An optional string parameter is not passed correctly by swagger ui

[GilShalit]

An Azure function (V3) is declared with an optional string parameter. it is sent incorrectly to the function from the swagger UI regardless if the parameter is specified or left empty.

        [OpenApiOperation(operationId: "Function1", tags: new[] { "Function" }, Summary = "Show ",Visibility = OpenApiVisibilityType.Important)]
        [OpenApiParameter("filter", Type = typeof(string), In = ParameterLocation.Path, Visibility = OpenApiVisibilityType.Important, Description = "Optional string", Required =false )]
        [Function("Function1")]
        public static HttpResponseData Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "MyRoute/{filter?}")] HttpRequestData req,
            FunctionContext executionContext, string filter)
        {
            var logger = executionContext.GetLogger("Function1");
            logger.LogInformation("C# HTTP trigger function processed a request.");

            var response = req.CreateResponse(HttpStatusCode.OK);
            response.Headers.Add("Content-Type", "text/plain; charset=utf-8");

            response.WriteString($"The filter value is {(filter==null?"null":filter)}");

            return response;
        }
    }

when tested from the address bar of a browser, the response is as expected: http://localhost:7071/api/myroute/XYZ returns: The filter value is XYZ http://localhost:7071/api/myroute returns: The filter value is null

but going through the Swagger UI, the response is: The filter value is {filter

I have created a repository at https://github.com/GilShalit/SwaggerBug to demonstrate.

[justinyoo]

@GilShalit Thanks for the issue! I'll take a look.

[GilShalit]

Hi, This is still happening in OpenAPI 1.0.0 on .Net 6 :-\

Thank you for your work!

[vrooijen]

Still the case in v1.1.0 Code by TS is the way to reproduce

[justinyoo]

I checked the OpenAPI spec (v3.0.1) about this: https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.1.md#paths-object

Unfortunately, the spec doesn't support the wildcard characters in the path template. In other words, if you declare path template, the path part MUST be required value, not optional - it MUST NOT be nullable.