src/docs/updater/dev_manual.md

# Chromium Updater Developer's Manual

This manual provides information on how to develop the
[Chromium Updater](https://source.chromium.org/chromium/chromium/src/+/main:chrome/updater/),
including tips and tricks.

[TOC]

## Code Organization

### Cross-platform Code
Where possible, cross-platform code is preferred to other alternatives. This
means that the source code of the updater is organized in sub-directories,
first by functionality (or feature), and second by platform name. For example,
the source code contains `updater\net` instead of `updater\mac\net`.

## Bots & Lab
>**_NOTE:_** Knowledge in this section may become out-of-date as LUCI evolves
quickly.
### Builders / Testers
There are two sets of configuration files for our builders/testers. One is
for chromium-branded and locates in `src`. The other one is for chrome-branded
and locates in `src-internal`.

#### Chromium-branded (`src`)
  - Console: https://ci.chromium.org/p/chromium/g/chromium.updater/console
  - `tools/mb/mb_config.pyl`: specifies GN args.
  - `testing/buildbot/gn_isolate_map.pyl`: maps a GN label to GN targets, and
    provides test arguments, for example test timeout values.
  - `testing/buildbot/test_suites.pyl`: maps test suite name to GN label, and
    provides optional swarming dimensions.
  - `testing/buildbot/waterfalls.pyl`: maps tester to test suites names, and
    specifies OS, architecture etc.
  - `infra/config/subprojects/chromium/ci/chromium.updater.star`: defines our
    testers and builders and how they appear on the console.

Command to update json files after configure update:
  - `tools\mb\mb train` (if `mb_config.pyl` is changed).
  - `lucicfg generate .\infra\config\main.star` (if `chromium.updater.star`
    is changed).
  - `vpython3 .\testing\buildbot\generate_buildbot_json.py`

Reference CLs:
  - Add a tester: https://crrev.com/c/4068601
  - Update GN args: https://crrev.com/c/3656357

#### Chrome-branded (`src-internal`)
  - Console: https://ci.chromium.org/p/chrome/g/chrome.updater/console
  - `tools/mb/mb_config.pyl`: specifies GN args.
  - `testing/buildbot/gn_isolate_map.pyl`: maps a GN label to GN targets, and
    provides test arguments, for example test timeout values.
  - `testing/buildbot/test_suites.pyl`: maps test suite name to GN label, and
    provides optional swarming dimensions.
  - `testing/buildbot/waterfalls.pyl`: maps tester to test suites names, and
    specifies OS, architecture etc.
  - `infra/config/subprojects/chrome/ci/chrome.updater.star`: defines our
    testers and builders and how they appear on the console.

Command to update json files after configure update:
  - `..\src\tools\mb\mb train -f tools\mb\mb_config.pyl` (if `mb_config.pyl`
    is changed).
  - `lucicfg generate .\infra\config\main.star` (if `chrome.updater.star`
    is changed).
  - `vpython3 .\testing\buildbot\generate_testing_json.py`

Please note changes in `src-internal` needs to roll into chromium/src to take
effect. This could take hours until a CL authored by
`chromium-internal-autoroll@` lands. During transition, the configure files
could be in inconsistent state and leads to infra error.

### Run tests on swarming
`mb` tool can upload your private build target (and all the dependencies,
 based on build rule) to swarming server and run the target on bots. The
 upload may take quite some time if the target changed a lot since the last
 upload and/or your network is slow.

* Simple scenario:

  ```
  .\tools\mb\mb.bat run -v --swarmed .\out\Default updater_tests -- --gtest_filter=*Integration*
  ```

* Sometimes the mb tool may fail to match the testing OS (when doing
 cross-compile) or you may want to run the task on certain kind of bots.
This can be done by specifying bots dimension with switch `-d`. Remember
`--no-default-dimensions` is necessary to avoid dimension value conflict.
Example:

  ```
  .\tools\mb\mb.bat run --swarmed --no-default-dimensions -d pool chromium.win.uac -d os Windows-10 .\out\Default updater_tests_system -- --gtest_filter=*Install*
  ```

* `mb` can schedule tests in the pools managed by different swarming servers.
  The default server is
  [chromium-swarm.appspot.com](https://chromium-swarm.appspot.com/botlist?k=pool).
  To schedule tests to pools managed by
  [chrome-swarming.appspot.com](https://chrome-swarming.appspot.com/botlist?k=pool),
  for example `chrome.tests`, add `--internal` flag in the command line:

  ```
    tools/mb/mb run -v --swarmed --internal --no-default-dimensions -d pool chrome.tests -d os Windows-10 out/WinDefault updater_tests
  ```

* If `mb` command failed with error `isolate: original error: interactive login is required`, you need to login:

  ```
   tools/luci-go/isolate login
  ```

* If your test introduces dependency on a new app on macOS, you need to let
 `mb` tool know so it can correctly figure out the dependency. Example:
  https://crrev.com/c/3470143.

