When I create a channel to a service, how do I know when the service is ready to process the data for that channel? A channel doesn't really know what the service is doing. The service might be actively processing the data being sent over the channel. Or, the service might not. There is a constant tension in the system between components that want to push data and components that want to pull data. Components that push data actively work as long as there is data available until a back pressure builds

How do I find the address of a client connection to make a trust decision? Don't base security decisions on the perceived client address. Any address that we have comes from the underlying socket implementation and could be spoofed. The data that the socket has is sourced by the client. You should be using a source of information that has a verification process that the server trusts, such as a certificate, to distinguish clients. Next time: Reader Trends

How do I detect when the other side of a TCP connection has gone away? Does TCP keep-alive take care of this for me? Although we take it for granted that change can be quickly detected for closely connected components, it turns out to be surprisingly difficult to detect change when two machines are isolated by more than a simple wire. Even a really big change to the system, like one of the machines disappearing, is hard to spot. Detecting that the other side has disappeared is a common request because,

How can I use reliable messaging together with a load balancer? The point of reliable messaging is to help ensure that messages get from one place to another. This means that the protocol notices when messages that were expected to be delivered go missing. On the other hand, the point of a load balancer is to make sure that messages are spread out and that there aren't too many messages going to the same place. You can see how these two goals might come into conflict at times. Many load balancers

Does WCF ever cache the DNS lookup for a service address? How do I clear this cache? There is just a tiny amount of caching that I know about. The TCP and MSMQ transports use a shared cache for recently used addresses. I think for MSMQ that this is only a factor for custom dead letter queue addresses. In any case, this cache is to speed up lookups in the case that you're hitting the same address over and over again very quickly. There's no way to clear the cache, but the lifetime of entries is two

My web service needs to periodically broadcast messages to clients. The service is an Internet-facing application hosted inside of IIS. What’s the best way to do this? The big limitation in this scenario is that your clients might be behind a firewall and non-addressable. There are basically two architecture camps for broadcasting messages to clients over the Internet. The push architecture camp has the clients maintain a continuous connection to the server and pushes data out at each update. The

I have a long-running service operation that needs to receive a response. What options do I have for designing my web services? The problem that most people run into with long-running operations is that the operation eventually hits some quota value and times out. For instance, if you want to run the operation over an HTTP connection, you have to configure the HTTP transport to not give up waiting before the operation completes. This configuration consists of setting the send and receive timeouts