Question

How can I rewrite the following CURL command, so that it doesn’t use the -F option, but still generates the exact same HTTP request? i.e. so that it passes the multipart/form-data in the body directly.

curl -X POST -F example=test http://localhost:3000/test

Answer 1

Solved:

curl \
  -X POST \
  -H "Content-Type: multipart/form-data; boundary=----------------------------4ebf00fbcf09" \
  --data-binary @test.txt \
  http://localhost:3000/test

Where test.txt contains the following text, and most importantly has CRLF (\r\n) line endings:

------------------------------4ebf00fbcf09
Content-Disposition: form-data; name="example"

test
------------------------------4ebf00fbcf09--

Notes: it is important to use --data-binary instead of plain old -d as the former preserves the line endings (which are very important). Also, note that the boundary in the body starts with an extra --.

I’m going to repeat it because it’s so important, but that request-body file must have CRLF line endings. A multi-platform text editor with good line-ending support is jEdit (how to set the line endings in jEdit).

If you’re interested in how I worked this out (debugging with a Ruby on Rails app) and not just the final solution, I wrote up my debugging steps on my blog.