WIP: An (ongoing) experiment with adding native logs listener

packages/core/ios/RNSentry.mm

@@ -41,6 +41,7 @@
 
 #import "RNSentryDependencyContainer.h"
 #import "RNSentryEvents.h"
+#import "RNSentryNativeLogsForwarder.h"
 
 #if SENTRY_TARGET_REPLAY_SUPPORTED
 #    import "RNSentryReplay.h"
@@ -311,17 +312,19 @@ - (void)initFramesTracking
 - (void)startObserving
 {
     hasListeners = YES;
+    [[RNSentryNativeLogsForwarder shared] configureWithEventEmitter:self];
 }
 
 // Will be called when this module's last listener is removed, or on dealloc.
 - (void)stopObserving
 {
     hasListeners = NO;
+    [[RNSentryNativeLogsForwarder shared] stopForwarding];
 }
 
 - (NSArray<NSString *> *)supportedEvents
 {
-    return @[ RNSentryNewFrameEvent ];
+    return @[ RNSentryNewFrameEvent, RNSentryNativeLogEvent ];
 }
 
 RCT_EXPORT_METHOD(

packages/core/ios/RNSentryEvents.h

@@ -1,3 +1,4 @@
 #import <Foundation/Foundation.h>
 
 extern NSString *const RNSentryNewFrameEvent;
+extern NSString *const RNSentryNativeLogEvent;

packages/core/ios/RNSentryEvents.m

@@ -1,3 +1,4 @@
 #import "RNSentryEvents.h"
 
 NSString *const RNSentryNewFrameEvent = @"rn_sentry_new_frame";
+NSString *const RNSentryNativeLogEvent = @"SentryNativeLog";

packages/core/ios/RNSentryExperimentalOptions.m

@@ -34,7 +34,7 @@ + (void)setEnableSessionReplayInUnreliableEnvironment:(BOOL)enabled
     if (sentryOptions == nil) {
         return;
     }
-    sentryOptions.experimental.enableSessionReplayInUnreliableEnvironment = enabled;
+    // sentryOptions.experimental.enableSessionReplayInUnreliableEnvironment = enabled;
 }
 
 + (void)configureProfilingWithOptions:(NSDictionary *)profilingOptions

packages/core/ios/RNSentryNativeLogsForwarder.h

@@ -0,0 +1,33 @@
+#import <Foundation/Foundation.h>
+#import <React/RCTEventEmitter.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ * Singleton class that forwards native Sentry SDK logs to JavaScript via React Native events.
+ * This allows React Native developers to see native SDK logs in the Metro console.
+ */
+@interface RNSentryNativeLogsForwarder : NSObject
+
+/**
+ * Returns the shared instance of the logs forwarder.
+ */
++ (instancetype)shared;
+
+/**
+ * Configures the forwarder with the event emitter to use for sending events to JS.
+ * Call this when the React Native module starts observing events.
+ *
+ * @param emitter The RCTEventEmitter instance (typically the RNSentry module).
+ */
+- (void)configureWithEventEmitter:(RCTEventEmitter *)emitter;
+
+/**
+ * Clears the event emitter reference.
+ * Call this when the React Native module stops observing events.
+ */
+- (void)stopForwarding;
+
+@end
+
+NS_ASSUME_NONNULL_END

