ANSI C in OpenWhisk

/*
 * evrtng functions – ANSI C action example
 * Reads JSON from argv[1] (OpenWhisk passes params as arg),
 * prints a JSON result to stdout.
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[]) {

    /* Log to stderr – shows up in wsk activation logs */
    fprintf(stderr,
        "[evrtng] ANSI C action invoked\n");

    /* Safely read the name param from argv[1] */
    const char *args = (argc > 1) ? argv[1] : "undefined";

    /* Print structured JSON result to stdout */
    printf(
        "{ \"msg\": \"Hello from ANSI C!\", \"args\": \"%s\" }\n",
        args
    );

    return 0;
}

# Compile
$ gcc -o example example.c

# Test with a mock argument
$ ./example '{"name":"evrtng"}'
{ "msg": "Hello from ANSI C!", "args": "{\"name\":\"evrtng\"}" }

# Stage 1 – Build
FROM ubuntu:22.04 AS builder

RUN apt-get update && \
    apt-get install -y gcc libc-dev && \
    rm -rf /var/lib/apt/lists/*

WORKDIR /build
COPY example.c .

# Compile with optimisations and static linking
RUN gcc -O2 -static -o example example.c

# Stage 2 – Runtime (minimal scratch image)
FROM ubuntu:22.04

RUN apt-get update && \
    apt-get install -y libc6 && \
    rm -rf /var/lib/apt/lists/*

COPY --from=builder /build/example /usr/local/bin/example

# OpenWhisk calls this entrypoint
ENTRYPOINT ["/usr/local/bin/example"]

# Build the image
$ docker build -t YOUR_DOCKERHUB_USER/openwhisk-ansi-c .

Step 1/8 : FROM ubuntu:22.04 AS builder
...
Successfully built a1b2c3d4e5f6
Successfully tagged yourusername/openwhisk-ansi-c:latest

# Log in to Docker Hub
$ docker login

# Push the image
$ docker push YOUR_DOCKERHUB_USER/openwhisk-ansi-c

The push refers to repository [docker.io/yourusername/openwhisk-ansi-c]
latest: digest: sha256:abc123... size: 27.4 MB

# Verify the image is accessible
$ docker pull YOUR_DOCKERHUB_USER/openwhisk-ansi-c

# Create the action with your Docker image
$ wsk action create ansiCAction \
    --docker YOUR_DOCKERHUB_USER/openwhisk-ansi-c \
    --web true

ok: created action ansiCAction

# Verify it was registered
$ wsk action list | grep ansiCAction
/guest/default/ansiCAction    private  blackbox

# Get the public web URL
$ wsk action get ansiCAction --url
https://fnc.evrtng.cloud/api/v1/web/guest/default/ansiCAction

# Blocking invocation with params
$ wsk action invoke ansiCAction \
    --result \
    --param args "test-input"

{
    "msg": "Hello from ANSI C!",
    "args": "test-input"
}

# Async invocation
$ wsk action invoke ansiCAction --param args "async-test"
ok: invoked /guest/default/ansiCAction with id a1b2c3d4...

# View the logs (stderr output from your C program)
$ wsk activation logs a1b2c3d4
2025-01-01T12:00:00.000Z stderr: [evrtng] ANSI C action invoked

# POST via curl
$ curl -X POST \
  https://fnc.evrtng.cloud/api/v1/web/guest/default/ansiCAction \
  -H "Content-Type: application/json" \
  -d '{"args": "curl-test"}'

{
    "msg": "Hello from ANSI C!",
    "args": "curl-test"
}

# GET with query param
$ curl "https://fnc.evrtng.cloud/api/v1/web/guest/default/ansiCAction?args=hello"
{ "msg": "Hello from ANSI C!", "args": "hello" }