rand.go

     1  // Copyright 2025 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
     6  
     7  import (
     8  	"crypto/internal/boring"
     9  	"crypto/internal/fips140/drbg"
    10  	"crypto/internal/randutil"
    11  	"internal/godebug"
    12  	"io"
    13  	_ "unsafe"
    14  )
    15  
    16  // defaultReader aliases [drbg.DefaultReader], so that [reader]
    17  // does not have an exported DefaultReader field.
    18  type defaultReader = drbg.DefaultReader
    19  
    20  type reader struct{ defaultReader }
    21  
    22  func (r reader) Read(b []byte) (n int, err error) {
    23  	if boring.Enabled {
    24  		if _, err := boring.RandReader.Read(b); err != nil {
    25  			panic("crypto/rand: boring RandReader failed: " + err.Error())
    26  		}
    27  		return len(b), nil
    28  	}
    29  	drbg.Read(b)
    30  	return len(b), nil
    31  }
    32  
    33  // Reader is an io.Reader that calls [drbg.Read].
    34  //
    35  // It should be used internally instead of [crypto/rand.Reader], because the
    36  // latter can be set by applications outside of tests. These applications then
    37  // risk breaking between Go releases, if the way the Reader is used changes.
    38  var Reader io.Reader = reader{}
    39  
    40  // SetTestingReader overrides all calls to [drbg.Read]. The Read method of
    41  // r must never return an error or return short.
    42  //
    43  // SetTestingReader panics when building against Go Cryptographic Module v1.0.0.
    44  //
    45  // SetTestingReader is pulled by [testing/cryptotest.SetGlobalRandom] via go:linkname.
    46  //
    47  //go:linkname SetTestingReader crypto/internal/rand.SetTestingReader
    48  func SetTestingReader(r io.Reader) {
    49  	testingReader = r
    50  	fips140SetTestingReader(r)
    51  }
    52  
    53  var testingReader io.Reader
    54  
    55  var cryptocustomrand = godebug.New("cryptocustomrand")
    56  
    57  // CustomReader returns [Reader] or, only if the GODEBUG setting
    58  // "cryptocustomrand=1" is set, the provided io.Reader.
    59  //
    60  // If returning a non-default Reader, it calls [randutil.MaybeReadByte] on it,
    61  // unless it's the global testing Reader set with [SetTestingReader].
    62  func CustomReader(r io.Reader) io.Reader {
    63  	if cryptocustomrand.Value() == "1" {
    64  		if !IsDefaultReader(r) {
    65  			if r != testingReader {
    66  				randutil.MaybeReadByte(r)
    67  			}
    68  			cryptocustomrand.IncNonDefault()
    69  		}
    70  		return r
    71  	}
    72  	return Reader
    73  }
    74
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