From d149f14b6b9282ac17ca3c4000c3033ee3eaeae8 Mon Sep 17 00:00:00 2001
From: Pavel Forkert <fxposter@gmail.com>
Date: Tue, 13 Dec 2016 10:49:37 +0200
Subject: [PATCH] Properly lock jws.nonces (#319)

Before read access to `nonces` field in jws structure (in `Nonces` method) was not synchronized and we were still able
to get `slice bounds out of range` panic when trying to "pop" value in `Nonces` method.

The race can be actually observed by running `Nonce` method multiple times in separate goroutines with th precondition is `len(jws.nonces) == 1`.
---
 acme/jws.go | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/acme/jws.go b/acme/jws.go
index f70513e3..80296081 100644
--- a/acme/jws.go
+++ b/acme/jws.go
@@ -44,6 +44,8 @@ func (j *jws) post(url string, content []byte) (*http.Response, error) {
 		return nil, err
 	}
 
+	j.Lock()
+	defer j.Unlock()
 	j.getNonceFromResponse(resp)
 
 	return resp, err
@@ -77,8 +79,6 @@ func (j *jws) signContent(content []byte) (*jose.JsonWebSignature, error) {
 }
 
 func (j *jws) getNonceFromResponse(resp *http.Response) error {
-	j.Lock()
-	defer j.Unlock()
 	nonce := resp.Header.Get("Replay-Nonce")
 	if nonce == "" {
 		return fmt.Errorf("Server did not respond with a proper nonce header.")
@@ -98,6 +98,8 @@ func (j *jws) getNonce() error {
 }
 
 func (j *jws) Nonce() (string, error) {
+	j.Lock()
+	defer j.Unlock()
 	nonce := ""
 	if len(j.nonces) == 0 {
 		err := j.getNonce()
@@ -108,8 +110,6 @@ func (j *jws) Nonce() (string, error) {
 	if len(j.nonces) == 0 {
 		return "", fmt.Errorf("Can't get nonce")
 	}
-	j.Lock()
-	defer j.Unlock()
 	nonce, j.nonces = j.nonces[len(j.nonces)-1], j.nonces[:len(j.nonces)-1]
 	return nonce, nil
 }