Creating a File Accessor Plugin¶

Experimental

Please note that this functionality is currently experimental. Creating and using a plugin is not guaranteed to work as expected at this time.

Description

GEE Server implements a plugin system for file accessors. That is, plugins can be implemented that provide the ability to read from different types of file systems, either local or remote. The default POSIX accessor is built in, but additional plugins can be loaded at runtime. Currently, file accessors are only used when serving data, not when building, pushing, and publishing. In those cases, the standard file system functions are used to read and write data.

How to Implement a Plugin

A file accessor plugin needs 3 components. The first is a function called get_factory_v1 that returns a FileAccessorFactory pointer. The signature should be as follows:

FileAccessorFactory* get_factory_v1 ();

The second component is a factory class that inherits from FileAccessorFactory and overrides the following method:

virtual AbstractFileAccessor* GetAccessor(const std::string &fileName);

The final component is a class that derives from AbstractFileAccessor and overrides all of the pure virtual methods. See FileAccessor.h for the complete interface.

Example

To see a barebones sample implementation, look at earthenterprise/earth_enterprise/src/common/test_plugins/FileAccessorTestPlugin.cpp.

Additional Information

• get_factory_v1 should be exported as extern "C" to avoid C++ name mangling.
• Plugins need to be built with the same version of the C++ compiler that is used to build Open GEE to ensure compatibility.
• Plugins should be built as shared libraries (.so)
• Once built, plugins can be placed in /opt/google/plugin/fileaccessor/ prior to running GEE Server. If a plugin fails to load, see the error log for more information.