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Node.js Swarmlet Host

The node host is used to instantiate and run accessors in Node.js.

Quick start with an interactive shell

Assuming you have Node.js between v5.10.0 and 7.10.1 installed and can invoke it on a command line, the following commands will download the node host and run it as an interactive shell:

git clone
cd accessors/web/hosts/node
node nodeHostShell.js

After executing these three commands, you can type help to get a list of commands understood by the host. The following sequence of commands to the host will instantiate an accessor, run it, and then exit the host:

var a = instantiate('a','test/TestGain')
a.setParameter('gain', 4)
a.provideInput('input', 5)

Below are the same commands shown along with the node shell prompt (nsh>) and the output:

Welcome to the Node swarmlet host (nsh). Type exit to exit, help for help.
nsh> var a = instantiate('a','test/TestGain')
Reading accessor at: /ptII/org/terraswarm/accessor/accessors/web/test/TestGain.js
Instantiated accessor a with class test/TestGain
nsh> a.initialize()
nsh> a.setParameter('gain', 4)
nsh> a.provideInput('input', 5)
nsh> a.react()
TestGain: inputHandler: input: 5 gain: 4
nsh> a.latestOutput('scaled')
nsh> exit

See also:

The Node host relies on and extends the common host, a platform-independent pure-JavaScript swarmlet host. At this time, the implementation is far from complete, with most optional JavaScript modules not yet implemented. See the To Do List.

The interactive shell can also be used to script a session. To run a sample script, assuming you are in the same directory:

bash-3.2$ node nodeHostShell.js < test/testNodeHost.js

You will see output similar to the session above.

Instantiating and running accessors from the command line

The Node host includes a command-line invocation mechanism that will instantiate and initialize accessors. The command-line arguments are the class names of accessors (such as net/REST) and can also include plain JavaScript files to evaluate before, after, or between instantiations and initialization of accessors. The general usage pattern is:

  node nodeHostInvoke.js [-js JavaScriptFile.js] [-k] [-t timeInMs] AccessorClass1 [AccessorClass2 ...]

The above assumes that the current directory is hosts/node in the accessors repository, where the nodeHostInvoke.js file is found. See documentation for the command-line arguments.

For example, the following command instantiates and initializes a Composite Accessor that stops its own execution using a Stop accessor after about 3 seconds.

  node nodeHostInvoke.js test/auto/Stop

You can run two instances of an accessor simultaneously:

  node nodeHostInvoke.js test/auto/Stop test/auto/Stop

The above command will return when both accessors have completed execution.

The following instantiates and initializes an accessor that does not stop its own execution:

  node nodeHostInvoke.js test/TestSpontaneous

The above command will not return, so you will need to stop it with control-C. The above TestSpontaneous accessor produces a sequence of outputs, one per second, but those outputs are not being monitored by anything, so the execution is not very interesting. You can follow instantiation of the accessor with a JavaScript file that monitors the outputs or stops the execution as follows:

  node nodeHostInvoke.js test/TestSpontaneous -js monitor.js

where, for example, monitor.js is a file containing the following code:

  var accessor = getTopLevelAccessors()[0];
  var count = 0;
  accessor.on('output', function() {
      if (count++ >= 4) {

The first line retrieves the accessor from the host using its getTopLevelAccessors() function. This script then monitors the output named 'output', and whenever the accessor produces such an output, it prints the value of the output. In addition, after five outputs have been produced, it invokes the wrapup() function, which stops execution of the accessor.

To run an accessor for three seconds and then terminate, specify a timeout option:

  node nodeHostInvoke.js -timeout 3000 test/auto/RampJSDisplay

The RampJSDisplay accessor is a composite accessor that produces a counting sequence and then displays it on the standard output. The execution looks like this:

bash-3.2$ node nodeHostInvoke.js -timeout 3000 test/auto/RampJSDisplay
Reading accessor at: /Users/cxh/ptII/org/terraswarm/accessor/accessors/web/test/auto/RampJSDisplay.js
Reading accessor at: /Users/cxh/ptII/org/terraswarm/accessor/accessors/web/test/TestDisplay.js
Reading accessor at: /Users/cxh/ptII/org/terraswarm/accessor/accessors/web/test/TestSpontaneous.js
Instantiated accessor RampJSDisplay with class test/auto/RampJSDisplay
commonHost.js: main(): Maximum time reached. Calling stopAllAccessors().
commonHost.js: invoking wrapup() for accessor: accessor1

You can create automated tests using the TrainableTest accessor. For example, test/auto/RampJSTestDisplay is a composite accessor with a TrainableTest accessor in it:

  node nodeHostInvoke.js test/auto/RampJSTestDisplay

This accessor generates a counting sequence, checks that the counting sequence is correct, and terminates upon receiving all expected values. It also displays the output values on standard out.

