Call Windows API for GetExtendedTcpTable and return a Byte Buffer containing the result.

get_extended_tcp_table_windows.go

package win32

import (
	"syscall"
	"unsafe"
)

var (
	iphlpapiDLL             = syscall.NewLazyDLL("iphlpapi.dll")
	procGetExtendedTcpTable = iphlpapiDLL.NewProc("GetExtendedTcpTable")
)

// GetExtendedTcpTable calls the Windows API GetExtendedTcpTable and returns a raw byte buffer
// containing the TCP Table requested. This buffer will need to be converted to the appropriate
// Go structure for use, depending on the combination of ulAf and tableClass requested.
func GetExtendedTcpTable(order uint32, ulAf uint32, tableClass uint32) ([]byte, error) {
	var buffer []byte
	var pTcpTable *byte
	var dwSize uint32
	for {
		// DWORD GetExtendedTcpTable(
		//  PVOID           pTcpTable,
		//  PDWORD          pdwSize,
		//  BOOL            bOrder,
		//  ULONG           ulAf,
		//  TCP_TABLE_CLASS TableClass,
		//  ULONG           Reserved
		// );
		// https://docs.microsoft.com/en-us/windows/desktop/api/iphlpapi/nf-iphlpapi-getextendedtcptable
		ret, _, errno := procGetExtendedTcpTable.Call(
			uintptr(unsafe.Pointer(pTcpTable)),
			uintptr(unsafe.Pointer(&dwSize)),
			uintptr(order),
			uintptr(ulAf),
			uintptr(tableClass),
			uintptr(uint32(0)),
		)
		if ret != 0 {
			if syscall.Errno(ret) == syscall.ERROR_INSUFFICIENT_BUFFER {
				buffer = make([]byte, int(dwSize))
				pTcpTable = &buffer[0]
				continue
			}
			return nil, syscall.Errno(errno)
		}
		return buffer, nil
	}
}