buffer data coming over serial and write out over single pair ethernet to another board

buffer_and_send_SPE.ino

#include </Users/jules/Documents/Arduino/libraries/CircularBuffer/CircularBuffer.h>
// #include <CircularBuffer.h>// issue with name conflict with core libary, use full path to library instead
#include "SparkFun_SinglePairEthernet.h"
CircularBuffer<char, 1024> buffer;
char outputString[1024];
SinglePairEthernet adin1110;

int msg = 0;
const int NUM_MSGS = 8;
const int MAX_MSG_SIZE = 200;

byte deviceMAC[6] = {0x00, 0xE0, 0x22, 0xFE, 0xDA, 0xC9};
byte destinationMAC[6] = {0x00, 0xE0, 0x22, 0xFE, 0xDA, 0xCA};

static void rxCallback(byte * data, int dataLen, byte * senderMac)
{
    Serial.print("Recieved:\t");
    Serial.println((char *)data); //This is ok since we know they are all null terminated strings
    if(!adin1110.indenticalMacs(senderMac, destinationMAC))
    {
        Serial.print("From an unknown source: ");
        for(int i = 0; i < 6; i++)
        {
          Serial.print(senderMac[i]);
          Serial.print(" ");    
        }
        
    }
    Serial.println();
}


void setup() {
  Serial.begin(115200);

    Serial.println("Single Pair Ethernet - Example 1a Basic Send and Recieve");
    /* Start up adin1110 */
    if (!adin1110.begin(deviceMAC)) 
    {
      Serial.print("Failed to connect to ADIN1110 MACPHY. Make sure board is connected and pins are defined for target.");
      while(1); //If we can't connect just stop here      
    }
    Serial.println("Connected to ADIN1110 MACPHY");

    /* Set up callback, to control what we do when data is recieved */
    adin1110.setRxCallback(rxCallback);

    /* Wait for link to be established */
    Serial.println("Device Configured, waiting for connection...");
    while (adin1110.getLinkStatus() != true);
  
  // put your setup code here, to run once:

}
String temp;
void loop() {
  while (Serial.available()) {       
    buffer.push(Serial.read());  
  }
  if(!(buffer.isEmpty()))
  {
     if(adin1110.getLinkStatus())
    {      
        
        while(!buffer.isEmpty())
        {
          temp = temp += buffer.shift();
        }
        Serial.print("Sending:\t");
        Serial.println(temp); //This is ok since we know they are all null terminated strings
        temp.toCharArray(outputString, sizeof(outputString));
        adin1110.sendData((byte *)outputString, sizeof(outputString), destinationMAC);
        temp = "";
        

    }
    else
    {
        Serial.println("Waiting for link to resume sending");
    }

    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));    
    delay(5000);
  }
  // put your main code here, to run repeatedly:

}