C# Netcore WebRequest and HttpClient functionality

[Blackclaws]

This is WIP work tracking the addition of WebRequest and HttpClient as replacements for RestSharp, as some environments might find it undesirable to include an additional library (Unity, Blazor, etc.).

This is a bit orthogonal to the already open pull request and could be considered a different take on the subject:

#8331

It tries to keep as much of the original interface intact as possible. WebRequest more so than HttpClient which simply does not offer many of the customizations that WebRequest and RestSharp do.

You can try it out by setting the library to httpclient by cliswitch or adding:

library: httpclient

to the global config in the config file you're using. Should hopefully alleviate/fix #6800 and #853

If you also want to get rid of the dependency on Polly add

additionalProperties:
supportsRetry: false

aswell

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  ./mvnw clean package 
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 @mandrean @frankyjuang @shibayan

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[Blackclaws]

I think this is at a point now where it is ready to be reviewed. It still doesn't work with Blazor but it should work with Unity, I'll test that later today.

In general I think a separate generator such as @shibayan or @devhl-labs has been working on might be needed to fully support Blazor because quite a few options simply aren't possible there.

[wing328]

Thanks for the PR. I played with it locally and it looks very good to start with 👍

I'll merge it so that users can try it out in the upcoming 5.1.0 release (this month or next), and will submit PRs to further improve it (e.g. README, petstore integration tests in CI, etc)

[wing328]

I'll create a separate ApiClient.mustache just for httpclient library similar to how we support multiple HTTP libraries in other client generators as too many {{#useRestSharp}} ... {{/useRestSharp}} etc make the template hard to maintain.

[gbt518]

Thank you for this PR!

I found one small issue as I was testing this out in 5.1.0. I noticed that a new HttpClient is created for each call.

From https://docs.microsoft.com/en-us/dotnet/api/system.net.http.httpclient?view=net-5.0:

HttpClient is intended to be instantiated once and re-used throughout the life of an application. Instantiating an HttpClient class for every request will exhaust the number of sockets available under heavy loads. This will result in SocketException errors.

[VincentNe]

I would like to try out the new HttpClient generator but I don't really have a clue on how to enable the new generator with the cli.

So far I've tried the following command:
openapi-generator-cli generate -i api.json -g csharp-netcore -o Api.Client.NetCore --additional-properties library=httpclient
And I see that it's still using the RestSharp library, can anyone give me an example cli command on how to make use of the new library.

[devhl-labs]

There are two versions of HttpClient, mine and Blackclaws. Mine only uses one instance of HttpClient that you pass in, however, it only supports basic requests and JWT tokens at the moment. Looks like Blackclaw's version may have made the 5.1 release, but mine didn't. I have a pr to add it though.

@VincentNe try just --library httpclient without the additional properties.

[Blackclaws]

Thank you for this PR!

I found one small issue as I was testing this out in 5.1.0. I noticed that a new HttpClient is created for each call.

From https://docs.microsoft.com/en-us/dotnet/api/system.net.http.httpclient?view=net-5.0:

HttpClient is intended to be instantiated once and re-used throughout the life of an application. Instantiating an HttpClient class for every request will exhaust the number of sockets available under heavy loads. This will result in SocketException errors.

Yes, this was indeed the case in order to be mostly a drop in replacement for restsharp. As creating new HttpClients for each request is indeed problematic in some cases there is now a new pull request to change this behaviour to be by default a static HttpClient for each ApiClient which however is also customizable from outside.

[sleipper]

Some great work here @Blackclaws. I have some feedback if you're interested:

1. ApiClient attempts to deserialise to a model regardless of status code. For example a 404, 401, 500 would likely have a different model say with validation or problem details (https://docs.microsoft.com/en-us/aspnet/core/web-api/handle-errors?view=aspnetcore-5.0). Could also not return JSON or no content in the case of a 204 response code. Typically in the case at present the error returned is:
   Most of ApiException : Unexpected character encountered while parsing value: P. Path '', line 0, position 0.
   Stack Trace:

2. Generated API doesn't work with just HttpClient only, this is called out in the Readme but would be better to not permit invalid use. E.g new PetApi(client); the use of this will error as you need to set disableHandlerFeatures to true.

3. ApiClient NewRequest method uses Properties e.g. request.Properties["CookieContainer"], but this is obsolete, should used options instead. There is a TODO but due to your PR to avoid HttpClient being used for each call looks like this is per request but doesn't appear to be a way to set Cookies as localVarRequestOptions is always created.

4. Minor issue

   • RetryConfiguration class not static