Large WCF Requests, Don’t forget httpRuntime settings

Recently, I was working on a project where the client was passing an array of bytes (byte[]) into a WCF service method. The array represented a file the user wanted to upload to the server. The WCF service was throwing cryptic error messages when the user attempted to upload a large file. There are obvious issues with this approach, but without a redesign of the upload process, my client was looking for a quick fix. There are many articles that cover the various options that one has to adjust under serviceBehaviors for WCF (e.g. maxReceivedMessageSize), but increasing all of those to their maximum value DID NOT solve the problem.

After looking at the issue through a packet filter, I finally figured out that IIS was rejecting the request at a level above WCF and then I remember the httpRuntime config section. You can read about it here:

The relevant attribute is maxRequestLength

The default is 4096KB as of the writing of this post.

Obviously, no matter what other settings you tweak, if you run into this limit, IIS will block the request.

This can also come up when writing plain old vanilla ASP.NET file upload if you’re not streaming the file to the server.

Streaming files to your server would avoid running into these problems, but if you’re in a pinch and working on an internal application used by a small number of users, this is the quick and dirty way to get around the limit.

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