Add support for filters to the otelgin package (#2965)

* Add support for filters to the otelgin package

* Make WithFilter() accept variadic arguments

* Update CHANGELOG.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -13,6 +13,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - The `WithLogger` option to `go.opentelemetry.io/contrib/samplers/jaegerremote` to allow users to pass a `logr.Logger` and have operations logged. (#2566)
 - Add the `messaging.url` & `messaging.system` attributes to all appropriate SQS operations in the `go.opentelemetry.io/contrib/instrumentation/github.com/aws/aws-sdk-go-v2/otelaws` package. (#2879)
 - Add example use of the metrics signal to `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp/example`. (#2610)
+- [otelgin] Add support for filters to the `go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin` package to provide the way to control which inbound requests are traced. (#2963)
 
 ### Fixed
 

instrumentation/github.com/gin-gonic/gin/otelgin/gintrace.go

@@ -54,6 +54,14 @@ func Middleware(service string, opts ...Option) gin.HandlerFunc {
 		cfg.Propagators = otel.GetTextMapPropagator()
 	}
 	return func(c *gin.Context) {
+		for _, f := range cfg.Filters {
+			if !f(c.Request) {
+				// Serve the request to the next middleware
+				// if a filter rejects the request.
+				c.Next()
+				return
+			}
+		}
 		c.Set(tracerKey, tracer)
 		savedCtx := c.Request.Context()
 		defer func() {

instrumentation/github.com/gin-gonic/gin/otelgin/option.go

@@ -17,15 +17,22 @@
 package otelgin // import "go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin"
 
 import (
+	"net/http"
+
 	"go.opentelemetry.io/otel/propagation"
 	oteltrace "go.opentelemetry.io/otel/trace"
 )
 
 type config struct {
 	TracerProvider oteltrace.TracerProvider
 	Propagators    propagation.TextMapPropagator
+	Filters        []Filter
 }
 
+// Filter is a predicate used to determine whether a given http.request should
+// be traced. A Filter must return true if the request should be traced.
+type Filter func(*http.Request) bool
+
 // Option specifies instrumentation configuration options.
 type Option interface {
 	apply(*config)
@@ -57,3 +64,15 @@ func WithTracerProvider(provider oteltrace.TracerProvider) Option {
 		}
 	})
 }
+
+// WithFilter adds a filter to the list of filters used by the handler.
+// If any filter indicates to exclude a request then the request will not be
+// traced. All filters must allow a request to be traced for a Span to be created.
+// If no filters are provided then all requests are traced.
+// Filters will be invoked for each processed request, it is advised to make them
+// simple and fast.
+func WithFilter(f ...Filter) Option {
+	return optionFunc(func(c *config) {
+		c.Filters = append(c.Filters, f...)
+	})
+}

instrumentation/github.com/gin-gonic/gin/otelgin/test/gintrace_test.go

@@ -203,3 +203,37 @@ func TestHTML(t *testing.T) {
 	require.NotNil(t, tspan)
 	assert.Contains(t, tspan.Attributes(), attribute.String("go.template", "hello"))
 }
+
+func TestWithFilter(t *testing.T) {
+	t.Run("custom filter filtering route", func(t *testing.T) {
+		sr := tracetest.NewSpanRecorder()
+		otel.SetTracerProvider(sdktrace.NewTracerProvider(sdktrace.WithSpanProcessor(sr)))
+
+		router := gin.New()
+		f := func(req *http.Request) bool { return req.URL.Path != "/healthcheck" }
+		router.Use(otelgin.Middleware("foobar", otelgin.WithFilter(f)))
+		router.GET("/healthcheck", func(c *gin.Context) {})
+
+		r := httptest.NewRequest("GET", "/healthcheck", nil)
+		w := httptest.NewRecorder()
+
+		router.ServeHTTP(w, r)
+		assert.Len(t, sr.Ended(), 0)
+	})
+
+	t.Run("custom filter not filtering route", func(t *testing.T) {
+		sr := tracetest.NewSpanRecorder()
+		otel.SetTracerProvider(sdktrace.NewTracerProvider(sdktrace.WithSpanProcessor(sr)))
+
+		router := gin.New()
+		f := func(req *http.Request) bool { return req.URL.Path != "/healthcheck" }
+		router.Use(otelgin.Middleware("foobar", otelgin.WithFilter(f)))
+		router.GET("/user/:id", func(c *gin.Context) {})
+
+		r := httptest.NewRequest("GET", "/user/123", nil)
+		w := httptest.NewRecorder()
+
+		router.ServeHTTP(w, r)
+		assert.Len(t, sr.Ended(), 1)
+	})
+}