使用golang访问已安装的卷（docker-compose）

I want to access my local volume to store files from user. I mapped volume using docker compose but i can't access it in golang.

webapi:
        image: golang:1.12.0-alpine3.9
        restart: always
        container_name: webapi
        ports:
          - "8081:8081"
        volumes:
          - ./api/ :/go/src/

tempFile, err := ioutil.TempFile("./images/", "upload-*.png")
    if err != nil {
        fmt.Println(err)
    }

    filestate, err := tempFile.Stat()
    filepath := filestate.Name()
    defer tempFile.Close()

    // read all of the contents of our uploaded file into a
    // byte array
    fileBytes, err := ioutil.ReadAll(file)
    if err != nil {
        fmt.Println(err)
    }
    // write this byte array to our temporary file
    tempFile.Write(fileBytes)