Possible QueryString Encoding Issue Causing NullReferenceException

[garfbradaz]

I first posted this Issue on stackoverflow here and @cgillum kindly answered and asked me to post here. I will though add that question here as well.

So I'm prototyping some Azure Durable Functions, to try and understand to see if they will fit within a proposed solution for our internal API system.

Based on examples, I've created a Orchestrator Client (HelloOrchestratorClient.cs), that responds to a HttpTrigger. This client extracts some information from the original request, then proceeds to fire off a Orchestrator Function (HelloOrchestrator.cs) passing in some of the information extracted:

Complex HelloOrchestratorClient.cs:

[FunctionName("HttpSyncStart")]
public static async Task<HttpResponseMessage> Run(
    [HttpTrigger(AuthorizationLevel.Anonymous, methods: "get", Route = "orchestrators/{functionName}/wait")]
    HttpRequestMessage req,
    [OrchestrationClient] DurableOrchestrationClient starter,
    string functionName,
    ILogger log)
{       
    HttpReq originalRequest = new HttpReq() {
            DeveloperId = GetDevKey(req,apiHeaderKey),
            QueryString = req.RequestUri.Query,
            APIName = GetQueryStringValue(req,APIName),
            APIVersion = GetQueryStringValue(req,APIVersion)

    };
    string instanceId =   await starter.StartNewAsync(functionName, originalRequest);

    TimeSpan timeout = GetTimeSpan(req, Timeout) ?? TimeSpan.FromSeconds(30);
    TimeSpan retryInterval = GetTimeSpan(req, RetryInterval) ?? TimeSpan.FromSeconds(1);

    return  await starter.WaitForCompletionOrCreateCheckStatusResponseAsync(
        req,
        instanceId,
        timeout,
        retryInterval);

}

The HelloOrchestrator.cs simply for now is just calling off to one of our internal API's and returning a JsonProduct payload (Simple POCO describing, you guessed it, a title), using a ActivityTigger named HelloOrchestrator.APICall to make the API call itself.

Complex HelloOrchestrator.cs:

[FunctionName("E1_JsonProduct")]
        public static async Task<List<JsonProduct>> Run(
            [OrchestrationTrigger] DurableOrchestrationContextBase context,
            ILogger log)
        {
            List<JsonProduct> output = new List<JsonProduct>();
            HttpReq r = context.GetInput<HttpReq>();
            if(r != null)
            {
                if(r.DeveloperId == null)
                {
                    return output;
                }
                output.Add(await context.CallActivityAsync<JsonProduct>("E1_CallAPI",r));
                return output;
            }
            return output;
        } 

[FunctionName("E1_CallAPI")]
public async static Task<JsonProduct> APICall([ActivityTrigger] HttpReq req,
    ILogger log)
{

    JsonProduct products  = null;
    string u = $"{baseAddress}{req.APIVersion}/{req.APIName}{req.QueryString}";  

    var request = new HttpRequestMessage(HttpMethod.Get, u);
    request.Headers.Accept.Add(
        new MediaTypeWithQualityHeaderValue("application/json")
    );
    request.Headers.Add("x-apikey",req.DeveloperId);
     log.LogInformation($"URL calling = '{request.RequestUri.AbsoluteUri}'.");
    HttpResponseMessage response = await client.SendAsync(request);
    // return await response.Content.ReadAsStringAsync();
    if(response.IsSuccessStatusCode)
    {
        var formatter = new JsonMediaTypeFormatter
        {
            SerializerSettings = HelloProj.CosmosDB.Models.Products.Converter.Settings
        };

        products = await response.Content.ReadAsAsync<JsonProduct>(new [] {formatter});
    }
    return products;
}

Side Note: The plan is if I can get this to work, is to fan out a bunch of processes to different API's and fan back in again and merge the JSON payload and return it back to the originator.

Issue I'm experiencing

So, when my List<JsonProduct> is returned back from HelloOrchestrator.Run, I receive the following NullReferenceException found on this Gist (Big stack trace) and I receive a 500 response from the Orchestrator Client.

The following proves the output returned does actually have an object at runtime:

Could it be due to the complexity of JsonProduct (Again find the model classes here)? I ask, because when I swap out my Orchestrator Function for a simpler model structure, I don't receive a 500, I receive my JSON Payload.

This example shows the Simple Orchestrator Function HelloOrchestrator.cs, returning a simple TestToDo (Gist for model) flat object that doesn't error:

Simple HelloOrchestrator.cs:

 [FunctionName("E1_Todo")]
    public static async Task<TestToDo> RunToDo(
    [OrchestrationTrigger] DurableOrchestrationContextBase context,
        ILogger log)
    {
        HttpReq r = context.GetInput<HttpReq>();
        TestToDo todo = new TestToDo();
        if(r != null)
        {
            todo = await context.CallActivityAsync<TestToDo>("E1_CallAPITodo",r);
        }
        return todo;
    }

[FunctionName("E1_CallAPITodo")]
public async static Task<TestToDo> APITodoCall([ActivityTrigger] HttpReq req,
    ILogger log)
{

    var request = new HttpRequestMessage(HttpMethod.Get, "https://jsonplaceholder.typicode.com/todos/1");
    request.Headers.Accept.Add(
        new MediaTypeWithQualityHeaderValue("application/json")
    );
     log.LogInformation($"URL calling = '{request.RequestUri.AbsoluteUri}'. for {req.QueryString}");
    HttpResponseMessage response = await client.SendAsync(request);
    return await response.Content.ReadAsAsync<TestToDo>();

More Information

If you require my full prototype projects, you can find them here:

• Complex Project (Throws 500 and exception)

When you run it, use the following in something like Postman (After F5ing it):

http://localhost:7071/api/orchestrators/E1_JsonProduct/wait?timeout=20&retryInterval=0.25&api=products&apiVersion=v1&filterByImprints=w%26n&limit=20

Interesting (Question that @cgillum asked in the SO post, was the error could be due to an QueryString encoding. So I tested again using the following and it worked, so it seems @cgillum could be right:

http://localhost:7071/api/orchestrators/E1_JsonProduct/wait?timeout=20&retryInterval=0.25&api=products&apiVersion=v1&filterByImprints=WANDN&limit=20

FYI: Both W&N and WANDN are valid values for our filterByImprints parameter.

• Simple Project (No 500 or Exception thrown)

When you run it, use the following in something like Postman (after F5ing it):

http://localhost:7071/api/orchestrators/E1_Todo/wait?timeout=20&retryInterval=0.25

[garfbradaz]

I will pull down the Azure Functions project and reference it in my project. and try and glean some more info.

[garfbradaz]

@cgillum This is still on my list of todos to get you more info.

[cgillum]

This will be fixed in the next release.