Load files from the local file system as arguments

[bergos]

In some cases it would be useful to read the content of files on the local file system. For example a ssh key can be loaded like this:

"${require('fs').readFileSync('/full/path/myKeyFile.key').toString()}"^^code:EcmaScriptTemplateLiteral

But it would be useful to have a datatype + loader that handles it:

"/full/path/myKeyFile.key"^^p:FileContent

It should also work with variables:

"keyFilename"^^p:VariableFileContent

[tpluscode]

This could also be implemented as as stream itself. The SHACL validation step does that to load the shapes graph. That is not as nice as a synchronous loader to plug in directly to the function but avoids the risk of loading large files to memory

The problem of using a pipeline is verbosity, requiring a more complex setup. Given the original example

<step>
  a :Step ;
  code:arguments (
    <loadStepFile>
  ) ;
.

<loadStepFile> a :Pipeline, :Readable ;
  :steps [ :stepList (
    [ 
      code:implementedBy [ code:link <node:fs#createReadStream> ] ;
      code:arguments ( "/full/path/myKeyFile.key" )
    ] 
  ) ] ;
.

Hypothetically, #85 could be a solution, where the <loadStepFile> becomes a reusable building block