path: root/sysfs.cpp
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* Add sysfs LED class wrapperAndrew Jeffery2019-03-181-0/+107
The Physical class implements private templated read() and write() methods. There are several properties that make this approach less than ideal: 1. read() and write() are non-virtual template functions, and we would have to link-seam mock the internals, which means hijacking std::fstream. 2. Even if read() and write() were virtual functions, this is made irrelevant by the fact that we want to traverse execution paths in setInitialState(), which is called from the Physical constructor. Methods invoked by class constructors are bound to the implementations specified in the constructor's class and will never dispatch to a descendant's override. As such we have no mechanism to manipulate the execution path without resorting to the pre-processor seam, which is undesirable for other reasons. 3. The abstraction is poor. Physical implements the business logic of converting interactions with the DBus interface into compatible interactions with the sysfs LED class attributes, and shouldn't have knowledge of how to directly interact with sysfs itself. 4. read() and write() are template functions, but the only type parameter used in the code-base is std::string, and conversions are left to the caller. This needlessly complicates the caller logic and reduces readability of the callee code. The change defines a separate class, SysfsLed, to map actions onto the LED sysfs class attributes. SysfsLed will be provided by the dependency-injection pattern to the Physical class by passing an instance reference through its constructor. The lifetime of the SysfsLed instance must exceed the lifetime of the associated Physical instance. Further, the methods of SysfsLed are all marked as virtual and defined to return concrete types (either unsigned long or std::string as appropriate). This opens the door for mocking without resorting to techniques such as using link seams, and removes templates as a point of complication. Further, defining only a concrete class and not an abstract base class minimises the boilerplate required as we're likely never going to have another descendant of SysfsLed that isn't a mock implementation (we don't need to exclude implementations by way of sibling types). Integration tests are provided for SysfsLed, which is necessary as the class must write to the filesystem (again, unless we want to hijack std::fstream, which seems unpalatable). Isolated temporary directories are used to ensure the tests can be run in parallel without interference. The tests provide 100% line coverage of SysfsLed. Change-Id: I81fc7d9fd07eed54035f515502f563f25aa1e58f Signed-off-by: Andrew Jeffery <>
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