NullReferenceException in CorrelationIdHandler

[Tom Robinson]

I'm trying to upgrade to 3.0.0 but having some problems when using AddCorrelationIdForwarding() (which enables the CorrelationIdHandler in AddHttpClient registrations).

When an HttpClient is used, the exception is:

System.NullReferenceException: Object reference not set to an instance of an object.
  at at CorrelationId.HttpClient.CorrelationIdHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
  at at System.Net.Http.DelegatingHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)

The exception is on this line: https://github.com/stevejgordon/CorrelationId/blob/master/src/CorrelationId/HttpClient/CorrelationIdHandler.cs#L22

this._correlationContextAccessor.CorrelationContext is null.

This only happens when I'm making a request as part of the application startup code, i.e. not as part of a wider request/response. And therefore the CorrelationIdMiddleware hasn't run, and had a chance to set up the CorrelationContext.

I've managed to work round this by implementing my own CorrelationIdMiddleware which adds a null check on this._correlationContextAccessor.CorrelationContext:

if (_correlationContextAccessor.CorrelationContext != null && !request.Headers.Contains(_correlationContextAccessor.CorrelationContext.Header))

Hope this makes sense, and hopefully helps if anyone else comes across this.

[Steve Gordon]

Thanks for reporting this @tjrobinson. It probably makes sense to check for this. The main use was intended for it to only be added to HttpClients used during the request flow but I can see how this assumption can be problematic.

[Viktor Kryzhanovskyi]

@stevejgordon could we please promote this PR ? We are also facing similar issues.

[capcom923]

We are facing the same issue. Sometimes, an API will trigger a Hangfire job which is detached from the CorrelationContext. In that case, if the Hangfire job use this HttpClient to call some other API. It will throw NPE.
Could you @stevejgordon please promote the PR of @VKAlwaysWin ?
Thanks,

[Steve Gordon]

This has no been merged and I'll get a patch release out with this ASAP.

[Steve Gordon]

This is now available in v3.0.1. Thanks @VKAlwaysWin for the PR and my apologies for taking sooo long to get around to focusing on this!

[Patrick]

Thank you for this update Steve, my team was having this exact same issue also . Thank you for the swift fix

[capcom923]

Thank you @stevejgordon! This issue is gone in 3.0.1.