go.mway.dev/x@v0.0.0-20240520034138-950aede9a3fb/unsafe/strings.go (about)

     1  // Copyright (c) 2022 Matt Way
     2  //
     3  // Permission is hereby granted, free of charge, to any person obtaining a copy
     4  // of this software and associated documentation files (the "Software"), to
     5  // deal in the Software without restriction, including without limitation the
     6  // rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
     7  // sell copies of the Software, and to permit persons to whom the Software is
     8  // furnished to do so, subject to the following conditions:
     9  //
    10  // The above copyright notice and this permission notice shall be included in
    11  // all copies or substantial portions of the Software.
    12  //
    13  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    14  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    15  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    16  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    17  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    18  // FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
    19  // IN THE THE SOFTWARE.
    20  
    21  package unsafe
    22  
    23  import (
    24  	"math"
    25  	"unsafe"
    26  )
    27  
    28  // StringToBytes returns the underlying byte storage of x. The returned storage
    29  // must not be modified: in the best case, it will cause undefined behavior; in
    30  // the worst case, the program will segfault.
    31  //
    32  // The lifetime of the resulting storage is inextricable from that of x: they
    33  // are both guaranteed to live for as long as there is a live reference to
    34  // either.
    35  //
    36  // Do not use this function lightly, and never leak the returned storage
    37  // outside of the lifetime of the caller.
    38  func StringToBytes(x string) []byte {
    39  	if len(x) == 0 {
    40  		return nil
    41  	}
    42  
    43  	const max = math.MaxInt32 - math.MaxInt16
    44  	if len(x) > max {
    45  		return []byte(x)
    46  	}
    47  
    48  	return (*[max]byte)((*stringHeader)(unsafe.Pointer(&x)).Data)[:len(x):len(x)]
    49  }
    50  
    51  // BytesToString returns a string that uses x as its underlying storage
    52  // verbatim. The provided bytes must not be modified: in the best case, it will
    53  // create subtle bugs; in the worst case, the program will segfault.
    54  //
    55  // The lifetime of the resulting string is inextricable from that of x: they
    56  // are both guaranteed to live for as long as there is a live reference to
    57  // either.
    58  //
    59  // Do not use this function lightly, and never leak the returned string outside
    60  // of the lifetime of the caller.
    61  func BytesToString(x []byte) string {
    62  	if len(x) == 0 {
    63  		return ""
    64  	}
    65  
    66  	var (
    67  		slice = (*sliceHeader)(unsafe.Pointer(&x))
    68  		str   = stringHeader{
    69  			Data: slice.Data,
    70  			Len:  slice.Len,
    71  		}
    72  	)
    73  
    74  	return *(*string)(unsafe.Pointer(&str))
    75  }
    76  
    77  type sliceHeader struct {
    78  	Data unsafe.Pointer
    79  	Len  int
    80  	Cap  int
    81  }
    82  
    83  type stringHeader struct {
    84  	Data unsafe.Pointer
    85  	Len  int
    86  }