RPC implementation

Table of contents

1. Example
2. Implementing ECHO

Now that you have specified the protocol for the ECHO RPC, you will be implementing its actual functionality.

Example

To give you an idea of how RPC implementations look, an implementation for the EXAMPLE RPC has been provided to you in server.c.

int* example_1_svc(int *argp, struct svc_req *rqstp) {
  static int result;
  result = *argp + 1;
  return &result;
}

This code is what runs on the server after it receives an EXAMPLE RPC request from the client. As a brief rundown of what the code is doing, the function takes in a pointer to the value received from the client, dereferences it and adds 1 to the received value, then returns a pointer to this new incremented value. The return value is then serialized and sent back to the client by the stubs generated by rpcgen.

If you run make, you will see an error since you defined the ECHO RPC in the KVSTORE program specification but have not yet implemented the corresponding server-side function.

Implementing ECHO

Now implement the ECHO RPC in server.c so that it echoes the received message string back to the client. After adding the ECHO RPC to kv_store.x and running make, you should be able to find the function signature for echo_1_svc, the function you will need to add to server.c and implement, in kv_store.h. You may want to copy the existing example_1_svc function and change the arguments and return types appropriately to make sure you are following the correct convention.

In your implementation, you will first need to recover the message string from your RPC request in a similar manner as the EXAMPLE RPC, then pass the message string back into the reply. You shouldn’t need to use malloc or free here, but you will need to place the pointer to the string in a static variable as shown in the EXAMPLE RPC stub (variables on the stack would be freed as soon as the function returns).

Before moving on, make sure that your code is now compiling with make.