mjhjmtu

What is the easiest way to set up something locally to listen for GET requests on a custom port?

So that I could do curl -X GET -i 'localhost:34331/hello'

And verify that the request was received and inspect the request to look at the headers if any were sent and the URL that was used for the request

You can use netcat. Something like:

nc -l 34331

If you want to see the detail of a call, It'd be easier to use -v option of curl and call the real service.

curl -v http://www.google.com > /dev/null
* Connected to localhost (127.0.0.1) port 3128 (#0)
> GET http://www.google.com/ HTTP/1.1
> Host: www.google.com
> User-Agent: curl/7.47.0
> Accept: */*
> Proxy-Connection: Keep-Alive
> 
< HTTP/1.1 200 OK
< Date: Fri, 22 Jun 2018 12:58:58 GMT
< Expires: -1
< Cache-Control: private, max-age=0
< P3P: CP="This is not a P3P policy! See g.co/p3phelp for more info."
< Server: gws
< X-XSS-Protection: 1; mode=block
< X-Frame-Options: SAMEORIGIN
< Set-Cookie: 1P_JAR=2018-06-22-12; expires=Sun, 22-Jul-2018 12:58:58 GMT; path=/; domain=.google.com
< Set-Cookie: NID=132=cLF8pa3SHRsg32-ZGzN5aZ3ipLfAbxqfmUvJ2NTvkYg2eWN6XaOqSofMK7o902-C9hdxL_wUn6cJW2AkngcQXvNUKCCdNi7Z-eBTu0Yc8-iTFR90OeZDR44hxZK95_Ny; expires=Sat, 22-Dec-2018 12:58:58 GMT; path=/; domain=.google.com; HttpOnly
< Accept-Ranges: none
< Vary: Accept-Encoding
< Transfer-Encoding: chunked
< Content-Type: text/html; charset=ISO-8859-1
< Connection: keep-alive
< Proxy-Connection: keep-alive
< 
{ [2035 bytes data]
100 11564 0 11564 0 0 69134 0 --:--:-- --:--:-- --:--:-- 68833
* Connection #0 to host localhost left intact

If you have perl installed, a very simple http daemon can be written using HTTP::Daemon module (which you need to have in your perl libs):

#!/usr/bin/perl
use strict;
use HTTP::Daemon;
use HTTP::Response;
use threads;

my $httpd = HTTP::Daemon->new( LocalPort => 8081, Listen => 20, Reuse=>1) || die;
print "httpd started...n";

sub process_one_req

 my $con = shift;
 my $rq = $con->get_request;

 print "<< ".$rq->uri." : ".$rq->header('User-Agent')."n";

 my $rsp = HTTP::Response->new(200, 'OK' );
 $con->send_response($rsp);
 

while (my $con = $httpd->accept)

 process_one_req $con;

see also https://metacpan.org/pod/HTTP::Daemon