JS7 JobScheduler

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Task

  • Users frequently find the situation that jobs in a workflow pass variables to subsequent jobs.

  • This can easily be achieved by appending a pair of name/value for the variable to a temporary file that is offered by the JS7_RETURN_VALUES environment variable like this:

    Example how to pass a variable to subsequent jobs with Unix
    MY_VAR="some text"
echo "my_variable=$MY_VAR" >> $JS7_RETURN_VALUES
    Example how to pass a variable to subsequent jobs with Windows
    set MY_VAR=some text
echo my_variable=%MY_VAR% >> %JS7_RETURN_VALUES%


    Explanation:

    • A variable my_variable is passed as an order variable to subsequent jobs and instructions in a workflow.
    • The variable can be assigned a constant value or a value from some environment variable as e.g. MY_VAR that holds some arbitrary value.
  • However, there are two limitations about this approach:
    • The length of values for environment variables is limited, the precise max. size of environment variables is OS dependent.
    • If the value of the variable includes special characters such as carriage return, newline, linefeed then this might break depending on capabilities of environment variables in the OS.

Solution

  • To address the problem of special characters use base64 encoding for variable values as this encoding results in a single printable string.
  • To address the limitation concerning the size of environment variables do not use them and think about ways how to directly append lines to the temporary file indicated by JS7_RETURN_VALUES. 

Example

  • Let's assume two jobs to be executed in sequence:
    • The first job creates a lengthy e-email body in HTML format,
    • The second job sends e-mail and makes use of the HTML body. Find a number of possible implementations:


      Example for Shell version using environment variables on Unix
      #!/user/bin/env bash

mailBody="<html><body><b>hello</b> <i>world</i></body></html>"
mailBodyEncoded=$(echo $mailBody | base64)
echo "body=base64:$mailBodyEncoded" >> $JS7_RETURN_VALUES
      Example for Shell version using files on Unix
      #!/user/bin/env bash

echo "<html><body><b>hello</b> <i>world</i></body></html>" > /tmp/mail-body.html
echo "body=base64:$(cat /tmp/mail-body.html | base64)" >> $JS7_RETURN_VALUES
      Example for PowerShell version on Unix
      #!/usr/bin/env pwsh

$mailBody = "<html><body><b>hello</b> <i>world</i></body></html>"
$mailBodyEncoded = [System.Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes( $mailBody ))
"body=base64:$mailBodyEncoded" | Out-File $env:JS7_RETURN_VALUES -Append
      Example for PowerShell version on Windows
      pwsh.exe -NoLogo -NonInteractive -Command "& { ""body=base64:$([System.Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes( '<html><body><b>hello</b> <i>world</i></body></html>' )) )"" | Out-File $env:JS7_RETURN_VALUES -Append }"


      Explanation:

      • In fact the e-mail body is not too lengthy, however, it suggests that an e-mail body would be imported by some template file as e.g. for PowerShell with $mailBody = Get-Content "mail-body.html"

        • The above bash version with files and the PowerShell version both work with arbitrary length values.
      • Base64 encoding is available from a number of sources such as the base64 Unix utility or the .Net Core class.
      • The value of the body variable is prefixed with base64: to indicate the encoding.
      • The subsequent JS7 - JITL MailJob accepts the body variable, identifies the encoding and automatically decodes the argument value.



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