Support configurable error codes in contrib/net/http

contrib/internal/httptrace/httptrace.go

@@ -9,7 +9,6 @@ package httptrace
 
 import (
 	"context"
-	"fmt"
 	"net/http"
 	"strconv"
 	"strings"
@@ -71,9 +70,6 @@ func FinishRequestSpan(s tracer.Span, status int, opts ...tracer.FinishOption) {
 		statusStr = strconv.Itoa(status)
 	}
 	s.SetTag(ext.HTTPCode, statusStr)
-	if status >= 500 && status < 600 {
-		s.SetTag(ext.Error, fmt.Errorf("%s: %s", statusStr, http.StatusText(status)))
-	}
 	s.Finish(opts...)
 }
 

contrib/net/http/http.go

@@ -60,10 +60,11 @@ func (mux *ServeMux) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	copy(so, mux.cfg.spanOpts)
 	so = append(so, httptrace.HeaderTagsFromRequest(r, mux.cfg.headerTags))
 	TraceAndServe(mux.ServeMux, w, r, &ServeConfig{
-		Service:  mux.cfg.serviceName,
-		Resource: resource,
-		SpanOpts: so,
-		Route:    route,
+		Service:       mux.cfg.serviceName,
+		Resource:      resource,
+		SpanOpts:      so,
+		Route:         route,
+		IsStatusError: mux.cfg.isStatusError,
 	})
 }
 

contrib/net/http/option.go

@@ -27,6 +27,7 @@ type config struct {
 	finishOpts    []ddtrace.FinishOption
 	ignoreRequest func(*http.Request) bool
 	resourceNamer func(*http.Request) string
+	isStatusError func(int) bool
 	headerTags    *internal.LockMap
 }
 
@@ -50,6 +51,7 @@ func defaults(cfg *config) {
 	}
 	cfg.ignoreRequest = func(_ *http.Request) bool { return false }
 	cfg.resourceNamer = func(_ *http.Request) string { return "" }
+	cfg.isStatusError = func(status int) bool { return status >= 500 && status < 600 }
 }
 
 // WithIgnoreRequest holds the function to use for determining if the
@@ -118,6 +120,14 @@ func WithResourceNamer(namer func(req *http.Request) string) Option {
 	}
 }
 
+// WithStatusCheck sets a span to be an error if the passed function
+// returns true for a given status code.
+func WithStatusCheck(checker func(statusCode int) bool) Option {
+	return func(cfg *config) {
+		cfg.isStatusError = checker
+	}
+}
+
 // NoDebugStack prevents stack traces from being attached to spans finishing
 // with an error. This is useful in situations where errors are frequent and
 // performance is critical.

contrib/net/http/trace.go

@@ -8,6 +8,7 @@ package http // import "gopkg.in/DataDog/dd-trace-go.v1/contrib/net/http"
 //go:generate sh -c "go run make_responsewriter.go | gofmt > trace_gen.go"
 
 import (
+	"fmt"
 	"net/http"
 
 	"gopkg.in/DataDog/dd-trace-go.v1/contrib/internal/httptrace"
@@ -42,6 +43,9 @@ type ServeConfig struct {
 	// in as /user/123 we'll have {"id": "123"}). This field is optional and is used for monitoring
 	// by AppSec. It is only taken into account when AppSec is enabled.
 	RouteParams map[string]string
+	// IsStatusError returns whether or not the passed status code should be marked as
+	// an error
+	IsStatusError func(int) bool
 	// FinishOpts specifies any options to be used when finishing the request span.
 	FinishOpts []ddtrace.FinishOption
 	// SpanOpts specifies any options to be applied to the request starting span.
@@ -67,6 +71,9 @@ func TraceAndServe(h http.Handler, w http.ResponseWriter, r *http.Request, cfg *
 	span, ctx := httptrace.StartRequestSpan(r, opts...)
 	rw, ddrw := wrapResponseWriter(w)
 	defer func() {
+		if cfg.IsStatusError != nil && cfg.IsStatusError(ddrw.status) {
+			span.SetTag(ext.Error, fmt.Errorf("%d: %s", ddrw.status, http.StatusText(ddrw.status)))
+		}
 		httptrace.FinishRequestSpan(span, ddrw.status, cfg.FinishOpts...)
 	}()
 

contrib/net/http/trace_test.go

@@ -260,6 +260,29 @@ func TestTraceAndServe(t *testing.T) {
 		assert.Equal("200", spans[0].Tag(ext.HTTPCode))
 	})
 
+	t.Run("isStatusError", func(t *testing.T) {
+		mt := mocktracer.Start()
+		assert := assert.New(t)
+		defer mt.Stop()
+
+		handler := func(w http.ResponseWriter, r *http.Request) {
+			w.WriteHeader(http.StatusBadRequest)
+		}
+		r, err := http.NewRequest("GET", "/", nil)
+		assert.NoError(err)
+		w := httptest.NewRecorder()
+		TraceAndServe(http.HandlerFunc(handler), w, r, &ServeConfig{
+			Service:       "service",
+			Resource:      "resource",
+			IsStatusError: func(i int) bool { return i >= 400 },
+		})
+
+		spans := mt.FinishedSpans()
+		assert.Len(spans, 1)
+		assert.Equal("400", spans[0].Tag(ext.HTTPCode))
+		assert.Equal("400: Bad Request", spans[0].Tag(ext.Error).(error).Error())
+	})
+
 	t.Run("empty", func(t *testing.T) {
 		mt := mocktracer.Start()
 		assert := assert.New(t)
@@ -319,6 +342,7 @@ func TestTraceAndServe(t *testing.T) {
 		assert.Equal("/path?<redacted>", span.Tag(ext.HTTPURL))
 		assert.Equal("200", span.Tag(ext.HTTPCode))
 	})
+
 }
 
 func TestTraceAndServeHost(t *testing.T) {