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POHow can I stream data from a managed assembly to a native library and back again?
 

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  1. POHow can I stream data from a managed assembly to a native library and back again?
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    <p>How can I stream data (text) from a managed assembly to a native library and stream data (text) back to the managed assembly?</p> <p>Specifically, I want to expose a <code>System.IO.Stream</code> of some sort on the .NET side, and (<strong>most importantly</strong>) a <code>FILE *</code> on the native side.</p> <p>The signature of the native method should be:</p> <p><code>FILE * foo(FILE * bar);</code></p> <p>The signature of a wrapper around the native p/invoke call should be:</p> <p><code>CustomStream foo(CustomStream bar);</code></p> <p><strong>I do not want to use callback methods on the native side</strong> (one for getting more data and one for setting more data). I want to use a <code>FILE *</code> on the native side - <strong>and all of the associated methods which operate upon it</strong> such as <code>fprintf</code>. </p> <p>I do not want any disk I/O. This needs to be an in-memory operation.</p> <p>I have complete control over both the managed assembly and the native library. </p> <p>The solution must work with .NET 2.0</p> <p>I'm willing to create any sort of managed or unmanaged shim layer required to pull this off.</p> <p>The "obvious" solution is to use <code>STDIN</code> and <code>STDOUT</code> and launch a child process - however I don't want a separate process. Also, my attempts to redirect the <code>STDIN</code> and <code>STDOUT</code> streams of a native library which isn't a console application on Windows have failed somewhat spectacularly (and with much head-banging).</p> <p>Based on this question: <a href="https://stackoverflow.com/questions/1579074/redirect-stdoutstderr-on-a-c-sharp-windows-service">Redirect stdout+stderr on a C# Windows service</a> I attempted to modify the approach to (at least) solve the "response" stream half of my problem - but without a <code>FileStream</code> (since I want something more analogous to a <code>MemoryStream</code>). However, <code>FileStream</code> is the only stream type which exposes a suitable low-level stream handle.</p> <p>Otherwise, I'm pretty well stuck and am currently thinking I'll need to dive deeper and come up with my own hand-rolled native&lt;->managed stream implementation but don't really know where to start. </p> <hr> <h2>Solution</h2> <p>Finally! </p> <p>I've posted a complete sample project here:</p> <p><a href="http://pastebin.com/jcjHdnwz" rel="nofollow noreferrer">http://pastebin.com/jcjHdnwz</a></p> <p>This is for .NET 3.5 and uses the <code>AnonymousPipeServerStream</code> - but with a little bit of reflector-ing, it's easy enough to duplicate the inner workings of the <code>AnonymousPipeServerStream</code> in .NET 2.0.</p> <p>Thanks for your help <strong>shf301</strong> for pointing me to the native pipe API, which got me looking into the Microsoft docs for a better understanding of what's going on, and for pointing out I needed to use the <code>_open_osfhandle</code> method to get the <code>FILE *</code> reference.</p>
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      1. USFelice Pollano
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    1. COJust replace the `FileStream` with your `MemoryStream`? What matters here is that the stream is wrapped in a `StreamWriter` and that writer is passed in as the new standard out and error streams.
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      1. POHow can I stream data from a managed assembly to a native library and back again?
      1. USJeff Mercado
    2. COYes, a pipe is required to get a writable handle. .NET 3.5
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      1. POHow can I stream data from a managed assembly to a native library and back again?
      1. USHans Passant
    3. CO@JeffMercado, The Win32 function `SetStdHandle` AFAIK requires a handle to a suitable pipe - and `MemoryStream` doesn't provide this - where as `FileStream` does via `.SafeFileHandle.DangerousGetHandle()`
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