调用GetExtendedTcpTable时为空响应（）

Question

I am new to Go, and I need to catch net information in Windows. I tried to call GetExtendedTcpTable() with pointers to byte arrays as params but get nothing after the call.

var (
    iphelp   = syscall.NewLazyDLL("iphlpapi.dll")
    tcptable = iphelp.NewProc("GetExtendedTcpTable")
)

var (
    buffer [20000]byte
    table  [20000]byte
    length int
)

res1, res2, err := tcptable.Call(
    uintptr(unsafe.Pointer(&buffer)),
    uintptr(unsafe.Pointer(&length)),
    1,
    syscall.AF_INET,
    uintptr(unsafe.Pointer(&table)),
    0,
)

I expected some data in 'buffer' and 'table', but there are only 0. What am I doing wrong?

Answer 1

Your code has two errors. First, you pass in legnth=0, which causes GetExtendedTcpTable() to return ERROR_INSUFFICIENT_BUFFER 122 (0x7A). Then, the fifth parameter is not a pointer to the table itself, but an input parameter that states the class (type) of the table to return (write into parameter 1. Here is a corrected version to get over these hurdles:

import (
        "fmt"
        "syscall"
        "unsafe"
)

const (
        TCP_TABLE_BASIC_LISTENER = iota
        TCP_TABLE_BASIC_CONNECTIONS
        TCP_TABLE_BASIC_ALL
        TCP_TABLE_OWNER_PID_LISTENER
        TCP_TABLE_OWNER_PID_CONNECTIONS
        TCP_TABLE_OWNER_PID_ALL
        TCP_TABLE_OWNER_MODULE_LISTENER
        TCP_TABLE_OWNER_MODULE_CONNECTIONS
        TCP_TABLE_OWNER_MODULE_ALL
)

func main() {
        var table [2000]byte
        var length int = len(table)

        iphelp := syscall.NewLazyDLL("iphlpapi.dll")
        tcptable := iphelp.NewProc("GetExtendedTcpTable")

        length = len(table)

        res1, res2, err := tcptable.Call(
                uintptr(unsafe.Pointer(&table)),
                uintptr(unsafe.Pointer(&length)),
                1,
                syscall.AF_INET,
                TCP_TABLE_BASIC_LISTENER,
                0,
        )

        fmt.Println(res1, res2, length, err)
        fmt.Println(table)
}

I figured this out by inspecting the return code of the GetExtendedTcpTable(). Microsoft system error codes are listed on: https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx