[C#] csharp client support for 'string/binary'

Created by: grmcdorman

Description

When generating code from a spec that has format: binary and type: string using the csharp client, the generated code builds an interface with System.IO.Stream but this usage pattern is not supported by restsharp, including the latest version.

openapi-generator version

Main branch.

OpenAPI declaration file content or url

Partial content:

"paths": {
   "/op": {
       "parameters": [
              {
                  "name": "data",
                  "in": "body",
                  "description": "Binary body data",
                  "required": true,
                  "schema": {
                      "type": "string",
                      "format": "binary"
                   }
              }
      ]
  }
}

Command line used for generation

java -jar openapi-generator-cli.jar generate -i swagger.json -l csharp -o ClientAPI -c openapi-generation-parameters.json

Steps to reproduce

Generate client, then either inspect code or try to use it. Trying to run results in an exception of type package_.Client.ApiException: Error getting value from 'ReadTimeout' on 'System.IO.MemoryStream'.

Related issues/PRs

#934 (closed) for cpprest client #1327 for aspdotnetcore server

Suggest a fix/enhancement

Internally, it appears that the type used is file. This is translated to a ''System.IO.Stream`` type in AbstractCSharpCodegen.java around line 172:

        typeMapping.put("file", "System.IO.Stream");

In the generated code, the method contains this code:

            if (body != null && body.GetType() != typeof(byte[]))
            {
                localVarPostBody = this.Configuration.ApiClient.Serialize(body); // http body (model) parameter
            }
            else
            {
                localVarPostBody = body; // byte array
            }

The localVarPostBody is eventually passed to PrepareRequest, which adds it as a parameter:

            if (postBody != null) // http body (model or byte[]) parameter
            {
                request.AddParameter(contentType, postBody, ParameterType.RequestBody);
            }

AddParameter is a method in restsharp object RestRequest. A type of System.IO.Stream is not supported here; the AddParameter method attempts to serialize the Stream object itself instead of the stream's contents.

Easiest fix is to not support binary file streams, and translate this specification to a byte array (byte []), just like a string/byte OpenAPI type. This would require an override in the CSharpClientCodegen.java code.

Actually streaming binary files with restsharp appears to be harder, as a web search only turns up sending byte arrays or files as MIME multi-part (i.e. base64 encoded). Neither apply here if a stream is to be used.

Note that while this would be a breaking change for the generated code, given that the current generated code doesn't work it's pretty unlikely anyone's using it.