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  	"unicode/utf16"
    13  	"unsafe"
    14  )
    15  
    16  // Default will return the default environment
    17  // variables based on the process attributes
    18  // provided.
    19  //
    20  // If the process attributes contain a token, then
    21  // the environment variables will be sourced from
    22  // the defaults for that user token, otherwise they
    23  // will be sourced from syscall.Environ().
    24  func Default(sys *syscall.SysProcAttr) (env []string, err error) {
    25  	if sys == nil || sys.Token == 0 {
    26  		return syscall.Environ(), nil
    27  	}
    28  	var block *uint16
    29  	err = windows.CreateEnvironmentBlock(&block, sys.Token, false)
    30  	if err != nil {
    31  		return nil, err
    32  	}
    33  	defer windows.DestroyEnvironmentBlock(block)
    34  	blockp := uintptr(unsafe.Pointer(block))
    35  	for {
    36  
    37  		// find NUL terminator
    38  		end := unsafe.Pointer(blockp)
    39  		for *(*uint16)(end) != 0 {
    40  			end = unsafe.Pointer(uintptr(end) + 2)
    41  		}
    42  
    43  		n := (uintptr(end) - uintptr(unsafe.Pointer(blockp))) / 2
    44  		if n == 0 {
    45  			// environment block ends with empty string
    46  			break
    47  		}
    48  
    49  		entry := (*[(1 << 30) - 1]uint16)(unsafe.Pointer(blockp))[:n:n]
    50  		env = append(env, string(utf16.Decode(entry)))
    51  		blockp += 2 * (uintptr(len(entry)) + 1)
    52  	}
    53  	return
    54  }
    55
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