Returning large collections from WCF Serivce

Question

I'm trying to determine the best approach for building a WCF Service, and the area I'm struggling with most is returning lists of objects.

The built-in maxMessageSize of 64k seems pretty high, and I really don't want to bump it up (quick googling finds 100s of places bumping the maxMessageSize up to multi-gigabyte range which seems foolish). But, when I'm returning a collection of objects (~150 items) I am exceeding the default 64k.

I'm almost to the point of returning my own class which inherits IEnumerable and has properties for hasNext, hasPrevious and PageSize so that I can implement paging on the client side -- this seems like alot of code. The other option is to jackup the maxMessageSize and hope for the best, but that feels wrong.

All other aspects of my service are working great, its just returning large collectiosn where I'm having issues.

For background, there are two types of consumers of this service, UI applications which will be primarly web and/or wpf applications, and data processing applications, .NET console apps, and maybe some other non-UI apps. For the UI applications, I would like to keep them responsive and keep the messageSize low, on the console apps it doesn't matter as much as they are just pulling data down to do processing and push it back up to the service.

Answer 1

I believe the reason the default value for maxMessageSize is so low is to reduce the risk of DoS attacks.

If response messages are large, it's the client configuration that needs an increased maxMessageSize. For a client, DoS is unlikely to be a risk, so it's safe to increase it to a very large value.

But this isn't "jacking up maxMessageSize and hoping for the best" - you should decide what the expected maximum size is for your application, taking into account whether or not you decide to use paging, and configure it appropriately.

On a server, maxMessageSize needs to be big enough for the maximum allowed request message. Here DoS is potentially an issue, though in some environments (e.g. Intranet) it is probably safe to use a very large value.

If your service is exposing an operation that allows a client to query a potentially large data set, an alternative approach to paging is to define a maximum number of items that a client can request in one call.

For example, you might have an operation that allows a client to request exchange rates for a list of currencies and a range of dates:

public IList<ExchangeRate> GetExchangeRates(string baseCurrency, IList<string> currencies, DateTime startDate, DateTime endDate);

You could then set a limit on the number of results your service will return, and expose this to the client:

public int GetMaximumResultCount();

The client would then be expected to query GetMaximumResultCount, and to ensure that:

(endDate - startDate).TotalDays * currencies.Count < maximumResultCount

If the client fails to respect this, the server throws a suitable FaultException

Answer 2

You can use MTOM Message Enconding. Its an alternative to Stream, when sending large data. Here is a configuration example:

 <system.serviceModel>
     …
    <bindings>
      <wsHttpBinding>
        <binding name="ExampleBinding" messageEncoding="Mtom"/>
      </wsHttpBinding>
    </bindings>
     …
<system.serviceModel>

Just set the messageEncoding attribute to Mtom, on your binding config. Also, change the maxReceivedMessageSize and maxBufferSize.

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