Put mitmdump in front of a HTTP server listening on port 8000 on the same machine:

shb.mitmdump.instances."my-instance" = {
  listenPort = 8001;
  upstreamHost = "http://127.0.0.1";
  upstreamPort = 8000;
  after = [ "server.service" ];
};

upstreamHost has its default value here and can be left out.

Put mitmdump in front of a HTTP server listening on port 8000 on another machine:

shb.mitmdump.instances."my-instance" = {
  listenPort = 8001;
  upstreamHost = "http://otherhost";
  upstreamPort = 8000;
  after = [ "server.service" ];
};

Replace http with https if the server expects an HTTPS connection.

Let’s assume a server is listening on port 8000 which responds a plain text response test1 and its related systemd service is named test1.service. Sorry, creative naming is not my forte.

Let’s put an mitmdump instance in front of it, like so:

shb.mitmdump.instances."test1" = {
  listenPort = 8001;
  upstreamPort = 8000;
  after = [ "test1.service" ];
};

This creates an mitmdump-test1.service systemd service. We can then use journalctl -u mitmdump-test1.service to see the output.

If we make a curl request to it: curl -v http://127.0.0.1:8001, we will get the following output:

mitmdump-test1[971]: 127.0.0.1:40878: GET http://127.0.0.1:8000/ HTTP/1.1
mitmdump-test1[971]:     Host: 127.0.0.1:8000
mitmdump-test1[971]:     User-Agent: curl/8.14.1
mitmdump-test1[971]:     Accept: */*
mitmdump-test1[971]:  << HTTP/1.0 200 OK 5b
mitmdump-test1[971]:     Server: BaseHTTP/0.6 Python/3.13.4
mitmdump-test1[971]:     Date: Thu, 31 Jul 2025 20:55:16 GMT
mitmdump-test1[971]:     Content-Type: text/plain
mitmdump-test1[971]:     Content-Length: 5
mitmdump-test1[971]:     test1

Specific integration tests are defined in /test/blocks/mitmdump.nix.