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)
    15  //     if available, and /dev/urandom otherwise.
    16  //   - On macOS and iOS, Reader uses arc4random_buf(3).
    17  //   - On OpenBSD and NetBSD, Reader uses getentropy(2).
    18  //   - On other Unix-like systems, Reader reads from /dev/urandom.
    19  //   - On Windows, Reader uses the ProcessPrng API.
    20  //   - On js/wasm, Reader uses the Web Crypto API.
    21  //   - On wasip1/wasm, Reader uses random_get from wasi_snapshot_preview1.
    22  var Reader io.Reader
    23  
    24  // Read is a helper function that calls Reader.Read using io.ReadFull.
    25  // On return, n == len(b) if and only if err == nil.
    26  func Read(b []byte) (n int, err error) {
    27  	return io.ReadFull(Reader, b)
    28  }
    29  
    30  // batched returns a function that calls f to populate a []byte by chunking it
    31  // into subslices of, at most, readMax bytes.
    32  func batched(f func([]byte) error, readMax int) func([]byte) error {
    33  	return func(out []byte) error {
    34  		for len(out) > 0 {
    35  			read := len(out)
    36  			if read > readMax {
    37  				read = readMax
    38  			}
    39  			if err := f(out[:read]); err != nil {
    40  				return err
    41  			}
    42  			out = out[read:]
    43  		}
    44  		return nil
    45  	}
    46  }
    47
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