Bug 254813

How to reproduce:

$ run-webkit-httpd
$ TEST_RUNNER_TEST_PLUGIN_PATH=this_env_var_is_no_longer_used_and_shouldnt_be_required_but_that_is_work_for_another_patch \
  webkit-flatpak --gtk --debug -c \
  /app/webkit/WebKitBuild/Debug/bin/WebKitTestRunner --show-window http://localhost:8000/media-resources/media-source/media-source-seek-unbuffered.html
[...]
ERROR: writeOriginToFile: Failed to open origin file '/home/ntrrgc/.local/share/WebKitTestRunner/storage/4NoLZrGDXutAmUUf2IXlV4GkA_dI4PpgaXiB2xqjhow/4NoLZrGDXutAmUUf2IXlV4GkA_dI4PpgaXiB2xqjhow/origin'
/app/webkit/Source/WebKit/NetworkProcess/storage/StorageUtilities.h(73) : bool WebKit::writeOriginToFile(const WTF::String &, const WebCore::ClientOrigin &)

There is nothing wrong about the path above. This is the call that is being made:

auto originFileHandle = FileSystem::openFile(filePath, FileSystem::FileOpenMode::ReadWrite[, failIfFileExists = false]);

The problem is openFile() is using g_file_open_readwrite() in this code path, which fails if the file doesn't exist.

The following is a table of valid GIO functions for creating an stream with permissions requested by WebKit:

+-----------+-------------------------+----------------------------+
|   Mode    |    failIfFileExists     |            Call            |
+-----------+-------------------------+----------------------------+
| Read      | (any, will always fail) | g_file_read()              |
| Truncate  | true                    | g_file_create()            |
| Truncate  | false                   | g_file_replace()           |
| ReadWrite | true                    | g_file_create_readwrite()  |
| ReadWrite | false                   | g_file_replace_readwrite() |
+-----------+-------------------------+----------------------------+