code review 1773041: crypto/rand for Windows

src/pkg/crypto/rand/rand_windows.go

+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package rand implements a cryptographically secure

[peterGo, 2010/07/09 16:49:25]

Redundant; we already said this in rand.go. 

+// pseudorandom number generator.
+
+// Windows cryptographically secure pseudorandom number
+// generator.
+
+package rand
+
+import (
+"os"
+"sync"
+"syscall"
+)
+

[peterGo, 2010/07/09 16:49:25]

There's an implementation comment for Unix. 

+type rngReader struct {

[peterGo, 2010/07/09 16:49:25]

This rates a comment in Unix. 

+prov uint32
+mu sync.Mutex
+}
+
+func (r *rngReader) Read(b []byte) (n int, err os.Error) {
+r.mu.Lock()
+if r.prov == 0 {

[brainman, 2010/07/09 05:00:42]

I would use once.Do(...) here instead. 

[peterGo, 2010/07/10 02:43:00]

By design, since they are solving the essentially same problem, the Unix and Windows Read methods use the same pattern. If you want to improve the Windows Read method by using once.Do(...), shouldn't you make the same improvement to the Unix Read method? Even if we do use once.Do(...), I would still test for nil or zero. If a pointer might be nil, now or in the future, I always use a guard to avoid panics; the same with zero value handles. The file could have been closed or the handle could have been released. I included rsc in the list of reviewers because he's the original author of the Unix-like crypto/rand version. Issue 569044: code review 569044: crypto/rand: new package http://codereview.appspot.com/569044 func (r *devReader) Read(b []byte) (n int, err os.Error) http://codereview.appspot.com/569044/diff/17001/18003#newcode36 

+const provType = syscall.PROV_RSA_FULL
+const flags = syscall.CRYPT_VERIFYCONTEXT | syscall.CRYPT_SILENT
+ok, errno := syscall.CryptAcquireContext(&r.prov, nil, nil, prov Type, flags)
+if !ok {
+return 0, os.NewSyscallError("CryptAcquireContext", errn o)
+}
+}
+r.mu.Unlock()
+ok, errno := syscall.CryptGenRandom(r.prov, uint32(len(b)), &b[0])
+if !ok {
+return 0, os.NewSyscallError("CryptGenRandom", errno)
+}
+return len(b), nil
+}
+
+func init() { Reader = &rngReader{} }

[peterGo, 2010/07/09 16:49:25]

The init() function should be in the same location in the source code for both Unix and Windows.