RL2: Carramba!#
A long, long time ago, a famous researcher of flying frogs – Professor Baltazar Gąbka – went missing in the Land of Raindwellers. An expedition sets out from Kraków to rescue him, led by the no less famous traveller – Wawel Dragon (buhuhahaha!) – who is accompanied on their perilous expedition by the princely cook Bartholomew Bartolini of Green Parsley coat of arms (mamma mia! at your service!). They are followed by the mysterious Don Pedro…
…a spy from the Land of Raindwellers.
The citizens of Kraków know very well that the Raindwellers are very unhappy after Professor’s visit and they are not going after the Dragon. They are going after them and the expedition is just standing in their way. Therefore, they want a live preview of the state of the rescue expedition to prepare in case of danger and ensure the success of the expedition. However, a clever spy has anticipated the fears of the inhabitants of Prince Krak’s city and, following Wawel Dragon and Bartholomew Bartolini, obliterates their tracks so that they are not visible from afar.
With little confidence in the students of the Jagiellonian University, the citizens of Kraków plan to ask a technical university to write an app for tracking the expedition. The choice fell on WUT, and it was you, the master of your trade, who were appointed to carry out the task. Help the people of Kraków secure the success of the expedition!
The file board_utils.h contains helper functions (along with their descriptions) used to initialize the board and perform the character movements. Make use of these functions in your code.
Stages:#
Stage 1 (5 pts)#
The program takes two integers greater than \(2\) as arguments: \(n\) and \(m\). Create a file named BOARD_FILE of size \(m \times (n+1)\) bytes, and map its contents to a shared memory area. Then, initialize the mapped memory using the provided function fill_board (from the file board_utils.h).
After initialization, in a loop make STEP_COUNT random expedition moves (get the move using the function get_random_move and perform it with move_pos), starting from a random position. Mark the position of the expedition (using set_char) with S and the trace after it with =. Sleep \(100\) ms after each movement.
At the end, print Smok-Expedition completed!, release all resources, and exit the program. You can view the contents of the created file to ensure that the memory has been filled correctly. To follow the changes in real time in the file, use watch -n 0.1 tail board while the program is running.
Stage 2 (5 pts)#
Create a Don Pedro process that will be used to keep track of the expedition. At this stage, the map becomes a critical section – secure access to it with a single shared mutex.
Don Pedro first sleeps WAIT_N*100 ms and then makes STEP_COUNT movements (in a loop), tracking the expedition (parent process). To accomplish this:
- if Don Pedro is on the track of Dragon (
has_trailreturns non-zero value), then change the content of the field where Don Pedro stays currently to a space (.) and printCarramba!to the terminal, - fetch the move to be executed using the function
get_trail_moveand perform it (move_pos).
Stage 3 (5 pts)#
The expedition realizes that it is being followed. Dragon therefore comes up with the idea of sending false signals to the spy about the direction the expedition would go. To do this, create (and open for writing) in the parent process a FIFO file named FIFO_NAME and open it for reading in the spy’s process.
After each move is made, the expedition sends a random move through the FIFO (use get_random_move function).
Don Pedro, now in an infinite loop, waits for messages in a FIFO. The clever spy knows that the messages he gets are a blunder, so after receiving each message he prints Direction <sign>? Don't try these tricks on me, carramba!, and then makes a move according to the previous stage.
The expedition’s process, once it has made STEP_COUNT moves, closes the queue, signaling the end of the journey. When Don Pedro detects that the queue has been closed, it breaks the loop and terminates. At the end, the parent process deletes the queue file.
Stage 4 (6 pts)#
Don Pedro bravely follows the steps of Wawel Dragon and Bartholomew Bartolini. Occasionally, however, an order will come from the Land of Raindwellers to carry out a special mission, which the spy must handle immediately. Create a network socket in Don Pedro’s process that listens on the port PORT. Whenever a connection is established, Don Pedro prints out Headquarters connected -- over! and closes that connection.
The connection can be established, for example, using the command netcat [-z] localhost <port> (the -z flag disconnects immediately after the connection is made). Important – Don Pedro should still wait for messages from the FIFO. To wait on multiple descriptors, utilize epoll (alternatively, poll or select).
Stage 5 (4 pts)#
Implement the execution of the special mission. Instead of closing the connection from headquarters (netcat), wait for one of four characters: W, A, S or D, indicating the direction of the move the spy should perform.
When a valid character is received, print Message <character> -- accepted!, place the character * on the current field, and then make a move using the function move_pos, passing the received character as the parameter. Other characters are ignored.
The characters are read (while simultaneously waiting for messages from the previous stages) until the client disconnects. Don Pedro can only be connected to one headquarters client at a time, reject redundant connections. However, once headquarters disconnects, the next connection should be accepted.