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HTTP / LESSON 03

Requests and responses

Read the actual text of an HTTP conversation, and then type one by hand.

So far, tools have written our requests for us. In this lesson, we'll see the messages themselves. HTTP/1.1 is a text protocol, so you can read them.

This lesson needs a terminal, because the runnable cells show only the response.

See the whole conversation

Run this in your terminal. The -v flag makes curl print the request as well as the response.

curl -v 'https://numbers.apps.pipal.in/add?a=3&b=4'

The output also has lines about the connection. Lines starting with > are what curl sent, and lines starting with < are what it received.

If your output shows HTTP/2, add --http1.1 to see the same messages in the older format. The messages have the same meaning in both versions.

The request

GET /add?a=3&b=4 HTTP/1.1
Host: numbers.apps.pipal.in
User-Agent: curl/7.81.0
Accept: */*
  • The request line has the method, the path with the query, and the HTTP version.
  • The headers come next, one per line, as Name: value.
  • A blank line ends the headers.
  • A body can follow. This request doesn't have one.

The Host header says which site the request is for, because one server can host many sites. It's required in HTTP/1.1.

The response

HTTP/1.1 200 OK
Server: nginx/1.24.0 (Ubuntu)
Date: Thu, 05 Nov 2026 01:31:20 GMT
Content-Type: text/plain; charset=utf-8
Content-Length: 2
Connection: keep-alive

7
  • The status line has the HTTP version, the status code, and a short description.
  • The headers come next, in the same format as before.
  • A blank line ends the headers.
  • The body comes last. Here, it's 7.

Content-Length: 2 counts the bytes in the body, which includes a line break after the 7.

Ask for only the headers

The HEAD method asks for the same response as GET, without the body. With curl, use -I.

Content-Length still says 2, even though no body came back. It describes the body that a GET would have returned.

Write a request by hand

nc (netcat) opens a connection and sends whatever you type. Run this in your terminal:

nc numbers.apps.pipal.in 80

Then type these lines, and press Enter twice at the end. You need to type them quickly, or the server may give up and close the connection.

GET /add?a=3&b=4 HTTP/1.1
Host: numbers.apps.pipal.in
Connection: close

The server replies with 301 Moved Permanently and a Location header. Port 80 is plain HTTP, and this server wants you to use HTTPS. That's still real HTTP: you wrote a request, and you got a response.

To use HTTPS, let openssl handle the encryption while you type the same request:

openssl s_client -quiet -connect numbers.apps.pipal.in:443

This time you get 200 OK and the answer.

Your turn: Remove the Host line and send the request again. What does the server say? Then ask for /fibs?n=5.

Summary

  • HTTP messages have a first line, headers, a blank line, and an optional body.
  • A request's first line has a method and a path. A response's first line has a status.
  • curl -v shows you the whole conversation.

Next, we'll use different methods to change data on a server.