From 5308c6d9325735ab4e69620e99aaa8d119e02941 Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@golang.org>
Date: Tue, 16 Dec 2014 15:11:43 +1100
Subject: [PATCH] crypto/rand: handle EAGAIN reads from /dev/urandom

Fixes #9205

Change-Id: Iacd608ba43332008984aa8ece17dcb5757f27b3f
Reviewed-on: https://go-review.googlesource.com/1611
Reviewed-by: Ian Lance Taylor <iant@golang.org>
---
 src/crypto/rand/eagain.go    | 27 +++++++++++++++++++++++++++
 src/crypto/rand/rand_unix.go | 18 +++++++++++++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 src/crypto/rand/eagain.go

diff --git a/src/crypto/rand/eagain.go b/src/crypto/rand/eagain.go
new file mode 100644
index 00000000000..2c853d0a134
--- /dev/null
+++ b/src/crypto/rand/eagain.go
@@ -0,0 +1,27 @@
+// Copyright 2014 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.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+
+package rand
+
+import (
+	"os"
+	"syscall"
+)
+
+func init() {
+	isEAGAIN = unixIsEAGAIN
+}
+
+// unixIsEAGAIN reports whether err is a syscall.EAGAIN wrapped in a PathError.
+// See golang.org/issue/9205
+func unixIsEAGAIN(err error) bool {
+	if pe, ok := err.(*os.PathError); ok {
+		if errno, ok := pe.Err.(syscall.Errno); ok && errno == syscall.EAGAIN {
+			return true
+		}
+	}
+	return false
+}
diff --git a/src/crypto/rand/rand_unix.go b/src/crypto/rand/rand_unix.go
index 62d0fbdb350..75c36e05b34 100644
--- a/src/crypto/rand/rand_unix.go
+++ b/src/crypto/rand/rand_unix.go
@@ -58,12 +58,28 @@ func (r *devReader) Read(b []byte) (n int, err error) {
 		if runtime.GOOS == "plan9" {
 			r.f = f
 		} else {
-			r.f = bufio.NewReader(f)
+			r.f = bufio.NewReader(hideAgainReader{f})
 		}
 	}
 	return r.f.Read(b)
 }
 
+var isEAGAIN func(error) bool // set by eagain.go on unix systems
+
+// hideAgainReader masks EAGAIN reads from /dev/urandom.
+// See golang.org/issue/9205
+type hideAgainReader struct {
+	r io.Reader
+}
+
+func (hr hideAgainReader) Read(p []byte) (n int, err error) {
+	n, err = hr.r.Read(p)
+	if err != nil && isEAGAIN != nil && isEAGAIN(err) {
+		err = nil
+	}
+	return
+}
+
 // Alternate pseudo-random implementation for use on
 // systems without a reliable /dev/urandom.