Decoding messages in WCF Data Services
Recently I had to solve an interesting problem while working with WCF Data Services and how to decode an incoming WCF message so I can do something useful with its content.
Let’s say that you have an already configured Data Service and you intercept the message using some sort extension/interceptors in WCF.
Here is an example of such function:
|
private static
string DecodeMessage(ref
Message message) { if
(message.IsEmpty) return null; using (MessageBuffer
buffer = message.CreateBufferedCopy(Int32.MaxValue)) {
Message copy =
buffer.CreateMessage();
using (MemoryStream
ms = new MemoryStream())
{
copy.Properties.Encoder.WriteMessage(copy, ms);
ms.Flush();
message = buffer.CreateMessage(); return
Encoding.UTF8.GetString(ms.ToArray()); } } } |
As you can notice, after some basic message validation, we create a copy of the message to avoid changing the state of the original message which is typically passed by reference. Then we write all the content to MemoryStream which is handy for read/write operations.
The key here is to use the encoder
specified in the message properties which may be MTOM for this
kind of streamed message but it might be different according to the configured
binding. After writing all the message content to memory, we may read from
memory and create a string so we can easily inspect the actual message. If we
know that we will always deal with XML content, we can use an XmlReader
or the like to manipulate the content without the string conversion which may pay
a performance penalty on large messages.
In the above code, we return the content as string because
we may get an XML or Text formatted message so we can process accordingly.
In the next post I will show how we
can use this code for inspecting a message to perform a custom authorization
with ServiceAuthorizationManager.
Stay tuned!