fix(otelgin): remove multipartform temporary file

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

@@ -85,6 +85,17 @@ func Middleware(service string, opts ...Option) gin.HandlerFunc {
 
 		// pass the span through the request context
 		c.Request = c.Request.WithContext(ctx)
+		defer func() {
+			// as we have created new http.Request object we need to make sure that temporary files created to hold MultipartForm
+			// files are cleaned up. This is done by http.Server at the end of request lifecycle but Server does not
+			// have reference to our new Request instance therefore it is our responsibility to fix the mess we caused.
+			//
+			// This means that when we are on returning path from handler middlewares up in chain from this middleware
+			// can not access these temporary files anymore because we deleted them here.
+			if c.Request.MultipartForm != nil {
+				c.Request.MultipartForm.RemoveAll()
+			}
+		}()
 
 		// serve the request to the next middleware
 		c.Next()

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

@@ -6,8 +6,11 @@
 package test
 
 import (
+	"bytes"
 	"errors"
 	"html/template"
+	"io/fs"
+	"mime/multipart"
 	"net/http"
 	"net/http/httptest"
 	"strconv"
@@ -430,3 +433,44 @@ func TestWithGinFilter(t *testing.T) {
 		assert.Len(t, sr.Ended(), 1)
 	})
 }
+
+func TestTemporaryFormFileRemove(t *testing.T) {
+	sr := tracetest.NewSpanRecorder()
+	provider := sdktrace.NewTracerProvider(sdktrace.WithSpanProcessor(sr))
+
+	router := gin.New()
+	router.MaxMultipartMemory = 1
+	router.Use(otelgin.Middleware("foobar", otelgin.WithTracerProvider(provider)))
+	var fileHeader *multipart.FileHeader
+	router.POST("/upload", func(c *gin.Context) {
+		ff, err := c.FormFile("file")
+		if err != nil {
+			_ = c.AbortWithError(http.StatusInternalServerError, err)
+			return
+		}
+		_ = ff
+		fileHeader = c.Request.MultipartForm.File["file"][0]
+		c.JSON(http.StatusOK, nil)
+	})
+
+	var body bytes.Buffer
+
+	mw := multipart.NewWriter(&body)
+	fw, err := mw.CreateFormFile("file", "file")
+	require.NoError(t, err)
+
+	_, err = fw.Write([]byte("hello world"))
+	require.NoError(t, err)
+	err = mw.Close()
+	require.NoError(t, err)
+	r := httptest.NewRequest("POST", "/upload", &body)
+	r.Header.Add("Content-Type", mw.FormDataContentType())
+	w := httptest.NewRecorder()
+
+	router.ServeHTTP(w, r)
+	assert.Len(t, sr.Ended(), 1)
+	require.Equal(t, http.StatusOK, w.Code)
+	_, err = fileHeader.Open()
+	require.ErrorIs(t, err, fs.ErrNotExist)
+
+}