Today I was faced with a challenge in a WCF Service where my host service returned http 504 response.
HTTP/1.1 504 Fiddler – Receive Failure
Date: Wed, 15 Jan 2014 18:53:11 GMT
Content-Type: text/html; charset=UTF-8
[Fiddler] ReadResponse() failed: The server did not return a response for this request.Server returned 0 bytes.
Initially my thought was this issue is due to WCF REST POST request without any inbound request data stream, but, after a bit of research I found that my hosted service was unable to output the huge xml data object I was returning from the datastore. I resolved this issue by adding maxItemsInObjectGraph in Service behaviour’s dataContractSerializer element of web.config.
I think WCF or any API’s is a game of correct configurations and understanding what this configurations mean is important for API design. Let’s understand what maxItemsInObjectGraph and dataContractSerializer is and how to use it in service configuration of a API.
As we know Service Behavior defines how the endpoint interacts with clients. Attributes like security, concurrency, caching, logging, etc. – are all part of the behavior and so does dataContractSerializer. DataContractSerializer serializes and deserializes an instance of a type into an XML stream or document using a supplied data contract and maxItemsInObjectGraph gets the maximum number of items in an object graph to serialize or deserialize. Why 2147483647? maxItemsInObjectGraph is a integer and integer value is a 32-bit number, and that’s the largest value that can be represented in 32-bit two’s complement. This will allow to obtain a xml/json response as huge as aproximately 2GB. I think if you are not sure or if you think data might grow over the period of time it is better to set this property to max.
Here is how my service behavior code block in web.config looks like.
<serviceMetadata httpGetEnabled=”true” />
<serviceDebug includeExceptionDetailInFaults=”true” />
<serviceThrottling maxConcurrentCalls=”100″ maxConcurrentSessions=”50″ maxConcurrentInstances=”50″ />
<serviceAuthorization serviceAuthorizationManagerType=”CCAService.AuthorizationManager, CCAService” />