github.com/MerlinKodo/gvisor@v0.0.0-20231110090155-957f62ecf90e/pkg/gohacks/string_go113_unsafe.go (about)

     1  // Copyright 2023 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  //go:build go1.13 && !go1.20
    16  // +build go1.13,!go1.20
    17  
    18  // TODO(go.dev/issue/8422): Remove this file once Go 1.19 is no longer
    19  // supported.
    20  
    21  package gohacks
    22  
    23  import (
    24  	"unsafe"
    25  )
    26  
    27  // stringHeader is equivalent to reflect.StringHeader, but represents the
    28  // pointer to the underlying array as unsafe.Pointer rather than uintptr,
    29  // allowing StringHeaders to be directly converted to strings.
    30  type stringHeader struct {
    31  	Data unsafe.Pointer
    32  	Len  int
    33  }
    34  
    35  // ImmutableBytesFromString is equivalent to []byte(s), except that it uses the
    36  // same memory backing s instead of making a heap-allocated copy. This is only
    37  // valid if the returned slice is never mutated.
    38  func ImmutableBytesFromString(s string) []byte {
    39  	shdr := (*stringHeader)(unsafe.Pointer(&s))
    40  	return Slice((*byte)(shdr.Data), shdr.Len)
    41  }
    42  
    43  // StringFromImmutableBytes is equivalent to string(bs), except that it uses
    44  // the same memory backing bs instead of making a heap-allocated copy. This is
    45  // only valid if bs is never mutated after StringFromImmutableBytes returns.
    46  func StringFromImmutableBytes(bs []byte) string {
    47  	// This is cheaper than messing with StringHeader and SliceHeader, which as
    48  	// of this writing produces many dead stores of zeroes. Compare
    49  	// strings.Builder.String().
    50  	return *(*string)(unsafe.Pointer(&bs))
    51  }