otelfiber: Add custom attributes support

otelfiber/README.md

@@ -39,6 +39,7 @@ otelfiber.Middleware(opts ...otelfiber.Option) fiber.Handler
 | Propagators       | `propagation.TextMapPropagator` | Specifies propagators to use for extracting information from the HTTP requests                     | If none are specified, global ones will be used                                                               |
 | ServerName        | `*string`                       | specifies the value to use when setting the `http.server_name` attribute on metrics/spans                                          | -                                                                   |
 | SpanNameFormatter | `func(*fiber.Ctx) string`       | Takes a function that will be called on every request and the returned string will become the Span Name                                   | default formatter returns the route pathRaw |
+| CustomAttributes  | `func(*fiber.Ctx) []attribute.KeyValue` | Define a function to add custom attributes to the span                  | nil                                                                 |
 
 ## Usage
 

otelfiber/config.go

@@ -2,6 +2,7 @@ package otelfiber
 
 import (
 	"github.com/gofiber/fiber/v2"
+	"go.opentelemetry.io/otel/attribute"
 	otelmetric "go.opentelemetry.io/otel/metric"
 	"go.opentelemetry.io/otel/propagation"
 	oteltrace "go.opentelemetry.io/otel/trace"
@@ -16,6 +17,7 @@ type config struct {
 	Propagators       propagation.TextMapPropagator
 	ServerName        *string
 	SpanNameFormatter func(*fiber.Ctx) string
+	CustomAttributes  func(*fiber.Ctx) []attribute.KeyValue
 }
 
 // Option specifies instrumentation configuration options.
@@ -87,3 +89,10 @@ func WithPort(port int) Option {
 	})
 }
 
+// WithCustomAttributes specifies a function that will be called on every
+// request and the returned attributes will be added to the span.
+func WithCustomAttributes(f func(ctx *fiber.Ctx) []attribute.KeyValue) Option {
+	return optionFunc(func(cfg *config) {
+		cfg.CustomAttributes = f
+	})
+}

otelfiber/fiber_test.go

@@ -401,3 +401,49 @@ func getHistogram(value float64, attrs []attribute.KeyValue) metricdata.Histogra
 		Temporality: metricdata.CumulativeTemporality,
 	}
 }
+
+func TestCustomAttributes(t *testing.T) {
+	sr := new(oteltest.SpanRecorder)
+	provider := oteltest.NewTracerProvider(oteltest.WithSpanRecorder(sr))
+
+	var gotSpan oteltrace.Span
+
+	app := fiber.New()
+	app.Use(
+		Middleware(
+			WithTracerProvider(provider),
+			WithCustomAttributes(func(ctx *fiber.Ctx) []attribute.KeyValue {
+				return []attribute.KeyValue{
+					attribute.Key("http.query_params").String(ctx.Request().URI().QueryArgs().String()),
+				}
+			}),
+		),
+	)
+
+	app.Get("/user/:id", func(ctx *fiber.Ctx) error {
+		gotSpan = oteltrace.SpanFromContext(ctx.UserContext())
+		id := ctx.Params("id")
+		return ctx.SendString(id)
+	})
+
+	resp, _ := app.Test(httptest.NewRequest("GET", "/user/123?foo=bar", nil), 3000)
+
+	// do and verify the request
+	require.Equal(t, http.StatusOK, resp.StatusCode)
+
+	mspan, ok := gotSpan.(*oteltest.Span)
+	require.True(t, ok)
+	assert.Equal(t, attribute.StringValue("foo=bar"), mspan.Attributes()["http.query_params"])
+
+	// verify traces look good
+	spans := sr.Completed()
+	require.Len(t, spans, 1)
+	span := spans[0]
+	assert.Equal(t, "/user/:id", span.Name())
+	assert.Equal(t, oteltrace.SpanKindServer, span.SpanKind())
+	assert.Equal(t, attribute.IntValue(http.StatusOK), span.Attributes()["http.status_code"])
+	assert.Equal(t, attribute.StringValue("GET"), span.Attributes()["http.method"])
+	assert.Equal(t, attribute.StringValue("/user/123?foo=bar"), span.Attributes()["http.target"])
+	assert.Equal(t, attribute.StringValue("/user/:id"), span.Attributes()["http.route"])
+	assert.Equal(t, attribute.StringValue("foo=bar"), span.Attributes()["http.query_params"])
+}

otelfiber/semconv.go

@@ -61,6 +61,10 @@ func httpServerTraceAttributesFromRequest(c *fiber.Ctx, cfg config) []attribute.
 		attrs = append(attrs, semconv.HTTPClientIPKey.String(utils.CopyString(clientIP)))
 	}
 
+	if cfg.CustomAttributes != nil {
+		attrs = append(attrs, cfg.CustomAttributes(c)...)
+	}
+
 	return attrs
 }