Simplify exception handling in PubSubMessageProcessor

Remove the catch-log-rethrow pattern in getCommand(). Catch
JsonParseException narrowly around getCommand() in handle() and return
a failed future, so that MessageReceiverProvider's exceptionally()
handler takes care of logging and nacking.

Change-Id: I7986b5cd6f670b76dee4753f261d10926a6a6964

src/main/java/com/googlesource/gerrit/plugins/highavailability/gcp/PubSubMessageProcessor.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/highavailability/gcp/PubSubMessageProcessor.java b/src/main/java/com/googlesource/gerrit/plugins/highavailability/gcp/PubSubMessageProcessor.java
index 7eb1749..4e3fafe 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/highavailability/gcp/PubSubMessageProcessor.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/highavailability/gcp/PubSubMessageProcessor.java
@@ -20,6 +20,7 @@
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.extensions.registration.DynamicItem;
 import com.google.gson.Gson;
+import com.google.gson.JsonParseException;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
 import com.google.pubsub.v1.PubsubMessage;
@@ -40,21 +41,17 @@
 
   public CompletableFuture<Boolean> handle(PubsubMessage msg) {
     log.atFine().log("Processing message: %s", msg);
+    Command command;
     try {
-      return processor.get().handle(getCommand(msg));
-    } catch (RuntimeException e) {
-      // getCommand() throws on deserialization failure; already logged there
-      return CompletableFuture.completedFuture(false);
+      command = getCommand(msg);
+    } catch (JsonParseException e) {
+      return CompletableFuture.failedFuture(e);
     }
+    return processor.get().handle(command);
   }
 
-  private Command getCommand(PubsubMessage msg) {
-    try {
-      String s = msg.getData().toStringUtf8();
-      return gson.fromJson(s, Command.class);
-    } catch (RuntimeException e) {
-      log.atSevere().withCause(e).log("Error parsing message %s", msg);
-      throw e;
-    }
+  private Command getCommand(PubsubMessage msg) throws JsonParseException {
+    String s = msg.getData().toStringUtf8();
+    return gson.fromJson(s, Command.class);
   }
 }