מישהו היה בראיון עם ראש צוות (אחרי המבחן המדובר) ויודע מה שואלים שם?

יש אולי גם פתרון לשאלה? תודה לכולם אם השגת פיתרון לשאלה אני אודה לך אם תוכלי לשתף תודה מראש

היי - הייתי שם בראיון לפני כשלושה שבועות. מתבקשים לפתור שאלה על מחשב. אני מצרפת את הקובץ המתאר את השאלה כפי שניתן ביום הבחינה. בהצלחה Overview Your assignment is to implement a function that verifies a protocol between A and B. The protocol name is CPTPv1 (Check Point Testing Protocol version 1). The function named do_test receives as an argument a message passing between A and B (or between B and A) and its task is to indicate to the calling application (The function is called from an application/program) whether this is a legitimate message (A legitimate message must comply CPTPv1). The calling application will call do_test for a large sequence of messages (each call handles only one message). You can think or imagine that this function could be used in some filtering device located between A and B that validates the protocol between A and B. The device captures all messages passing between A and B (and between B and A) and using your implementation of do_test function decides whether the message is valid (in this case the message would be forwarded to its destination) or invalid (in this case the device will indicate to the administrator about an error and will drop the message). Scoring is based on (in declining priority): 1. Security (Validity) - Your implementation of do_test must be 100% accurate. It must categorize all invalid messages as invalid and all valid messages as valid. An implementation that will not be 100% accurate will fail the test. 2. Styling – Your code should be structured and modular. Use clear remarks. . 3. Performance – Your implementation of do_test will be evalutated using a test program (the same test program will execute all candidate’s implementations on the same computer). Performance is measured by number of messages tested per second (or the average duration of processing a message in micro seconds). In order to enable you to test your implementation before submitting your solution, a test program that tests both the Security and the Performance of your code is available. The MFC Project is organized in such a way that this program will be compiled with your implementation of do_test. It is highly recommended to use this test program prior to submitting your implementation. Test Details CPTPv1 protocol details • • Protocol runs between A and B. A is always the client and B is always the server. There is only one client (A) and one server (B). Each message is passed to do_test function using test_unit structure (see defs.h header file) that contains information about the direction and a pointer to a nil terminated string (array of char …) containing the message itself. The following table describes the protocol: • • Protocol Allowed message(s) in given state State Direction Text 1 A to B OPEN_CONNECTION (Initial) 2 B to A OPEN_CONNECTION_ACKED 3 A to B One of: LIST GETFILE LISTEN GETALL GEAR LIFT SAVE SAVEALL SAVETHEQUEEN 3 A to B EXIT 4 B to A Previous-state-match-name {*} Previous-state- match-name Note: 1. Previous-state-match- name means the last command processed (in state 3) 2. Always a total of 2 white spaces. 5 B to A EXIT_ACKED • Given the protocol is at state x (described in Protocol State column) and it receives a message that matches on of the messages that are allowed for the given state (described in Allowed messages columns), then this message is defined as a legitimate and the new state is defined in new-state column. In this case do_test New State 2 3 4 Example OPEN_CONNECTION OPEN_CONNECTION_ACKED LIST 5 3 EXIT LIST LIST Or LIST 0123z4b56aaaz2 LIST 1 EXIT_ACKED has to return RET_VALID. When match does not occur the return value should be RET_INVALID, and the protocol moves to the initial state (1). • A communication example (20 messages) and expected results: Number Direction Text do_test Notes expected result 1 A to B OPEN_CONNECTION RET_VALID 2 B to A OPEN_CONNECTION_ACKED RET_VALID 3 A to B LIST RET_VALID 4 B to A LIST 0123z4b56aaaz2 LIST RET_VALID 5 A to B GEAR RET_VALID 6 B to A GEAR 1111 GEAR RET_VALID 7 A to B EXIT RET_VALID 8 B to A EXIT_ACKED RET_VALID 9 A to B OPEN_CONNECTION_ACKED RET_INVALID Message out of state and in wrong direction 10 A to B OPEN_CONNECTION RET_VALID 11 B to A OPEN_CONNECTION_ACKED RET_VALID 12 A to B LIST RET_VALID 13 B to A LIST 0123z4b5T6aaaz2 LIST RET_INVALID Wrong char in response + 2 spaces between “ …2” and the second LIST. 15 B to A LIST 0123z4b56aaaz2 LIST RET_INVALID Message out of state 16 A to B GEAR RET_INVALID Message out of state 17 A to B OPEN_CONNECTION RET_VALID 18 B to A OPEN_CONNECTION_ACKED RET_VALID 21 A to B GEAR RET_VALID 22 B to A GEAR GEAR RET_VALID Note: In this case 2 spaces are required 19 A to B GEAR RET_VALID 20 B to A GEAR GEAR RET_INVALID Only 1 space … Instruction for do_test implementation and coding • • Prototype of the function (given in defs.h header file) is: int do_test(struct TestUnit *test_unit); You are not allowed to change the prototype of the function. Parameters: test_unit - point to test_unit structure. Important – Assume the memory pointed by test_unit is deallocated (free-d or reused) after the application called do_test. Returns values: RET_VALID RET_INVALID • • • More Notes: o Use only the specified source files. o You can modify defs.h and test.c files. You can’t modify main.c file. o You can add/define as many functions as you like (You don’t need to implement every thing in do_test, you can call other helper function that you write…). o The basic structure of do_test can’t be modified. o If the program won't compile on instructors machine result your score will be score penalized. Don’t modify the compiler setting and environment given to you. o The only allowed coding language is C. Basic HOWTO about MFC Project is already open. Ctrl+F7, F7 – Compile, Build. (Both are located under Build Menu). Ctrl+F5 – Runs the test program (shows validity test and performance test results). F1 – Alt+F7 – Opens project’s setting. At Debug tab you can control Program arguments (file name containing messages and number of test cycles). How to submit your implementation? Call the instructor he will copy defs.h and test.c files to the testing computer. Tips • Before coding anything: o Read the instructions and the example carefully. o Spend time on designing/planning your solution. Make use of the test program to validate your implementation and to test performance. You can change program arguments to test specific files that you • can craft from the test file and control the number of cycles. Once you have an implementation that works and returns correct results for all messages, backup it before trying further to improve it. You can use MSDN (Start > Programs > Microsoft Development Network > MSDN Library …) for help about C standard functions etc. You can debug your program if necessary. • • •