execenv_windows.go

     1  // Copyright 2020 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build windows
     6  
     7  package execenv
     8  
     9  import (
    10  	"internal/syscall/windows"
    11  	"syscall"
    12  	"unsafe"
    13  )
    14  
    15  // Default will return the default environment
    16  // variables based on the process attributes
    17  // provided.
    18  //
    19  // If the process attributes contain a token, then
    20  // the environment variables will be sourced from
    21  // the defaults for that user token, otherwise they
    22  // will be sourced from syscall.Environ().
    23  func Default(sys *syscall.SysProcAttr) (env []string, err error) {
    24  	if sys == nil || sys.Token == 0 {
    25  		return syscall.Environ(), nil
    26  	}
    27  	var blockp *uint16
    28  	err = windows.CreateEnvironmentBlock(&blockp, sys.Token, false)
    29  	if err != nil {
    30  		return nil, err
    31  	}
    32  	defer windows.DestroyEnvironmentBlock(blockp)
    33  
    34  	const size = unsafe.Sizeof(*blockp)
    35  	for *blockp != 0 { // environment block ends with empty string
    36  		// find NUL terminator
    37  		end := unsafe.Add(unsafe.Pointer(blockp), size)
    38  		for *(*uint16)(end) != 0 {
    39  			end = unsafe.Add(end, size)
    40  		}
    41  
    42  		entry := unsafe.Slice(blockp, (uintptr(end)-uintptr(unsafe.Pointer(blockp)))/2)
    43  		env = append(env, syscall.UTF16ToString(entry))
    44  		blockp = (*uint16)(unsafe.Add(end, size))
    45  	}
    46  	return
    47  }
    48
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