计算多部分表单帖子的内容长度 [英] Computing the Content Length of a Multipart form Post

问题描述

我试图上传文件而不将其加载到内存中，如下所示。像S3这样的服务需要在这种情况下设置 Content-Length 。

  package main $ b是否有内置的功能可以做到这一点，或者我必须自己计算它。 
 $ b导入（
io
mime / multipart
net / http
os
路径/文件路径
）
 
 func newfileUploadRequest（uri string，params map [string] string，paramName，path string）（* http.Request，chan error，error）{
 file，err： = os.Open（path）
 if err！= nil {
 return nil，nil，err 
} 
 bodyReader，bodyWriter：= io.Pipe（）
 multiWriter：= multipart.NewWriter（bodyWriter）
 errChan：= make（chan error，1）
去func（）{
 defer bodyWriter.Close（）
 defer file.Close （）
 part，err：= multiWriter.CreateFormFile（paramName，filepath.Base（path））
 if err！= nil {
 errChan < -  err 
 return 
} 
 if _，err：= io.Copy（part，file）; err！= nil {
 errChan < -  err 
 return 
} 
 for k，v：= range params {
 if err：= multiWriter.WriteField（k ，v）; err！= nil {
 errChan<  -  err 
 return 
} 
} 
 errChan<  -  multiWriter.Close（）
}（）
 req，err：= http.NewRequest（POST，uri，bodyReader）
 return req，errChan，err 
} 
  

任何帮助都将非常感谢。

解决方案

在 http.Request.Write的文档它表明了/ b

如果Body存在，Content-Length <= 0并且TransferEncoding没有将
设置为identity，Write添加Transfer-Encoding：chunked 到
头

这意味着如果您没有设置 Content-Length ， http.Request.Write 将使用分块传输编码。这已被添加到 HTTP / 1.1 中，以避免需要计算流式传输的 Content-Length ，就像这样。

所以通常Go程序使用分块编码，并且不需要设置 Content-Length 。任何现代的HTTP堆栈都应该支持分块传输编码。

然而 S3不支持分块传输编码，所以我认为你必须自己计算 Content-Length 。

I'm trying to upload a file without loading it into memory, as shown below. Services like S3 need a Content-Length set in such cases. Is there a go-lang built-in to do that, or do I have to compute it myself.

package main

import (
    "io"
    "mime/multipart"
    "net/http"
    "os"
    "path/filepath"
)

func newfileUploadRequest(uri string, params map[string]string, paramName, path string) (*http.Request, chan error, error) {
    file, err := os.Open(path)
    if err != nil {
        return nil, nil, err
    }
    bodyReader, bodyWriter := io.Pipe()
    multiWriter := multipart.NewWriter(bodyWriter)
    errChan := make(chan error, 1)
    go func() {
        defer bodyWriter.Close()
        defer file.Close()
        part, err := multiWriter.CreateFormFile(paramName, filepath.Base(path))
        if err != nil {
            errChan <- err
            return
        }
        if _, err := io.Copy(part, file); err != nil {
            errChan <- err
            return
        }
        for k, v := range params {
            if err := multiWriter.WriteField(k, v); err != nil {
                errChan <- err
                return
            }
        }
        errChan <- multiWriter.Close()
    }()
    req, err := http.NewRequest("POST", uri, bodyReader)
    return req, errChan, err
}

Any help would be much appreciated.

解决方案

In the docs for http.Request.Write it states

If Body is present, Content-Length is <= 0 and TransferEncoding hasn't been set to "identity", Write adds "Transfer-Encoding: chunked" to the header

Which means if you don't set a Content-Length, http.Request.Write will use chunked transfer encoding. This was added to HTTP/1.1 to get rid of the need to calculate the Content-Length for streaming transfers just like this.

So normally Go programs use chunked encoding and there is no need to set Content-Length. Any modern HTTP stack should support chunked transfer encoding.

However S3 does not support chunked transfer encoding, so I think you'll have to calculate Content-Length yourself.

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