multipart 申请是多部件申请体，个别来多用于上传文件等场景，因为文件上传，申请领会比拟大，就不适宜在内存中构建残缺的申请体（例如应用bytes.Buffer）。

这种状况就能够思考应用Pipe，它会返回一个Writer和一个Reader，管道流，顾名思义，一头读，一头写。读取磁盘文件，写入网络，并不会缓存在内存中。非常适合这种场景。

func Pipe() (*PipeReader, *PipeWriter) {    p := &pipe{        wrCh: make(chan []byte),        rdCh: make(chan int),        done: make(chan struct{}),    }    return &PipeReader{p}, &PipeWriter{p}}

Demo

package mainimport (    "context"    "encoding/json"    "fmt"    "github.com/gin-gonic/gin"    "io"    "io/ioutil"    "log"    "mime/multipart"    "net/http"    "net/textproto"    "strings"    "time")func main(){    // Http 服务    ctx, cancel := context.WithCancel(context.Background())    ch := make(chan struct{})    go server(ctx, ch)    // 管道流    r, w := io.Pipe()    defer r.Close()    // 创立 multipart，指定writer    formWriter := multipart.NewWriter(w)    go func() {        defer w.Close()        var writer io.Writer        // 疾速构建一般表单项，key/value都是字符串        formWriter.WriteField("lang", "PHP是宇宙最好的语言")        // 构建一般的表单项，通过Writer写入数据        writer, _ = formWriter.CreateFormField("lang")        writer.Write([]byte("Java是世界上最好的语言"))        // 构建文件表单项，指定表单名称，以及文件名称，通过Writer写入数据，默认的ContentType 是 application/octet-stream        writer, _ = formWriter.CreateFormFile("file", "app.json")        jsonVal, _ := json.Marshal(map[string] string {"name": "KevinBlandy"})        writer.Write(jsonVal)        // 自定义part表单项，能够增加自定义的header        header := textproto.MIMEHeader{}        header.Set("Content-Disposition", `form-data; name="file"; filename="app1.json"`)        // 自定表单字段名称，文件名称，这是必须的        header.Set("Content-Type", `application/octet-stream`)                                    // 指定ContentType，这是必须的        writer, _ = formWriter.CreatePart(header)        writer.Write([]byte("foo"))        // 实现写入，须要调用close办法        formWriter.Close()    }()    // 创立http客户端    client := http.Client{}    // 创立request申请，指定body reader    req, _ := http.NewRequest(http.MethodPost, "http://127.0.0.1/upload", r)    req.Header.Set("Content-Type", formWriter.FormDataContentType()) // 须要正确的设置ContentType    // 执行申请获取响应    resp, _ := client.Do(req)    defer resp.Body.Close()    // 获取响应    data, _ := ioutil.ReadAll(resp.Body)    fmt.Println(string(data))    // 进行服务器    cancel()    // 期待退出    <- ch}func server(ctx context.Context, ch chan <- struct{}){    router := gin.Default()    router.POST("/upload", func(ctx *gin.Context) {        form, _ := ctx.MultipartForm()        fmt.Println("一般表单项-------------------")        for key, value := range form.Value {            fmt.Printf("name=%s, value=%s\n", key, strings.Join(value, ","))        }        fmt.Println("文件表单项-------------------")        for key, value := range form.File {            for _, file := range value {                fmt.Printf("name=%s, size=%d, fileName=%s, headers=%v\n", key, file.Size, file.Filename, file.Header)            }        }        ctx.Writer.Header().Set("Content-Type", "text/plan")        ctx.Writer.WriteString("success")    })    server := http.Server{        Addr: ":80",        Handler: router,    }    // 启动服务    go func() {        if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {            log.Panic(err)        }    }()    for {        select {            case <- ctx.Done():{                ctx, _ := context.WithTimeout(context.Background(), time.Second * 2)                server.Shutdown(ctx)                log.Println("服务器进行...")                ch <- struct{}{}                return            }        }    }}

日志输入

[GIN-debug] [WARNING] Creating an Engine instance with the Logger and Recovery middleware already attached.[GIN-debug] [WARNING] Running in "debug" mode. Switch to "release" mode in production. - using env:    export GIN_MODE=release - using code:    gin.SetMode(gin.ReleaseMode)[GIN-debug] POST   /upload                   --> main.server.func1 (3 handlers)一般表单项-------------------name=lang, value=PHP是宇宙最好的语言,Java是世界上最好的语言文件表单项-------------------name=file, size=22, fileName=app.json, headers=map[Content-Disposition:[form-data; name="file"; filename="app.json"] Content-Type:[application/octet-stream]]name=file, size=3, fileName=app1.json, headers=map[Content-Disposition:[form-data; name="file"; filename="app1.json"] Content-Type:[application/octet-stream]][GIN] 2021/01/17 - 14:00:33 | 200 |            0s |       127.0.0.1 | POST     "/upload"success2021/01/17 14:00:34 服务器进行...