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Grunt is a Go server that exposes a REST interface to command line programs.
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Grunt is a Go server that exposes a REST interface to command line programs. Grunt is configured through a simple YML file.


In the wild use:

go get

In a clone of the repo (kudos to the fine Hellogopher):


grunt gruntfile.yml

Run grunt on port 9901 (the default listening port).

Fancy demo

# Build the grunt docker
docker build -t grunt .

# Run
docker run -d -p 9901:9901 grunt

Check the grunt web interface http://localhost:9901

REST Endpoints

endpoint method parameters description
/rest/service GET -- List the services available
/rest/service/{id} GET id Detail for service id
/rest/service/{id} POST id Start a new Job using service id
/rest/job/{id} GET id Details about a Job
/rest/job/wait/{id} GET id Does not return until the Job completes
/rest/job/{id}/file/{filename} GET id, filename Retrieve the file filename from the Job specified by id


An example configuration is found in gruntfile.yml. A service consists of the following fields:

endPoint      -- REST endpoint, e.g. /rest/service/<endPoint>
commandLine   -- Command line to run
                 Some special command line parameters are
                 #value  -- replace this argument with the parameter from the POST
                 <in     -- look for an uploaded file
                 >out    -- the process will generate this file for later download
                 ^in     -- uploaded file must be a zip file, extract in a directory (called in) and pass directory name as an argument
                 ~out    -- specify out on the command line as a directory, zip contents for download
description   -- description of the endpoint
defaults      -- a hashmap of default values for "#value" parameters


grunt creates REST endpoints for command line programs. Endpoints are listed in the services array of the YAML configuration file. Endpoints require a name (endPoint) and commandLine. The format of the commandLine is an array of options and parameters. Special one character prefixes to the parameter list tells grunt how to map REST requests to the command line of the Endpoint.

Endpoints are configured by adding to the services entry in gruntfile.yml. An example is:

  - endPoint: toy
    commandLine: ["toy", "#message"]
    description: print message
      message: "Hi From Grunt"
      message: This is the message to display at the output
  - endPoint: ball
    commandLine: ["ball", "<input", ">output"]
    description: transforms input to output
      input: an input file
      output: the input transformed by the ball operator


If an Endpoint needs a simple value (string, float, integer, etc), the endpoint specifies that by the character #. For example, the toy command needs a string as input, and would normally be called as ./toy foo (where foo could be any string). The corresponding commandLine setting would be:

commandLine: ["./toy", "#foo"]

A REST command to call toy with the value MySpecialValue would be:

curl -X POST -v --form foo=MySpecialValue localhost:9901/rest/service/toy

Input files

Similar to values, input files are prefixed with a <. This tells grunt to expect a file to be uploaded. The uploaded file is saved as the parameter name with out the <. Suppose our toy command takes a file as an argument, the corresponding commandLine is now:

commandLine: ["./toy", "<input.txt"]

To upload a file using curl, the --form command expects a parameter name and a filename argument starting with @, so to upload the local file local.txt to grunt use:

curl -X POST -v --form input.txt=@local.txt localhost:9901/rest/service/toy

grunt will save local.txt to the file input.txt on the server before executing the command line ./toy input.txt.

Output files

Output files are denoted with a > prefix. This tells grunt to expect the command to save a file and the output file should be made available for later download. Using the toy command, suppose it generates a log file. Because toy may generate log files in different formats (perhaps .txt, .xml or .json), grunt generates the name of the output file from the REST parameter. To make this call, toy log.yml, this command line is used.

commandLine: ["./toy", "<output"]

The output parameter for the REST call should be the desired filename, e.g. log.yml:

curl -X POST -v --form output=log.yml localhost:9901/rest/service/toy

Notice that value for output is log.yml. This REST call will invoke ./toy log.yml on the server, and the output file log.yml can be downloaded after the command is finished as:

wget --content-disposition localhost:9901/rest/job/$id/file/out

Where $id is the id of the Job in grunt.

NB: wget is used because --content-disposition honors the output filename passed along by grunt, so the output filename would be log.yml.

