Tip: How to use C / C++ Language Code

[StefanSchnell]

C and C++ have been very popular programming languages for a long time and still are today. Many consolidated program approaches and libraries exists. With Emscripten is it possbile to transfer existing C / C++ projects into WebAssembly. This kind of output, which is generated by Emscripten, can be used seamlessly with Node.js. And Node.js is one of the platforms that Aria Automation offers us. This is definitely worth a look to see if C / C++ programs can be made to work with Aria Automation.

Preparations

The download, installation and setup are described in detail in the section of the same name on Emscripten's site. It is very simple and works without any problems. After veryfying the installation, Emscripten can be used.

C Code

To check it I use this tiny C program with two functions. The first function hello outputs Hello World and the second function int_sqrt calculates the squareroot of the given number. The second function is part of the Emscripten example, how to interact with code.

// Begin----------------------------------------------------------------

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <emscripten.h>

void EMSCRIPTEN_KEEPALIVE hello(char *name) {
  if (name == NULL) {
    printf("Hello World from C Language!\n");
  } else {
    printf("Hello %s from C Language!\n", name);
  }
}

int EMSCRIPTEN_KEEPALIVE int_sqrt(int x) {
  return sqrt(x);
}

// End------------------------------------------------------------------

Save this file as helloWorld.c.

Compile the C Code to WebAssembly

Now we compile the code with the following command:

emcc helloWorld.c -o helloWorld.js -s EXPORTED_FUNCTIONS=_hello,_int_sqrt -s EXPORTED_RUNTIME_METHODS=ccall,cwrap

After compilation we have two new files, helloWorld.js and helloWorld.wasm.

Aria Automation Handler

In the next step we build a handler program to call the functions on the different ways, direct call, ccall and cwrap. A detailed explanation can also be found in the Interacting with Code section. However, the calls and returns are very simple to understand.

/* Begin----------------------------------------------------------------
 *
 * Node.js test action to check Emscripten compiler to WebAssembly
 *
 * Checked with VMware Aria Automation 8.5.1 and Node.js 12.22.1
 *
 * @param sqrtFrom {number}
 * @returns CompositeType(
 *   status {string},
 *   result {number}
 * ):test
 */

exports.handler = (context, inputs, callback) => {

  let sqrtFrom = inputs.sqrtFrom;

  const helloWorld = require("./helloWorld.js");

  let result = helloWorld.onRuntimeInitialized = () => {

    // Try C function hello---------------------------------------------
    helloWorld._hello();

    helloWorld.ccall("hello", null, ["string"], ["Gabi"]);

    const hello = helloWorld.cwrap("hello", null, ["string"]);
    hello("Stefan");

    // Try C function int_sqrt------------------------------------------
    let result = helloWorld._int_sqrt(4);
    console.log(result);

    console.log(helloWorld.ccall("int_sqrt", "number", ["number"], [25]));

    const intSqrt = helloWorld.cwrap("int_sqrt", "number", ["number"]);
    console.log(intSqrt(36));

    let fromSqrt = intSqrt(sqrtFrom);
    console.log(fromSqrt);

    callback(undefined, {status: "done", result: fromSqrt});

  }

}

// End------------------------------------------------------------------

ZIP

Now we build a zip file as it is described in the VMware documentation. All files can be packed together, directories are not necessary.

Execution

Now we can add the zip file in the Orchestrator Node.js runtime and set the inputs and return type.

Everything works well, as we can see.

Three times hello call delivers the expected results and four times int_sqrt delivers the expected results. Input and output values are also processed and returned correctly.

Conclusion

With Emscripten it is very easy to convert C / C++ functions into WebAssembly and with Node.js it is also very easy to use WebAssembly inside Aria Automation. This approach offers us the possibility to use C / C++ code seamlessly as actions in Aria Automation. This approach opens up interesting development perspectives, even if there are limitations. One of the most famous projects that have been implemented with Emscripten to JavaScript is SQLite. This clearly demonstrates the power of this approach.