`crypt/digest` module cannot be used because of native code

[lilioid]

I'm trying to build an application with Alloy that requires computing an HMAC to communicate to external systems. I have found the relevant JS support in the $(MODULES)/crypt/hmac.js file but as far as I can see this also requires including `$(MODULES)/crypt/digest/manifest.json) in my manifest. This, however, fails because the digest is module requires native code which is not compiled automatically.´

My Manifest

I am using the following manifest file:

{
 	"include":  [
		"$(MODDABLE)/examples/manifest_mod.json",
		"$(MODDABLE)/examples/manifest_typings.json",
		"$(MODULES)/crypt/digest/manifest.json"
	],
	"modules": {
		"crypt/hmac": "$(MODULES)/crypt/etc/hmac.js",
		"*": [
			"./main.js",
		]
	}
}

The Error

Whe running pebble build I get the following output:

Running Moddable prebuild.
Running mcrun -m ./src/embeddedjs/manifest.json -f x -p pebble/emery -t build -o ./build/mods/emery/mcrun -s tech.moddable.pebble
### -p pebble/emery
Native code detected:
  /home/lilly/.local/share/pebble-sdk/SDKs/4.9.169/toolchain/moddable/modules/crypt/digest/modCrypt.c
  /home/lilly/.local/share/pebble-sdk/SDKs/4.9.169/toolchain/moddable/modules/crypt/digest/kcl/chacha.c
  /home/lilly/.local/share/pebble-sdk/SDKs/4.9.169/toolchain/moddable/modules/crypt/digest/kcl/fips180.c
  /home/lilly/.local/share/pebble-sdk/SDKs/4.9.169/toolchain/moddable/modules/crypt/digest/kcl/fips197.c
  /home/lilly/.local/share/pebble-sdk/SDKs/4.9.169/toolchain/moddable/modules/crypt/digest/kcl/fips46.c
  /home/lilly/.local/share/pebble-sdk/SDKs/4.9.169/toolchain/moddable/modules/crypt/digest/kcl/ghash.c
  /home/lilly/.local/share/pebble-sdk/SDKs/4.9.169/toolchain/moddable/modules/crypt/digest/kcl/rc.c
  /home/lilly/.local/share/pebble-sdk/SDKs/4.9.169/toolchain/moddable/modules/crypt/digest/kcl/rfc1321.c
Mods cannot contain native code. Did you intend to build using mcconfig?
### Error: mod cannot contain native code
Moddable prebuild failed: Command '['mcrun', '-m', './src/embeddedjs/manifest.json', '-f', 'x', '-p', 'pebble/emery', '-t', 'build', '-o', './build/mods/emery/mcrun', '-s', 'tech.moddable.pebble']' returned non-zero exit status 1.

[phoddie]

Thank you for the report.

Everything is working as expected. Alloy apps are built using mods, which contain JavaScript and resources (data), not native code.

There are three options for HMAC support:

1. Add cryptographic support to the Alloy host (runtime). That's straightforward, but feels like a bit of a stretch for Pebble since it isn't a feature of Pebble OS's applib, at least as far as I'm aware.
2. Use a JavaScript implementation of HMAC in your Alloy app. This probably possible but also probably impractical. That kind of heavy math isn't what Alloy is designed for, especially on a low-energy MCU.
3. Use a JavaScript implementation of HMAC in PebbleKitJS. This is a little more complicated because you'll need to move data around using Pebble's App Messages (see the Alloy hellomessage example) but performance and code size won't be a concern.

If you would share a bit more about what you are using the HMAC for, and the particulars of what algorithms in requires, that would be helpful, certainly in evaluating option (1).