* To run tests on `Arm64`, the mb tool needs to be invoked as follows:

  ```
  .\tools\mb\mb run -v --swarmed --no-default-dimensions --internal -d pool chrome.tests.arm64 out\Default updater_tests_system -- --gtest_filter=LegacyAppCommandWebImplTest.FailedToLaunchStatus
  ```

* When system tests crash, the stack is missing from the swarming log. This can be avoided if you suppress the test bot mode:

  ```
  .\tools\mb\mb run -v --swarmed  --no-bot-mode out\Default updater_tests_system
  ```

### Accessing Bots
 TODO(crbug.com/1327486): Document how to remote into bots for debugging.

### Updating the Checked-In Version of the Updater
An older version of the updater is checked in under `//third_party/updater`.
This version of the updater is used in some integration tests. The updater is
pulled from
[CIPD](https://chrome-infra-packages.appspot.com/p/chromium/third_party/updater)
based on the versions specified in `//DEPS`. A system called `3pp` periodically
updates the packages in CIPD, based on a combination of the Chromium build
output and what is actually released through Omaha servers. The configuration
for 3pp can be found in `//third_party/updater/*/3pp`.

To update these copies of the updaters:
1.  Land whatever CLs need to be committed on trunk.
2.  Wait for builds to be available in CIPD that have the needed changes.
    *   Instead of waiting, you can instead modify the `fetch.py` scripts for
        3pp. For Chrome builds, make sure the build has been released in Omaha
        then update the fetch script with the desired version number. For
        Chromium, make sure the build exists in GCS (the
        chromium-browser-snapshots bucket), then update the min version in the
        script. The min version usually is different per-platform, since
        Chromium does not archive a version at every CL. After making these
        changes, 3pp will import the new versions within a few hours.
3.  Update //DEPS to point to the new versions.

## Building

### Configuring the build

After creating your build configuration directory via
[`gn gen`](https://chromium.googlesource.com/chromium/src/+/main/docs/linux/build_instructions.md#Setting-up-the-build)
(this step is equivalent across all platforms), you will need to use
[`gn args`](https://www.chromium.org/developers/gn-build-configuration/) to
configure the build appropriately.

#### Flags required for building successfully

As of 2023-05-24, the updater cannot be built in component mode. It is also not
specifically designed to be built without the updater being enabled. You must
specify these options to `gn` via `gn args`:

```
is_component_build=false
enable_updater=true
```

Depending on other configuration options, the default `symbol_level`, 2, might
produce object files too large for the linker to handle (in debug builds).
Partial symbols, via `symbol_level=1`, fix this. Omitting almost all symbols
via `symbol_level=0` reuslts in a smaller and faster build but makes debugging
nearly impossible (call stacks will not be symbolicated).

#### Faster builds

Building on Goma is typically much faster than your workstation. After you've
set up Goma, specify it in `gn args` with `use_goma=true`.

To get started on Goma, and for more information on how to use it, review its
[public documentation](https://chromium.googlesource.com/infra/goma/client/+/HEAD/doc/early-access-guide.md)
or its
[Google-internal documentation](https://go.corp.google.com/how-to-use-goma).

#### More release-like builds

Chromium projects build in debug mode by default. Release builds (also called
"opt", or "optimized", builds) are faster to link and run more efficiently;
they are, of course, much harder to debug. For a release build, add the
following to the build configuration's `gn args`:

```
is_debug=false
```

With a Google `src-internal` checkout, you can create a Chrome-branded build:

```
is_chrome_branded=true
include_branded_entitlements=false
```

Updater branding affects the path the updater installs itself to, among other
things. Differently-branded copies of Chromium Updater are intended to coexist
on a machine, operating independently from each other.

### Cleaning the build output
Running `ninja` with `t clean` cleans the build out directory. For example:
```
ninja -C out\Default chrome/updater:all -t clean
```

### How to generate the cross-compilation IDL COM headers and TLB files

6 different build flavors need to be built in sequence. If you see errors
similar to the following:
```
midl.exe output different from files in gen/chrome/updater/app/server/win, see C:\src\temp\tmppbfwi0ds
To rebaseline:
  copy /y C:\src\temp\tmppbfwi0ds\* c:\src\chromium\src\third_party\win_build_output\midl\chrome\updater\app\server\win\x64
ninja: build stopped: subcommand failed.
```

You can then run the following command to update IDL COM files for all flavors:
```
python3 tools/win/update_idl.py
```

### Build artifacts

Build outputs will land in the directory created by `gn gen` that you have been
providing to assorted `gn`, `ninja`, and `autoninja` commands. `updater.zip`
contains copies of the "final" outputs created by the build. `UpdaterSetup` is
probably what you want for installing the updater you have built.

