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Looking back at my old code with bemusement and horror.
About 3 years ago I put a lot of effort into a set of golang packages called mediocre-go-lib. The idea was to create a framework around the ideas I had laid out in this blog post around the structure and composability of programs. What I found in using the framework was that it was quite bulky, not fully thought out, and ultimately difficult for anyone but me to use. So.... a typical framework then.
My ideas about program structure haven't changed a ton since then, but my ideas around the patterns which enable that structure have simplified dramatically (see my more recent post for more on that). So in that spirit I've decided to cut a `v2` branch of `mediocre-go-lib` and start trimming the fat.
This is going to be an exercise both in deleting old code (very fun) and re-examining old code which I used to think was good but now know is bad (even more fun), and I've been looking forward to it for some time.
The two foundational pieces of `mediocre-go-lib` are the `mcmp` and `mctx` packages. `mcmp` primarily deals with its mcmp.Component type, which is a key/value store which can be used by other packages to store and retrieve component-level information. Each `mcmp.Component` exists as a node in a tree of `mcmp.Component`s, and these form the structure of a program. `mcmp.Component` is able to provide information about its place in that tree as well (i.e. its path, parents, children, etc...).
If this sounds cumbersome and of questionable utility that's because it is. It's also not even correct, because a component in a program exists in a DAG, not a tree. Moreover, each component can keep track of whatever data it needs for itself using typed fields on a struct. Pretty much all other packages in `mediocre-go-lib` depend on `mcmp` to function, but they don't *need* to, I just designed it that way.
So my plan of attack is going to be to delete `mcmp` completely, and repair all the other packages.
The other foundational piece of `mediocre-go-lib` is mctx. Where `mcmp` dealt with arbitrary key/value storage on the component level, `mctx` deals with it on the contextual level, where each go-routine (i.e. thread) corresponds to a `context.Context`. The primary function of `mctx` is this one:
// Annotate takes in one or more key/value pairs (kvs' length must be even) and
// returns a Context carrying them.
func Annotate(ctx context.Context, kvs ...interface{}) context.Context
I'm inclined to keep this around for now because it will be useful for logging, but there's one change I'd like to make to it. In its current form the value of every key/value pair must already exist before being used to annotate the `context.Context`, but this can be cumbersome in cases where the data you'd want to annotate is quite hefty to generate but also not necessarily going to be used. I'd like to have the option to make annotating occur lazily. For this I add an `Annotator` interface and a `WithAnnotator` function which takes it as an argument, as well as some internal refactoring to make it all work right:
// Annotations is a set of key/value pairs representing a set of annotations. It
// implements the Annotator interface along with other useful post-processing
// methods.
type Annotations map[interface{}]interface{}
// Annotator is a type which can add annotation data to an existing set of
// annotations. The Annotate method should be expected to be called in a
// non-thread-safe manner.
type Annotator interface {
Annotate(Annotations)
}
// WithAnnotator takes in an Annotator and returns a Context which will produce
// that Annotator's annotations when the Annotations function is called. The
// Annotator will be not be evaluated until the first call to Annotations.
func WithAnnotator(ctx context.Context, annotator Annotator) context.Context
`Annotator` is designed like it is for two reasons. The more obvious design, where the method has no arguments and returns a map, would cause a memory allocation on every invocation, which could be a drag for long chains of contexts whose annotations are being evaluated frequently. The obvious design also leaves open questions about whether the returned map can be modified by whoever receives it. The design given here dodges these problems without any obvious drawbacks.
The original implementation also had this unnecessary `Annotation` type:
// Annotation describes the annotation of a key/value pair made on a Context via
// the Annotate call.
type Annotation struct {
Key, Value interface{}
}
I don't know why this was ever needed, as an `Annotation` was never passed into nor returned from any function. It was part of the type `AnnotationSet`, but that could easily be refactored into a `map[interface{}]interface{}` instead. So I factored `Annotation` out completely.
The next package to tackle is mcfg, which deals with configuration via command line arguments and environment variables. The package is set up to use the old `mcmp.Component` type such that each component could declare its own configuration parameters in the global configuration. In this way the configuration would have a hierarchy of its own which matches the component tree.
Given that I now think `mcmp.Component` isn't the right course of action it would be the natural step to take that aspect out of `mcfg`, leaving only a basic command-line and environment variable parser. There are many other basic parsers of this sort out there, including one or two I wrote myself, and frankly I don't think the world needs another. So `mcfg` is going away.
The mrun package is the corresponding package to `mcfg`; where `mcfg` dealt with configuration of components `mrun` deals with the initialization and shutdown of those same components. Like `mcfg`, `mrun` relies heavily on `mcmp.Component`, and doesn't really have any function with that type gone. So `mrun` is a gonner too.
The mlog package is primarily concerned with, as you might guess, logging. While there are many useful logging packages out there none of them integrate with `mctx`'s annotations, so it is useful to have a custom logging package here. `mlog` also has the nice property of not being extremely coupled to `mcmp.Component` like other packages; it's only necessary to delete a handful of global functions which aren't a direct part of the `mlog.Logger` type in order to free the package from that burden.
With that said, the `mlog.Logger` type could still use some work. It's primary pattern looks like this:
// Message describes a message to be logged.
type Message struct {
Level
Description string
Contexts []context.Context
}
// Info logs an InfoLevel message.
func (l *Logger) Info(descr string, ctxs ...context.Context) {
l.Log(mkMsg(InfoLevel, descr, ctxs...))
}
The idea was that if the user has multiple `Contexts` in hand, each one possibly having some relevant annotations, all of those `Context`s' annotations could be merged together for the log entry.
Looking back it seems to me that the only thing `mlog` should care about is the annotations, and not *where* those annotations came from. So the new pattern looks like this:
// Message describes a message to be logged.
type Message struct {
Context context.Context
Level
Description string
Annotators []Annotators
}
// Info logs a LevelInfo message.
func (l *Logger) Info(ctx context.Context, descr string, annotators ...mctx.Annotator)
The annotations on the given `Context` will be included, and then any further `Annotator`s can be added on. This will leave room for `merr` later.
There's some other warts in `mlog.Logger` that should be dealt with as well, including some extraneous methods which were only used due to `mcmp.Component`, some poorly named types, a message handler which didn't properly clean itself up, and making `NewLogger` take in parameters with which it can be customized as needed (previously it only allowed for a single configuration). I've also extended `Message` to include a timestamp, a namespace field, and some other useful information.
I've run out of time for today, but future work on this package includes:
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Published 2021-02-06