feat: add exception middleware to allow dropping exceptions clientside

Author: mworzala

src/main/java/net/hollowcube/posthog/PostHogClient.java

@@ -3,6 +3,7 @@
 import com.google.gson.FieldNamingPolicy;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
+import com.google.gson.JsonObject;
 import org.jetbrains.annotations.Blocking;
 import org.jetbrains.annotations.Contract;
 import org.jetbrains.annotations.NotNull;
@@ -12,6 +13,8 @@
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Objects;
+import java.util.function.BiFunction;
+import java.util.function.Consumer;
 
 import static net.hollowcube.posthog.PostHogNames.*;
 
@@ -368,6 +371,8 @@ final class Builder {
         private Duration featureFlagsPollingInterval = Duration.ofMinutes(5);
         private Duration featureFlagsRequestTimeout = Duration.ofSeconds(3);
 
+        private BiFunction<Throwable, JsonObject, Boolean> exceptionMiddleware = null;
+
         private Gson gson = null; // Set on build if not overridden
 
         private Builder(@NotNull String projectApiKey) {
@@ -440,6 +445,12 @@ private Builder(@NotNull String projectApiKey) {
             return this;
         }
 
+        @Contract(pure = true)
+        public @NotNull Builder exceptionMiddleware(@NotNull BiFunction<Throwable, JsonObject, Boolean> exceptionMiddleware) {
+            this.exceptionMiddleware = Objects.requireNonNull(exceptionMiddleware);
+            return this;
+        }
+
         /**
          * Allows overriding the {@link Gson} instance used for de/serializing events.
          * Can be useful for handling custom types.
@@ -465,7 +476,8 @@ private Builder(@NotNull String projectApiKey) {
                     flushInterval, maxBatchSize, defaultEventProperties, // Events
                     eventBatchTimeout,
                     allowRemoteFeatureFlagEvaluation, sendFeatureFlagEvents, // Feature flags
-                    featureFlagsPollingInterval, featureFlagsRequestTimeout
+                    featureFlagsPollingInterval, featureFlagsRequestTimeout,
+                    exceptionMiddleware // Exceptions
             );
         }
     }

src/main/java/net/hollowcube/posthog/PostHogClientImpl.java

@@ -19,6 +19,7 @@
 import java.util.Objects;
 import java.util.UUID;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.BiFunction;
 
 import static net.hollowcube.posthog.FeatureFlagEvaluator.evaluateFeatureFlag;
 import static net.hollowcube.posthog.FeatureFlagState.REMOTE_EVAL_NOT_ALLOWED;
@@ -50,6 +51,8 @@ public final class PostHogClientImpl implements PostHogClient {
     private final boolean sendFeatureFlagEvents;
     private final Duration featureFlagsRequestTimeout;
 
+    private final BiFunction<Throwable, JsonObject, Boolean> exceptionMiddleware;
+
     PostHogClientImpl(
             @NotNull Gson gson,
 
@@ -65,7 +68,8 @@ public final class PostHogClientImpl implements PostHogClient {
             boolean allowRemoteFeatureFlagEvaluation,
             boolean sendFeatureFlagEvents,
             @NotNull Duration featureFlagsPollingInterval,
-            @NotNull Duration featureFlagsRequestTimeout
+            @NotNull Duration featureFlagsRequestTimeout,
+            @Nullable BiFunction<Throwable, JsonObject, Boolean> exceptionMiddleware
     ) {
         this.queue = new EventQueue(this::sendEventBatch, flushInterval, maxBatchSize);
         this.gson = gson;
@@ -88,6 +92,8 @@ public final class PostHogClientImpl implements PostHogClient {
         this.allowRemoteFeatureFlagEvaluation = allowRemoteFeatureFlagEvaluation;
         this.sendFeatureFlagEvents = sendFeatureFlagEvents;
         this.featureFlagsRequestTimeout = featureFlagsRequestTimeout;
+
+        this.exceptionMiddleware = exceptionMiddleware;
     }
 
     @Override
@@ -345,7 +351,6 @@ private boolean trackCapturedFeatureFlagCall(@NotNull String distinctId, @NotNul
 
     // Exceptions
 
-
     @Override
     public void captureException(@NotNull Throwable throwable, @Nullable String distinctId, @Nullable Object properties) {
         // this function shouldn't ever throw an error, so it logs exceptions instead of allowing them to propagate.
@@ -367,6 +372,9 @@ public void captureException(@NotNull Throwable throwable, @Nullable String dist
             eventProps.addProperty(EXCEPTION_PERSON_URL, String.format("%s/project/%s/person/%s",
                     endpoint, projectApiKey, distinctId));
 
+            if (exceptionMiddleware != null && !exceptionMiddleware.apply(throwable, eventProps))
+                return;
+
             capture(distinctId, EXCEPTION, eventProps);
         } catch (Exception e) {
             log.error("failed to capture exception", e);
@@ -426,7 +434,7 @@ public void captureException(@NotNull Throwable throwable, @Nullable String dist
             // We lie and tell PostHog that this is a Python exception because they don't actually support
             // Java yet :) As far as i can tell this is only actually used for syntax highlighting in source
             // code (which we don't send) so this is probably OK for now.
-            frame.addProperty("platform", "python");
+            frame.addProperty("platform", "java");
             frame.addProperty("filename", element.getFileName());
             frame.addProperty("abs_path", element.getFileName());