tag

Documentation

Overview

Package tag provides support for telemetry tagging.

Package tag provides support for telemetry tagging. This package is a thin shim over contexts with the main addition being the the ability to observe when contexts get tagged with new values.

Index

• func Observe(observer Observer)
• func With(ctx context.Context, tags ...Tag) context.Context
• type Key
  • func (k Key) Of(v interface{}) Tag
  • func (k Key) Tag(ctx context.Context) Tag
  • func (k Key) With(ctx context.Context, v interface{}) context.Context
• type List
  • func Get(ctx context.Context, keys ...interface{}) List
  • func Tags(ctx context.Context, taggers ...Tagger) List
  • func (l List) Equal(other List) bool
  • func (l List) Format(f fmt.State, r rune)
  • func (l List) Get(k interface{}) interface{}
  • func (l List) Less(other List) bool
• type Observer
• type Tag
  • func Of(key interface{}, value interface{}) Tag
  • func (t Tag) Format(f fmt.State, r rune)
  • func (t Tag) Tag(ctx context.Context) Tag
• type Tagger

Functions

func Observe

func Observe(observer Observer)

Observe adds a new tag observer to the registered set. There is no way to ever unregister a observer. Observers are free to use context information to control their behavior.

func With

func With(ctx context.Context, tags ...Tag) context.Context

With is roughly equivalent to context.WithValue except that it also notifies registered observers. Unlike WithValue, it takes a list of tags so that you can set many values at once if needed. Each call to With results in one invocation of each observer.

Types

type Key

type Key string

Key represents the key for a context tag. It is a helper to make use of context tagging slightly easier to read, it is not strictly needed to use it at all. It is intended that your common tagging keys are declared as constants of this type, and then you can use the methods of this type to apply and find those values in the context.

func (Key) Of

func (k Key) Of(v interface{}) Tag

Of creates a new Tag with this key and the supplied value. You can use this when building a tag list.

func (Key) Tag

func (k Key) Tag(ctx context.Context) Tag

Tag can be used to get a tag for the key from a context. It makes Key conform to the Tagger interface.

func (Key) With

func (k Key) With(ctx context.Context, v interface{}) context.Context

With applies sets this key to the supplied value on the context and returns the new context generated. It uses the With package level function so that observers are also notified.

type List

type List []Tag

List is a way of passing around a collection of key value pairs. It is an alternative to the less efficient and unordered method of using maps.

func Get

func Get(ctx context.Context, keys ...interface{}) List

Get collects a set of values from the context and returns them as a tag list.

func Tags

func Tags(ctx context.Context, taggers ...Tagger) List

Tags collects a list of tags for the taggers from the context.

func (List) Equal

func (l List) Equal(other List) bool

Equal returns true if two lists are identical.

func (List) Format

func (l List) Format(f fmt.State, r rune)

Format pretty prints a list. It is intended only for debugging.

func (List) Get

func (l List) Get(k interface{}) interface{}

Get will get a single key's value from the list.

func (List) Less

func (l List) Less(other List) bool

Less is intended only for using tag lists as a sorting key.

type Observer

type Observer func(ctx context.Context, at time.Time, tags List)

Observer is the type for a function that wants to be notified when new tags are set on a context. If you use context.WithValue (or equivalent) it will bypass the observers, you must use the setters in this package for tags that should be observed. Register new observers with the Observe function.

type Tag

type Tag struct {
	Key   interface{}
	Value interface{}
}

Tag holds a key and value pair. It is normally used when passing around lists of tags.

func Of

func Of(key interface{}, value interface{}) Tag

Of returns a Tag for a key and value. This is a trivial helper that makes common logging easier to read.

func (Tag) Format

func (t Tag) Format(f fmt.State, r rune)

Format is used for debug printing of tags.

func (Tag) Tag

func (t Tag) Tag(ctx context.Context) Tag

Get returns the tag unmodified. It makes Key conform to the Tagger interface.

type Tagger

type Tagger interface {
	// Tag returns a Tag potentially using information from the Context.
	Tag(context.Context) Tag
}

Tagger is the interface to somthing that returns a Tag given a context. Both Tag itself and Key support this interface, allowing methods that can take either (and other implementations as well)