Generating multipart boundary

multipart
August Lilleaas picture August Lilleaas · Jan 15, 2010 · Viewed 33.2k times · Source

I'm writing a script that uploads a file to a cgi script that expects a multipart request, such as a form on a HTML page. The boundary is a unique token that annotates the file contents in the request body. Here's an example body:

--BOUNDARY
Content-Disposition: form-data; name="paramname"; filename="foo.txt"
Content-Type: text/plain

... file contents here ...
--BOUNDARY--

The boundary cannot be present in the file contents, for obvious reasons.

What should I do in order to create an unique boundary? Should I generate a random string, check to see if it is in the file contents, and if it is, generate a new, rinse and repeat, until I have a unique string? Or would a "pretty random token" (say, combination of timestamp, process id, etc) be enough?

Answer

AnthonyWJones picture AnthonyWJones · Jan 15, 2010

If you use something random enough like a GUID there shouldn't be any need to hunt through the payload to check for an alias of the boundary. Something like:-

----=NextPart_3676416B-9AD6-440C-B3C8-FC66DDC7DB45
Header:....

Payload
----=NextPart_3676416B-9AD6-440C-B3C8-FC66DDC7DB45--

Related questions

What is http multipart request?

I have been writing iPhone applications for some time now, sending data to server, receiving data (via HTTP protocol), without thinking too much about it. Mostly I am theoretically familiar with process, but the part I am not so familiar …

Read More
Example of multipart/form-data

I am wondering if anyone can share with me an example of multipart/form-data that contains: Some form parameters Multiple files

Read More
How can I make a multipart/form-data POST request using Java?

In the days of version 3.x of Apache Commons HttpClient, making a multipart/form-data POST request was possible (an example from 2004). Unfortunately this is no longer possible in version 4.0 of HttpClient. For our core activity "HTTP", multipart is somewhat out …

Read More