android_webview/docs/net-debugging.md

# Net debugging in WebView

## Net log

WebView supports the `kLogNetLog` flag to log debugging network info to a JSON
file on disk.

*** aside
For more info on commandline flags, see
[commandline-flags.md](./commandline-flags.md).
***

*** note
**Note:** this requires either a `userdebug` or `eng` Android build (you can
check with `adb shell getprop ro.build.type`). Flags cannot be enabled on
production builds of Android.
***

1. Figure out the app's data directory
   ```sh
   # appPackageName is the package name of whatever app you're interested (ex.
   # WebView shell is "org.chromium.webview_shell").
   appDataDir="$(adb shell dumpsys package ${appPackageName} | grep 'dataDir=' | sed 's/^ *dataDir=//')" && \
   ```
1. Pick a name for the JSON file. This must be under the WebView folder in the
   app's data directory (ex. `jsonFile="${appDataDir}/app_webview/foo.json"`).
   **Note:** it's important this is inside the data directory, otherwise
   multiple WebView apps might try (and succeed) to write to the file
   simultaneously.
1. Kill the app, if running
1. Set the netlog flag:
   ```sh
   build/android/adb_system_webview_command_line --log-net-log=${jsonFile}
   ```
1. Restart the app. Reproduce whatever is of interest, and then kill the app
   when finished
1. Get the netlog off the device:
   ```sh
   adb pull "${appDataDir}/app_webview/${jsonFile}"
   ```
1. Import the JSON file into [the NetLog
   viewer](https://chromium.googlesource.com/catapult/+/master/netlog_viewer/)

For more details, see the implementation in
[AwUrlRequestContextGetter](/android_webview/browser/net/aw_url_request_context_getter.cc).
For support in the network service code path, see http://crbug.com/902039.