implement disk usage on Windows

disk.go

@@ -3,12 +3,11 @@ package main
 type Disk struct{}
 
 type Disk_usage struct {
-	Path      string  `json:"path"`
-	Total     uint64  `json:"total"`
-	Free      uint64  `json:"free"`
-	Available uint64  `json:"available"`
-	Used      uint64  `json:"used"`
-	Percent   float64 `json:"percent"`
+	Path        string  `json:"path"`
+	Total       uint64  `json:"total"`
+	Free        uint64  `json:"free"`
+	Used        uint64  `json:"used"`
+	UsedPercent float64 `json:"usedPercent"`
 }
 
 type Disk_IO_Counters struct {

disk_test.go

@@ -3,13 +3,18 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"runtime"
 	"testing"
 )
 
 func TestDisk_usage(t *testing.T) {
 	disk := NewDisk()
 
-	v, err := disk.Disk_usage("/")
+	path := "/"
+	if runtime.GOOS == "windows" {
+		path = "C:"
+	}
+	v, err := disk.Disk_usage(path)
 	if err != nil {
 		t.Errorf("error %v", err)
 	}

disk_windows.go

@@ -2,9 +2,36 @@
 
 package main
 
-func (d Disk) Disk_usage(path string) (Disk_usage, error) {
+import (
+	"syscall"
+	"unsafe"
+)
+
+var (
+	procGetDiskFreeSpaceExW = modkernel32.NewProc("GetDiskFreeSpaceExW")
+	//GetLogicalDriveStrings, _ = syscall.GetProcAddress(modkernel32, "GetLogicalDriveStringsW")
+)
 
+func (d Disk) Disk_usage(path string) (Disk_usage, error) {
 	ret := Disk_usage{}
 
+	ret.Path = path
+	lpFreeBytesAvailable := int64(0)
+	lpTotalNumberOfBytes := int64(0)
+	lpTotalNumberOfFreeBytes := int64(0)
+	diskret, _, _ := procGetDiskFreeSpaceExW.Call(
+		uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(path))),
+		uintptr(unsafe.Pointer(&lpFreeBytesAvailable)),
+		uintptr(unsafe.Pointer(&lpTotalNumberOfBytes)),
+		uintptr(unsafe.Pointer(&lpTotalNumberOfFreeBytes)))
+	if diskret == 0 {
+		return ret, syscall.GetLastError()
+	}
+	ret.Total = uint64(lpTotalNumberOfBytes)
+	//	ret.Free = uint64(lpFreeBytesAvailable) // python psutil does not use this
+	ret.Free = uint64(lpTotalNumberOfFreeBytes)
+	ret.Used = ret.Total - ret.Free
+	ret.UsedPercent = float64(ret.Used) / float64(ret.Total) * 100.0
+
 	return ret, nil
 }