Net debugging in WebView

This guide explains how to capture network logs net logs 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 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 and commandline flags for more information.

Net Logs in the DevTools are available from M128

Steps:

1. Open WebView DevTools and navigate to the "Flags" section.
2. Locate the "net-log" flag and enable it within the DevTools flags menu.
3. Launch your app and perform actions that trigger the network behavior you want to debug. Once you've reproduced the issue, close your app.
4. Locate and share the net log file generated using Android's Quick Share.

*** 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 and commandline flags 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:

# 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.

Manual steps

1. Figure out the app's data directory
   shCopy

   # 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=//')" && \
   

2. 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.
3. Kill the app, if running
4. Set the netlog flag:
   shCopy

   FLAG_FILE=/data/local/tmp/webview-command-line
   adb shell "echo '_ --log-net-log=${jsonFile}' > ${FLAG_FILE}"
   

5. Restart the app. Reproduce whatever is of interest, and then kill the app when finished
6. Get the netlog off the device:
   shCopy

   adb pull "${appDataDir}/app_webview/${jsonFile}"
   adb shell "rm '${appDataDir}/app_webview/${jsonFile}'"
   

7. Optional: view the data in the NetLog viewer
8. Optional: clear the commandline flags:
   shCopy

   FLAG_FILE=/data/local/tmp/webview-command-line
   adb shell "rm ${FLAG_FILE}"