rand_js.go

     1  // Copyright 2018 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 js && wasm
     6  
     7  package rand
     8  
     9  import "syscall/js"
    10  
    11  // The maximum buffer size for crypto.getRandomValues is 65536 bytes.
    12  // https://developer.mozilla.org/en-US/docs/Web/API/Crypto/getRandomValues#exceptions
    13  const maxGetRandomRead = 64 << 10
    14  
    15  var batchedGetRandom func([]byte) error
    16  
    17  func init() {
    18  	Reader = &reader{}
    19  	batchedGetRandom = batched(getRandom, maxGetRandomRead)
    20  }
    21  
    22  var jsCrypto = js.Global().Get("crypto")
    23  var uint8Array = js.Global().Get("Uint8Array")
    24  
    25  // reader implements a pseudorandom generator
    26  // using JavaScript crypto.getRandomValues method.
    27  // See https://developer.mozilla.org/en-US/docs/Web/API/Crypto/getRandomValues.
    28  type reader struct{}
    29  
    30  func (r *reader) Read(b []byte) (int, error) {
    31  	if err := batchedGetRandom(b); err != nil {
    32  		return 0, err
    33  	}
    34  	return len(b), nil
    35  }
    36  
    37  func getRandom(b []byte) error {
    38  	a := uint8Array.New(len(b))
    39  	jsCrypto.Call("getRandomValues", a)
    40  	js.CopyBytesToGo(b, a)
    41  	return nil
    42  }
    43
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