HTTP 文件上传是如何工作的? [英] How does HTTP file upload work?

问题描述

当我提交这样一个带有文件的简单表单时:

When I submit a simple form like this with a file attached:

<form enctype="multipart/form-data" action="http://localhost:3000/upload?upload_progress_id=12344" method="POST">
<input type="hidden" name="MAX_FILE_SIZE" value="100000" />
Choose a file to upload: <input name="uploadedfile" type="file" /><br />
<input type="submit" value="Upload File" />
</form>

它如何在内部发送文件?文件是否作为数据作为 HTTP 正文的一部分发送?在此请求的标头中，我没有看到与文件名称相关的任何内容.

How does it send the file internally? Is the file sent as part of the HTTP body as data? In the headers of this request, I don't see anything related to the name of the file.

我只想知道发送文件时 HTTP 的内部工作原理.

I just would like the know the internal workings of the HTTP when sending a file.

推荐答案

让我们来看看当你选择一个文件并提交你的表单时会发生什么(为了简洁起见，我已经截断了标题):

Let's take a look at what happens when you select a file and submit your form (I've truncated the headers for brevity):

POST /upload?upload_progress_id=12344 HTTP/1.1
Host: localhost:3000
Content-Length: 1325
Origin: http://localhost:3000
... other headers ...
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryePkpFF7tjBAqx29L

------WebKitFormBoundaryePkpFF7tjBAqx29L
Content-Disposition: form-data; name="MAX_FILE_SIZE"

100000
------WebKitFormBoundaryePkpFF7tjBAqx29L
Content-Disposition: form-data; name="uploadedfile"; filename="hello.o"
Content-Type: application/x-object

... contents of file goes here ...
------WebKitFormBoundaryePkpFF7tjBAqx29L--

注意:每个边界字符串必须以额外的 -- 为前缀，就像在最后一个边界字符串的末尾一样.上面的例子已经包含了这一点，但很容易错过.请参阅下面@Andreas 的评论.

NOTE: each boundary string must be prefixed with an extra --, just like in the end of the last boundary string. The example above already includes this, but it can be easy to miss. See comment by @Andreas below.

不是对表单参数进行 URL 编码，而是将表单参数(包括文件数据)作为请求正文中的多部分文档中的部分发送.

Instead of URL encoding the form parameters, the form parameters (including the file data) are sent as sections in a multipart document in the body of the request.

在上面的示例中，您可以看到输入 MAX_FILE_SIZE 和表单中设置的值，以及包含文件数据的部分.文件名是 Content-Disposition 标头的一部分.

In the example above, you can see the input MAX_FILE_SIZE with the value set in the form, as well as a section containing the file data. The file name is part of the Content-Disposition header.

完整的细节在这里.

这篇关于HTTP 文件上传是如何工作的?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！