rand.go

     1  // Copyright 2010 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  // Package rand implements a cryptographically secure
     6  // random number generator.
     7  package rand
     8  
     9  import "io"
    10  
    11  // Reader is a global, shared instance of a cryptographically
    12  // secure random number generator.
    13  //
    14  // On Linux, FreeBSD, Dragonfly and Solaris, Reader uses getrandom(2) if
    15  // available, /dev/urandom otherwise.
    16  // On OpenBSD and macOS, Reader uses getentropy(2).
    17  // On other Unix-like systems, Reader reads from /dev/urandom.
    18  // On Windows systems, Reader uses the RtlGenRandom API.
    19  // On Wasm, Reader uses the Web Crypto API.
    20  var Reader io.Reader
    21  
    22  // Read is a helper function that calls Reader.Read using io.ReadFull.
    23  // On return, n == len(b) if and only if err == nil.
    24  func Read(b []byte) (n int, err error) {
    25  	return io.ReadFull(Reader, b)
    26  }
    27  
    28  // batched returns a function that calls f to populate a []byte by chunking it
    29  // into subslices of, at most, readMax bytes.
    30  func batched(f func([]byte) error, readMax int) func([]byte) error {
    31  	return func(out []byte) error {
    32  		for len(out) > 0 {
    33  			read := len(out)
    34  			if read > readMax {
    35  				read = readMax
    36  			}
    37  			if err := f(out[:read]); err != nil {
    38  				return err
    39  			}
    40  			out = out[read:]
    41  		}
    42  		return nil
    43  	}
    44  }
    45
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