile”:

FROM scratch
COPY cucumber-json-formatter-linux-386 /formatter
ENTRYPOINT ["/formatter"]

Also copy the Linux executable (cucumber-json-formatter-linux-386) into the same folder.

Then cd into that folder and build the container like this:

docker build -t cucumber-json-formatter .

Now you can run the container like this:

docker run --rm -i cucumber-json-formatter < input.ndjson > output.json

The argument --rm removes the container after usage. Do this if you don't want a pile of dead containers to build up over time.
The argument -i is needed to keep the input stream open, while the file is piped in.

I tried this on a Windows host (cmd, not Powershell), but should work the same on Linux.

If you want to use it automatically in @badeball/cypress-cucumber-preprocessor add a file .cypress-cucumber-preprocessorrc.json on your project root, containing:

{
    "json": {
        "enabled": true,
        "formatter": "docker",
        "args": ["run", "--rm", "-i", "cucumber-json-formatter"]
    }
}

On test execution this will create a file cucumber-messages.ndjson and then cucumber-report.json, both on the project root.

container to pipe to an executable and out again

1 Answers1