otelhttp: Treat http.NoBody the same as a nil body

CHANGELOG.md

@@ -18,6 +18,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Fixed
 
 - Set the status_code span attribute even if the HTTP handler hasn't written anything. (#2822)
+- Do not wrap http.NoBody in `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp`, which fixes handling of that special request body. (#2983)
 
 ## [1.11.1/0.36.4/0.5.2]
 

instrumentation/net/http/otelhttp/handler.go

@@ -164,10 +164,10 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 
 	var bw bodyWrapper
-	// if request body is nil we don't want to mutate the body as it will affect
-	// the identity of it in an unforeseeable way because we assert ReadCloser
-	// fulfills a certain interface and it is indeed nil.
-	if r.Body != nil {
+	// if request body is nil or NoBody, we don't want to mutate the body as it
+	// will affect the identity of it in an unforeseeable way because we assert
+	// ReadCloser fulfills a certain interface and it is indeed nil or NoBody.
+	if r.Body != nil && r.Body != http.NoBody {
 		bw.ReadCloser = r.Body
 		bw.record = readRecordFunc
 		r.Body = &bw

instrumentation/net/http/otelhttp/handler_test.go

@@ -59,3 +59,23 @@ func TestHandlerReadingNilBodySuccess(t *testing.T) {
 	h.ServeHTTP(rr, r)
 	assert.Equal(t, 200, rr.Result().StatusCode)
 }
+
+// This use case is important as we make sure the body isn't mutated
+// when it is NoBody.
+func TestHandlerReadingNoBodySuccess(t *testing.T) {
+	h := otelhttp.NewHandler(
+		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if r.Body != http.NoBody {
+				_, err := io.ReadAll(r.Body)
+				assert.NoError(t, err)
+			}
+		}), "test_handler",
+	)
+
+	r, err := http.NewRequest(http.MethodGet, "http://localhost/", http.NoBody)
+	require.NoError(t, err)
+
+	rr := httptest.NewRecorder()
+	h.ServeHTTP(rr, r)
+	assert.Equal(t, 200, rr.Result().StatusCode)
+}