Broader exception catch for FilePersistenceLayer

Summary: folly::readFile can throw. Additionally, let's make sure we catch any sort of exception here and log it. Not being able to load the file is already not considered to be fatal.

Reviewed By: vchynarov

Differential Revision: D29366955

fbshipit-source-id: a450bf9880627f355fa9aaffb15bd99784d25a91

Author: mjoras

wangle/client/persistence/FilePersistenceLayer.cpp

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include <exception>
+
 #include <folly/FileUtil.h>
 #include <folly/portability/Unistd.h>
 #include <folly/json.h>
@@ -70,18 +72,22 @@ folly::Optional<folly::dynamic> FilePersistenceLayer::load() noexcept {
   // not being able to read the backing storage means we just
   // start with an empty cache. Failing to deserialize, or write,
   // is a real error so we report errors there.
-  if (!folly::readFile(file_.c_str(), serializedCache)) {
-    return folly::none;
-  }
-
+  std::string exceptionWhat;
   try {
+    if (!folly::readFile(file_.c_str(), serializedCache)) {
+      return folly::none;
+    }
+
     folly::json::serialization_opts opts;
     opts.allow_non_string_keys = true;
     return folly::parseJson(serializedCache, opts);
   } catch (const std::exception& err) {
-    LOG(ERROR) << "Deserialization of cache file " << file_
-               << " failed with parse error: " << err.what();
+    exceptionWhat = err.what();
+  } catch (...) {
+    exceptionWhat = "Non-standard excpetion";
   }
+  LOG(ERROR) << "Deserialization of cache file " << file_
+             << " failed with error: " << exceptionWhat;
   return folly::none;
 }