Golang gin receive json data and image

I have this code for request handler:

func (h *Handlers) UpdateProfile() gin.HandlerFunc {
    type request struct {
        Username    string `json:"username" binding:"required,min=4,max=20"`
        Description string `json:"description" binding:"required,max=100"`
    }

    return func(c *gin.Context) {
        var updateRequest request

        if err := c.BindJSON(&updateRequest); err != nil {
            var validationErrors validator.ValidationErrors

            if errors.As(err, &validationErrors) {
                validateErrors := base.BindingError(validationErrors)
                c.AbortWithStatusJSON(http.StatusBadRequest, gin.H{"error": validateErrors})
            } else {
                c.AbortWithError(http.StatusBadRequest, err)
            }

            return
        }

        avatar, err := c.FormFile("avatar")
        if err != nil {
            c.AbortWithStatusJSON(http.StatusBadRequest, gin.H{
                "error": "image not contains in request",
            })
            return
        }

        log.Print(avatar)

        if avatar.Size > 3<<20 { // if avatar size more than 3mb
            c.AbortWithStatusJSON(http.StatusBadRequest, gin.H{
                "error": "image is too large",
            })
            return
        }

        file, err := avatar.Open()
        if err != nil {
            c.AbortWithError(http.StatusInternalServerError, err)
        }

        session := sessions.Default(c)
        id := session.Get("sessionId")
        log.Printf("ID type: %T", id)

        err = h.userService.UpdateProfile(fmt.Sprintf("%v", id), file, updateRequest.Username, updateRequest.Description)
        if err != nil {
            c.AbortWithStatusJSON(http.StatusBadRequest, gin.H{})
            return
        }

        c.IndentedJSON(http.StatusNoContent, gin.H{"message": "succesfull update"})
    }
}

And I have this unit test for this handler:

func TestUser_UpdateProfile(t *testing.T) {
    type testCase struct {
        name               string
        image              io.Reader
        username           string
        description        string
        expectedStatusCode int
    }

    router := gin.Default()

    memStore := memstore.NewStore([]byte("secret"))
    router.Use(sessions.Sessions("session", memStore))

    userGroup := router.Group("user")
    repo := user.NewMemory()
    service := userService.New(repo)
    userHandlers.Register(userGroup, service)

    testImage := make([]byte, 100)
    rand.Read(testImage)
    image := bytes.NewReader(testImage)

    testCases := []testCase{
        {
            name:               "Request With Image",
            image:              image,
            username:           "bobik",
            description:        "wanna be sharik",
            expectedStatusCode: http.StatusNoContent,
        },
        {
            name:               "Request Without Image",
            image:              nil,
            username:           "sharik",
            description:        "wanna be bobik",
            expectedStatusCode: http.StatusNoContent,
        },
    }

    for _, tc := range testCases {
        t.Run(tc.name, func(t *testing.T) {
            body := &bytes.Buffer{}
            writer := multipart.NewWriter(body)

            imageWriter, err := writer.CreateFormFile("avatar", "test_avatar.jpg")
            if err != nil {
                t.Fatal(err)
            }

            if _, err := io.Copy(imageWriter, image); err != nil {
                t.Fatal(err)
            }

            data := map[string]interface{}{
                "username":    tc.username,
                "description": tc.description,
            }
            jsonData, err := json.Marshal(data)
            if err != nil {
                t.Fatal(err)
            }

            jsonWriter, err := writer.CreateFormField("json")
            if err != nil {
                t.Fatal(err)
            }

            if _, err := jsonWriter.Write(jsonData); err != nil {
                t.Fatal(err)
            }

            writer.Close()

            // Creating request
            req := httptest.NewRequest(
                http.MethodPost,
                "http://localhost:8080/user/account/updateprofile",
                body,
            )
            req.Header.Set("Content-Type", writer.FormDataContentType())
            log.Print(req)

            w := httptest.NewRecorder()
            router.ServeHTTP(w, req)

            assert.Equal(t, tc.expectedStatusCode, w.Result().StatusCode)
        })
    }
}

During test I have this error:
Error #01: invalid character ‘-‘ in numeric literal

And here is request body (I am printing it with log.Print(req)):

&{POST http://localhost:8080/user/account/updateprofile HTTP/1.1 1 1 map[Content-Type:[multipart/form-data; boundary=30b24345de9d8d83ecbdd146262d86894c45b4f3485e4615553621fd2035]] {--30b24345de9d8d83ecbdd146262d86894c45b4f3485e4615553621fd2035
Content-Disposition: form-data; name="avatar"; filename="test_avatar.jpg"
Content-Type: application/octet-stream


--30b24345de9d8d83ecbdd146262d86894c45b4f3485e4615553621fd2035
Content-Disposition: form-data; name="json"

{"description":"wanna be bobik","username":"sharik"}
--30b24345de9d8d83ecbdd146262d86894c45b4f3485e4615553621fd2035--
} <nil> 414 [] false localhost:8080 map[] map[] <nil> map[] 192.0.2.1:1234 http://localhost:8080/user/account/updateprofile <nil> <nil> <nil> <nil>}

First I just have strings as json data and converted it to bytes. When error appeared I converted json data using json.Marshal, but it didn’t work out. I want to parse json data with c.Bind and parse given image with c.FormFile, does it possible?

Upd. I replaced code to get avatar first, and then get json by Bind structure. Now I have EOF error.