mask.go

Documentation: github.com/gorilla/websocket

     1  // Copyright 2016 The Gorilla WebSocket Authors. All rights reserved.  Use of
     2  // this source code is governed by a BSD-style license that can be found in the
     3  // LICENSE file.
     4  
     5  //go:build !appengine
     6  // +build !appengine
     7  
     8  package websocket
     9  
    10  import "unsafe"
    11  
    12  const wordSize = int(unsafe.Sizeof(uintptr(0)))
    13  
    14  func maskBytes(key [4]byte, pos int, b []byte) int {
    15  	// Mask one byte at a time for small buffers.
    16  	if len(b) < 2*wordSize {
    17  		for i := range b {
    18  			b[i] ^= key[pos&3]
    19  			pos++
    20  		}
    21  		return pos & 3
    22  	}
    23  
    24  	// Mask one byte at a time to word boundary.
    25  	if n := int(uintptr(unsafe.Pointer(&b[0]))) % wordSize; n != 0 {
    26  		n = wordSize - n
    27  		for i := range b[:n] {
    28  			b[i] ^= key[pos&3]
    29  			pos++
    30  		}
    31  		b = b[n:]
    32  	}
    33  
    34  	// Create aligned word size key.
    35  	var k [wordSize]byte
    36  	for i := range k {
    37  		k[i] = key[(pos+i)&3]
    38  	}
    39  	kw := *(*uintptr)(unsafe.Pointer(&k))
    40  
    41  	// Mask one word at a time.
    42  	n := (len(b) / wordSize) * wordSize
    43  	for i := 0; i < n; i += wordSize {
    44  		*(*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(&b[0])) + uintptr(i))) ^= kw
    45  	}
    46  
    47  	// Mask one byte at a time for remaining bytes.
    48  	b = b[n:]
    49  	for i := range b {
    50  		b[i] ^= key[pos&3]
    51  		pos++
    52  	}
    53  
    54  	return pos & 3
    55  }
    56
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