feat: add WithSampler option (open-telemetry#454)

Add a new `WithSampler` method allowing end-users to provide their own implementation of OpenTelemetry sampler directly through the package API.

Signed-off-by: thomasgouveia <gouveia.thomas@outlook.fr>

CHANGELOG.md

@@ -17,6 +17,7 @@ OpenTelemetry Go Automatic Instrumentation adheres to [Semantic Versioning](http
 - Add the `WithTraceExporter` `InstrumentationOption` to configure the trace `SpanExporter` used by an `Instrumentation`. ([#426](https://github.com/open-telemetry/opentelemetry-go-instrumentation/pull/426))
 - Add HTTP status code attribute to `net/http` server instrumentation. ([#428](https://github.com/open-telemetry/opentelemetry-go-instrumentation/pull/428))
 - The instrumentation scope now includes the version of the auto-instrumentation project. ([#442](https://github.com/open-telemetry/opentelemetry-go-instrumentation/pull/442))
+- Add a new `WithSampler` method allowing end-users to provide their own implementation of OpenTelemetry sampler directly through the package API. ([#468](https://github.com/open-telemetry/opentelemetry-go-instrumentation/pull/468)).
 
 ### Changed
 

instrumentation.go

@@ -163,6 +163,7 @@ type InstrumentationOption interface {
 }
 
 type instConfig struct {
+	sampler     trace.Sampler
 	traceExp    trace.SpanExporter
 	target      process.TargetArgs
 	serviceName string
@@ -192,6 +193,10 @@ func newInstConfig(ctx context.Context, opts []InstrumentationOption) (instConfi
 		err = errors.Join(err, e)
 	}
 
+	if c.sampler == nil {
+		c.sampler = trace.AlwaysSample()
+	}
+
 	return c, err
 }
 
@@ -216,7 +221,7 @@ func (c instConfig) validate() error {
 
 func (c instConfig) tracerProvider() *trace.TracerProvider {
 	return trace.NewTracerProvider(
-		trace.WithSampler(trace.AlwaysSample()),
+		trace.WithSampler(c.sampler),
 		trace.WithResource(c.res()),
 		trace.WithBatcher(c.traceExp),
 		trace.WithIDGenerator(opentelemetry.NewEBPFSourceIDGenerator()),
@@ -382,3 +387,12 @@ func WithTraceExporter(exp trace.SpanExporter) InstrumentationOption {
 		return c, nil
 	})
 }
+
+// WithSampler returns an [InstrumentationOption] that will configure
+// an [Instrumentation] to use the provided sampler to sample OpenTelemetry traces.
+func WithSampler(sampler trace.Sampler) InstrumentationOption {
+	return fnOpt(func(_ context.Context, c instConfig) (instConfig, error) {
+		c.sampler = sampler
+		return c, nil
+	})
+}