Greengrass IPC using c

Question

Hello,  
  
We have a _Lambda executable_ developed using \[1] as mentioned here - \[2].  
This is working completely fine with _Greengrass Version 1_ (GGv1)  
  
We are currently exploring the _Greengrass Version 2_ (GGv2).  
Since _Lambda executable_ is not supported in _GGv2_ . We followed a **client device pattern** as mentioned here - \[3]   
 >    
 >The only time you would use the client device pattern is if your components are written in a programming language where an AWS IoT device SDK exists. In that case you can have a component act as a client device, but you will have to manage the creation of a thing and certificate in AWS IoT Core.  
  
This is working well but we came across an issue recently.  
  
The custom _component_ developed using _client device pattern_ fails to connect with the _Greengrass core_ when _Greengrass core_ is not connected to internet.  
The same issue does not occur when _component_ is developed to perform _IPC_ using _AWS IoT Greengrass Core IPC_ libraries \[4].  
We wanted the custom _component_ we developed using _client device pattern_ to work in consistent like other components developed using _AWS IoT Greengrass Core IPC_ libraries \[4] .  
  
**Question 1** - Is it the correct approach to use _client device pattern_ ?  
  
We also thought about few alternative approaches as below -   
- As mentioned here \[7] , we can use \[6] . But this wont seem to be feasible to convert complete application already written in C to C++  
- It seems it is possible to perform _IPC_ by writing custom code \[5]  
  
**Question 2** - if it is the better approach to write custom code to perform _IPC_. How feasible is this approach, I mean is it possible to do the same. Could some one provide some steps or guidelines or links to do the same?   
  
Could some one help with the above queries?  
  
Thank you.  
  
References -   
\[1] -   
\[2] -   
\[3] -   
\[4] -   
\[5] -   
\[6] -   
\[7] -

Accepted Answer

Hi,   
So from what I understand, you want to develop a component which can run your executable and talk to Greengrass core.  
I think the best path forward is to use the C++ IPC SDK as you pointed out \[6]. It should be pretty straightforward to write a layer over the C++ SDK to expose the functionality you need (Make sure the symbols are not mangled - example method https://isocpp.org/wiki/faq/mixing-c-and-cpp#call-cpp). You won't need to rewrite your existing C application.  
  
I want to hear what are the challenges you think you will face with the approach. Thanks  
  
PS. I have used this approach to use C++ SDK from C code but don't have the code handy ATM.

Answer

Hi sushantAtAws,  
  
Thank you for the response.  
It seems it could be possible as suggested by you to write a layer over the C++ SDK to expose the functionality and looks the better approach.   
  
I am able to run the mixed C and  C++ code.  
Thank you so much again.

Greengrass IPC using c

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