TODO(crbug.com/1448700): list the relevant/interesting outputs here and what
they are, why they're relevant/interesting, etc.

## Code Coverage
Gerrit now down-votes the changes that do not have enough coverage. And it's
nice to have good coverage regardless. To improve code-coverage, we need to
know what are already covered and what are not.

#### Coverage on Gerrit
It's automatically generated. But the coverage shown is the combined result
from all OS platforms.

#### Coverage Dashboard
The [updater code coverage dashboard](https://analysis.chromium.org/coverage/p/chromium/dir?host=chromium.googlesource.com&project=chromium/src&ref=refs/heads/main&path=//chrome/updater/&platform=mac)
supports breakdown by OS platform or test type. But it is only for the code in
trunk.

#### Run Coverage Locally
We can quickly get OS-specific coverage result with the local changes:

* macOS/Linux
```
gn gen out/coverage --args="use_clang_coverage=true is_component_build=false is_chrome_branded=true is_debug=true use_debug_fission=true use_goma=true symbol_level=2"

vpython3 tools/code_coverage/coverage.py  updater_tests -b out/coverage -o out/report -c 'out/coverage/updater_tests' -f chrome/updater
```

* Windows
```
gn gen out\coverage --args="use_clang_coverage=true is_component_build=false is_chrome_branded=true is_debug=true use_debug_fission=true use_goma=true symbol_level=2"

vpython3 tools\code_coverage\coverage.py updater_tests -b out\coverage -o out\report -c out\coverage\updater_tests.exe  -f chrome/updater
```
The last command outputs an HTML file and you can open it in browser to see the
coverages.


## Debugging
### Debug into Windows update service

* Install updater: ```UpdaterSetup.exe --install [--system]```
> **_TIP:_**  Debugger may have trouble to find the symbols at the service
 side even if you add your build output directory to the symbol paths. To
workaournd the issue, you can copy `updater.exe*` to the versioned
installation directory.
* Set a breakpoint at the client side after service instantiation but before
calling into the service API. Most likely this will be somewhere in file
`update_service_proxy.*`.
* Start the client, wait for it to hit the break point. At this time, the
service process should have started.
* Find the server process, which contains the command line switch `--server`
(user-level server) or `--system --windows-service` (system-level server).
Start another debugger and attach the server process. Then set a server-side
breakpoint at the place you want to debug.
* Continue the client process.

### Logging

Both the updater and the unit tests can create program logs.

#### Updater logs

The updater itself logs in the product directory.

#### Unit test logs

The unit tests log into a directory defined by the environment variable
`${ISOLATED_OUTDIR}`. When run by Swarming, the updater logs are copied
into `${ISOLATED_OUTDIR}` too, so that after the swarming task has completed,
both types of logs are available as CAS outputs. The logs for
`updater_tests_system` and `integration_test_helper` are merged into
`updater_tests_system.log`.

Non-bot systems can set up this environment variable to collect logs for
debugging when the tests are run locally.

## Testing src changes with trybots

In some cases, you will want to test the changes you make within
[chromium/src](https://chromium.googlesource.com/chromium/src.git) on
specific builders/testers before landing these changes. It is possible
to do this with the use of the trybots available on the
[tryserver.chromium.updater](https://ci.chromium.org/ui/p/chromium/g/tryserver.chromium.updater/builders)
 waterfall. The steps are as follows:

1. Find a trybot to run your tests with. All of the trybots on the
tryserver.chromium.updater waterfall have a corresponding builder and
tester, so find one that runs a workflow to test your changes.
2. Apply your configuration changes to chromium/src and upload a CL
using the typical workflow: `git cl upload`
3. Run `git cl try -B luci.chromium.try -b {TRYBOT_NAME}` with the
name of the trybot you found.
4. Monitor and debug any failures as you normally would for any
builder or tester.

## Troubleshooting

### Build errors

* **Maybe it's not you.** If you pulled from `origin/main` since your last
  successful build, or have never successfully built on your current branch,
  and the build errors you're seeing aren't obviously related to any changes
  you've made,
  [check the tree status](https://chromium-status.appspot.com/status_viewer).
  Did you pull down a broken version? If so, and the revert is in, pull again
  and see if it works better. Or skip checking the tree status and just try
  this as your first debugging step for build breaks after a pull.
* **Dependencies are a fast-moving target.** Remember to run `gclient sync -D`
  after every pull from `origin/main` _and_ every branch change. If you aren't
  sure whether you ran it, just run it, it's fast if you don't need it.
* **Is the Goma client ready?** If your build is failing quickly with a
  bunch of errors related to Goma, run `goma_ctl ensure_start` and try again.
* **Symbols too big?** If your build is failing during linking, check your
  `gn args` to verify that `symbol_level=1` (or `0`) is present. If it's not,
  you're running into a known issue where the default symbol level, `2`,
  outputs symbols too large for the linker to comprehend.