Aspects

According to Wikipedia:

In computing, aspect-oriented programming (AoP) is a programming paradigm that aims to increase modularity by allowing the separation of cross-cutting concerns. It does so by adding behavior to existing code (an advice) without modifying the code, instead separately specifying which code is modified via a “pointcut” specification, such as “log all function calls when the function’s name begins with ‘set’”. This allows behaviors that are not central to the business logic (such as logging) to be added to a program without cluttering the code of core functions.

One can easily understand how Observability and Security Monitoring of an application are cross-cutting concerns… As such, the automatic instrumentation performed by orchestrion is modeled using aspects. That being said, the AoP language is used somewhat loosely by Orchestrion.

Aspect

An aspect is the combination of a join point (a pointcut, as mentioned in the Wikipedia definition above, is a set of join points) and advice.

Join Points

Orchestrion performs code injection by traversing (and modifying) each and every Go source file’s AST. In this perspective, one can think of a Join Point as a function that selects or rejects an AST node based on its attributes.

Orchestrion evaluates Join Points in context, where each node is presented to these functions with:

• its complete ancestry in the AST, meaning Join Points are able to walk up the AST to decide whether to select a node or not;
• information about the surrounding package, such as its fully qualified import path;
• a configuration object (effectively string key-value pairs).

Join Points are composable, forming a simple yet versatile language for addressing AST nodes.

Advice

Advice are functions that transform an AST node. This can mean replacing the node with something else, modifying certain attributes of the node, or adding new nodes before or after it.

Orchestrion executes Advice on all AST nodes matched by the associated Join Point in post-order; meaning a node is being modified only after all its children have been considered already. This implies nodes modified by an Aspect are not evaluated by further Join Points, and eliminates the risk of endless recursive instrumentation.

Next