Send HTTP requests with netcat

Occasionally I need to call HTTP API from a bare-bones environment, where we don’t have curl or wget. Nowadays, it’s so common that we run everything in the dockerized environment, and we are apt to use a slim docker image without many utility libraries.

Of course, you would say installing the curl is the most straightforward solution here. Still, unfortunately, we don’t always have the privilege to install packages in a built container, so we need an alternative to make the HTTP request; here comes the netcat command, it’s usually pre-installed in Linix based system out-of-box.

Before I try to use netcat to send the HTTP request, I need APIs to be called. I use https://github.com/namshi/mockserver to create two simple APIs(one GET and one POST)

Response definition of mocks/foo/GET.mock

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8

{
   "Random": "content"
}

Response definition of mocks/foo/POST.mock

HTTP/1.1 200 OK
Content-Type: text/xml; charset=utf-8

{
   "Accept-Language": "en-US,en;q=0.8",
   "Host": "headers.jsontest.com",
   "Accept-Charset": "ISO-8859-1,utf-8;q=0.7,*;q=0.3",
   "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
}

You can run mockserver -p 8080 -m mocks so you have two APIS available for testing.

use nc to send HTTP GET request

printf 'GET /foo HTTP/1.0\r\nHost:localhost\r\n\r\n' | nc  -v localhost 8080

Caveat: you have to specify the Host as it’s mandaory according to the HTTP protocol.
You will see the response is printed as the stdout.

Connection to localhost port 8080 [tcp/http-alt] succeeded!
HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Date: Mon, 15 Nov 2021 09:47:02 GMT
Connection: close

{
   "Random": "content"
}

use nc to send HTTP POST request

POST needs more work as you have to orchestrate the body and related headers, so I ended up with a bash script.

#!/bin/bash
BODY="{ \"bar\" : \"Hello\", \"baz\" : \"11111\"}"

echo -ne "POST /foo HTTP/1.0\r\nHost: localhost\r\nContent-Type: application/json\r\nContent-Length: ${#BODY}\r\n\r\n${BODY}" | nc -i 3 localhost 8080

That’s pretty much it.