# Net debugging in WebView

This guide explains how to capture network logs [net logs](https://www.chromium.org/for-testers/providing-network-details/)
for debugging WebView using DevTools. Net logs provide detailed information about
network requests and responses made by your WebView, helping you diagnose
network-related issues.

## Net Logs In WebView DevTools

*** note
**Important**: Enabling net logging through DevTools requires enabling
[setWebContentsDebuggingEnabled](https://developer.chrome.com/docs/devtools/remote-debugging/webviews)
in your app. This setting is automatically enabled by default if you use a
either a `userdebug` or `eng` Android image. it is also enabled by default if
you use a debug app build. See [device setup](device-setup.md) and [commandline flags](commandline-flags.md)
for more information.

Net Logs in the DevTools are available from M128
***

### Steps:

1. Open [WebView DevTools](https://chromium.googlesource.com/chromium/src/+/a326b853919f482d7e9c67fe7e492ae060cb4851/android_webview/docs/developer-ui.md)
and navigate to the "Flags" section.
1. Locate the "net-log" flag and enable it within the DevTools flags menu.
1. Launch your app and perform actions that trigger the network behavior you
want to debug. Once you've reproduced the issue, close your app.
1. Locate and share the net log file generated using [Android's Quick Share](https://support.google.com/android/answer/9286773?hl=en).

*** note
Please note, there are file limitations:

**File Size:** Net log files are limited to 100 MB each.

**File Age:** Files older than 30 days will be automatically deleted.

**Storage Capacity:** If the total net log storage exceeds 1 GB, older files
will be deleted until the total storage is under the threshold.
***

## Manually setting the flag (WebView developers only)

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

*** note
**Important**: if you are unable to use net logs in WebView DevTools, all
alternate approaches require applying commandline flags. **It's not typically
possible for external reporters to apply commandline flags, so please do not
ask them to follow this guide.**

This guide is only for chromium developers who are set up for WebView
development. Specifically, this guide requires the reader to use a `userdebug`
or `eng` Android image, see [device setup](device-setup.md) and [commandline
flags](commandline-flags.md) for more information.
***

### Python script

If you have a chromium checkout, the preferred way to set the netlog flag is to
use the `record_netlog.py` script like so:

```shell
# Optional: set any flags of your choosing before running the script. Don't set
# --log-net-log though; this is set by record_netlog.py.
$ build/android/adb_system_webview_command_line --enable-features=MyFeature,MyOtherFeature
Wrote command line file. Current flags (in webview-command-line):
  005d1ac915b0c7d6 (bullhead-userdebug 6.0 MDB08M 2353240 dev-keys): --enable-features=MyFeature,MyOtherFeature

# Replace "<app package name>" with your app's package name (ex. the
# WebView Shell is "org.chromium.webview_shell"). This script will set an
# appropriate value for --log-net-log and handle setup/cleanup.
$ android_webview/tools/record_netlog.py --package="<app package name>"
Netlog will start recording as soon as app starts up. Press ctrl-C to stop recording.
^C
Pulling netlog to "netlog.json"
```

Then import the JSON file (`netlog.json` in the working directory) into [the
NetLog viewer][1].

### Manual steps

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](commandline-flags.md):
   ```sh
   FLAG_FILE=/data/local/tmp/webview-command-line
   adb shell "echo '_ --log-net-log=${jsonFile}' > ${FLAG_FILE}"
   ```
1. Restart the app. Reproduce whatever is of interest, and then kill the app
   when finished
1. Get the netlog off the device:
   ```sh
   adb pull "${appDataDir}/app_webview/${jsonFile}"
   adb shell "rm '${appDataDir}/app_webview/${jsonFile}'"
   ```
1. Optional: view the data in [the NetLog viewer][1]
1. Optional: [clear the commandline flags](commandline-flags.md):
   ```sh
   FLAG_FILE=/data/local/tmp/webview-command-line
   adb shell "rm ${FLAG_FILE}"
   ```

[1]: https://netlog-viewer.appspot.com/#import