Server辅导、代TCP connection编程、辅导IP/TCP语言、辅导Network辅导Python编程|解析Haskell程序

3.1. Server
The server has the following responsibilities - User Authentication - When a new client requests for a connection, the server should prompt the
user to input the username and password and authenticate the user. The valid username and
password combinations will be stored in a file called credentials.txt which will be in the same
directory as the server program. An example credentials.txt file is provided on the assignment page. Username and passwords are case -sensitive. We may use a different file for testing so DO NOT
hardcode this information in your program. You may assume that each username and password will
be on a separate line and that there will be one white space between the two. If the credentials are
correct, the client is considered to be logged in (i.e. online) and a welcome message is displayed. When all messaging is done, a user should be able to logout from the server. On entering invalid credentials, the user is prompted to retry. After 3 consecutive failed attempts, the user is blocked for a duration of block_duration seconds (block_duration is a command line
argument supplied to the server) and cannot login during this duration (even from another IP
address). While a user is online, if someone uses the same username/password to log in (even from
another IP address), then this new login attempt is denied. Timeout - The server should keep track of all online users. If the server does not receive any
commands from a user for a period of timeout seconds (timeout is a command line argument
supplied to the server), then the server should automatically log this user out. Note that, to be
considered active, a user must actively issue a command. The receipt of a message does not count. Pr esence Broadcasts - The server should notify the presence/absence of other users logged into the
server, i.e. send a broadcast notification to all online users when a user logs in and logs out. List of online users - The server should provide a list of users that are currently online in response
to such a query from a user. Online history – The sever should provide a list of users that logged in for a user specified time in
the past (e.g. users who logged in within the past 15 minutes). Message Forwarding - The server should forward each instant message to the correct recipient
assuming they are online. Offline Messaging - When the recipient of a message is not logged in (i.e. is offline), the message
will be saved by the server. When the recipient logs in next, the server will send all the unread
messages stored for that user (timestamps are not required). Message Broadcast – The server should allow a user to broadcast a message to all online users. Offline messaging is not required for broadcast messages. Blacklisting - The server should allow a user to block / unblock any other user. For example, if user
A has blocked user B, B can no longer send messages to A i.e. the server should intercept such
messages and inform B that the message cannot be forwarded. Blocked users also do not get
presence notifications i.e. B will not be informed each time A logs in or logs out. 3.2. Client
The client has the following responsibilities -
Authentication - The client should provide a login prompt to enable the user to authenticate with
the server. Message - The client should allow the user to send a message to any other user and display
messages sent by other users. The client should also allow the user to send a broadcast message to
all online users. Notifications - The client should display presence notifications sent by the server about users
logging in and out from the server. Find users online - The client should provide a way for the user to obtain a list of all the users
currently online from the server. Find online history – The client should provide a way for the user to obtain a list of all users who
had logged in within a user specified time period. Blacklist – The client should allow a user to block a user from sending any further messages. The
client should also allow a user to unblock a user that was earlier blocked. 3.3 Commands supported by the client
After a user is logged in, the client should support all the commands shown in the table below. For
the following, assume that commands were run by user A. Command Description
message Send to through the server. If the user is
online then deliver the message immediately, else store the
message for offline delivery. If has blocked A, then a
message to that effect should be displayed for A. If the is
not present in the credentials file (i.e. invalid user) or is self (A)
then an appropriate error message should be displayed. The
used in our tests will be a few words at most. broadcast Send to all online users except A and those users who
have blocked A. Inform A that message could not be sent to some
recipients. whoelse This should display the names of all users that are currently
online excluding A. Users can be displayed in any order. whoelsesince This should display the names of all users who were logged in at
any time within the past seconds excluding A. Note that
this, may include users that may currently be offline. If is
greater than the time since when the server has been running, then
all users who logged in since the sever initiation time should be
listed. This suggests that you will need to keep a login history
since the start of the server. Users can be displayed in any order. block blocks the from sending messages to A. A message
should be displayed to A confirming the blocking action. If
is self (i.e., A) or is invalid, then an appropriate error
message should be displayed. must not be informed that
A has blocked them. unblock unblocks the who has been previously blocked by A. A
message should be displayed to A confirming the unblocking
action. If is self (i.e., A) or is invalid or was not already
blocked, then an appropriate error message should be displayed. logout log out user A. Any command that is not listed above should result in an error message being displayed to the user. The
interaction with the user should be via the terminal (i.e. console). All messages must be displayed in the
same terminal. There is no need to create separate terminals for messaging with different users. We do not mandate the exact text that should be displayed by the client to the user for the various
messages. However, you must make sure that the displayed text is easy to comprehend. Please make
sure that you DO NOT print any debugging information on the client terminal. We also prefer that you do not print anything at the terminal running the server. We suggest that
you use an optional debug flag (e.g. –d) for the server. When this flag is turned on, your server can
print debugging information to the terminal. Some examples illustrating client server interaction using the above commands are provided in
Section 8. 3.4 Peer to Peer Messaging
Some users may prefer to have some privacy during messaging. They may want to message their
friends directly without all their conversation being routed via the server. A peer-to-peer messaging
