Fix bug: 416 RangeNotSatisfiable exception is swallowed unintentionally

Author: Jinming-Hu

Microsoft.WindowsAzure.Storage/src/cloud_blob.cpp

@@ -666,8 +666,15 @@ namespace azure { namespace storage {
                 single_blob_download_threshold = protocol::default_single_block_download_threshold;
             }
 
+            // We use this variable to track if we are trying to download the whole blob or just a range.
+            // In the former case, no exception should be thrown if the blob is empty.
+            // In the latter case, exception should be thrown.
+            // And the behavior should be consistent no matter we're downloading with multiple or single thread.
+            bool no_throw_on_empty = false;
+
             if (offset >= std::numeric_limits<utility::size64_t>::max())
             {
+                no_throw_on_empty = true;
                 if (length == 0)
                 {
                     offset = 0;
@@ -690,9 +697,9 @@ namespace azure { namespace storage {
                 }
                 catch (storage_exception &e)
                 {
-                    // For empty blob, swallow the exception and update the attributes.
-                    if (e.result().http_status_code() == web::http::status_codes::RangeNotSatisfiable
-                        && offset == 0)
+                    // If offset equals to 0 and HTTP status code is 416 RangeNotSatisfiable, then this is an empty blob.
+                    // For empty blob, update the attributes or throw an exception.
+                    if (e.result().http_status_code() == web::http::status_codes::RangeNotSatisfiable && offset == 0 && no_throw_on_empty)
                     {
                         return instance->download_attributes_async_impl(condition, options, context, timer_handler->get_cancellation_token(), false, timer_handler);
                     }

Microsoft.WindowsAzure.Storage/tests/cloud_blob_test.cpp

@@ -1082,6 +1082,47 @@ SUITE(Blob)
         CHECK(blob.properties().size() == target_length);
     }
 
+    TEST_FIXTURE(blob_test_base, range_not_satisfiable_exception)
+    {
+        auto blob_name = get_random_string(20);
+        auto blob = m_container.get_block_blob_reference(blob_name);
+        blob.upload_text(utility::string_t());
+
+        auto blob2 = m_container.get_block_blob_reference(blob_name + _XPLATSTR("2"));
+        blob2.upload_text(_XPLATSTR("abcd"));
+
+        azure::storage::blob_request_options options1;
+        options1.set_parallelism_factor(1);
+        options1.set_use_transactional_crc64(false);
+
+        azure::storage::blob_request_options options2;
+        options2.set_parallelism_factor(2);
+        options2.set_use_transactional_crc64(false);
+
+        azure::storage::blob_request_options options3;
+        options3.set_parallelism_factor(1);
+        options3.set_use_transactional_crc64(true);
+
+        for (const auto& option : { options1, options2, options3 }) {
+            concurrency::streams::container_buffer<std::vector<uint8_t>> download_buffer;
+
+            // download whole blob, no exception
+            blob.download_to_stream(download_buffer.create_ostream(), azure::storage::access_condition(), option, azure::storage::operation_context());
+
+            // download range, should throw
+            CHECK_THROW(blob.download_range_to_stream(download_buffer.create_ostream(), 0, 100, azure::storage::access_condition(), option, azure::storage::operation_context()), azure::storage::storage_exception);
+
+            // download range(max, ...), no exception
+            blob.download_range_to_stream(download_buffer.create_ostream(), std::numeric_limits<utility::size64_t>::max(), 0, azure::storage::access_condition(), option, azure::storage::operation_context());
+
+            // download range(3, very large), no exception
+            blob2.download_range_to_stream(download_buffer.create_ostream(), 3, 100, azure::storage::access_condition(), option, azure::storage::operation_context());
+
+            // download range(4, ...), should throw
+            CHECK_THROW(blob2.download_range_to_stream(download_buffer.create_ostream(), 4, 100, azure::storage::access_condition(), option, azure::storage::operation_context()), azure::storage::storage_exception);
+        }
+    }
+
     TEST_FIXTURE(blob_test_base, read_blob_with_invalid_if_none_match)
     {
         auto blob_name = get_random_string(20);