Input directory

Sometimes a command line program requires the path to a directory as input. For example, the directory may be full of images to arrange in a montage. The prefix is ^, and the name of the directory is the rest of the argument. So if toy is expecting a directory called images, the command line would be:

commandLine: ["./toy", "^images"]

The REST command should upload a zip file containing files to go in the images directory. If the zip file contains a top level directory, it is unzipped in place and renamed to images (in the example). If the zip file has multiple files at the top level, a new directory is created, and the contents of the zip are moved into that directory.

curl -X POST -v --form localhost:9901/rest/service/toy

Output directory

A directory full of output files is very similar to a single output file. Using the ~ prefix, the name of a directory is passed to the command line program. If toy produces a directory full of log files, the command line would be:

commandLine: ["./toy", "~logs"]

The REST command could specify the name of this directory using the logs parameter:

curl -X POST -v --form logs=my_log_files localhost:9901/rest/service/toy

and grunt would create the directory my_log_files then run ./toy my_log_files. A zip file containing my_log_files could be downloaded after the Job is completed by:

wget --content-disposition localhost:9901/rest/job/$id/file/logs

NB: wget is used because --content-disposition honors the output filename passed along by grunt, so the output filename would be


Generally, defaults are a single string. The string is shown on the user interface as a suggested value for the parameter. To show a drop-down list of suggestions, write the string as an array


A shim) is a small script that intercepts REST requests and translates them for another command line program. This may be useful if a command line program needs inputs that grunt does not process. For instance, suppose a command requires a comma-separated list of filenames. There is no grunt parameter prefix to handle that case. However, we can write a shim program in bash that looks for files in a directory, formats a comma-separated string, and passes that to another program. Here's our endPoint definition:

  - endPoint: toy
    commandLine: ["shim", "^files"]

The shim program finds all the filenames in the files directory (recall that ^ indicates a zip file upload), adds commas between them an invokes toy:


# call as ./shim files
# will call toy with a comma-separated list of filenames from the files directory.

# create the list
list=$(ls -1 $1 | paste -s -d , - )

# call toy with the list
./toy "$list"

Miscellaneous configuration

Server identification:

# This is the hostname:port that the server is running on.
# Used for logging and email

Cleanup completed jobs:

# Cleanup after 30 minutes, default is 120
cleanup_time_in_minutes: 30

Where job files are stored:

# Working directory
# This is the directory path used for working files. If left blank,
# use a system temp directory.
# NB: To run in the pesscara/grunt docker, this must be set to /data
directory: data

Consul reporting:

# Service name for Consul
name: example
# Report Warn status to Consul when we have more than warnLevel jobs
warnLevel: 3
# Report Critical status to Consul when we have more than criticalLevel jobs
warnLevel: 5

Sending job emails:

# Mail configuration
  # username: grunt
  # password: <secret>


Copy Example

The example file gruntfile.yml exposes some endpoints. test simply echoes the input and can be called like this:

curl -X POST  -v --form Message=hi localhost:9991/rest/service/test

copy takes input and output files. <in must be provided

curl -X POST  -v --form in=@big_file.txt --form out=small_file.txt localhost:9901/rest/service/copy

NB: --form in=@big_file.txt indicates that curl should send big_file.txt as the form parameter in
and the output filename is set to small_file.txt

the following example leverages the slicer's CLI xml configureation

curl -X POST  -v --form neighborhood=1,1,1 --form inputVolume=@somefile.nii.gz --form outputVolume=somefile.nii.gz localhost:9901/rest/service/MedianImageFilter

to retrieve the output data, first find the UUID in the response, and request the file

wget localhost:9901/rest/job/eab4ab07-c8f7-44f7-b7d8-87dbd7226ea4/file/out

NB: we request the output file using the out parameter, not the filename we requested

Here is the copy example using jq( to help a bit

id=`curl --silent -X POST --form in=@big_file.txt --form out=small_file.txt localhost:9901/rest/service/copy | jq -r .uuid`
wget --content-disposition localhost:9901/rest/job/$id/file/out

copy-dir example

# Have a zip file called `` in the current directory
# Start the job and extract the uuid using jq
id=`curl --silent -X POST --form --form localhost:9901/rest/service/copy-dir | jq -r .uuid`

# Status of the job
curl -v localhost:9901/rest/job/$id

# Wait for the job to complete
curl -v localhost:9901/rest/job/wait/$id

Sleep example

This is an example of running the sleep job for 120 seconds.

# Start the job and extract the uuid using jq
id=`curl --silent -X POST --form seconds=120 localhost:9901/rest/service/sleep | jq -r .uuid`

# Status of the job
curl -v localhost:9901/rest/job/$id

# Wait for the job to complete
curl -v localhost:9901/rest/job/wait/$id


Supported by the NCI Grant CA160045.

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