CS 33600 Exam 2 Review

The exam is on Tuesday, May 5, at 2:45 pm.

These problems review the material we covered since the last exam.
The topics include the client/server model, URLs, fetching URLs,
sockets, network connections, application layer protocols, and HTTP.

http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_10_network_clients/
http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_11_sockets/
http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_12_http/
http://cs.pnw.edu/~rlkraft/cs33600/for-class/HTTP-1.1_Syntax.txt
http://cs.pnw.edu/~rlkraft/cs33600/for-class/Web_and_HTTP.pdf
http://cs.pnw.edu/~rlkraft/cs33600/for-class/Socket_API.png
https://csapp.cs.cmu.edu/2e/ch11-preview.pdf
https://link.springer.com/content/pdf/10.1007/978-1-4842-7135-3_8#page=22

http://cs.pnw.edu/~rlkraft/cs33600/for-class/network_clients.zip
http://cs.pnw.edu/~rlkraft/cs33600/for-class/simple_client-server_pairs.zip
http://cs.pnw.edu/~rlkraft/cs33600/for-class/http_server.zip


Here are a few review problems.


Problem 1.) Identify all the parts of the following URLs.
(See  http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_10_network_clients/#url-and-uri

http://www.bigcompany.com:42/consumer/products/lookup.php?sku=0&color=greenish

http://www.bigcompany.edu:4242/where/was/that/file?x=2+2&bob=a4s56d7v83n

https://people.scs.carleton.ca/~lanthier/teaching/COMP1406/Notes/COMP1406_Ch12_NetworkProgramming.pdf#page=6



Problem 2.) What does a hostname identify?
            What does an IP address identify?
            What does a port number identify?



Problem 3.) Here is an IP address in binary form.

    1011 0011 0001 0011 1010 1000 1110 1010

Write the IP address in "dotted-quad" notation.
(See  http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_10_network_clients/#host-hostname-ip-address-port-number


Problem 4.) The following picture is a picture of a TCP
connection that is not yet a communicating TCP connection.
Explain why. Also explain why this connection may stay in
this state for a long time. Then draw a new picture that
describes the communicating TCP connection.
(See  http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_11_sockets/#bind-listen-accept-connect

         Socket                                ServerSocket
   +----------------+                      +------------------+
   |                |    tcp connection    |                  |
   |  16.52.9.4:75  O----------------------O  10.12.3.2:1234  |
   |                |                      |                  |
   |                |                      |                  |
   +----------------+                      +------------------+



Problem 5.) Fill in as much detail as you can in this
outline of a client/server socket connection.

                                         +----------------+
                                         |                |
                                         |                |
                                         |                |
                                         +----------------+
                                                 |
                                                 |
                                                 |
                                         +----------------+
                                         |                |
                                         |                |
                                         |                |
                                         +----------------+
                                                 |
                                                 |
                                                 |
      +-------------+                    +----------------+
      |             |                    |                |
      |             |                    |                |
      |             |                    |                |
      +-------------+                    +----------------+
              |                                  |
              |                                  |
              |                                  |
      +-------------+                    +----------------+
      |             |                    |                |
      |             |- - - - - - - - - ->|                |<--------+
      |             |                    |                |         |
      +-------------+                    +----------------+         |
             |                                   |                  |
 +-------------------------------------------------------------+    |
 |           |                                   |             |    |
 |    +-------------+                    +----------------+    |    |
 |    |             |                    |                |    |    |
 |    |             |--------------------|                |    |    |
 |    |             |                    |                |    |    |
 |    +-------------+                    +----------------+    |    |
 |           |                                   |             |    |
 |           |                                   |             |    |
 |           |                                   |             |    |
 |    +-------------+                    +----------------+    |    |
 |    |             |                    |                |    |    |
 |    |             |--------------------|                |    |    |
 |    |             |                    |                |    |    |
 |    +-------------+                    +----------------+    }    |
 |           |                                   |             |    |
 +-------------------------------------------------------------+    |
             |                                   |                  |
      +-------------+                    +----------------+         |
      |             |                    |                |         |
      |             |                    |                |---------+
      |             |                    |                |
      +-------------+                    +----------------+



Problem 6.) Write five lines of Java code that creates a server
socket, waits for a connection on that socket, reads one line
from the connecting process, writes that line back to the process,
and then closes the communicating socket, but not the server socket.
(See  http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_11_sockets/#using-jshell



Problem 7.) Suppose we have three processes, P1, P2, and P3 that
communicate using sockets. The processes are supposed to form a ring
in which P1 can send messages to P2, P2 can send messages to P3, and P3
can send messages to P1, and the processes do not communicate in any
other way. More specifically, suppose that when process P1 starts,
it prompts a user at a console to type in a message, and then P1 sends
that message to P2. P2 receives the message and prints it on its console
and then prompts a user at the console to type a new message that P2 sends
to P3. P3 receives its message, prints it to its console, prompts a user
for a new message, and sends that to P1. P1 receives the message from P3,
prints it to its console window, and prompts its user for a message to
send to P2, etc. Write a Java pseudo-code outline of the steps that P1
must go through to implement this "ring protocol". How many sockets, and
what kind of sockets, will P1 need? What information would P1 need at its
startup time? Would the pseudo-code for processes P2 and P3 be the same
or different than P1's?



Problem 8.) Suppose we have this base URL.

    http://myCompany.com/our/private/information/index.html

Using that base URL, what do the following relative URIs resolve to?

    myVacation.html
    ../../public/info/index.html
    /index.html
    /catalog/index.html
    ../../../catalog/index.html

Write a few lines of Java code that would solve this problem.
See http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_10_network_clients/#url-and-uri



Problem 9.) A web page with this URL,

   http://www.interesting.org/reports/june/doucument.html

contains the following fragment of html.

