How to make a webserver with netcat (nc)
The netcat tool nc
can operate as a TCP client.
Because HTTP works over TCP, nc
can be used as an HTTP server!
Because nc
is a UNIX tool,
we can use it to make custom web servers:
servers which return any HTTP headers you want,
servers which return the response very slowly,
servers which return invalid HTTP,
etc.
You can also use nc
as a quick-and-dirty static file server.
Here’s an example.
Run your web server by
telling nc
to listen for new connections on port 8000:
$ nc -l 8000
Then run your web browser.
Here I use curl
but you could also use Chrome etc:
$ curl localhost:8000/index.html
Back at nc
, you’ll see the HTTP request come through from curl
:
$ nc -l 8000
GET /index.html HTTP/1.1
Host: localhost:8000
User-Agent: curl/7.54.0
Accept: */*
nc
is now waiting for you to type the response!
Type out the following:
HTTP/1.1 200 Everything Is Just Fine
Server: netcat!
Content-Type: text/html; charset=UTF-8
<!doctype html>
<html>
<body>
<h1>A webpage served with netcat</h1>
</body>
</html>
Once you start typing the HTML,
you’ll see it come line-by-line in your curl
command.
When you’ve finished typing the HTTP response,
hit Ctrl-D
.
This tells nc
to close the TCP connection and exit.
The server is no more!
To run a persistent static server without typing anything in,
write your HTTP response to a file like index.http
:
$ cat index.http
HTTP/1.1 200 OK
Content-Type: text/html; charset=UTF-8
Server: netcat!
<!doctype html>
<html><body><h1>A webpage served by netcat</h1></body></html>
Then run nc
in an infinite loop to serve this file for every response:
$ while true; do cat index.http | nc -l 8000; done
As an example of a “weird web server” you can make with nc
,
you can simulate a very slow web server.
Use pv --rate-limit 10
to read the file at 10 bytes per second:
while true; do pv --rate-limit 10 index.http | nc -l 8000; done
If you view this in Chrome,
you can see Chrome’s “progressive rendering”!
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Tagged #programming, #unix, #networking. All content copyright James Fisher 2018. This post is not associated with my employer.Found an error? Edit this page.