Nicholas Allen's Indigo Blog

Windows Communication Foundation From the Inside

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  • Blog Post: Channel Development Survey

    The WCF channels team has posted a short survey on channel development to collect some of your feedback about what to work on after .Net 4 is released. You can help them out if you've previously written or tried to write a layered channel, transport channel, or message encoder. The survey should only...
  • Blog Post: Parsing Standard Uris, Part 2

    Here's another look at defining what it means to have a URI for the TCP or named pipe transports. You can compare these definitions to the version I gave yesterday using the parser syntax flags. I'll only cover the net.tcp URI scheme as the two are almost identical except for the use of ports. What...
  • Blog Post: Parsing Standard Uris

    The System.Uri class has built-in parsing rules for a variety of schemes, including http, https, file, ftp, gopher, mailto, news, nntp, telnet, and ldap. There are also parsers for the WCF net.tcp and net.pipe schemes. These parsing rules allow a uri using the scheme to be recognized, broken into its...
  • Blog Post: Finding the Remote Client Address

    After being a highly-requested feature, back in .Net 3.5 we added the ability to see the network address from which the client request had arrived. Here's how it works. Participating transports capture the client's network address using whatever sources of information they have available. The transport...
  • Blog Post: Three Networking Questions Answered with Samples

    How do I remove or change the framing headers used for a TCP connection? By writing a transport channel you can control exactly what information is read or written to the TCP socket. An example of doing this is in the WSE interoperability sample . How do I pass credentials from the client to...
  • Blog Post: What’s New in WCF 4: Channels

    As we get closer to the release of .Net 4 it becomes easier to talk about exactly what new features we’re planning to provide. This list is a bit different in places from what you’ve seen in the beta 1 release and there’s always a chance that things might change again. The first part of the list...
  • Blog Post: Finding Free Ports, Part 2

    Yesterday I talked about the algorithm the TCP transport uses to reserve a unique port when listening on both IPv4 and IPv6 addreses is enabled for a service. Why are the random port numbers drawn from the range 49152-65535? Because that’s the range the operating system uses for dynamic port allocations...
  • Blog Post: Finding Free Ports

    One of the options for the listen URI for the TCP transport is to let the transport make the address unique by filling in details such as the port number. The socket API allows specifying a wildcard port but at the time WCF was written the wildcard port option could only be used with a single IP version...
  • Blog Post: Top Down Binding Element Order

    Why does a message encoder have to be specified before the transport when constructing a binding? A message encoder doesn’t directly fit into a channel stack because the message encoder type doesn’t implement any of the channel shapes. Instead, a message encoder is an auxilliary piece used by one...
  • Blog Post: Just Exactly What You Asked For

    When implementing a transport or layered channel class the marker used to indicate that your class is a channel is to implement the IChannel interface. Therefore, all channels will implement one of the known channel shapes: IInputChannel, IOutputChannel, IDuplexChannel, IRequestChannel, or IReplyChannel...
  • Blog Post: Levels of Tracing, Part 6

    The last article in the levels of tracing series covers the logging of messages at the transport level. Transport level logging generally occurs in the message encoder as that is where the message bytes are actually processed but in some rare cases there are times when the transport sends messages without...
  • Blog Post: Non-Destructive Queue Receive State Machine

    The state machine for a non-destructive receive has some noticeable similarities to the state machine for a general-purpose communication object, but it's intentional for these two state machines to be different. A non-destructive receive tries with minimal overhead to provide support for at-least once...
  • Blog Post: Non-Destructive Queue Receive

    You should take the time to understand the earlier articles in the series for context if you haven't already. Future of Queuing An Alternative Queuing Model The three basic operations that we talked about for queuing with non-destructive receives are peek, lock, and delete. Rather than...
  • Blog Post: Advanced Windows Debugging

    Channel 9 has put up a new video that mostly plugs the Advanced Windows Debugging book by Mario Hewardt and Daniel Pravat. I recommend the book for someone that needs to debug difficult issues dealing with native resources. For most people working with WCF this is never really a concern, but custom transport...
  • Blog Post: Waiting for Ready Channels

    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...
  • Blog Post: Adding Headers to a Call

    How do I add SOAP headers to an outgoing request? There are a few different ways to add headers to a message depending on how you need to control the header content and where you need to insert the header. I like to think of these methods as being split among the application, the proxy, and the...
  • Blog Post: Building with Encoders

    The basis of a channel stack is that there is a series of objects that share a common interface for communication. This leaves message encoders with something of a problem as the primitive operations for encoding and decoding messages are different than the primitive operations for sending and receiving...
  • Blog Post: TIBCO Announces WCF Integration

    At their user conference in San Francisco yesterday, TIBCO announced two integration initiatives to bring the TIBCO and Microsoft platforms closer together. TIBCO is developing a TIBCO EMS transport channel for WCF. Although Microsoft doesn't have a formal certification process for releasing third...
  • Blog Post: Context Channel Shapes

    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...
  • Blog Post: The Pipe DACL

    When a named pipe channel listener creates a new named pipe it has to supply a discretionary ACL that describes who can connect to the pipe. Here is how that DACL is constructed: An access control entry is added to deny GENERIC_ALL access to the well-known network SID (S-1-5-2). Access control...
  • Blog Post: A Proxy Proxy Factory

    I have a system that sometimes uses a fast local object and sometimes needs to communicate over a network. I have built a proxy object that wraps the proxy factory for creating typed proxies together with a proxy factory for creating local objects. Are there any downsides to this strategy? Historically...
  • Blog Post: Concurrent Channel Performance

    Being thread-safe is different than being concurrent. The channel interfaces are thread-safe so that multiple callers can use them at the same time without getting garbled messages. However, if multiple callers try to send messages on a single channel at the same time then a few different things might...
  • Blog Post: Custom Transport Retry Logic

    What are the best practices for building retry logic around network transport failures? Let's define some terms first so that we have a common language for communication. I'll say that "retry logic" is any automatically applied compensation activity that replays the same messages to either the same...
  • Blog Post: Substituting for TryAccept

    We're back to the channel pump for another round. In the previous channel pump article we had introduced an asynchronous coroutine between the main channel pump loop and a callback on acquiring a channel throttle. This use of coroutines let us suspend the channel pump until a throttle was available without...
  • Blog Post: No Session Before Sending

    When you create a sessionful channel, that implies the existence of some correlation factor for all of the messages that are associated with the session. For example, the correlation factor for a TCP session is that all of the messages travel over the same TCP connection and the correlation factor for...
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