   <ul>
      <li><img src="../photos/cow.png>/li>
      <li><img src="/horse.png></li>
      <li><img src="camel.png></li>
   </ul>

(a) What is the resolved URL for the cow.png file?
(b) What is the resolved URL for the horse.png file?
(c) What is the resolved URL for the camel.png file?



Problem 10.) Explain why, when a browser is told to GET a single URL, like

   https://www.pnw.edu/

that single URL can easily lead to many actual HTTP GET requests.

On the other hand, if you use curl to get the same URL, that does
not lead to more GET requests. Why not?

   > curl https://www.pnw.edu/



Problem 11.) What would be the HTTP request message (request line
and the most important request headers) for the following URL?

http://cs.pnw.edu:80/~rlkraft/cs33600/class.html#2026-04-02



Problem 12.) If a browser sends the following HTTP request to a server,
then what was the (complete) URL in the browser's address bar?

GET /~rlkraft/cs33600/dynamic.html?data1=cats&data2=dogs HTTP/1.1
Host: cs.pnw.edu
Accept: text/html,application/xhtml+xml,application/xml
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Cache-Control: no-cache
Connection: keep-alive



Problem 13.) (a) If a browser makes an HTTP GET request for
the following HTML file, how many other HTTP requests will the
browser make? Explain why.
(See  http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_10_network_clients/#htmlcssjavascript

<!doctype html>
<html lang="en">
  <head>
    <link rel="stylesheet" href="styles/home.css">
    <script src="src/home.js"></script>
  </head>
  <body>
    <p><img src="images/logo.png"></p>
    <p>Go to <a href="page2.html">Page 2</a></p>
    <p>Go to <a href="page3.html">Page 3</a></p>
    <p>Go to <a href="page4.html">Page 4</a></p>
    <p><img src="images/footer.png"></p>
  </body>
</html>


(b) If the original GET request was to this URL

       http://www.example.com/page1.html

then show exactly what the HTTP request message will
look like for each one of the additional GET requests.



Problem 14.)
See  http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_11_sockets/#the-end-of-message-problem

(a) How does an HTTP server know when it has received the last request header?

(b) How does an HTTP client know when it has received the last response header?

(c) How does an HTTP server or client know when it has received all of the entity body?

(d) An entity body is an array of bytes. An array of bytes can be any kind of data.
    How does an HTTP server or client know what the bytes in an entity body mean?

(e) Why doesn't the HTTP protocol use a sentinel value to mark the end of an entity body?



Problem 15.) The next few problems use the Windows curl program.

See  http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_10_network_clients/#using-curl

Explain the difference in the results of this curl command

  > curl -v -H "Accept-Encoding: gzip"  http://cs.pnw.edu/~rlkraft/

and this curl command.

  > curl -v  http://cs.pnw.edu/~rlkraft/



Problem 16.) Explain the difference in the results of these two curl commands.

  > curl -H "If-Modified-Since: Mon, 06 Jan 2025 00:00:00 GMT"  http://cs.pnw.edu/~rlkraft/cs33600/cs33600.html

  > curl -H "If-Modified-Since: Wed, 14 Jan 2026 21:37:06 GMT"  http://cs.pnw.edu/~rlkraft/cs33600/cs33600.html

Hint: Add the -v option to the curl command-lines to get more clues.



Problem 17.) Explain the difference in the results of this curl command

  > curl  http://cs.pnw.edu/~rlkraft/cs33600/cs33600.html

and this curl command.

  > curl -H "Range: bytes=1000-1400"  http://cs.pnw.edu/~rlkraft/cs33600/cs33600.html

Hint: Add the -v option to the curl command-lines to get more clues.



Problem 18.) Run the http server from class.

   http://cs.pnw.edu/~rlkraft/cs33600/for-class/http_server.zip

Enter this URL into your browser.

   http://localhost:8080/static.html#part2

What URL is sent by the browser to the server? Why?
What is displayed by the browser? Why?

Use curl with the same URL.

> curl -v  http://localhost:8080/static.html#part2

What URL did curl send to the server? What was sent back
by the server to the curl client? What happened to the
fragment?



Problem 19.) The following four URLs all work and will get you
to the Google search page. But these URLs are not equivalent
to each other. How are they related? Give your answer in terms
of the HTTP protocol. That is, what happens when you do an HTTP
GET on each of these URLs?

   http://google.com
   http://www.google.com
   https://google.com
   https://www.google.com

Which URL is really the Google search URL? Why?

Hint: Load each URL into Chrome with Chrome's Dev-Tools
open to its "Network" tab. Or, download each URL using
the curl program with appropriate command-line options.



Problem 20.) What is the meaning of this HTTP response line
and headers?
(See http://cs.pnw.edu/~rlkraft/cs33600/for-class/readmes/Readme_12_http/#redirections

HTTP/1.0 301 Moved Permanently
Location: http://www.MergedCompany.com/
Server: BigIP
Connection: close
Content-Length: 0



Problem 21.) (a) What happens if the server says Content-Length
is 200 but the server only sends 100 bytes?

(b) What happens if the server says Conten-Length is 100
but the server sends 200 bytes?

(c) How do the answers to (a) and (b) depend on a persistent connection?

Hint: You can modify the source code to the server HttpServer_v2.java in
http://cs.pnw.edu/~rlkraft/cs33600/for-class/http_server.zip
so that the server lies about the content length. Then see how
the Chrome browser or the Curl client react.