SDSU CS 596: Client-Server Programming
Spring Semester, 1997
Doc 17, Assignment 3 Comments

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San Diego State University -- This page last updated Mar 20, 1997
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Contents of Doc 17, Assignment 3 Comments

Escaping Special Characters slide # 2
Meta Characters in Grammar slide # 4
Protocol Requirement or Example Consistency slide # 5
If you have BNF then use it slide # 6
BNF, Structure and Content slide # 7
Specify all parts of the Protocol slide # 8
Positional Data slide # 10

Doc 17, Assignment 3 Comments Slide # 1

Escaping Special Characters


If you have special characters in your protocol then what happens if the character appears in text?

Example

Special characters: "{", "=", ";", "}"

{ command=login;
user=Roger Whitney;
password=my;pa=ssw}ord
}
This will be parsed as:

{ command=login;
user=Roger Whitney;
password=my;
pa=ssw
}
ord
}

Some people did not address this problem at all
Some people would talk about some of the special characters, but forget others

What are the different ways one can address special characters?

Doc 17, Assignment 3 Comments Slide # 2

Problem: Meta Characters in Grammar


When the protocol has special characters how does on indicate this?

So I would see:

The special characters are "{", "=", ";", "}". So an example of a command is:

"{" command"="login";"
user"="Roger Whitney";"
password"="mypassword
"}"

Now will the client send the string:

"{" command"="login";"
user"="Roger Whitney";"
password"="mypassword
"}"

or will it send:

{ command=login;
user=Roger Whitney;
password=mypassword
}
Doc 17, Assignment 3 Comments Slide # 3

Protocol Requirement or Example Consistency?


If you always give examples like:

{ COMMAND=login;
USER=Roger Whitney;
PASSWORD=mypassword
}
Does that mean the protocol requires the keys be all capital letters or does it mean you are putting them in all capital letters so the reader knows they are keys?


If all examples have space around the special characters, is that part of the protocol or just for readability of the document?


{ COMMAND = login;
USER = Roger Whitney;
PASSWORD = mypassword
}
Doc 17, Assignment 3 Comments Slide # 4

If you have BNF then use it!


BNF rules

OCTET = <BLAH>
CHAR = <BLAH>
UPALPHA = <BLAH>
LOALPHA = <BLAH>
ALPHA = <BLAH>
DIGIT = <BLAH>
CTL = <BLAH>
CR = <BLAH>
LF = <BLAH>
SP = <BLAH>
HT = <BLAH>
CRLF = <BLAH>
LWS = <BLAH>
TEXT = <BLAH>

Protocol

{ command=login;
user=string;
password=string
}

What is a string

Doc 17, Assignment 3 Comments Slide # 5

BNF, Structure and Content

Some BNF Rules

PASSENGER_NAME = *( ALPHA | SP )

TELEPHONE = AREACODE "-" PREFIX "-" SUFFIX |
PREFIX "-" SUFFIX

AREACODE = "(" DIGIT DIGIT DIGIT ")"
PREFIX = DIGIT DIGIT DIGIT
SUFFIX = DIGIT DIGIT DIGIT DIGIT

PLANE_TYPE = "A" | "B" | "C"

FLIGHT_NUMBER = "1201" | "1202" | etc.

MONTH = "Jan" | "Feb" | "Mar" | etc.


Doc 17, Assignment 3 Comments Slide # 6

Specify all parts of the Protocol

Example 1

departureMonth: month
departureDay: day
departureHour: hour

What is a month - Jan, January, Januar, 1?
What is a an hour - 1:30 pm, 13:30?


Example 2 - Reserving a Seat

Arguments (client):
- seat

Returns (Server):
confirmation message OK with code

ex: OK Roger Whitney reservation number is: 21de09


The code returned will be of 6 digits and is unique


Example 3 - Tim the Toolman

The cities command will return a labeledTable with column headers: "City" and "Code"
Doc 17, Assignment 3 Comments Slide # 7
Example 4

LISTFLIGHT Command

Arguments: optional "FULL", origin city name, destination city name

Returned Data: simple response: FLIGHT_NUMBER

full response: FLIGHT_NUMBER, DEPART_TIME, ARRIVAL_TIME, FLIGHT_TYPE, AVAILABLE_SEAT

Example:

C: LISTFLIGHT, FLAG=FULL, FROM=DFW, TO=LAX
S: LISTFLIGHT, FLIGHT_NUMBER = 302 304 306
S: LISTFLIGHT, DEPART_TIME = 12:30 14:30 19:30
S: LISTFLIGHT, ARRIVAL_TIME = 15:30 17:30 22:30
S: LISTFLIGHT, FLIGHT_TYPE = B C A
S: LISTFLIGHT, AVAILABLE_SEAT = 2 3 4

Elsewhere in the BNF we have:

name-value pair =

"FLIGHT_NUMBER=" 1*( SPACE flight_number) |
"DEPART_TIME=" 1*( SPACE time) |
etc.
flight_number = *digit
Doc 17, Assignment 3 Comments Slide # 8

Positional Data


RESV date flightNumber

Example:
C: RESV 3,25,1997 108
S: +OK



CITY

Possible Responses:
+OK list of cities follows-
ERR there aren't any cities

Example:
C: CITY
S: +OK 2 cities
S: San Diego, SAN
S: Denver, DEN
S:.

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