Open Source Contributions

Contributing to open source can be a struggle given the variety of concerns from the community. Overall, however, my view is that code is made stronger by surviving the gauntlet. There are many skilled developers in the community who will often see things you miss.

The community has undergone rather a lot of growth lately and so is still adapting to an overall group where it it not the case that every one knows every one else from chat and summits and there is a shared understanding of what makes a good pull request. The following are I think the most basic and important things to keep in mind that will help ease the process.

Separability
Pull requests should be as small as possible. This yields the important result that isolating changes that cause problems and recovering from them is much easier. This means that if new classes / technology / support is required for a pull request, it is almost always better to contribute it in a separate, prior pull request. Pull requests that have a lot of new classes and other things have a very difficult time, both because the additional support obscures the real point of the pull request and that discussions can get bogged down on details in the support that aren’t critical for the overall work.
Parsimony
There is a general concern about code bloat and much effort has been made in the past to decrease the over all code size. For what Traffic Server can do it has a remarkably small code base. This is not an accident. For this reason think twice, then reconsider again, if you really need to add a support class. Avoid this if you can, especially if the class is used only once or in limited circumstances. Also avoid putting classes in separate files if the class isn’t used in other file scopes. See if there are existing classes or other techniques which, with a bit of work, could be made to suffice.
Consistency
Traffic Server is an old project with people who have been working on it for over a decade. They are comfortable with where things are and how things are done. This doesn’t mean it’s perfect but unless there is a strong reason to change, you should peruse the code and try to do things in a similar way. One example would be initialization. There are various ways to do this in C++, most of which result in the same machine code. Therefore it’s a reasonable expectation that you will do this in the same way as the existing code. As a newcomer to the community, try to show a bit of respect for existing customs and habits, especially when such things have no real impact on code quality.

C++ Guidelines

Some basics are here in the C++11 Usage Guide.

Memory and Allocation

The main path of Traffic Server execution is very sensitve to blocking or delay. For this reason memory allocation should be strongly minimized. It is frequently the case the reasonable maximums can be determined and needed memory allocated on the stack or statically. This is particularly true for temporaries. One example is file path names. There is a operating system based maximum length, PATH_NAME_MAX, which is the longest path Traffic Server will handle. A path used only in a local scope can be put in stack allocated buffer of that length without any memory allocation at all.

Use of STL containers should be avoided where possible, except for std::vector.

Additional reference pages

Basic coding style.