Questions
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>
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.
I just would like the know the internal workings of the HTTP when sending a file.
Answers
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--
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.
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.
http://tools.ietf.org/html/rfc1867
http://tools.ietf.org/html/rfc1867
Source
License : cc by-sa 3.0
http://stackoverflow.com/questions/8659808/how-does-http-file-upload-work
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