feat: add observer package (#230)

README.md

@@ -48,6 +48,7 @@ func yourAction(c *cli.Context) error {
     // Run your application here...
 }
 ```
+
 ## Flags
 
 ### Logger
@@ -154,3 +155,50 @@ Example: `--tracing.endpoint="agent-host:port"` or `--tracing.endpoint="http://h
 This flag sets the sample ratio of spans that will be reported to the exporter. This should be between 0 and 1.
 
 Example: `--tracing.ratio=0.2`
+
+### Observer
+
+The observe package exposes an `Observer` type which is essentially a helper that combines a logger, tracer and statter.
+It is useful if you use all three for your services and want to avoid carrying around many arguments.
+
+Here is an example of how one might use it:
+
+```go
+func runServer(c *cli.Context) error {
+    ctx, cancel := context.WithCancel(c.Context)
+    defer cancel()
+
+    obsvr, err := cmd.New(c, svcName, version)
+    if err != nil {
+        return err
+    }
+    defer obsvr.Close()
+
+    // Initialize components by passing the obsvr variable.
+    return nil
+}
+
+func New(c *cli.Context, svc, version string) (*observe.Observer, error) {
+	log, logCancel, err := NewLogger(c, svc)
+	if err != nil {
+		return nil, err
+	}
+
+	stats, statsCancel, err := NewStatter(c, log, svc)
+	if err != nil {
+		logCancel()
+		return nil, err
+	}
+
+	tracer, traceCancel, err := NewTracer(c, log, svc, version)
+	if err != nil {
+		logCancel()
+		statsCancel()
+		return nil, err
+	}
+
+	return observe.New(log, stats, tracer, traceCancel, statsCancel, logCancel), nil
+}
+```
+
+It also exposes `NewFake` which allows you to pass fake loggers, tracers and statters in your tests easily.

observe/doc.go

@@ -0,0 +1,28 @@
+/*
+Package observe implements a type that combines statter, logger and tracer.
+
+Example usage:
+
+	func New(c *cli.Context, svc, version string) (*observe.Observer, error) {
+		log, logCancel, err := NewLogger(c, svc)
+		if err != nil {
+			return nil, err
+		}
+
+		stats, statsCancel, err := NewStatter(c, log, svc)
+		if err != nil {
+			logCancel()
+			return nil, err
+		}
+
+		tracer, traceCancel, err := NewTracer(c, log, svc, version)
+		if err != nil {
+			logCancel()
+			statsCancel()
+			return nil, err
+		}
+
+		return observe.New(log, stats, tracer, traceCancel, statsCancel, logCancel), nil
+	}
+*/
+package observe

observe/observer.go

@@ -0,0 +1,56 @@
+package observe
+
+import (
+	"io"
+	"time"
+
+	"github.com/hamba/logger/v2"
+	"github.com/hamba/statter/v2"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/trace"
+)
+
+// Observer contains observability primitives.
+type Observer struct {
+	Log       *logger.Logger
+	Stats     *statter.Statter
+	TraceProv trace.TracerProvider
+
+	closeFns []func()
+}
+
+// New returns an observer with the given observability primitives.
+func New(log *logger.Logger, stats *statter.Statter, traceProv trace.TracerProvider, closeFns ...func()) *Observer {
+	return &Observer{
+		Log:       log,
+		Stats:     stats,
+		TraceProv: traceProv,
+		closeFns:  closeFns,
+	}
+}
+
+// Tracer returns a tracer with the given name and options.
+// If no trace provider has been set, this function will panic.
+func (o *Observer) Tracer(name string, opts ...trace.TracerOption) trace.Tracer {
+	if o.TraceProv == nil {
+		panic("calling tracer when no trace provider has been set")
+	}
+	return o.TraceProv.Tracer(name, opts...)
+}
+
+// Close closes the observability primitives.
+func (o *Observer) Close() {
+	for _, cancel := range o.closeFns {
+		cancel()
+	}
+}
+
+// NewFake returns a fake observer that reports nothing.
+// This is useful for tests.
+func NewFake() *Observer {
+	log := logger.New(io.Discard, logger.LogfmtFormat(), logger.Error)
+	stats := statter.New(statter.DiscardReporter, time.Minute)
+	tracer := otel.GetTracerProvider()
+
+	return New(log, stats, tracer)
+}