EDIT: I am maintaining a similar, but more in-depth answer at: https://stackoverflow.com/a/28380690/895245
To see exactly what is happening, use nc -l and an user agent like a browser or cURL.
Save the form to an .html file:
<form action="http://localhost:8000" method="post" enctype="multipart/form-data">
<p><input type="text" name="text" value="text default">
<p><input type="file" name="file1">
<p><input type="file" name="file2">
<p><button type="submit">Submit</button>
</form>
Create files to upload:
echo 'Content of a.txt.' > a.txt
echo '<!DOCTYPE html><title>Content of a.html.</title>' > a.html
Run:
nc -l localhost 8000
Open the HTML on your browser, select the files and click on submit and check the terminal.
nc prints the request received. Firefox sent:
POST / HTTP/1.1
Host: localhost:8000
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:29.0) Gecko/20100101 Firefox/29.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: __atuvc=34%7C7; permanent=0; _gitlab_session=226ad8a0be43681acf38c2fab9497240; __profilin=p%3Dt; request_method=GET
Connection: keep-alive
Content-Type: multipart/form-data; boundary=---------------------------9051914041544843365972754266
Content-Length: 554
-----------------------------9051914041544843365972754266
Content-Disposition: form-data; name="text"
text default
-----------------------------9051914041544843365972754266
Content-Disposition: form-data; name="file1"; filename="a.txt"
Content-Type: text/plain
Content of a.txt.
-----------------------------9051914041544843365972754266
Content-Disposition: form-data; name="file2"; filename="a.html"
Content-Type: text/html
<!DOCTYPE html><title>Content of a.html.</title>
-----------------------------9051914041544843365972754266--
Aternativelly, cURL should send the same POST request as your a browser form:
nc -l localhost 8000
curl -F "text=default" -F "[email protected]" -F "[email protected]" localhost:8000
You can do multiple tests with:
while true; do printf '' | nc -l localhost 8000; done