Snap Cache

Snap Cache creates a local cache of snaps and assertions for snaps in a brand store. Why? Some devices have very limited network bandwidth e.g. a zigbee mesh, so it is not practical for them to download snaps directly from a snap store.

Once Snap Cache is authorized to access a brand store, snaps can be registered to be watched. Whenever a new version appears at the brand store, the snap is downloaded to the local cache. The application provides an API for external applications to retrieve the cached files and distribute them to the low-bandwidth network.

Snap Cache downloads the snap and its assertion from the brand store, so it can be installed onto a device without using the --dangerous flag. An example of an that handles the installation of the assertion and snap is Snap Sideloader.

Web interface

Snap Cache provides a web interface to help get started with the application. Just browse to http://edge-server-ip:8888/ e.g. http://localhost:8888 if testing locally.

The web interface allows a user to:

• Login to a brand store (storing the authentication macaroon locally)
• Manage which snaps are cached
• View and download the files in the local cache

API

Login to the store

POST /v1/login

Authenticate with the store and cache the macaroon in the local database.

Request

Attribute	Type	Description
email	string	Ubuntu SSO email address
password	string	Ubuntu SSO password
otp	string	One-time password
store	string	Brand store ID
series	string	Model assertion series

Response

Attribute	Type	Description
code	string	Error code
message	string	Error message

curl -X POST -d '{"email":"john@example.com", "password":"notasecret", "store":"my-great-store", "series":"16", "otp":"123456"}' http://localhost:8888/v1/login

List snaps to watch

GET /v1/snaps

List the snaps that will be watched for updates

Response

Attribute	Type	Description
code	string	Error code
message	string	Error message
records	array	List of snaps

curl http://localhost:8888/v1/snaps

{
    "code": "",
    "message": "",
    "records": [
        {
            "id": "bu9eiuh105lr9jbvh130",
            "name": "iotdevice-verticals",
            "arch": "amd64",
            "created": "2020-10-23T14:32:26Z",
            "modified": "2020-10-23T14:32:26Z"
        },
        {
            "id": "bu9ej01105lr9jbvh13g",
            "name": "logsync-james",
            "arch": "amd64",
            "created": "2020-10-23T14:32:32Z",
            "modified": "2020-10-23T14:32:32Z"
        }
    ]
}

List the downloaded snaps

GET /v1/downloads

List the snaps in the download cache.

curl http://localhost:8888/v1/downloads 

{
    "code": "",
    "message": "",
    "records": [
        {
            "name": "iotdevice-verticals",
            "arch": "amd64",
            "revision": 2,
            "assertion": "iotdevice-verticals_2_amd64.assert",
            "size": 6283264,
            "filename": "iotdevice-verticals_2_amd64.snap"
        },
        {
            "name": "logsync-james",
            "arch": "amd64",
            "revision": 38,
            "assertion": "logsync-james_38_amd64.assert",
            "size": 4419584,
            "filename": "logsync-james_38_amd64.snap"
        },
        {
            "name": "logsync-james",
            "arch": "amd64",
            "revision": 72,
            "assertion": "logsync-james_72_amd64.assert",
            "size": 4419584,
            "filename": "logsync-james_72_amd64.snap"
        }
    ]
}

Download a snap file or assertion

GET /v1/downloads/{name}/{filename}

Download a snap file or its assertion. The name of the file can be seen in the List downloads response.

curl -o output.assert http://localhost:8888/v1/downloads/logsync-james/logsync-james_72_amd64.assert

Download a snap delta

GET /v1/delta/{name}/{arch}/from-revision/to-revision

Generate a binary delta of a snap file from one specific revision to another. Both revisions must be in the download cache. The delta is created using xdelta3.

curl -o output.delta3 http://localhost:8888/v1/delta/logsync-james/amd64/38/72