F# Azure Functions独立进程SignalR协商方法访问异常问题

问题原因 #

F#对protected成员的访问限制比C#更严格：基类的protected成员仅允许在派生类的直接成员方法中通过base调用，无法在嵌套的计算表达式（如task {}）或lambda表达式里使用base访问，这就是报错FS0491的核心原因。

解决思路一：封装protected成员调用 #

在派生类中新增一个辅助方法，直接调用基类的NegotiateAsync，然后在task表达式里通过当前实例调用这个辅助方法：

open System.Net
open System.Threading.Tasks
open Microsoft.Azure.Functions.Worker
open Microsoft.Azure.Functions.Worker.Http
open Microsoft.Azure.Functions.Worker.SignalRService
open Microsoft.Extensions.Logging

type SignalRNegotiateFunction(loggerFactory: ILoggerFactory, hub : ServiceHubContext, serviceProvider: IServiceProvider) =
    inherit ServerlessHub(serviceProvider: IServiceProvider)

    let logger = loggerFactory.CreateLogger<SignalRNegotiateFunction>()

    // 封装基类的protected调用
    member private this.Negotiate(options: NegotiationOptions) =
        base.NegotiateAsync(options)

    [<Function("SignalRNegotiate")>]
    member _.Run([<HttpTrigger(AuthorizationLevel.Anonymous, "post", Route = "negotiate")>] req: HttpRequestData) : Task<HttpResponseData> =
        task {
            let translator = req |> RequestHandler.determineTranslator
            let! remoteHubConnectionRequest = RequestHandler.decodeAsyncHubConnection translator req

            let userIdStr = remoteHubConnectionRequest.UserID
            let attribute = userIdStr |> Negotiator.infoAttributeFromUserIdStr

            let negoptions = NegotiationOptions(UserId = userIdStr)

            // 通过当前实例调用封装的方法，替代base直接调用
            let! negotiateResponse = this.Negotiate(negoptions)
            
            // 后续将negotiateResponse转换为HttpResponseData返回的逻辑
            let response = req.CreateResponse(HttpStatusCode.OK)
            do! response.WriteAsJsonAsync(negotiateResponse)
            return response
        }

解决思路二：改用依赖注入直接调用协商服务 #

绕开继承ServerlessHub的方式，直接注入INegotiationService来处理SignalR协商，更符合依赖注入的设计原则，同时避免F#的继承访问限制：

open System.Net
open System.Threading
open System.Threading.Tasks
open Microsoft.Azure.Functions.Worker
open Microsoft.Azure.Functions.Worker.Http
open Microsoft.Azure.Functions.Worker.SignalRService
open Microsoft.Extensions.Logging

type SignalRNegotiateFunction(loggerFactory: ILoggerFactory, negotiationService: INegotiationService) =
    let logger = loggerFactory.CreateLogger<SignalRNegotiateFunction>()

    [<Function("SignalRNegotiate")>]
    member _.Run([<HttpTrigger(AuthorizationLevel.Anonymous, "post", Route = "negotiate")>] req: HttpRequestData) : Task<HttpResponseData> =
        task {
            let translator = req |> RequestHandler.determineTranslator
            let! remoteHubConnectionRequest = RequestHandler.decodeAsyncHubConnection translator req

            let userIdStr = remoteHubConnectionRequest.UserID
            let attribute = userIdStr |> Negotiator.infoAttributeFromUserIdStr

            let negoptions = NegotiationOptions(UserId = userIdStr)

            // 直接使用注入的INegotiationService完成协商
            let! negotiateResponse = negotiationService.NegotiateAsync(negoptions, CancellationToken.None)
            
            let response = req.CreateResponse(HttpStatusCode.OK)
            do! response.WriteAsJsonAsync(negotiateResponse)
            return response
        }

内容的提问来源于stack exchange，提问作者SteelCityRKP