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  type reader struct {
    17  	drbg.DefaultReader
    18  }
    19  
    20  func (r reader) Read(b []byte) (n int, err error) {
    21  	if boring.Enabled {
    22  		if _, err := boring.RandReader.Read(b); err != nil {
    23  			panic("crypto/rand: boring RandReader failed: " + err.Error())
    24  		}
    25  		return len(b), nil
    26  	}
    27  	drbg.Read(b)
    28  	return len(b), nil
    29  }
    30  
    31  // Reader is an io.Reader that calls [drbg.Read].
    32  //
    33  // It should be used internally instead of [crypto/rand.Reader], because the
    34  // latter can be set by applications outside of tests. These applications then
    35  // risk breaking between Go releases, if the way the Reader is used changes.
    36  var Reader io.Reader = reader{}
    37  
    38  // SetTestingReader overrides all calls to [drbg.Read]. The Read method of
    39  // r must never return an error or return short.
    40  //
    41  // SetTestingReader panics when building against Go Cryptographic Module v1.0.0.
    42  //
    43  // SetTestingReader is pulled by [testing/cryptotest.setGlobalRandom] via go:linkname.
    44  //
    45  //go:linkname SetTestingReader crypto/internal/rand.SetTestingReader
    46  func SetTestingReader(r io.Reader) {
    47  	fips140SetTestingReader(r)
    48  }
    49  
    50  var cryptocustomrand = godebug.New("cryptocustomrand")
    51  
    52  // CustomReader returns [Reader] or, only if the GODEBUG setting
    53  // "cryptocustomrand=1" is set, the provided io.Reader.
    54  //
    55  // If returning a non-default Reader, it calls [randutil.MaybeReadByte] on it.
    56  func CustomReader(r io.Reader) io.Reader {
    57  	if cryptocustomrand.Value() == "1" {
    58  		if _, ok := r.(drbg.DefaultReader); !ok {
    59  			randutil.MaybeReadByte(r)
    60  			cryptocustomrand.IncNonDefault()
    61  		}
    62  		return r
    63  	}
    64  	return Reader
    65  }
    66
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