Support the STORAGE_EMULATOR_HOST environment variable for StorageClient

[EricStG]

Is your feature request related to a problem? Please describe.
We're using the firebase emulator, and we want to be able to configure the StorageClient via environment variables

Describe the solution you'd like
We'd like to be able to configure the StorageClient's host via the STORAGE_EMULATOR_HOST environment variable

Describe alternatives you've considered
We are currently setting the address via code, as described here.

Additional context
This is already supported by the GO and Node clients

[jskeet]

Will have a look at this. One thing that the .NET libraries are consistent about is not just using an environment variable. We'd do this in the same way - see https://cloud.google.com/dotnet/docs/reference/help/emulators for examples.

(I wasn't aware that the Firebase emulator implemented a full Storage service... Will need to test it thoroughly.)

[jskeet]

Hmmm... I've just had made a first attempt at this, and the emulator just rejects all requests. I need to look in more detail as to what it will accept.

[jskeet]

Ah - my mistake, I'd used the emulator UI port instead of the API port. Doh. Looks like it's working now - with the limitations around no bucket operations, etc. Will see if I can get it more production-ready and create a PR.

[EricStG]

We have it working here without any changes, at least for basic upload/download
Except for a workaround on UpdateObjectAsync, which fails (we haven't dug too much into it for our needs though)

[jskeet]

Will look into UpdateObjectAsync as part of the work - thanks for calling that out.

[EricStG]

We were having errors trying to update both CacheControl and Metadata with UpdateObjectAsync.
The error was:

The service storage has thrown an exception.
HttpStatusCode is NotImplemented.
No JSON error details were specified.
Raw error details are: Not Implemented

Could be a limitation on the emulator, but it would not be documented.

[jskeet]

Yes, I suspect it's an emulator limitation - as you say, object update claims to be supported, but I get the same results as you, even changing a different field (customDateTime). I can patch a change to metadata, but not a change to customDateTime. I don't know how the Firebase Emulator versioning keeps up with the Storage API versioning. I'll ask internally about the object update part not working, but obviously that's somewhat separate to the client library support itself.

[jskeet]

This is implemented in #11535, which will be in the next release.