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Updated ReseekFile

I updated ReseekFile. I wrote it two years ago to help probe the contents of file stream coming over a socket connection. I was working with a server that would normally return XML but returned a simple text file if there was an error. It didn't change the headers so I couldn't check the content-type or status code. Instead I checked the first line of the input to check the content directly. If it's XML I needed to reset the data stream so I could pass the file handle to the XML processor.

I'm currently working on a similar project. One quibble I have with ReseekFile is that it keeps everything in memory. Machines have a lot of memory these days but I wanted the option to use the filesystem if need be. For example, if the file is indeed XML then I will be using jing, a Relax-NG validator. That takes a filename so I would prefer just pointing it to that backing file.

I started to write a new class that would have been more complicated than ReseekFile. It would have allowed arbitrary seeks into the file. In the spirit of YAGNI I thought better about it and looked to see if I could modify ReseekFile. I could. It just needed a factory function, to specify how to create a backing store. Turns out I was using the cStringIO's getvalue() to get the size of the buffer file. Real files don't have that so I added a bit of code to track how many bytes I've written to the file.


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