The command-line arguments are file names, accessor class names (such as net/REST), or any of the following options:

  • -e|--e|-echo|--echo: Echo the command-line arguments. This is helpful for use under Ant apply.
  • -h|--h|-help|--help: Print a usage message.
  • -j|--j|-js|--js: Interpret the next argument as the name of a regular JavaScript file to evaluate, as opposed to an accessor.
  • -k|--k|-keepalive|--keepalive: Keep the process alive until either all accessors specified on the command line have wrapped up, or if no accessors were given, then until the timeout specified by the -timeout option expires. If no timeout is given and no accessors are given, then the process does not exit.
  • -t|--t|-timeout|--timeout milliseconds: The maximum amount of time the script can run. When this time is reached, stop() is called on all accessors that have been instantiated, and then
  • -v|--v|-version|--version: Print out the version number

See the nodeHost module JSDoc documentation.

Installing the node host using npm

The Node Package Manager (npm) installation is not yet updated regularly, download using the git repo until we get npm to update automatically.

  1. Install node.js, which should also install the npm executable.
  2. Optional: Update npm, to the most recent version. Typically, this is done with
    sudo npm install npm -g
    See Installing Node for details
  3. Install the accessors Node Accessor Host module:
    npm install @terraswarm/accessors
  4. Install one of many modules (used by the RampJSDisplay example below):
    npm install @accessors-modules/text-display
  5. Create a .js file such as accessors.js:
    var accessors = require('@terraswarm/accessors');
    var accessor = accessors.instantiate("myAccessor", "test/auto/RampJSDisplay");
  6. In the shell, invoke node
    [cxh@terra accessors]$ node accessors.js
    Reading accessor at: /tmp/accessors/node_modules/@terraswarm/accessors/test/auto/RampJSDisplay.js
    Reading accessor at: /tmp/accessors/node_modules/@terraswarm/accessors/test/TestDisplay.js
    Reading accessor at: /tmp/accessors/node_modules/@terraswarm/accessors/test/TestSpontaneous.js
    Instantiated accessor RampJSDisplay with class test/auto/RampJSDisplay
      C-c C-c
    ^CnodeHost.js: About to invoke wrapup().
    nodeHost.js: invoking wrapup() for accessor: myAccessor.TestDisplay
    nodeHost.js: invoking wrapup() for accessor: myAccessor.TestSpontaneous
    nodeHost.js: invoking wrapup() for accessor: JavaScriptRamp
    [cxh@terra accessors]$

For more information about the Node Package Manager (npm), see npm.

Testing using Mocha

We use Mocha to test the Node accessor host. To run the tests,

1. Install two modules:

sudo npm install -g mocha
sudo npm install -g mocha-junit-reporter

2. cd to the web/ directory in the accessors repository and run ant test.mocha:

bash-3.2$ pwd
bash-3.2$ ant tests.mocha
Buildfile: /Users/cxh/ptII/org/terraswarm/accessor/accessors/web/build.xml

     [echo]       ==test.mocha==
     [echo]       This target uses mocha to test Node.js tests in **/mocha/test*.js files.
     [echo]       This target requires setup:
     [echo]         sudo npm install -g mocha
     [echo]         sudo npm install -g mocha-junit-reporter
     [echo]       See
     [exec]   CommonTests
     [exec] Instance of TestAccessor: [Circular]
     [exec] Tests:
     [exec] Test passed: TestAccessor: getParameter
     [exec] Test passed: TestAccessor: setParameter
     [exec] Test passed: TestAccessor: get
     [exec] Test passed: TestAccessor: get with undefined
     [exec] Test passed: TestAccessor: get with undefined
     [exec] Test passed: TestAccessor: provideInput()
     [exec] invoked.
     [exec] Reading accessor at: /Users/cxh/ptII/org/terraswarm/accessor/accessors/web/test/TestGain.js
     [exec] Reading accessor at: /Users/cxh/ptII/org/terraswarm/accessor/accessors/web/test/TestAdder.js
     [exec] Instantiated accessor testComposite with class test/testComposite
     [exec]     &#10003; load testCommon
     [exec]   4 passing (22ms)

Total time: 0 seconds

Other Node Host Tests

In the root directory of the accessors repository:

ant -p
List the ant targets
ant tests
Run the CapeCode, Browser, Duktape, eduk and node host tests.
ant tests.mocha
Use mocha to test the Node host and generate output on stdout.
ant tests.mocha.composites
Use mocha to test just the composite accessors using the Node Host
mocha hosts/node/test/testNodeOneAuto.js --Dauto=XXX/test/auto
Use mocha to test the composite accessors using the Node Host in the XXX/test/auto directory.
(cd net/test; ./runNodeAutoTests)
Run just the composite accessors in the net/test/auto. This is a convenience script for the mocha command above. Each test/ directory that has a auto/ directory that contains composite accessors should have a runNodeAutoTests script.

Node Version

Node 5.10.0 or later is required because accessor modules such as socket use Buffer

The npm 5.x and later, shipped with Node 8.x and later remove files from the node_modules/ directory, so Node 7.10.1 or earlier must be used with accessors.

See Also

Back to main accessors wiki

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Page last modified on December 25, 2020, at 08:41 AM