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fix: cache webview top frame url in onPageStarted #38

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Merged
jkadamczyk merged 1 commit into from
Mar 5, 2026
+14 −1
Merged

fix: cache webview top frame url in onPageStarted #38

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14 changes: 13 additions & 1 deletion android/src/main/java/com/reactnativecommunity/webview/RNCWebView.java
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Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,7 @@ public class RNCWebView extends WebView implements LifecycleEventListener {
protected boolean nestedScrollEnabled = false;
protected ProgressChangedFilter progressChangedFilter;
protected boolean mActive = true;
protected @Nullable String mLastCommittedUrl;
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⚠️ Potential issue | 🟠 Major

Protect mLastCommittedUrl with cross-thread visibility guarantees.

mLastCommittedUrl is shared mutable state across WebView callback flow and @JavascriptInterface bridge flow. As currently implemented, stale reads are possible; this can still produce incorrect topFrameUrl under timing races.

Proposed fix 
-    protected `@Nullable` String mLastCommittedUrl;
+    protected volatile `@Nullable` String mLastCommittedUrl;
According to Android WebView documentation, are methods annotated with `@JavascriptInterface` invoked on the UI thread or on a background thread, and what synchronization/visibility guarantees are required when sharing fields with UI-thread callbacks?

Also applies to: 260-266, 497-502

🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@android/src/main/java/com/reactnativecommunity/webview/RNCWebView.java` at
line 82, mLastCommittedUrl is shared between WebView callbacks and
`@JavascriptInterface` bridge code and needs cross-thread visibility; make
mLastCommittedUrl volatile (and apply the same volatile protection to the other
shared mutable fields noted at lines 260-266 and 497-502) so updates on the UI
thread are immediately visible to background/bridge threads, and ensure any
compound read-modify-write sequences use a synchronized block or explicit lock
to preserve atomicity where used (search for mLastCommittedUrl and the other
listed fields to locate usages).


/**
* WebView must be created with an context of the current activity
Expand Down Expand Up @@ -256,6 +257,14 @@ public boolean getMessagingEnabled() {
return this.messagingEnabled;
}

public void setLastCommittedUrl(@Nullable String url) {
this.mLastCommittedUrl = url;
}

public @Nullable String getLastCommittedUrl() {
return this.mLastCommittedUrl;
}

@SuppressLint("RestrictedApi")
protected void createRNCWebViewBridge(RNCWebView webView) {
if (WebViewFeature.isFeatureSupported(WebViewFeature.WEB_MESSAGE_LISTENER)){
Expand Down Expand Up @@ -485,8 +494,11 @@ protected class RNCWebViewBridge {
@JavascriptInterface
public void postMessage(String message) {
if (mWebView.getMessagingEnabled()) {
// Capture top frame URL eagerly to avoid race condition if a navigation
// occurs between now and when the runnable executes on the main thread.
String topFrameUrl = mWebView.getLastCommittedUrl();
// Post to main thread because `mWebView.getUrl()` requires to be executed on main.
mWebView.post(() -> mWebView.onMessage(message, mWebView.getUrl(), null, mWebView.getUrl()));
mWebView.post(() -> mWebView.onMessage(message, mWebView.getUrl(), null, topFrameUrl));
} else {
FLog.w(TAG, "ReactNativeWebView.postMessage method was called but messaging is disabled. Pass an onMessage handler to the WebView.");
}
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1 change: 1 addition & 0 deletions android/src/main/java/com/reactnativecommunity/webview/RNCWebViewClient.java
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Original file line number Diff line number Diff line change
Expand Up @@ -87,6 +87,7 @@ public void onPageStarted(WebView webView, String url, Bitmap favicon) {
mLastLoadFailed = false;

RNCWebView reactWebView = (RNCWebView) webView;
reactWebView.setLastCommittedUrl(url);
reactWebView.callInjectedJavaScriptBeforeContentLoaded();
}

Expand Down
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