Append to existing apps.json preload state instead of overwriting

[alexgg]

This is to remain in draft state until the v3 target state API changes are merged

---

If the image we are preloading to contains an existing apps.json append
the preloaded app to it instead of overwriting it.

Fixes balena-io/balena-cli#2262

Relates to balena-io/balena-cli#2263

Change-type: patch
Signed-off-by: Alex Gonzalez [email protected]

---

Tested on a raspberrypi4-64-2.75.0+rev1 image that does not contain a preloaded apps.json, and on a genericx86-64-ext development build with an existing apps.json with preloaded state.

[alexgg]

Validation on a devenv with a draft v3 state endpoint:

[x] Preloading on an image with preloaded apps.json with a v3 state supervisor
* v3 style app is appended to apps.json
[x] Preloading on an image with preloaded apps.json with a v2 state supervisor (should not happen)
Fails with:

The preloaded app state and the current state in the image have a version mismatch. Please use afresh, not previously preloaded image file

[x] Preloading on an image without apps.json with a v2 state supervisor
* v2 stype app appears in apps.json
[x] Preloading on an image without apps.json with a v3 state supervisor (should not happen)

• v3 state app appears in apps.json

[pdcastro]

Small things while it is still a draft -- I'd have approved the PR if it wasn't a draft. :-)

[pdcastro]

To avoid logic duplication, _supervisorLT7 could be renamed _supervisorLT and take the version as a parameter. To preserve the existing "typo safety feature", the version strings could be assigned to module-level constants. For example:

const v7 = '7.0.0';
const v13 = '13.0.0';

class Preloader extends EventEmitter {
	...
	_supervisorLT(version) {
		try {
			return compareVersions(this.supervisorVersion, version) === -1;
		...
	}

• this._supervisorLT7() → this._supervisorLT(v7)
• this._supervisorLT13() → this._supervisorLT(v13)

[pdcastro]

The image property is guaranteed to exist, right? Otherwise, .get() could be used instead of the bracket syntax to avoid a KeyError, plus providing the empty string as a default value:

Suggested change

	for service in app['services']:
	image_name = app['services'][service]['image']
	for service in app['services'].values():
	image_name = service.get('image', '')

[pdcastro]

A line of code can be deleted (app = current_state['apps'][uuid]) later on by using items() instead of keys():

Suggested change

	for uuid in list(current_state['apps'].keys()):
	for [uuid, app] in current_state['apps'].items():

In Python 3 (the version used by preload), keys() values() items() return iterators and list() can be used to create an indexable list/array out of the iterators where needed, but it doesn't look needed here.

[pdcastro]

This line can be deleted if the [uuid, app] unpacking suggested in another comment is used.