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@@ -64,3 +64,71 @@ Last updated: September 23, 2025 (PRH).
             ```bash
             zx run erltris
             ```
+
+
+## Notes
+
+### Big Picture: telnet chat server -> HTTP server
+
+- The default project (see initial commit) is a telnet echo server. It's like
+  the most ghetto low-budget chat server imaginable.
+
+  ![screenshot of `gh_httpd` running](./etc/gh-telnet.png)
+
+  Lefty and middley can chat just like normal.
+
+  However, righty (`curl`) foolishly thinks he is talking to an HTTP server.
+  His request is echoed to lefty and middley.
+
+  Curl crashed because instead of a valid HTTP response back, he got something
+  like
+
+  ```
+  MESSAGE from YOU: GET / HTTP/1.1
+  ```
+
+- We make this into an HTTP server by replacing the "echo my message to
+  everyone else" logic with "parse this message as an HTTP request and send
+  back an HTTP response" logic.
+- Our "application logic" or "business logic" or whatever is contained in that
+  process of how the request is mapped to a response.
+- It really is not more complicated than that.
+
+### Basics of Erlang Processes
+
+These are heuristics that are good starting points
+
+- each module ~= 1 process
+- it helps to think of erlang as an operating system, and erlang modules as
+  shell scripts that run in that operating system.
+- some modules correspond to fungible processes, some are non-fungible
+- in Observer (`observer:start()`)
+    - named processes are non-fungible (e.g. `gh_client_sup`)
+    - the name can be anything, but conventionally it's the module name
+    - fungible processes have numbers (PIDs) (e.g. the `gh_client` code)
+    - named processes also have PIDs, they just also have names
+
+    ![](./etc/observer.png)
+
+
+### Following the call chain of `gex_httpd:listen(8080)`
+
+- Reference commit: `49a09d192c6f2380c5186ec7d81e98785d667214`
+- By default, the telnet server doesn't occupy a port
+- `gex_httpd:listen(8080)` tells it to listen on port 8080
+
+```
+%% gex_httpd.erl
+-spec listen(PortNum) -> Result
+    when PortNum :: inet:port_num(),
+         Result  :: ok
+                  | {error, {listening, inet:port_num()}}.
+%% @doc
+%% Make the server start listening on a port.
+%% Returns an {error, Reason} tuple if it is already listening.
+
+listen(PortNum) ->
+    gh_client_man:listen(PortNum).
+
+
+%%
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