packages/core/ios/RNSentryNativeLogsForwarder.m

@@ -0,0 +1,143 @@
+#import "RNSentryNativeLogsForwarder.h"
+
+@import Sentry;
+
+static NSString *const RNSentryNativeLogEventName = @"SentryNativeLog";
+
+@interface RNSentryNativeLogsForwarder ()
+
+@property (nonatomic, weak) RCTEventEmitter *eventEmitter;
+
+@end
+
+@implementation RNSentryNativeLogsForwarder
+
++ (instancetype)shared
+{
+    static RNSentryNativeLogsForwarder *instance = nil;
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{ instance = [[RNSentryNativeLogsForwarder alloc] init]; });
+    return instance;
+}
+
+- (void)configureWithEventEmitter:(RCTEventEmitter *)emitter
+{
+    self.eventEmitter = emitter;
+
+    __weak RNSentryNativeLogsForwarder *weakSelf = self;
+
+    // Set up the Sentry SDK log output to forward logs to JS
+    [SentrySDKLog setOutput:^(NSString *_Nonnull message) {
+        // Always print to console (default behavior)
+        NSLog(@"%@", message);
+
+        // Forward to JS if we have an emitter
+        RNSentryNativeLogsForwarder *strongSelf = weakSelf;
+        if (strongSelf) {
+            [strongSelf forwardLogMessage:message];
+        }
+    }];
+
+    // Send a test log to verify the forwarding works
+    [self forwardLogMessage:@"[Sentry] [info] [0] [RNSentryNativeLogsForwarder] Native log forwarding "
+                            @"configured successfully"];
+}
+
+- (void)stopForwarding
+{
+    self.eventEmitter = nil;
+
+    // Reset to default print behavior
+    [SentrySDKLog setOutput:^(NSString *_Nonnull message) { NSLog(@"%@", message); }];
+}
+
+- (void)forwardLogMessage:(NSString *)message
+{
+    RCTEventEmitter *emitter = self.eventEmitter;
+    if (emitter == nil) {
+        return;
+    }
+
+    // Only forward messages that look like Sentry SDK logs
+    if (![message hasPrefix:@"[Sentry]"]) {
+        return;
+    }
+
+    // Parse the log message to extract level and component
+    // Format: "[Sentry] [level] [timestamp] [Component:line] message"
+    // or: "[Sentry] [level] [timestamp] message"
+    NSString *level = [self extractLevelFromMessage:message];
+    NSString *component = [self extractComponentFromMessage:message];
+    NSString *cleanMessage = [self extractCleanMessageFromMessage:message];
+
+    NSDictionary *body = @{
+        @"level" : level,
+        @"component" : component,
+        @"message" : cleanMessage,
+    };
+
+    // Dispatch async to avoid blocking the calling thread and potential deadlocks
+    dispatch_async(dispatch_get_main_queue(), ^{
+        RCTEventEmitter *currentEmitter = self.eventEmitter;
+        if (currentEmitter != nil) {
+            [currentEmitter sendEventWithName:RNSentryNativeLogEventName body:body];
+        }
+    });
+}
+
+- (NSString *)extractLevelFromMessage:(NSString *)message
+{
+    // Look for patterns like [debug], [info], [warning], [error], [fatal]
+    NSRegularExpression *regex =
+        [NSRegularExpression regularExpressionWithPattern:@"\\[(debug|info|warning|error|fatal)\\]"
+                                                  options:NSRegularExpressionCaseInsensitive
+                                                    error:nil];
+
+    NSTextCheckingResult *match = [regex firstMatchInString:message
+                                                    options:0
+                                                      range:NSMakeRange(0, message.length)];
+
+    if (match && match.numberOfRanges > 1) {
+        return [[message substringWithRange:[match rangeAtIndex:1]] lowercaseString];
+    }
+
+    return @"info";
+}
+
+- (NSString *)extractComponentFromMessage:(NSString *)message
+{
+    // Look for pattern like [ComponentName:123]
+    NSRegularExpression *regex =
+        [NSRegularExpression regularExpressionWithPattern:@"\\[([A-Za-z]+):\\d+\\]"
+                                                  options:0
+                                                    error:nil];
+
+    NSTextCheckingResult *match = [regex firstMatchInString:message
+                                                    options:0
+                                                      range:NSMakeRange(0, message.length)];
+
+    if (match && match.numberOfRanges > 1) {
+        return [message substringWithRange:[match rangeAtIndex:1]];
+    }
+
+    return @"Sentry";
+}
+
+- (NSString *)extractCleanMessageFromMessage:(NSString *)message
+{
+    // Remove the prefix parts: [Sentry] [level] [timestamp] [Component:line]
+    // and return just the actual message content
+    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:
+            @"^\\[Sentry\\]\\s*\\[[^\\]]+\\]\\s*\\[[^\\]]+\\]\\s*(?:\\[[^\\]]+\\]\\s*)?"
+                                                                           options:0
+                                                                             error:nil];
+
+    NSString *cleanMessage = [regex stringByReplacingMatchesInString:message
+                                                             options:0
+                                                               range:NSMakeRange(0, message.length)
+                                                        withTemplate:@""];
+
+    return [cleanMessage stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
+}
+
+@end

