You are to write your own connectionless (UDP) client. Print out everything.
You can start with any open-source UDP client as a template and may want to include some parts of the template from Program 1. UDP packets will have the following format:
FM:##_TO:##_ NP:#_HC:#_NO:###_VL:xxx_DATA:xxxxx...
FM - the source address (a number from 1 to 40, 00 as "no name yet" and 99 as "all") TO - the destination address (same range)
NP - number of the protocol
1 = registration request 2= registration response
3= data 4= data confirmation
5= registry dump request 6= registry dump response
8= serial broadcast 9= serial broadcast confirmation
HC - a count of possible hops remaining (0-9), used only for relaying in Step 5.
NO - a message ID number; you will generate these in order (start with whatever number you want), and match the number in the request to its corresponding response
VL - visited list, a sequence of 2-digit numbers separated by commas that indicates which nodes have already seen this message, e.g., VL:03,04,08,05 - note that VL is empty (VL:_) unless the message has been relayed in Step 5.
DATA - the contents of the message The entire UDP payload can be up to 500 bytes. Underscore (_) indicates a single space.
The # fields indicate decimal numbers; they are exactly as many digits as there are #s above. The xxxx... DATA field indicates text data; it can contain any printable ASCII character and \n. The program should take the following arguments (i.e., see similar values from Program 1):
-s server DNS name or IPv4 address
-p server port number
General instructions and user interface:
Upon starting, your program should:
A. "Register" with the name server (as described in Step 1 below)
B. Run a loop with commands that use the following syntaxes:
REG (as described in Step 2, below)
UNI__. (as described in Step 3, below)
BRD_. (as described in Step 4, below)
FWD__VIA__. (as described in Step 5, below)
UNI, REG, BRD, FWD, and VIA can be in upper, lower, or mixed case
"_" (underscore) represents one or more blank spaces or tabs (whitespace)
represents a two-digit number, i.e., [0-9][0-9]
represents any sequence of printable asci characters (including spaces and tabs) EXCEPT "."
Print out anything that you receive that is correct. Deal with all errors "gracefully" (as always).
Components to implement (each is worth 1 point):
1. Send a UDP packet to "register" your program
At the start of your program, you need to register to get a (numeric) name. Send a UDP packet to DNS.POSTEL.ORG on port 60450, from your server IP address and port number, and wait up to 2 seconds for a response.
The message should read:
FM:00_TO:01_ NP:1_HC:1_NO:nnn_VL:_DATA:register_me (remember that underscores "_" mean one or more blank spaces) The response will read:
FM:01_TO:00_ NP:2_HC:1_NO:nnn_VL:_DATA:you_have_been_registered_as_## Repeat up to a total of 5 times until you succeed, or stop and report an error.
2. Pull down the registry
When the user requests a registry (by typing "REG"), send a message to DNS.POSTEL.ORG to get the registry map of currently active nodes. Do this up to 5 times until a response is received.
Make sure the FM node number is the one you received when you registered (step 1, above): FM:##_TO:01_ NP:5_HC:1_NO:###_VL:_DATA:GET MAP
The response will be:
FM:01_TO:##_ NP:6_HC:1_NO:###_VL:_DATA:nn=ip@port,nn=ip@port,...
Where "ip" is an IPv4 address, in dotted decimal, and "port" is a port number, in decimal.
There will always be at least one node in the map, but there may be more. The entire list will fit in a single message (the list is YOUR entire list; it may not reflect ALL available nodes).
Print out the received info as a table.
3. Implement a server program to send/receive short messages
Loop waiting for either the user to ask to send a message (the UNI command) or download the registry again or for a packet to arrive.
If a packet arrives with NP:3 that matches your registered address, print it to the screen.
The user indicates they want to send something (e.g., by typing "UNI") followed by a destination (a 2-digit integer from 01 to 99, presumably from the registry you showed them in step 2), and a message ending with ".".
Send the message to the appropriate IP address and port (from the table in Step
2) from your node identifier to theirs: FM:##_TO:##_ NP:3_HC:1_NO:###_VL:_DATA:xxxx...
Send this message up to 5 times until you get a matching response with the FM and TO identifiers swapped with the same NO field and
NP:4 and DATA:OK
If you receive such a message from anyone, send a matching response with the FM and TO identifiers swapped with the same NO field and NP:4 and DATA:OK
4. Serial broadcast
When the user requests to send a broadcast (by typing "BRD"), let them type a message (ending in ".") and send one copy to every node in your registry EXCEPT yourself and the nameserver (01):
FM:##_TO:##_ NP:8_HC:1_NO:###_ VL:_DATA:xxxx...
The FM: address will be your node number, HC: (hopcount) should be set to 1. Send the message up to 5 times until you get a confirmation response with NP:9 from each party or give up (and report that as an error). If you receive such a message correctly, respond by swapping TO and FM identifiers, NP:9, HC:1, and DATA:OK
5. Forwarding
Recall that step 3 will handle messages with NP:3 that are TO: your node number. Augment your code to handle the FWD command, in which you use the first number as the destination in the packet (the TO: field) and the second number as the node to send your packet to first.
Forward NP:3 messages that are NOT TO: you as follows:
- Send a confirmation back to the source (swap TO:/FM: identifiers, NP:4, HC:1, DATA:OK), just as you would for messages that are addressed to you
If HC=0, then print out the message "dropped - hopcount exceeded" (and any message info. for the user).
If HC>0 and your node number IS in the VL list, then print out the message "dropped - node revisited" (and any message info. for the user).
If HC>0 and your node number IS NOT in the VL list, then send a relay copy to 5 nodes selected at random in the registry EXCEPT yourself and the nameserver (with HC decremented by 1, retaining the original TO:/FM: fields, and append ",##" with your node number to VL list)