Azure function middleware - Get response data before return to user

Question

I want to retrieve data and format it before return to the user but don't know how to retrieve it, I see that the context only provides the request.

public class CustomResponse : IFunctionsWorkerMiddleware
    {
        public async Task Invoke(FunctionContext context, FunctionExecutionDelegate next)
        {
            try
            {
                await next(context);
                if (!context.IsHttpTriggerFunction())
                {
                    return;
                }
                /// format response here
            } catch (Exception ex)
            {
                await context.CreateJsonResponse(System.Net.HttpStatusCode.InternalServerError, new
                {
                    errorMessage = ex.Message
                });
            }
        }
    }

Does FunctionContext support us to get response data? If yes, how can i get it?

Answer 1

After research, I think FunctionContext doesn't support us to get the data returned from the function, so I choose another way instead of middleware.

I write a static function to convert object to json string

private JsonSerializerOptions camelOpt = new JsonSerializerOptions
    {
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
    };

public static string ToJsonString(this object input, bool camelCase = false) => JsonSerializer.Serialize(input, camelCase ? camelOpt : null);

[Function(nameof(Temp))]
public object Temp([HttpTrigger(AuthorizationLevel.Function,"get", "post", Route = ESignRoutes.Temp)]
     HttpRequestData req,
     FunctionContext context)
    {
        object data = null;
        //todo
        return data.ToJsonString(camelCase: true);
    }

Besides, still need middleware to handle exception

public class CustomResponse : IFunctionsWorkerMiddleware
{
    public async Task Invoke(FunctionContext context, FunctionExecutionDelegate next)
    {
        try
        {
            await next(context);
            if (!context.IsHttpTriggerFunction())
            {
                return;
            }
        }
        catch (Exception ex)
        {
            var message = ex.Message ?? " ";
            message = message.Replace("One or more errors occurred. (", "");
            message = message[..^1];
            await context.CreateJsonResponse(
                System.Net.HttpStatusCode.InternalServerError,
                new
                {
                    error = new
                    {
                        message = message
                    }
                });
        }
    }
}