Menu

Tech

English

The Scheme Picks the Port

Lesson 39 of 47 in Coddy's Networking with the Terminal course.

http:// and https:// differ in more than a letter. The scheme decides two things: which default port to use, 80 or 443, and whether to start a TLS handshake before sending anything.

That handshake is the first thing that happens, before any request line is written. Both sides agree on encryption and the server presents its certificate. Only then does the HTTP you know get sent, inside the encrypted channel.

So a port either speaks TLS or it does not. Ask for https:// from a plain HTTP port and there is no polite fallback: the handshake fails immediately, and curl reports exit code 35, an SSL connect error.

This is worth recognising, because it looks like the server is down when it is happily serving plain HTTP one scheme away.

Challenge

Hard

Ask a plain HTTP server for TLS and watch it refuse.

Serve a folder on port 9129 in the usual way, which is plain HTTP
Request https://127.0.0.1:9129/ and print tls= followed by curl's exit code

Expected output:

tls=35

35 is curl's code for an SSL connect error.

Try it yourself

Terminal

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Networking with the Terminal

1How Networks Talk

What Is a Network Clients and Servers IP Addresses Your First Request

4Is It Reachable?

ICMP and ping Reading Ping Output When Ping Lies Refused or Timed Out Recap: Reachability

7Sending Data

POST with -d What -d Actually Sends Form Encoding Sending JSON PUT and DELETE Recap: Writing Data

2Names and DNS

Why Names Exist The Hosts File Looking Up a Name Record Types Recap: Names

5HTTP by Hand

Anatomy of a Request Request Methods Status Codes Response Headers Writing a Response Recap: HTTP Basics

8HTTPS and TLS

Why HTTPSThe Scheme Picks the PortCertificates and Trust When TLS Fails Recap: HTTPS

3Ports and Sockets

What Is a Port Well-Known Ports Localhost Listening vs Connecting Recap: Ports

6curl in Depth

Seeing the Headers Saving Responses Custom Headers Status and Timing curl Exit Codes Recap: curl Flags

9Auth and Debugging

API Keys and Bearer The User Agent Timeouts and Retries Reading a Failure Recap: Debugging

Practice on your own: Terminal playground