Flurl: Support Gzip in Requests

[dagostinelli]

This idea was first discussed here.

It would be nice if Flurl would natively support gzip uploading of strings and files and such. Something like so:

    // gzip a string
    var t = await "https://www.example.com"
        .WithHeader("Content-Type", "application/json")
        .WithHeader("Content-Encoding", "gzip")
        .PostGZipStringAsync(clear_text_json);

    // gzip a text file
    var t = await "https://www.example.com"
        .WithHeader("Content-Type", "application/json")
        .WithHeader("Content-Encoding", "gzip")
        .PostAsync(new GzipFileContent(filePath))

An implementation for GZipFileContent was proposed here and @tmenier proposed using CompressedContent.

Using CompressedContent, the result looks like this (for posting a string)

    var t = await "https://www.example.com"
        .WithHeader("Content-Type", "application/json")
        .PostAsync(new CompressedContent(new StringContent(statusMessage), "gzip"));

[Maly-Lemire]

It would also be nice to have a setting to enable compression for json content.

[tmenier]

@Maly-Lemire Do you mean compressed JSON _responses_? Support for that (by default) was added in #266. If you mean compressed JSON _requests_ (i.e. posted data), that's what this issue is all about.

[MNF]

@tmenier, can you rename this issue to “Support Gzip in Requests” and change title of
https://github.com/tmenier/Flurl/issues/266 to mention “Response”? I’ve read https://github.com/tmenier/Flurl/issues/266 first and decided that flurl defaults gzip for both Requests and Responses

[dagostinelli]

@MNF I renamed this one (since I opened it, I can rename it) I'll let @tmenier rename the other if he wants to.

[tmenier]

I'm actively gathering feedback to help prioritize issues for 3.0. If this one is important to you, please vote for it here!