Correct handling of ERR_CACHE_LOCK_TIMEOUT for read only transactions.

net/http/http_cache_unittest.cc

Index: net/http/http_cache_unittest.cc
diff --git a/net/http/http_cache_unittest.cc b/net/http/http_cache_unittest.cc
index 60c7ed7c8d75d286465b15c12b4806d86acc6b87..de5ddd0d4c2e6b33ae0ab370055c36fdaf802335 100644
--- a/net/http/http_cache_unittest.cc
+++ b/net/http/http_cache_unittest.cc
@@ -1769,6 +1769,36 @@ TEST(HttpCache, SimpleGET_WriterTimeout) {
   ReadAndVerifyTransaction(c1.trans.get(), kSimpleGET_Transaction);
 }
 
+// Tests that a (simulated) timeout allows transactions waiting on the cache
+// lock to continue but read only transactions to error out.
+TEST(HttpCache, SimpleGET_WriterTimeoutReadOnlyError) {
+  MockHttpCache cache;
+
+  // Simulate timeout.
+  cache.BypassCacheLock();

[asanka, 2017/02/07 22:56:03]

This method is poorly named :-(

[shivanisha, 2017/02/08 19:14:13]

Updated to SimulateCacheLockTimeout for clarity and removed the comment over it.

+
+  MockHttpRequest request(kSimpleGET_Transaction);
+  Context c1, c2;
+  ASSERT_THAT(cache.CreateTransaction(&c1.trans), IsOk());
+  ASSERT_EQ(ERR_IO_PENDING, c1.trans->Start(&request, c1.callback.callback(),
+                                            NetLogWithSource()));
+
+  // Using load flags similar to MetadataWriter.

[asanka, 2017/02/07 22:56:03]

There are two things to test:

1) That HttpCache::WriteMetadata() will fail if the cache lock times out.
2) That HttpCache::Transaction fails if LOAD_ONLY_FROM_CACHE is set and the
cache lock times out.

Due to the additional flags set by WriteMetadata, it's not robust to assume that
#1 implies #2. But the inverse is defensible. So let's change this test to only
specify LOAD_ONLY_FROM_CACHE. The other flags should be moot.

To close the loop I'd suggest adding a test case to the WriteMetadata_* group
above which simulates the cache lock timeout while invoking
HttpCache::WriteMetadata().

[shivanisha, 2017/02/08 19:14:13]

Done.

The new test added for WriteMetadata_* group cannot test 2 simultaneous metadata
writers because of an issue in the way MetadataWriter uses the load flags. I
have added a todo note and created a bug for the same. In the test I have added
one normal (non read only) transaction and one MetadataWriter to achieve cache
lock timeout. 

+  request.load_flags =
+      LOAD_ONLY_FROM_CACHE | LOAD_SKIP_CACHE_VALIDATION | LOAD_SKIP_VARY_CHECK;
+  ASSERT_THAT(cache.CreateTransaction(&c2.trans), IsOk());
+  ASSERT_EQ(ERR_IO_PENDING, c2.trans->Start(&request, c2.callback.callback(),
+                                            NetLogWithSource()));
+
+  // The second request is queued after the first one.
+  int res = c2.callback.WaitForResult();
+  ASSERT_EQ(ERR_CACHE_MISS, res);
+
+  // Complete the first transaction.
+  c1.callback.WaitForResult();
+  ReadAndVerifyTransaction(c1.trans.get(), kSimpleGET_Transaction);
+}
+
 TEST(HttpCache, SimpleGET_AbandonedCacheRead) {
   MockHttpCache cache;