From 39770792ca624a611eaaca6e973306938771fe83 Mon Sep 17 00:00:00 2001
From: Mark Nelson <mdjnelson@gmail.com>
Date: Mon, 20 Apr 2020 14:32:37 +0200
Subject: [PATCH] MDL-58018 core: add support to redis for read-only sessions

---
 lib/classes/session/redis.php    | 6 ++++--
 lib/tests/session_redis_test.php | 9 +++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/lib/classes/session/redis.php b/lib/classes/session/redis.php
index d4758675de0..b54639a064c 100644
--- a/lib/classes/session/redis.php
+++ b/lib/classes/session/redis.php
@@ -255,9 +255,11 @@ class redis extends handler {
      */
     public function handler_read($id) {
         try {
-            $this->lock_session($id);
+            if ($this->requires_write_lock()) {
+                $this->lock_session($id);
+            }
             $sessiondata = $this->connection->get($id);
-            if ($sessiondata === false) {
+            if ($sessiondata === false && $this->requires_write_lock()) {
                 $this->unlock_session($id);
                 return '';
             }
diff --git a/lib/tests/session_redis_test.php b/lib/tests/session_redis_test.php
index ff9ddd3383c..938491a3cb6 100644
--- a/lib/tests/session_redis_test.php
+++ b/lib/tests/session_redis_test.php
@@ -94,6 +94,7 @@ class core_session_redis_testcase extends advanced_testcase {
     public function test_normal_session_start_stop_works() {
         $sess = new \core\session\redis();
         $sess->init();
+        $sess->set_requires_write_lock(true);
         $this->assertTrue($sess->handler_open('Not used', 'Not used'));
         $this->assertSame('', $sess->handler_read('sess1'));
         $this->assertTrue($sess->handler_write('sess1', 'DATA'));
@@ -110,6 +111,7 @@ class core_session_redis_testcase extends advanced_testcase {
     public function test_session_blocks_with_existing_session() {
         $sess = new \core\session\redis();
         $sess->init();
+        $sess->set_requires_write_lock(true);
         $this->assertTrue($sess->handler_open('Not used', 'Not used'));
         $this->assertSame('', $sess->handler_read('sess1'));
         $this->assertTrue($sess->handler_write('sess1', 'DATA'));
@@ -121,6 +123,7 @@ class core_session_redis_testcase extends advanced_testcase {
 
         $sessblocked = new \core\session\redis();
         $sessblocked->init();
+        $sessblocked->set_requires_write_lock(true);
         $this->assertTrue($sessblocked->handler_open('Not used', 'Not used'));
 
         // Trap the error log and send it to stdOut so we can expect output at the right times.
@@ -143,6 +146,7 @@ class core_session_redis_testcase extends advanced_testcase {
     public function test_session_is_destroyed_when_it_does_not_exist() {
         $sess = new \core\session\redis();
         $sess->init();
+        $sess->set_requires_write_lock(true);
         $this->assertTrue($sess->handler_open('Not used', 'Not used'));
         $this->assertTrue($sess->handler_destroy('sess-destroy'));
         $this->assertSessionNoLocks();
@@ -151,6 +155,7 @@ class core_session_redis_testcase extends advanced_testcase {
     public function test_session_is_destroyed_when_we_have_it_open() {
         $sess = new \core\session\redis();
         $sess->init();
+        $sess->set_requires_write_lock(true);
         $this->assertTrue($sess->handler_open('Not used', 'Not used'));
         $this->assertSame('', $sess->handler_read('sess-destroy'));
         $this->assertTrue($sess->handler_destroy('sess-destroy'));
@@ -160,8 +165,10 @@ class core_session_redis_testcase extends advanced_testcase {
 
     public function test_multiple_sessions_do_not_interfere_with_each_other() {
         $sess1 = new \core\session\redis();
+        $sess1->set_requires_write_lock(true);
         $sess1->init();
         $sess2 = new \core\session\redis();
+        $sess2->set_requires_write_lock(true);
         $sess2->init();
 
         // Initialize session 1.
@@ -203,6 +210,7 @@ class core_session_redis_testcase extends advanced_testcase {
     public function test_multiple_sessions_work_with_a_single_instance() {
         $sess = new \core\session\redis();
         $sess->init();
+        $sess->set_requires_write_lock(true);
 
         // Initialize session 1.
         $this->assertTrue($sess->handler_open('Not used', 'Not used'));
@@ -223,6 +231,7 @@ class core_session_redis_testcase extends advanced_testcase {
     public function test_session_exists_returns_valid_values() {
         $sess = new \core\session\redis();
         $sess->init();
+        $sess->set_requires_write_lock(true);
 
         $this->assertTrue($sess->handler_open('Not used', 'Not used'));
         $this->assertSame('', $sess->handler_read('sess1'));
-- 
2.43.0