raspberry pi - Working with node-gyp and C++, is there a way to make a dependency on a particular library optional? - Stack Over

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Automatically optional too, simply by testing for the presence of the library, avoiding making the user pass arguments or define environment variables or the like.

I'm working on making a Raspberry Pi project of mine, a project that depends on GPIO, compatible with the Raspberry Pi 5. (The Raspberry Pi 5, in general, has caused a lot of grief due to a new GPIO chipset.)

Having reached the point where I'd solved all of my own GPIO issues, I had left to handle one library of someone else's in need of upgrade. I could, of course, just take my own fork of their project and go my own merry way now that I have working code, but I'd like to offer what I've done as a pull request.

There's one thing now that could be a sticking point, however, which I'd like to avoid if possible. I've introduced a new dependency on the libgpiod library.

I'm pretty sure the original author wouldn't want to deal with that. I'd like for this new code to compile on a Raspberry Pi 3 or 4 without libgpiod having been installed, but take full advantage of libgpiod if present.

Here's my binding.gyp file:

{
  "targets": [
    {
      "variables": {
        "dht_verbose%": "false"
      },
      "target_name": "node_dht_sensor",
      "sources": [
        "src/bcm2835/bcm2835.c",
        "src/node-dht-sensor.cpp",
        "src/dht-sensor.cpp",
        "src/util.cpp",
        "src/abstract-gpio.cpp", // <-- My code to handle GPIO using either bcm2835 or libgpiod
      ],
      "include_dirs": [
        "<!@(node -p \"require('node-addon-api').include\")"
      ],
      "dependencies": [
        "<!(node -p \"require('node-addon-api').gyp\")"
      ],
      'libraries': [
        '-lgpiod' // <-- New dependency
      ],
      "defines": [ 'NAPI_DISABLE_CPP_EXCEPTIONS' ],
      "conditions": [
        ["dht_verbose=='true'", {
          "defines": [ "VERBOSE" ]
        }]
      ]
    }
  ]
}

Here's the start of my abstract-gpio.cpp:

#include "abstract-gpio.h"

#include <algorithm>
#include "bcm2835/bcm2835.h"
#include <fstream>
#include <gpiod.h> // <-- What to do here to make this optional? Can node-gyp
#include <regex>   //     conditionally create a symbol for #ifndef-ing here?
#include <stdio.h>
#include <string>

My C++ skills are rusty at best. Until now I hadn't touched my own C++ code for five years, and five years ago I hadn't touched C++ for well over a decade.

node-gyp? I've merely followed examples and simple recipes at this point.

The big trick is that consumers of this library will use this library via npm install node-dht-sensor. I don't want the user to have to worry about libgpiod unless they're using a Raspberry Pi and have a good reason to install it.

Is there some combination of node-gyp options and perhaps, if needed, dummy libgpiod C++ stubs (that won't interfere with the real libgpiod if present) that can solve this problem for me?

Update:

Here's a somewhat, but not fully satisfactory solution, which requires a user to install the module like this:

npm install node-dht-sensor --use_libgpiod=true

...if they need (or want... this does work on a RPi 4 too) to use libgpiod, allowing the standard installation without the extra parameter to impose no new library dependencies.

{
  "targets": [
    {
      "variables": {
        "dht_verbose%": "false",
        "use_libgpiod%" : "false"
      },
      "target_name": "node_dht_sensor",
      "sources": [
        "src/bcm2835/bcm2835.c",
        "src/node-dht-sensor.cpp",
        "src/dht-sensor.cpp",
        "src/util.cpp",
        "src/abstract-gpio.cpp",
      ],
      "include_dirs": [
        "<!@(node -p \"require('node-addon-api').include\")"
      ],
      "dependencies": [
        "<!(node -p \"require('node-addon-api').gyp\")"
      ],
      "defines": [ 'NAPI_DISABLE_CPP_EXCEPTIONS' ],
      "conditions": [
        ["dht_verbose=='true'", {
          "defines": [ "VERBOSE" ]
        }],
        ["use_libgpiod=='true'", {
          "defines": [ "USE_LIBGPIOD" ],
          'libraries': [
            '-lgpiod'
          ]
        }]
      ]
    }
  ]
}

What I'd really like to do, however, if it's at all possible, is to replace "use_libgpiod=='true'" with something automatic, the moral equivalent of "available(libgpiod)" or "exists('/usr/include/gpiod.h')", in case any such node-gyp capability exists which simply can't be easily found in the documentation.

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