Copy your InetServer.java source (or your jokeserver) to a file called
MyListener.java. Modify, and simplify, the code so that it simply displays
everything sent to it on the server console. Have it send back a valid
ascii-based response to the client, acknowledging receipt of the "request" (
but note that this is just some minor elegance, not really needed).
That is, if the client sends the message, "ABC Hello there in Server land! "
then the server will display the message "ABC Hello there in Server land! "
on the server console, and send some message such as "Got your request"
back to the client.
You now have a simple "listener" program which echos all input on the server
console .
If you want to be fancy, your MyListener program can, in addition to the
console display, also send all of the information back to the client as
HTML-formatted data. This is not required, and note that you will have to
send back the corrent MIME type for HMTL: "Content-Type: text/html [cr/lf]
[cr/lf]" (see below).
Start MyListener and connect to it with internet explorer as follows:
(if you wish you can use another browser, but for simplicity in grading,
your finished product must be compatible with IE). Make valid webserver
requests of MyListener by entering URLS such as
http://localhost:2566/~elliott/dog.txt,
http://localhost:2566/~elliott/cat.html, and
http://localhost:2566/~elliott/lion.wml. Notice, and record, what the
browser sends your MyListener program in each case (it is displayed on the
server console). This is the HTTP stream that the browser sends when it is
requesting files from a web server. You have now hacked it.
Capture the output from MyListener into some file, for submission as
part of the assignment.
Note that the port number is whatever you have chosen for your
MyListener (where mine happened to be 2566 --- but note that 2540 is used
for the MyWebServer program), and the namestring should be whatever the name
is for your shrike account (where mine happens to be elliott). [Using your
shrike acocunt name is not relevant to this step, because we are not having
anything to do with the shrike here, but it will be important in future
steps.]
For example, following the above procedure, while running my listener
at port 2566, I get the following information for a request of dog.txt in
the (hypothetical) root web server directory for elliott:
C:\dp\420\java>java MyListener
Clark Elliott's Port listener running at 2566.
GET /~elliott/dog.txt HTTP/1.1
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, application/x-shockwave-flash, */*
Accept-Language: en-us
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.0.3705; .NET CLR 1.1.4322)
Host: localhost:2566
Connection: Keep-Alive
(Note: you may wish to experiment with "Connection: close" with your
webserver if you are having buffering problems.)
We are now going to use the HTTP stream we have just captured to
manually retrieve files from a web server.
- Log into the shrike and use an editor to create some VERY SIMPLE files
dog.txt, cat.html and lion.wml. Optionally you can create the files
elsewhere and use ftp to move them to your public_html directory. Dog and
cat should be easy as an html file and a text file. You can use Lion.wml as an example wireless
markup language file. [To make it easier to view, I changed to the .wml.txt
extension. You should "view source" and save it as "lion.wml"]
- Verify that the files are accessible from the web on shrike by retrieving dog and
cat with a web browser.
- Log into shrike, or some other unix machine, using telnet or
ssh. Repeat the following steps until you are comfortable, then start a
"script" session, or use emacs, or some other mechanism, to capture your
output for later use.
- Use the telnet program to manually enter into a dialog with the shrike,
or some other, web server [you do not need to connect to the server where
you are currently logged in]. I recommend working from a standard
ssh-or-telnet/command shell session under unix, because under Windows the
command shell will usually close when the web server disconnects, before you
can get a look at your response. That is, we are *working* under a unix
command shell through ssh or telnet as our working environment, and we also,
incidentally, just *happen* to be working on the subject matter of
telnet. [To say a different way: we are using ssh (or telnet, possibly) to
LOG IN to a unix system, and then, next, FROM THERE, are going to use telnet
to speak to a web server. You might ask, why not simply use a command window
from Windows and run telnet from there to the web server? The answer is that
the default telnet under windows does not typically display all of the
information we want to capture. So, we first log in to a unix system to use
the unix version of telnet (which DOES display everything we want), and, as
it happens, we use telnet, or ssh, to do so.]
In addition, we are working on the shrike for convenience, and just
happen to be connecting to the web server that is running on shrike, because
that is where we put our files. However, we could just as easily work on
hawk.depaul.edu, and manually get files from the web server at
www.cnn.com.
You will connect at port 80 instead of the default telnet port of 23,
because you want to talk to the web server, instead of the telnet server.
Do this by entering the shell command,
telnet students.depaul.edu 80
The shrike web server is now waiting for input from you.
- Enter the valid HTTP request stream that you captured using your
listener, for retrieving the file dog.txt from a web server. Note that you
will have to be careful to include all of the necessary information,
including carriage return / linefeeds (cr/lfs), and that you will have to
make changes as needed for the different server. You could probably use cut
and paste if you were clever, but unless you do this many times it is
probably not worth it.
Hint: some of the information, such as the "Accept" and "User-Information"
info is not needed by the web server, and you can find this through
experimentation.
If you enter the HTTP correctly the web server will now send your
requested file back to you as an ascii stream response to your telnet
client. If you enter it incorrectly you will still usually get some kind of
valid response, albeit one containing an error message.
Here is a sample session, yours will be similar, but may differ in some
of the details (for example, I am not using the shrike web server):
students> script
students> telnet condor.depaul.edu 80
GET /~elliott/dog.txt HTTP/1.1
Host: condor.depaul.edu:80
[Elliott note: two carriage return / linefeeds (crlfs) go here.]
and we get back the response something like the following:
HTTP/1.1 200 OK
Date: Fri, 16 Sep 2005 18:09:38 GMT
Server: Apache/2.0.53 HP-UX_Apache-based_Web_Server (Unix) PHP/4.3.8
Last-Modified: Fri, 16 Sep 2005 18:08:50 GMT
ETag: "5e1c1-2f-7c517080"
Accept-Ranges: bytes
Content-Length: 47
Content-Type: text/plain
This is Elliott's dog file on condor and hawk.
Connection closed by foreign host.
students>[control-d] [your session is stored in a file called typescript]
Put this captured output into a file for submission with the assignment.
So, in summary: Create the simple files dog.txt, cat.html, and lion.wml
in your home web directory. Verify that they can be reached from the
web. Retrieve your files manually using telnet to port 80.
You have now captured both the request coming from a web client, and the
response coming from a web server. Ta-duh.
Name Last modified Size Description
Parent Directory -
first-file.txt 16-Sep-2005 14:09 39
z-directory/ 16-Sep-2005 15:08 -