客户端通过multipart.Write把文件的文本流写入一个缓存中，然后调用http的Post方法把缓存传到服务器。

package mainimport (    "bytes"    "fmt"    "io"    "io/ioutil"    "mime/multipart"    "net/http"    "os")func postFile(filename string, targetUrl string) error {    bodyBuf := &bytes.Buffer{}    bodyWriter := multipart.NewWriter(bodyBuf)    //关键的一步操作    fileWriter, err := bodyWriter.CreateFormFile("uploadfile", filename)    if err != nil {        fmt.Println("error writing to buffer")        return err    }    //打开文件句柄操作    fh, err := os.Open(filename)    if err != nil {        fmt.Println("error opening file")        return err    }    defer fh.Close()    //iocopy    _, err = io.Copy(fileWriter, fh)    if err != nil {        return err    }    contentType := bodyWriter.FormDataContentType()    bodyWriter.Close()    resp, err := http.Post(targetUrl, contentType, bodyBuf)    if err != nil {        return err    }    defer resp.Body.Close()    resp_body, err := ioutil.ReadAll(resp.Body)    if err != nil {        return err    }    fmt.Println(resp.Status)    fmt.Println(string(resp_body))    return nil}// sample usagefunc main() {    target_url := "http://localhost/upload"    filename := "./example.pdf"    postFile(filename, target_url)}