Too Busy For Words - the PaulWay Blog

Wed 4th Oct, 2006

Working with other people's code

I've long been a convert to the talloc library for memory allocation, after Tridge's talk mentioned it at LCA 2005. Granted, it's not a sinecure for memory problems - you can still have memory leaking out your program's ears, but at least it's not completely unfreeable. And because it's typed and it does all the things you're supposed to do with memory, like zero the memory immediately after it's allocated and nullify the pointer immediately after it's freed, it does help you avoid the worst excesses of pointer mishandling.

For my own sake, I've written a little library that allows you to treat a gzip-compressed file (with the .gz extension) as being functionally identical to a normal file - you use the same library of functions to read or write to it (although not at the same time) regardless of whether it's compressed or not. When you open the file, the file type is determined automatically and the correct lower-level functions are used transparently. It also provides a useful 'getline' routine, which reallocates your string buffer (using talloc_realloc) on the fly to make enough space for whatever line you're reading.

Now, I've just embarked on a project to read and write information in a simple dictionary section/key/value format - much like a .ini file. So I've started looking at a parser library rather than reinventing this particular wheel (I know, I know, shock horror, has Paul actually learned to do some research?). But it doesn't use talloc and it definitely hasn't heard of my CFile library.

It seems likely to me that someone's going to suggest an object oriented language like C++ here, so that I can extend the class. But as far as I can see this doesn't actually solve the problem. I don't want to add functionality to it (yet), I want to replace functionality that it relies on with other functions of my own choosing. Which means that Nicolas would have had to have written his library with a file and memory abstraction class, so that I could then extend those classes and have iniparser use that new functionality with no recompilation or reprogramming. What if he'd thought to abstract the file functions, but not the memory functions (after all, who expects to not use malloc in C?) I'd still be looking at rewriting part of his code. And, since I'm writing in C, it's all a bit of wishful thinking anyway.

So is there any way to do this? Do I have to modify Nicolas's code? I can search through the Samba codebase, because I'm sure they've implemented a .ini file reader in there, but I want to write the file too and maybe they haven't done that. And they won't be using my CFile library.

So is there a solution? Do we have to go to a new, revolutionary programming language, where somehow you not only override these and perhaps other even more basic functions, but do so knowing what other functions you're overriding and what guarantees you're providing to the code 'above'? Does such a thing exist?

Because you can bet Linus Torvalds' hair that there's no library so good, so all-encompassingly correct, that everyone will use it. talloc, for all its plusses, is not ideal in an environment where every byte may count; or at least there will be some people who will fight to the death to avoid using it. My CFile library is perhaps no-one's idea of good (or someone else would have done it way earlier, and I haven't seen one yet), but I reckon it solves a problem that I think is worth solving. It would be good to have ways of using these libraries without having to rework other people's code - it gives one the temptation to just write everything myself and save myself the trouble.

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