Add support to download only the updated ranges using Etags, keeping …

[CNScott]

…resiliency and updating to match current version

This is based almost entirely off of eduardo010174's work. I just added the resiliency support in from the newer version.

[eduardo010174]

Don't have problem for me.
But it's an important feature.

Other solution it's generate on server side on file with indexed Etag's of all files.
If I have time, I will make on repository for get every possible Etag and store cache of the day for not lose more time on make fake queries.

@CNScott
I have docker image on github with compile binary ready for daily use.
I will update binary with you commit if not have problems for you.

[CNScott]

Don't have problem for me. But it's an important feature.

Other solution it's generate on server side on file with indexed Etag's of all files. If I have time, I will make on repository for get every possible Etag and store cache of the day for not lose more time on make fake queries.

@CNScott I have docker image on github with compile binary ready for daily use. I will update binary with you commit if not have problems for you.

No problem from me. Thank you! We really needed this feature!

[aseigler]

Given the content, why not serialize like this, to make the output cleaner?

string json = JsonSerializer.Serialize(_etag, s_jsonOptions);

Using this:

private static JsonSerializerOptions s_jsonOptions = new() { Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping };

[aseigler]

Why not use the built in string constants?

request.Headers.IfNoneMatch.Add(new EntityTagHeaderValue(_etag[i]));

[aseigler]

Would this be clearer?

if (data_updated)
{
    _etag[i] = response.Headers.ETag?.Tag ?? "";
}