Added check for maximum size of downloaded file names

[jedieaston]

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Resolves #1808.

This PR adds a check to GetInstallerPostHashValidationFileName that ensures that the filename in the URL does not exceed 260 characters (the maximum path size file name size in Windows). If it does, then the "older" naming style (manifest.version.ext) is used for the downloaded file. Technically this could still fail if the full length of the path is 260 instead of just the file name, but I thought that was fairly unlikely. If it isn't I can adjust for that too.

Tested: manually via the manifest given in the issue. As always, I'm happy to add tests if needed.

Edit: corrected explanation, thanks.

Microsoft Reviewers: Open in CodeFlow

[JohnMcPMS]

Is this something you are seeing in practice?

Edit: Doh, just look at the linked issue dummy 😄

[ghost]

the maximum path size in Windows

Nope. The Maximum "FIle Name String" can be 260 char long. In windows, from v1607 onwards the Maximum "Path Length" is UTF-16 32K char provided that the executable use longPathAware embedded manifest. (i.e MAX_PATH no longer becomes effective for that executable.)

[JohnMcPMS]

/azp run

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Azure Pipelines successfully started running 1 pipeline(s).

[jedieaston]

It looks like the component governance checker is down:

[INFO] Submitting 65 registrations. 

[ERROR] There was an unexpected error:  
[ERROR] SafelyExecute logged TimeoutException: The HTTP request timed out after 00:01:40.
[INFO] For more information about configuring the build task please visit: https://aka.ms/cgbuildtaskdocs 
Execution finished, status: -1
Process terminating.
##[error]The Component Detection tool experienced a failure. See the logs for more information
Finishing: Component Governance

[JohnMcPMS]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).