client is a good solution for this scenario. In addition to the above functionalities, you should
implement peer-to-peer messaging (also referred to as private messaging). To implement this functionality your client should support the following commands (in addition to
those listed in Section 3.3)
Command Description
startprivate This command indicates that user A wishes to commence p2p
messaging with . The client should obtain the IP address
and port number being used by the from the server. The
client should try to establish a TCP connection to this IP address
and port number combination. A confirmation message should be
displayed to A. If has blocked A, then server should not
provide the IP address and port number and an appropriate error
message should be displayed. If is offline, invalid or self
then appropriate error messages should be displayed. private Send to directly without routing through the
server. If the user is no longer online at the address obtained via
the previous command then a message to that effect should be
displayed for A. If A has not executed startprivate before this
command then an appropriate error message should be displayed. Note that, A may execute startprivate before has
blocked A. In this instance, A can still use this command to send
a message to . Other error messages (e.g. offline, invalid, etc.) are consistent with those indicated in the above command. stopprivate This command indicates that user A wishes to discontinue the
p2p messaging session with . A message to this effect
should be displayed on the terminal for . The TCP
connection established between the two end points should be
closed. An appropriate error message should be displayed if there
does not exist an active p2p messaging session with
3.5 Extension
Once you have your P2P messaging in place, the next logical step is to utilize the setup to transfer
files in a distributed manner (similar to BitTorrent). Assume that a user ‘A’ has a file (assume a
binary format) that they are willing to serve to other users in a P2P manner. User A divides the file
into N chunks (we will use N=10 for this part of the assignment) and registers the details of the file
(name, size and number of chunks) with the server. Any client can search for the availability of a
specific file name in the system from the server. The server will reply back with either ‘Not
available’ or ‘Available’ along with list of online users that have one or more chunks of the
requested file name. A client can also search for specific chunks of a file. The client will then select peers that have chunks and request the transfer of the selected chunks. Once a chunk has been downloaded, the client will also register the availability of this chunk with
the server. The algorithm to select the peers for downloading the chunks is for you to decide. The
objective is to finish the download in an efficient and distributed manner. As a rule of thumb, you
cannot download all chunks of a file from a single peer, if other peers have some chunks of that file
available for download. You need to provide the following additional features in order to support the file transfer. Command Description
register This command indicates that user A wishes to register a
with the server. contains names, number & size of chunks. The server will respond with ‘Ok’ if
the file is successfully registered. A confirmation message should
be displayed to A. If the file is already registered, the server will
respond appropriately and registers the availability of chunks at
user A. searchFile User A wishes to search for the availability of a filename in the
system. The server will reply back with either ‘Not available’ or
‘Available’ along with list of online users that have one or more
chunks of the requested . searchChunk User A searches for the availability of specific for a
in the system. The server will reply back with either
‘Not available’ or ‘Available’ along with list of online users that
have one or more requested of the . private The client should obtain the IP address and port number being
used by the from the server. If has blocked A, then
the server should not provide the IP address and port number and
an appropriate error message should be displayed. If is
offline, invalid or self then appropriate error messages should be
displayed. The client should try to establish a TCP connection to
this IP address and port number combination. Once the
connection is established, it requests the download of a
of a specific . An appropriate error message should be
displayed if there does not exist an active p2p messaging session
with . When running all clients and server on the same machine, make sure that a client only has access to
chunks that it has currently downloaded from the system. Only the original owner has access to all
chunks from the start. 3.6 File Names & Execution
The main code for the server and client should be contained in the following files: server.c, or
Server.java or server.py, and client.c or Client.java or client.py. You are
free to create additional files such as header files or other class files and name them as you wish. The server should accept the following three arguments: ? server_port: this is the port number which the server will use to communicate with the
clients. Recall that a TCP socket is NOT uniquely identified by the server port number. So it
is possible for multiple TCP connections to use the same server-side port number. ? block_duration: this is the duration in seconds for which a user should be blocked after
three unsuccessful authentication attempts. ? timeout: this is the duration in seconds of inactivity after which a user is logged off by the
server. The server should be executed before any of the clients. It should be initiated as follows:
If you use Java:
java Server server_port block_duration timeout
If you use C: ./server server_port block_duration timeout
If you use Python:
python server.py server_port block_duration timeout
The client should accept the following two arguments: ? server_IP: this is the IP address of the machine on which the server is running. ? server_port: this is the port number being used by the server. This argument should be
the same as the first argument of the server. Note that, you do not have to specify the port to be used by the client. You should allow the OS to
pick a random available port. Each client should be initiated in a separate terminal as follows:
If you use Java:
java Client server_IP server_port
If you use C: ./client server_IP server_port
If you use Python:
python client.py server_IP server_port
Note: When you are testing your assignment, you can run the server and multiple clients on the
same machine on separate terminals. In this case, use 127.0.0.1 (local host) as the server IP address. 8. Sample Interaction
Note that the following list is not exhaustive but should be useful to get a sense of what is expected. We are assuming Java as the implementation language. Case 1: Successful Login
Terminal 1
>java Server 4000 60 120
Terminal 2
>java Client 10.11.0.3 4000 (assume that server is executing on 10.11.0.3)
>Username: yoda
>Password: wise
>Welcome to the greatest messaging application ever!
