Reland of [Fetch API] Start reading blob only when the reader wants to read contents.

third_party/WebKit/Source/modules/fetch/FetchBlobDataConsumerHandleTest.cpp

Index: third_party/WebKit/Source/modules/fetch/FetchBlobDataConsumerHandleTest.cpp
diff --git a/third_party/WebKit/Source/modules/fetch/FetchBlobDataConsumerHandleTest.cpp b/third_party/WebKit/Source/modules/fetch/FetchBlobDataConsumerHandleTest.cpp
index b49316cadfc7d072962900eae4f12073d30c9d11..a7f6a85451c8baf143e87cbb463802a025418a6d 100644
--- a/third_party/WebKit/Source/modules/fetch/FetchBlobDataConsumerHandleTest.cpp
+++ b/third_party/WebKit/Source/modules/fetch/FetchBlobDataConsumerHandleTest.cpp
@@ -112,8 +112,9 @@
         = FetchBlobDataConsumerHandle::create(&document(), blobDataHandle, factory);
     testing::runPendingTasks();
 
-    size_t size = 0;
-    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
+    char buffer[1];
+    size_t size = 0;
+    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -134,6 +135,27 @@
     EXPECT_EQ(NotCORSEnabled, resourceLoaderOptions.corsEnabled);
 }
 
+TEST_F(FetchBlobDataConsumerHandleTest, ZeroByteReadDoesNotCreateLoader)
+{
+    auto factory = new StrictMock<MockLoaderFactory>;
+    Checkpoint checkpoint;
+
+    InSequence s;
+    EXPECT_CALL(checkpoint, Call(1));
+    EXPECT_CALL(checkpoint, Call(2));
+
+    RefPtr<BlobDataHandle> blobDataHandle = createBlobDataHandle("Once upon a time");
+    std::unique_ptr<WebDataConsumerHandle> handle
+        = FetchBlobDataConsumerHandle::create(&document(), blobDataHandle, factory);
+    testing::runPendingTasks();
+
+    size_t size = 0;
+    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size));
+    checkpoint.Call(1);
+    testing::runPendingTasks();
+    checkpoint.Call(2);
+}
+
 TEST_F(FetchBlobDataConsumerHandleTest, CancelLoaderWhenStopped)
 {
     auto factory = new StrictMock<MockLoaderFactory>;
@@ -154,8 +176,9 @@
         = FetchBlobDataConsumerHandle::create(&document(), blobDataHandle, factory);
     testing::runPendingTasks();
 
-    size_t size = 0;
-    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
+    char buffer[1];
+    size_t size = 0;
+    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -185,8 +208,9 @@
     std::unique_ptr<WebDataConsumerHandle::Reader> reader = handle->obtainReader(nullptr);
     testing::runPendingTasks();
 
-    size_t size = 0;
-    reader->read(nullptr, 0, kNone, &size);
+    char buffer[1];
+    size_t size = 0;
+    ASSERT_EQ(kShouldWait, reader->read(buffer, sizeof(buffer), kNone, &size));
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -223,8 +247,9 @@
     src->add(Command(Command::Wait));
     src->add(Command(Command::Done));
 
-    size_t size = 0;
-    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
+    char buffer[1];
+    size_t size = 0;
+    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -261,8 +286,9 @@
     src->add(Command(Command::Wait));
     src->add(Command(Command::Done));
 
-    size_t size = 0;
-    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
+    char buffer[1];
+    size_t size = 0;
+    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -291,8 +317,9 @@
     std::unique_ptr<WebDataConsumerHandle> handle
         = FetchBlobDataConsumerHandle::create(&document(), blobDataHandle, factory);
 
-    size_t size = 0;
-    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
+    char buffer[1];
+    size_t size = 0;
+    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -326,8 +353,9 @@
     src->add(Command(Command::Data, "hello, "));
     src->add(Command(Command::Error));
 
-    size_t size = 0;
-    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
+    char buffer[1];
+    size_t size = 0;
+    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);