packages/core/src/js/NativeLogListener.ts

@@ -0,0 +1,90 @@
+import { debug } from '@sentry/core';
+import { NativeEventEmitter, NativeModules, Platform } from 'react-native';
+import type { NativeLogEntry } from './options';
+
+const NATIVE_LOG_EVENT_NAME = 'SentryNativeLog';
+
+let nativeLogListener: ReturnType<NativeEventEmitter['addListener']> | null = null;
+
+/**
+ * Sets up the native log listener that forwards logs from the native SDK to JS.
+ * This only works when `debug: true` is set in Sentry options.
+ *
+ * @param callback - The callback to invoke when a native log is received.
+ * @returns A function to remove the listener, or undefined if setup failed.
+ */
+export function setupNativeLogListener(callback: (log: NativeLogEntry) => void): (() => void) | undefined {
+  if (Platform.OS !== 'ios' && Platform.OS !== 'android') {
+    debug.log('Native log listener is only supported on iOS and Android.');
+    return undefined;
+  }
+
+  if (!NativeModules.RNSentry) {
+    debug.warn('Could not set up native log listener: RNSentry module not found.');
+    return undefined;
+  }
+
+  try {
+    // Remove existing listener if any
+    if (nativeLogListener) {
+      nativeLogListener.remove();
+      nativeLogListener = null;
+    }
+
+    const eventEmitter = new NativeEventEmitter(NativeModules.RNSentry);
+
+    nativeLogListener = eventEmitter.addListener(
+      NATIVE_LOG_EVENT_NAME,
+      (event: { level?: string; component?: string; message?: string }) => {
+        const logEntry: NativeLogEntry = {
+          level: event.level ?? 'info',
+          component: event.component ?? 'Sentry',
+          message: event.message ?? '',
+        };
+        callback(logEntry);
+      },
+    );
+
+    debug.log('Native log listener set up successfully.');
+
+    return () => {
+      if (nativeLogListener) {
+        nativeLogListener.remove();
+        nativeLogListener = null;
+        debug.log('Native log listener removed.');
+      }
+    };
+  } catch (error) {
+    debug.warn('Failed to set up native log listener:', error);
+    return undefined;
+  }
+}
+
+/**
+ * Default handler for native logs that logs to the JS console.
+ */
+export function defaultNativeLogHandler(log: NativeLogEntry): void {
+  const prefix = `[Sentry] [${log.level.toUpperCase()}] [${log.component}]`;
+  const message = `${prefix} ${log.message}`;
+
+  switch (log.level.toLowerCase()) {
+    case 'fatal':
+    case 'error':
+      // eslint-disable-next-line no-console
+      console.error(message);
+      break;
+    case 'warning':
+      // eslint-disable-next-line no-console
+      console.warn(message);
+      break;
+    case 'info':
+      // eslint-disable-next-line no-console
+      console.info(message);
+      break;
+    case 'debug':
+    default:
+      // eslint-disable-next-line no-console
+      console.log(message);
+      break;
+  }
+}

packages/core/src/js/client.ts

@@ -22,6 +22,7 @@ import { Alert } from 'react-native';
 import { getDevServer } from './integrations/debugsymbolicatorutils';
 import { defaultSdkInfo } from './integrations/sdkinfo';
 import { getDefaultSidecarUrl } from './integrations/spotlight';
+import { defaultNativeLogHandler, setupNativeLogListener } from './NativeLogListener';
 import type { ReactNativeClientOptions } from './options';
 import type { mobileReplayIntegration } from './replay/mobilereplay';
 import { MOBILE_REPLAY_INTEGRATION_NAME } from './replay/mobilereplay';
@@ -42,6 +43,7 @@ const DEFAULT_FLUSH_INTERVAL = 5000;
 export class ReactNativeClient extends Client<ReactNativeClientOptions> {
   private _outcomesBuffer: Outcome[];
   private _logFlushIdleTimeout: ReturnType<typeof setTimeout> | undefined;
+  private _removeNativeLogListener: (() => void) | undefined;
 
   /**
    * Creates a new React Native SDK instance.
@@ -127,6 +129,12 @@ export class ReactNativeClient extends Client<ReactNativeClientOptions> {
    * @inheritDoc
    */
   public close(): PromiseLike<boolean> {
+    // Clean up native log listener
+    if (this._removeNativeLogListener) {
+      this._removeNativeLogListener();
+      this._removeNativeLogListener = undefined;
+    }
+
     // As super.close() flushes queued events, we wait for that to finish before closing the native SDK.
     return super.close().then((result: boolean) => {
       return NATIVE.closeNativeSdk().then(() => result);
@@ -215,6 +223,12 @@ export class ReactNativeClient extends Client<ReactNativeClientOptions> {
    * Starts native client with dsn and options
    */
   private _initNativeSdk(): void {
+    // Set up native log listener if debug is enabled
+    if (this._options.debug) {
+      const logHandler = this._options.onNativeLog ?? defaultNativeLogHandler;
+      this._removeNativeLogListener = setupNativeLogListener(logHandler);
+    }
+
     NATIVE.initNativeSdk({
       ...this._options,
       defaultSidecarUrl: getDefaultSidecarUrl(),

packages/core/src/js/index.ts

@@ -69,7 +69,7 @@ export {
 export * from './integrations/exports';
 
 export { SDK_NAME, SDK_VERSION } from './version';
-export type { ReactNativeOptions } from './options';
+export type { ReactNativeOptions, NativeLogEntry } from './options';
 export { ReactNativeClient } from './client';
 
 export { init, wrap, nativeCrash, flush, close, withScope, crashedLastRun } from './sdk';