fix: Record NSException details immediately from C++ handler

This avoids a case where if the NSException handler is overridden
without calling the previous handler, no report is recorded. In the case
that the handler is invoked twice for a given exception, it is only
recorded once by checking that the last recorded exception is the same.

CHANGELOG.md

@@ -1,6 +1,13 @@
 Changelog
 =========
 
+## TBD
+
+### Bug Fixes
+
+* Ensure NSException is captured when handler is overridden
+  [#313](https://github.com/bugsnag/bugsnag-cocoa/pull/313)
+
 ## 5.16.3 (14 Aug 2018)
 
 ### Bug Fixes

Source/KSCrash/Source/KSCrash/Recording/Sentry/BSG_KSCrashSentry_CPPException.mm

@@ -44,6 +44,15 @@
 #define likely_if(x) if (__builtin_expect(x, 1))
 #define unlikely_if(x) if (__builtin_expect(x, 0))
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+// Internal NSException recorder
+void bsg_recordException(NSException *exception);
+#ifdef __cplusplus
+}
+#endif
+
 // ============================================================================
 #pragma mark - Globals -
 // ============================================================================
@@ -114,9 +123,11 @@ static void CPPExceptionTerminate(void) {
     try {
         throw;
     } catch (NSException *exception) {
-        BSG_KSLOG_DEBUG(@"Detected NSException. Letting the current "
+        BSG_KSLOG_DEBUG(@"Detected NSException. Recording details "
+                        @"and letting the current "
                         @"NSException handler deal with it.");
         isNSException = true;
+        bsg_recordException(exception);
     } catch (std::exception &exc) {
         strncpy(descriptionBuff, exc.what(), sizeof(descriptionBuff));
     }

Source/KSCrash/Source/KSCrash/Recording/Sentry/BSG_KSCrashSentry_NSException.m

@@ -47,32 +47,30 @@
 /** Context to fill with crash information. */
 static BSG_KSCrash_SentryContext *bsg_g_context;
 
+static NSException *bsg_lastHandledException = NULL;
+
 // ============================================================================
 #pragma mark - Callbacks -
 // ============================================================================
 
 // Avoiding static methods due to linker issue.
 
-/** Our custom excepetion handler.
- * Fetch the stack trace from the exception and write a report.
- *
- * @param exception The exception that was raised.
+/**
+ Capture exception details and write a new report. If the exception was
+ recorded before, no new report will be generated.
+
+ @param exception The exception to process
  */
-void bsg_ksnsexc_i_handleException(NSException *exception) {
-    BSG_KSLOG_DEBUG(@"Trapped exception %@", exception);
+void bsg_recordException(NSException *exception) {
     if (bsg_g_installed) {
-        bool wasHandlingCrash = bsg_g_context->handlingCrash;
-        bsg_kscrashsentry_beginHandlingCrash(bsg_g_context);
-
-        BSG_KSLOG_DEBUG(
-            @"Exception handler is installed. Continuing exception handling.");
-
-        if (wasHandlingCrash) {
-            BSG_KSLOG_INFO(@"Detected crash in the crash reporter. Restoring "
-                           @"original handlers.");
-            bsg_g_context->crashedDuringCrashHandling = true;
-            bsg_kscrashsentry_uninstall(BSG_KSCrashTypeAll);
+        BOOL previouslyHandled = exception == bsg_lastHandledException;
+        if (previouslyHandled) {
+            BSG_KSLOG_DEBUG(@"Handled exception previously, "
+                            @"exiting exception recorder.");
+            return;
         }
+        bsg_lastHandledException = exception;
+        BSG_KSLOG_DEBUG(@"Writing exception info into a new report");
 
         BSG_KSLOG_DEBUG(@"Suspending all threads.");
         bsg_kscrashsentry_suspendThreads();
@@ -95,6 +93,31 @@ void bsg_ksnsexc_i_handleException(NSException *exception) {
 
         BSG_KSLOG_DEBUG(@"Calling main crash handler.");
         bsg_g_context->onCrash();
+    }
+}
+
+/** Our custom excepetion handler.
+ * Fetch the stack trace from the exception and write a report.
+ *
+ * @param exception The exception that was raised.
+ */
+void bsg_ksnsexc_i_handleException(NSException *exception) {
+    BSG_KSLOG_DEBUG(@"Trapped exception %@", exception);
+    if (bsg_g_installed) {
+        bool wasHandlingCrash = bsg_g_context->handlingCrash;
+        bsg_kscrashsentry_beginHandlingCrash(bsg_g_context);
+
+        BSG_KSLOG_DEBUG(
+            @"Exception handler is installed. Continuing exception handling.");
+
+        if (wasHandlingCrash) {
+            BSG_KSLOG_INFO(@"Detected crash in the crash reporter. Restoring "
+                           @"original handlers.");
+            bsg_g_context->crashedDuringCrashHandling = true;
+            bsg_kscrashsentry_uninstall(BSG_KSCrashTypeAll);
+        }
+
+        bsg_recordException(exception);
 
         BSG_KSLOG_DEBUG(
             @"Crash handling complete. Restoring original handlers.");