Windows routing table dumper

JSONRoutingTableDumper.cpp

#include <iostream>
#include <string>
#include <sstream>
#include <ws2tcpip.h>
#include <iphlpapi.h>

#pragma comment(lib, "iphlpapi.lib")
#pragma comment(lib, "ws2_32.lib")

int main()
{
    PMIB_IPFORWARDTABLE ip_routing_table;
  DWORD size = 0;
    DWORD retval = 0;
	std::stringstream jsonstream;
	char ip_buffer[16];

	ip_routing_table = (PMIB_IPFORWARDTABLE) malloc(sizeof(MIB_IPFORWARDTABLE));
    if (ip_routing_table == NULL) {
		std::cout << "{ \"error_desc\": \"error_allocating_memory\", \"error_code\": " << 1 << "}";
		return 1;
    }

	PMIB_IFROW interface_row = (PMIB_IFROW) malloc(sizeof(MIB_IFROW));
	if( interface_row == NULL ) { 
		std::cout << "{ \"error_desc\": \"error_allocating_memory\", \"error_code\": " << 1 << "}";
		return 1;
	}

	retval = GetIpForwardTable(ip_routing_table, &size, 0);

    if (retval == ERROR_INSUFFICIENT_BUFFER) {
		// buffer wasn\"t big enough, use the size passed by windows API and re-allocate/re-call API
        free(ip_routing_table);
        ip_routing_table = (MIB_IPFORWARDTABLE*) malloc(size);
        if (ip_routing_table == NULL) {
			// Failed to allocate memory after initially allocated buffer was too small for routing table.
			std::cout << "{ \"error_desc\": \"error_allocating_memory\", \"error_code\": " << 1 << "}";
			return 1;
        }
		// re-try
		retval = GetIpForwardTable(ip_routing_table, &size, 0);
    }

    if (retval != NO_ERROR) {
		std::cout << "{ \"error_desc\": \"error_obtaining_routing_table\", \"error_code\": " << retval << "}";
		return retval;
	}

	// open array
	jsonstream << "[";

	for(int i = 0; i < (int) ip_routing_table->dwNumEntries; i++)
	{
		// open object
		jsonstream << "{";
		// destination ip address
		inet_ntop(AF_INET /* ipv4 */, &ip_routing_table->table[i].dwForwardDest, ip_buffer, 16);
		jsonstream << "\"destination_ip\":\"" << ip_buffer << "\",";
		// subnet mask
		inet_ntop(AF_INET, &ip_routing_table->table[i].dwForwardMask, ip_buffer, 16);
		jsonstream << "\"subnet_mask\":\"" << ip_buffer << "\",";
		// gateway
		inet_ntop(AF_INET, &ip_routing_table->table[i].dwForwardNextHop, ip_buffer, 16);
		jsonstream << "\"gateway\":\"" << ip_buffer << "\",";

		// interface
		interface_row->dwIndex = ip_routing_table->table[i].dwForwardIfIndex;
		retval = GetIfEntry(interface_row);
		if( retval != NO_ERROR ) { 
			std::cout << "{ \"error_desc\": \"error_getting_interface_row\", \"error_code\": " << retval << "}";
			return 1;
		}
		jsonstream << "\"interface_description\":\"" << interface_row->bDescr  << "\",";
		

		// metric
		jsonstream << "\"metric\":" << ip_routing_table->table[i].dwForwardMetric1;

		// close object
		jsonstream << "}";
		if( ip_routing_table->dwNumEntries - i != 1) { 
			jsonstream << ",";
		}
	}

	// close array
	jsonstream << "]";

	std::cout << jsonstream.str();
	free(ip_routing_table);
	free(interface_row);
	return 0;

}