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.