>
Case 2: Unsuccessful Login (assume server is running on Terminal 1 as in Case 1)
Terminal 2
>java Client 10.11.0.3 4000 (assume that server is executing on 10.11.0.3)
>Username: yoda
>Password: weird
>Invalid Password. Please try again
>Password: green
>Invalid Password. Please try again
>Password: password
>Invalid Password. Your account has been blocked. Please try again later
The user should now be blocked for 60 seconds (since block_time is 60). The terminal should shut
down at this point. Terminal 2 (r eopened befor e 60 seconds ar e over)
>java Client 10.11.0.3 4000 (assume that server is executing on 10.11.0.3)
>Username: yoda
>Password: wise
>Your account is blocked due to multiple login failures. Please try again later Terminal 2 (r eopened after 60 seconds ar e over)
>java Client 10.11.0.3 4000 (assume that server is executing on 10.11.0.3)
>Username: yoda
>Password: wise
>Welcome to the greatest messaging application ever!
>
Example Interactions
Consider a scenario where three users Hans, Yoda and Luke are currently logged in. No one has yet
blocked anyone else. In the following we will illustrate the text displayed at the terminals for all three
users as they execute various commands. Some other examples with different users are also provided. 1. Hans executes whoelse followed by a command that is not supported
hans’s Terminal yoda’s Terminal luke’s Terminal
>whoelse > >
>yoda
>luke
>whatsthetime
>Error. Invalid command
2. Hans messages Yoda and then messages an invalid user
hans’s Terminal yoda’s Terminal luke’s Terminal
>message yoda Hey Dude
>hans: Hey Dude
>message bob party time
>Error. Invalid user 3. Hans broadcasts a message
hans’s Terminal yoda’s Terminal luke’s Terminal
>broadcast vader sucks
>hans: vader sucks >hans: vader sucks
4.Luke blocks Hans followed by a few interactions that illustrate the effect of blocking and
unblocking. hans’s Terminal yoda’s Terminal luke’s Terminal
>block hans
>hans is blocked
>broadcast I rock
>Your message could not
be delivered to some
recipients
>hans: I rock
>message luke You angry?
>Your message could not
be delivered as the
recipient has blocked you
>block hans
>Error. Cannot block self
>unblock yoda
>Error. yoda was not
blocked
>unblock hans
>hans is unblocked
>broadcast stormtroopers
>hans: stormtroppers >hans: stormtroppers
5. Assume that Vader was logged in 5 minutes ago but logged out 2 minutes ago and that R2D2 was
logged in 10 minutes ago but logged out 5 minutes ago. hans’s Terminal yoda’s Terminal luke’s Terminal
>whoelsesince 200
>hans
>yoda
>vader
>whoelsesince 500
>hans
>luke
>vader
>r2d2
6. Now assume that Hans and Yoda are logged on but that Luke is currently offline. Luke joins in
later and receives a stored message from Hans. It also shows presence notification. Later, Yoda logs
out and the corresponding notification is shown to others. hans’s Terminal yoda’s Terminal luke’s Terminal
>message luke Let’s rock (Assume that luke logs in
after this message)
>luke logged in >luke logged in >hans: Let’s rock
>logout
>yoda logged out >yoda logged out
7. Assume that Hans, Yoda and Luke are currently logged in. Hans first tries to send a private
message to Yoda without first executing startprivate. This is followed by the correct sequence of
commands for private messaging. Observe that a non-private message (i.e. through the server) can
also be sent by a user engaged in a private conversation. hans’s Terminal yoda’s Terminal luke’s Terminal
>private luke hey dude
>Error. Private messaging
to luke not enabled
>startprivate luke
>Start private messaging
with luke
>private luke hey dude
>hans(private): hey dude
>private hans hello
>luke(private): hello
>message yoda force is
strong
>hans: force is strong
>logout
>hans logged out >hans logged out