From 8fc3715a17a1b764143d0b37652a07a45d1cdf01 Mon Sep 17 00:00:00 2001
From: Vijay Pai <vpai@google.com>
Date: Mon, 18 Dec 2017 14:33:51 -0800
Subject: Catch exceptions from sync method handlers without crashing server

---
 include/grpc++/impl/codegen/method_handler_impl.h | 35 ++++++++++++++++++++---
 1 file changed, 31 insertions(+), 4 deletions(-)

(limited to 'include/grpc++')

diff --git a/include/grpc++/impl/codegen/method_handler_impl.h b/include/grpc++/impl/codegen/method_handler_impl.h
index c0af4ca130..b72dceb1b4 100644
--- a/include/grpc++/impl/codegen/method_handler_impl.h
+++ b/include/grpc++/impl/codegen/method_handler_impl.h
@@ -27,6 +27,25 @@
 namespace grpc {
 
 namespace internal {
+
+// Invoke the method handler, fill in the status, and
+// return whether or not we finished safely (without an exception).
+// Note that exception handling is 0-cost in most compiler/library
+// implementations (except when an exception is actually thrown),
+// so this process doesn't require additional overhead in the common case.
+// Additionally, we don't need to return if we caught an exception or not;
+// the handling is the same in either case.
+template <class F>
+Status CatchingFunctionHandler(F&& callable) {
+  try {
+    return callable();
+  } catch (const std::exception& e) {
+    return Status(StatusCode::UNKNOWN, e.what());
+  } catch (...) {
+    return Status(StatusCode::UNKNOWN, "Exception in method handler");
+  }
+}
+
 /// A wrapper class of an application provided rpc method handler.
 template <class ServiceType, class RequestType, class ResponseType>
 class RpcMethodHandler : public MethodHandler {
@@ -43,7 +62,9 @@ class RpcMethodHandler : public MethodHandler {
         param.request.bbuf_ptr(), &req);
     ResponseType rsp;
     if (status.ok()) {
-      status = func_(service_, param.server_context, &req, &rsp);
+      status = CatchingFunctionHandler([this, &param, &req, &rsp] {
+        return func_(service_, param.server_context, &req, &rsp);
+      });
     }
 
     GPR_CODEGEN_ASSERT(!param.server_context->sent_initial_metadata_);
@@ -86,7 +107,9 @@ class ClientStreamingHandler : public MethodHandler {
   void RunHandler(const HandlerParameter& param) final {
     ServerReader<RequestType> reader(param.call, param.server_context);
     ResponseType rsp;
-    Status status = func_(service_, param.server_context, &reader, &rsp);
+    Status status = CatchingFunctionHandler([this, &param, &reader, &rsp] {
+      return func_(service_, param.server_context, &reader, &rsp);
+    });
 
     GPR_CODEGEN_ASSERT(!param.server_context->sent_initial_metadata_);
     CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage,
@@ -130,7 +153,9 @@ class ServerStreamingHandler : public MethodHandler {
 
     if (status.ok()) {
       ServerWriter<ResponseType> writer(param.call, param.server_context);
-      status = func_(service_, param.server_context, &req, &writer);
+      status = CatchingFunctionHandler([this, &param, &req, &writer] {
+        return func_(service_, param.server_context, &req, &writer);
+      });
     }
 
     CallOpSet<CallOpSendInitialMetadata, CallOpServerSendStatus> ops;
@@ -172,7 +197,9 @@ class TemplatedBidiStreamingHandler : public MethodHandler {
 
   void RunHandler(const HandlerParameter& param) final {
     Streamer stream(param.call, param.server_context);
-    Status status = func_(param.server_context, &stream);
+    Status status = CatchingFunctionHandler([this, &param, &stream] {
+      return func_(param.server_context, &stream);
+    });
 
     CallOpSet<CallOpSendInitialMetadata, CallOpServerSendStatus> ops;
     if (!param.server_context->sent_initial_metadata_) {
-- 
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