1# SystemUpdaterSample 2 3This app demonstrates how to use Android system updates APIs to install 4[OTA updates](https://source.android.com/devices/tech/ota/). It contains a 5sample client for `update_engine` to install A/B (seamless) updates. 6 7A/B (seamless) update is available since Android Nougat (API 24), but this sample 8targets the latest android. 9 10 11## Workflow 12 13SystemUpdaterSample app shows list of available updates on the UI. User is allowed 14to select an update and apply it to the device. App shows installation progress, 15logs can be found in `adb logcat`. User can stop or reset an update. Resetting 16the update requests update engine to cancel any ongoing update, and revert 17if the update has been applied. Stopping does not revert the applied update. 18 19 20## Update Config file 21 22In this sample updates are defined in JSON update config files. 23The structure of a config file is defined in 24`com.example.android.systemupdatersample.UpdateConfig`, example file is located 25at `res/raw/sample.json`. 26 27In real-life update system the config files expected to be served from a server 28to the app, but in this sample, the config files are stored on the device. 29The directory can be found in logs or on the UI. In most cases it should be located at 30`/data/user/0/com.example.android.systemupdatersample/files/configs/`. 31 32SystemUpdaterSample app downloads OTA package from `url`. In this sample app 33`url` is expected to point to file system, e.g. `file:///data/my-sample-ota-builds-dir/ota-002.zip`. 34 35If `ab_install_type` is `NON_STREAMING` then app checks if `url` starts 36with `file://` and passes `url` to the `update_engine`. 37 38If `ab_install_type` is `STREAMING`, app downloads only the entries in need, as 39opposed to the entire package, to initiate a streaming update. The `payload.bin` 40entry, which takes up the majority of the space in an OTA package, will be 41streamed by `update_engine` directly. The ZIP entries in such a package need to be 42saved uncompressed (`ZIP_STORED`), so that their data can be downloaded directly 43with the offset and length. As `payload.bin` itself is already in compressed 44format, the size penalty is marginal. 45 46if `ab_config.force_switch_slot` set true device will boot to the 47updated partition on next reboot; otherwise button "Switch Slot" will 48become active, and user can manually set updated partition as the active slot. 49 50Config files can be generated using `tools/gen_update_config.py`. 51Running `./tools/gen_update_config.py --help` shows usage of the script. 52 53 54## Sample App State vs UpdateEngine Status 55 56UpdateEngine provides status for different stages of update application 57process. But it lacks of proper status codes when update fails. 58 59This creates two problems: 60 611. If sample app is unbound from update_engine (MainActivity is paused, destroyed), 62 app doesn't receive onStatusUpdate and onPayloadApplicationCompleted notifications. 63 If app binds to update_engine after update is completed, 64 only onStatusUpdate is called, but status becomes IDLE in most cases. 65 And there is no way to know if update was successful or not. 66 672. This sample app demostrates suspend/resume using update_engins's 68 `cancel` and `applyPayload` (which picks up from where it left). 69 When `cancel` is called, status is set to `IDLE`, which doesn't allow 70 tracking suspended state properly. 71 72To solve these problems sample app implements its own separate update 73state - `UpdaterState`. To solve the first problem, sample app persists 74`UpdaterState` on a device. When app is resumed, it checks if `UpdaterState` 75matches the update_engine's status (as onStatusUpdate is guaranteed to be called). 76If they doesn't match, sample app calls `applyPayload` again with the same 77parameters, and handles update completion properly using `onPayloadApplicationCompleted` 78callback. The second problem is solved by adding `PAUSED` updater state. 79 80 81## Sample App UI 82 83### Text fields 84 85- `Current Build:` - shows current active build. 86- `Updater state:` - SystemUpdaterSample app state. 87- `Engine status:` - last reported update_engine status. 88- `Engine error:` - last reported payload application error. 89 90### Buttons 91 92- `Reload` - reloads update configs from device storage. 93- `View config` - shows selected update config. 94- `Apply` - applies selected update config. 95- `Stop` - cancel running update, calls `UpdateEngine#cancel`. 96- `Reset` - reset update, calls `UpdateEngine#resetStatus`, can be called 97 only when update is not running. 98- `Suspend` - suspend running update, uses `UpdateEngine#cancel`. 99- `Resume` - resumes suspended update, uses `UpdateEngine#applyPayload`. 100- `Switch Slot` - if `ab_config.force_switch_slot` config set true, 101 this button will be enabled after payload is applied, 102 to switch A/B slot on next reboot. 103 104 105## Sending HTTP headers from UpdateEngine 106 107Sometimes OTA package server might require some HTTP headers to be present, 108e.g. `Authorization` header to contain valid auth token. While performing 109streaming update, `UpdateEngine` allows passing on certain HTTP headers; 110as of writing this sample app, these headers are `Authorization` and `User-Agent`. 111 112`android.os.UpdateEngine#applyPayload` contains information on 113which HTTP headers are supported. 114 115 116## Used update_engine APIs 117 118### UpdateEngine#bind 119 120Binds given callbacks to update_engine. When update_engine successfully 121initialized, it's guaranteed to invoke callback onStatusUpdate. 122 123### UpdateEngine#applyPayload 124 125Start an update attempt to download an apply the provided `payload_url` if 126no other update is running. The extra `key_value_pair_headers` will be 127included when fetching the payload. 