grpc: Interceptor to catch panics and convert them to Internal errors.

grpc/grpcutil/paniccatcher.go

Index: grpc/grpcutil/paniccatcher.go
diff --git a/grpc/grpcutil/paniccatcher.go b/grpc/grpcutil/paniccatcher.go
new file mode 100644
index 0000000000000000000000000000000000000000..6ce1cb6b33d6279aebb6663bf2348ba93ec22c20
--- /dev/null
+++ b/grpc/grpcutil/paniccatcher.go
@@ -0,0 +1,33 @@
+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package grpcutil
+
+import (
+	"golang.org/x/net/context"
+	"google.golang.org/grpc"
+
+	"github.com/luci/luci-go/common/logging"
+	"github.com/luci/luci-go/common/runtime/paniccatcher"
+)
+
+// NewUnaryServerPanicCatcher returns a unary interceptor that catches panics
+// in RPC handlers, recovers them and returns codes.Internal gRPC errors
+// instead.
+//
+// It can be optionally chained with other interceptor.
+func NewUnaryServerPanicCatcher(next grpc.UnaryServerInterceptor) grpc.UnaryServerInterceptor {
+	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (resp interface{}, err error) {
+		defer paniccatcher.Catch(func(p *paniccatcher.Panic) {
+			logging.Fields{
+				"panic.error": p.Reason,
+			}.Errorf(ctx, "Caught panic during handling of %q: %s\n%s", info.FullMethod, p.Reason, p.Stack)
+			err = Internal
+		})
+		if next != nil {
+			return next(ctx, req, info, handler)
+		}
+		return handler(ctx, req)
+	}
+}