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What channels can be used in a context binding? The primary limitation for building a context binding is that the channel stack has to have the right shape. The context exchange protocol used by a context binding requires that the first invoked operation be a request-reply operation. This is so that the initial context can be established. In order to support a request-reply operation, the channel stack needs to support one of a particular set of shapes. There are currently five channel shapes allowed when using a context binding: IRequestChannel IRequestSessionChannel IReplyChannel IReplySessionChannel IDuplexSessionChannel The request and reply channel shapes are paired for the client and server so on any particular endpoint there are three valid channel shapes. Conditions are limited further if you want to use HTTP cookies as your context exchange mechanism rather than the default of SOAP headers. In that case it's no longer possible to use a duplex channel so you're limited to variations on the request-reply message exchange pattern. Next time: Manual Context Management Read More...
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I've done a bit of grouping for the remaining binding elements as there are fourteen non-transport binding elements that I'm covering in this list. I've pointed out the ones that respond to a type with GetProperty on the base class as opposed to repeating the same code in each subclass. Our standard message encoders respond to two types, although only one is on the base class. These two interfaces will override the ones given by the transport if a message encoder is in the binding. The transport delegates to the message encoder before giving its useless default response. MessageVersion (on the message encoder base class) XmlDictionaryReaderQuotas (on the Text, MTOM, and Binary encoders) The one-way and transaction channels both support just a single interface. ChannelProtectionRequirements All of the security binding elements support a pair of interfaces and the actual security channels add an additional type. ISecurityCapabilities (on the security base class and on the Windows and SSL stream upgrades) IdentityVerifier (on the security base class and on the Windows and SSL stream upgrades) ChannelProtectionRequirements (on the asymmetric, symmetric, and transport security binding elements) The reliable message binding element supports a pair of interfaces as well. ChannelProtectionRequirements IBindingDeliveryCapabilities Finally, the composite duplex binding element has a pair of types. If you're curious why composite duplex is interacting with a security interface, then you should read the earlier article on layering between composite duplex and security . ISecurityCapabilities ChannelProtectionRequirements Next time: Starting a Hosted Service Read More...
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I've created a custom implementation of GetProperty for my binding but now I'm getting errors when I go to use the channels. Why is the validation for these channels failing? This is an implementation problem that I've talked about in the past. There is a requirement that the values queried from design time objects, such as bindings and binding elements, match the values queried from runtime objects, such as a channels. If the two don't agree on a property value, then you can experience problems ranging from an error creating the channel to mysterious failures sending and receiving messages. This problem most commonly happens when you override an existing property value on the binding but forget to override the property in the same way on the channels. Use this picture illustrating GetProperty to follow the chain of property values. However, this problem can also happen even when you're not overriding an existing value. If you write a GetProperty implementation but forget to delegate to the inner channel or binding element, then the chain of GetProperty calls terminates right there. Any further channels or binding elements do not get to contribute to GetProperty evaluations. This can easily cause a discrepancy between the design time and runtime values of a property despite the fact that you didn't explicitly modify that property. In most cases, this is a severe enough problem to fail very quickly. If you've written a GetProperty method and are suddenly seeing property value mismatches for properties that you didn't touch though, then make sure that your GetProperty method is delegating any unhandled properties to the right place. Next time: Preventing Anonymous Access Read More...
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The story from yesterday: there is an important setting for composite duplex that is only settable through the binding context. Unfortunately, proxy clients automatically create and use their own binding context so there is no convenient time to poke in a replacement value for the setting. What kind of a workaround can we come up with? Since there is no convenient way to intercept the binding context at the producer, we'll instead need to intercept the binding context at the consumer. The consumer of the binding context is the channel construction process of the binding. In particular, we need to modify the ListenUri setting before we reach the BuildChannelListener method of the composite duplex binding element. That means our opportunities for interception are going to be in methods such as CanBuildChannelFactory, CanBuildChannelListener, BuildChannelFactory, and BuildChannelListener. The binding context instance gets passed along from binding element to binding element so it is safe to modify the setting at any opportunity along the way. We don't have to worry about finding the correct instance of the binding context. Every instance that we see is one that we want to modify. The solution that I came up with for this problem was to write a binding element that modified the ListenUri as the binding context went by. Other than this change, the binding element simply delegates every method to the next binding element down. You can position the binding element in the channel stack so that your customization is always reached before the composite duplex binding element. The binding context that composite duplex receives contains your modifications, giving you full control over the ListenUri setting that was otherwise hidden. This solution is generally reusable for other situations where you need to modify the binding context or channel construction process. I won't say that there are many such situations, but it is a tool for you to use. An interesting coincidence about this problem was that two different people on consecutive days with different scenarios were looking for a solution. Mike Taulty was the second person and he's done a write up of why he was interested in composite duplex and the code I gave him for the ListenUri modifying binding element . Mike added configuration support, which I hadn't bothered with. From configuration, you'll need to build out a complete custom binding. From code, it's simpler because you can start with an existing binding and Read More...
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The ListenUri is a three-part setting on the BindingContext that gives the server-side address of a connection. The ListenUri has a base and a relative address, plus a mode switch. The mode switch controls whether the uri should be used as-is or whether parts of the uri have been left unspecified and need to be automatically generated. A common automatic address generation scenario is picking an unallocated network port. There are only a few places where the ListenUri is actually used. One spot is in the transport, which needs to construct a uri for the remote address. The spot that I'll actually talk about though is the composite duplex channel. The composite duplex client channel uses the ListenUri for the backchannel address. I've already covered the basics of composite duplex and how the ListenUri factors into the backchannel construction process . One of the interesting things about the composite duplex channel is that it has a partial fallback for the ListenUri, described in the article above. The ClientBaseAddress setting on the composite duplex binding element lets you specify a base address if the ListenUri is not provided. However, there's no equivalent ClientRelativeAddress that lets you complete the ListenUri. Therefore, if you use this fallback, then you'll always get some randomized component in your backchannel address. You generally want a randomized address because the backchannel address has to be unique across all of your current composite duplex clients. Having a randomized address doesn't work though when you need to allocate a resource with a particular name for the backchannel. MSMQ is an example where randomized addresses don't work because you need to allocate a queue whose name is tied to the backchannel address. When you're programming against the channel model, working around this situation is not difficult because you own creating the binding context. This means that you have an opportunity to directly set the ListenUri. If you are using an automatically generated proxy client like most people do, then you have no opportunity to set the ListenUri. The proxy takes the configured binding and instantiates a copy, including the binding context, automatically. This is entirely hidden from the proxy client user. There are mechanisms for passing information to the channel construction process, called binding and channel parameters, but there is no binding parameter that corresponds to the ListenUri on the binding context. With no way for Read More...
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