128 129`key_value_pair_headers` argument also accepts properties other than HTTP Headers. 130List of allowed properties can be found in `system/update_engine/common/constants.cc`. 131 132### UpdateEngine#cancel 133 134Cancel the ongoing update. The update could be running or suspended, but it 135can't be canceled after it was done. 136 137### UpdateEngine#resetStatus 138 139Reset the already applied update back to an idle state. This method can 140only be called when no update attempt is going on, and it will reset the 141status back to idle, deleting the currently applied update if any. 142 143### Callback: onStatusUpdate 144 145Called whenever the value of `status` or `progress` changes. For 146`progress` values changes, this method will be called only if it changes significantly. 147At this time of writing this doc, delta for `progress` is `0.005`. 148 149`onStatusUpdate` is always called when app binds to update_engine, 150except when update_engine fails to initialize. 151 152### Callback: onPayloadApplicationComplete 153 154Called whenever an update attempt is completed or failed. 155 156 157## Running on a device 158 159The commands are expected to be run from `$ANDROID_BUILD_TOP` and for demo 160purpose only. 161 162### Without the privileged system permissions 163 1641. Compile the app `mmma -j bootable/recovery/updater_sample`. 1652. Install the app to the device using `adb install <APK_PATH>`. 1663. Change permissions on `/data/ota_package/` to `0777` on the device. 1674. Set SELinux mode to permissive. See instructions below. 1685. Add update config files; look above at [Update Config file](#Update-Config-file). 1696. Push OTA packages to the device. 1707. Run the sample app. 171 172### With the privileged system permissions 173 174To run sample app as a privileged system app, it needs to be installed in `/system/priv-app/`. 175This directory is expected to be read-only, unless explicitly remounted. 176 177The recommended way to run the app is to build and install it as a 178privileged system app, so it's granted the required permissions to access 179`update_engine` service as well as OTA package files. Detailed steps are as follows: 180 1811. [Prepare to build](https://source.android.com/setup/build/building) 1822. Add the module (SystemUpdaterSample) to the `PRODUCT_PACKAGES` list for the 183 lunch target. 184 e.g. add a line containing `PRODUCT_PACKAGES += SystemUpdaterSample` 185 to `device/google/marlin/device-common.mk`. 1863. [Whitelist the sample app](https://source.android.com/devices/tech/config/perms-whitelist) 187 * Add 188 ``` 189 <privapp-permissions package="com.example.android.systemupdatersample"> 190 <permission name="android.permission.ACCESS_CACHE_FILESYSTEM"/> 191 </privapp-permissions> 192 ``` 193 to `frameworks/base/data/etc/privapp-permissions-platform.xml` 1944. Add `privileged: true` to SystemUpdaterSample 195 [building rule](https://android.googlesource.com/platform/bootable/recovery/+/refs/heads/master/updater_sample/Android.bp). 1965. Build sample app `make -j SystemUpdaterSample`. 1976. Build Android `make -j` 1987. [Flash the device](https://source.android.com/setup/build/running) 1998. Add update config files; look above at `## Update Config file`; 200 `adb root` might be required. 2019. Push OTA packages to the device if there is no server to stream packages from; 202 changing of SELinux labels of OTA packages directory might be required 203 `chcon -R u:object_r:ota_package_file:s0 /data/my-sample-ota-builds-dir` 20410. Run the sample app. 205 206 207## Development 208 209- [x] Create a UI with list of configs, current version, 210 control buttons, progress bar and log viewer 211- [x] Add `PayloadSpec` and `PayloadSpecs` for working with 212 update zip file 213- [x] Add `UpdateConfig` for working with json config files 214- [x] Add applying non-streaming update 215- [x] Prepare streaming update (partially downloading package) 216- [x] Add applying streaming update 217- [x] Add stop/reset the update 218- [x] Add demo for passing HTTP headers to `UpdateEngine#applyPayload` 219- [x] [Package compatibility check](https://source.android.com/devices/architecture/vintf/match-rules) 220- [x] Deferred switch slot demo 221- [x] Add UpdateManager; extract update logic from MainActivity 222- [x] Add Sample app update state (separate from update_engine status) 223- [x] Add smart update completion detection using onStatusUpdate 224- [x] Add pause/resume demo 225- [x] Verify system partition checksum for package 226 227 228## Running tests 229 230The commands are expected to be run from `$ANDROID_BUILD_TOP`. 231 2321. Build `make -j SystemUpdaterSample` and `make -j SystemUpdaterSampleTests`. 2332. Install app 234 `adb install $OUT/system/app/SystemUpdaterSample/SystemUpdaterSample.apk` 2353. Install tests 236 `adb install $OUT/testcases/SystemUpdaterSampleTests/arm64/SystemUpdaterSampleTests.apk` 2374. Run tests 238 `adb shell am instrument -w com.example.android.systemupdatersample.tests/android.support.test.runner.AndroidJUnitRunner` 2395. Run a test file 240 ``` 241 adb shell am instrument \ 242 -w -e class com.example.android.systemupdatersample.UpdateManagerTest#applyUpdate_appliesPayloadToUpdateEngine \ 243 com.example.android.systemupdatersample.tests/android.support.test.runner.AndroidJUnitRunner 244 ``` 245 246 247## Accessing `android.os.UpdateEngine` API 248 249`android.os.UpdateEngine` APIs are marked as `@SystemApi`, meaning only system 250apps can access them. 251 252 253## Getting read/write access to `/data/ota_package/` 254 255Access to cache filesystem is granted only to system apps. 256 257 258## Setting SELinux mode to permissive (0) 259 260```txt 261local$ adb root 262local$ adb shell 263android# setenforce 0 264android# getenforce 265``` 266 267 268## License 269 270SystemUpdaterSample app is released under 271[Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0). 272