Hot Reload File IO -> React to 1 file change notification per file change

[seantleonard]

Why make this change?

• Closes #2423
  • Hot reloading reacts to >1 file change notification representing a single "Save File" action. DAB should only react to the first file change event which represents processing the changed file. DAB should only react to subsequent file change events when the file has actually changed.

What is this change?

• Modifies ConfigFileWatcher class such that it no longer needs to have FileSystemRuntimeConfigLoader as a dependency/constructor parameter. ConfigFileWatcher just called the passed in loader's methods which was a confusing layer of abstraction.
• ConfigFileWatcher now (due to this PR's changes) has a hash persistence mechanism of runtimeconfig file contents and compares the currently tracked hash to a new hash calculated on the file after a "file change" event is emitted from the file watcher. One file change (e.g. clicking save in a text editor) causes multiple file change events to be detected by the file watcher (Added code comments to clarify). Dotnet docs describe the hashing mechanism included in this PR as a way to "ignore" subsequent file change events and only act on one event per file change.
  • Hash mechanism is SHA256 (32 bytes) as recommended by this .NET documentation guidance That's why my implementation of the hash mechanism differs from the ChangeToken documentation referenced implementation which uses SHA1. We are not using the hash for encryption.

    Due to collision problems with SHA1, Microsoft recommends a security model based on SHA256 or better.

• ConfigFileWatcher now raises an event (NewFileContentsDetected) when the hash of the old versus new runtime config file is detected. FileSystemRuntimeConfigLoader subscribes to NewFileContentsDetected and reacts by calling HotReloadConfig(...)
• Fixes how FileSystemRuntimeConfigLoader reads the config file to avoid issues where the disposable doesn't immediately close the file handle and we get occurrences of "IOException file being used by another process". Now using File.ReadAllText so that the file handle is closed immediately.
• Adds field _isCliLoader to FIleSystemRuntimeConfigLoader so DAB knows not to init filewatcher for CLI usage. This fixed a pipeline file IO bug due to CLI usage of filesystemruntimeconfigloader initializing the file watcher.

How was this tested?

The following two integration tests are added to validate the functionality of the modified ConfigFileWatcher class. These tests immitate a user change the runtime config file's contents (or not changing contents) and the test check that the NewFileContentsDetected is raised the expected number times.

• [x] Integration Tests
  1. ConfigFileWatcher_NotifiedOfOneNetNewChanges
  2. ConfigFileWatcher_NotifiedOfZeroNetNewChange

[seantleonard]

/azp run

[seantleonard]

/azp run

[seantleonard]

/azp run