Native Messaging - C

host.json

{
    "name": "pingpong",
    "description": "Native messaging host example",
    "path": "path/to/release_executable",
    "type": "stdio",
    "allowed_origins": [
      "chrome-extension://extension_id/"
    ]
  }
  

main.js

var start;

/*
On a click on the browser action, send the app a message.
*/
chrome.browserAction.onClicked.addListener(() => {
    console.log('Sending: ping')
    start = performance.now();
    chrome.runtime.sendNativeMessage("pingpong", {text: "ping"}, onResponse);
});

function onResponse(res) {
    let end = performance.now();
    console.log(`Received: ${res.msg}, Took: ${end - start} ms`);
}

manifest.json

{
    "name": "Native Messaging Example",
    "version": "1.0",
    "manifest_version": 2,
    "description": "Send a message to a native application.",
    "background": {
        "scripts": ["main.js"]
    },
    "browser_action": {
        "default_icon": "message.svg"
    },
    "permissions": [
      "nativeMessaging"
    ]
  }

source.c

#include<stdio.h>
#include<stdlib.h>
#include<stdint.h>

uint8_t* read_input()
{
    uint32_t length;
    size_t count;
    int err;
    count = fread(&length, sizeof(uint32_t), 1, stdin);
    if (count != 1)
    {
        if (feof(stdin))
        {
            fprintf(stderr, "Unexpectedly encountered EOF while reading file\n");
        }
        else if ((err = ferror(stdin)))
        {
            fprintf(stderr, "An error occured while reading file, err code: %d\n", err);
            clearerr(stdin);
        }
        return NULL;
    }
    uint8_t* value = malloc((length + 1) * sizeof(*value));
    if (value == NULL)
    {
        fprintf(stderr, "An error occured while allocating memory for value");
        return NULL;
    }
    count = fread(value, sizeof(*value), length, stdin);
    if (count != length)
    {
        if (feof(stdin))
        {
            fprintf(stderr, "Unexpectedly encountered EOF while reading file\n");
        }
        else if ((err = ferror(stdin)))
        {
            fprintf(stderr, "An error occured while reading file, err code: %d\n", err);
            clearerr(stdin);
        }
        free(value);
        return NULL;
    }
    return value;
}

size_t write_output(const uint8_t* const value, uint32_t length)
{
    size_t count;
    int err;
    if (length > (1024 * 1024)) {
        fprintf(stderr, "Message too large");
        return 0;
    }
    count = fwrite(&length, sizeof(uint32_t), 1, stdout);
    if (count != 1)
    {
        if (feof(stdout))
        {
            fprintf(stderr, "Unexpectedly encountered EOF while reading file\n");
        }
        else if ((err = ferror(stdout)))
        {
            fprintf(stderr, "An error occured while reading file, err code: %d\n", err);
            clearerr(stdout);
        }
        return 0;
    }
    count = fwrite(value, sizeof(char), length, stdout);
    if (count != length)
    {
        if (feof(stdout))
        {
            fprintf(stderr, "Unexpectedly encountered EOF while writing file\n");
        }
        else if ((err = ferror(stdout)))
        {
            fprintf(stderr, "An error occured while writing file, err code: %d\n", err);
            clearerr(stdout);
        }
        return 0;
    }
    fflush(stdout);
    return length + 4;
}

int main()
{
    size_t count;
    uint8_t* val = read_input();
    if (val == NULL)
    {
        exit(EXIT_FAILURE);
    }
    count = write_output((uint8_t*)"{\"msg\":\"pong\"}", 14);
    if (count != 18)
    {
        free(val);
        exit(EXIT_FAILURE);
    }
    free(val);
}