/* Required #include header files. */#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <fcntl.h>#include <limits.h>#include <sys/types.h>#include <sys/stat.h>/*We then define the named pipes. We use one pipe for the server and one pipe for each client.Since there may be multiple clients, the client incorporates a process ID into the name to ensure that its pipe is unique.*/#define SERVER_PIPE "/tmp/server_pipe"#define CLIENT_PIPE "/tmp/client_%d_pipe"#define ERR_TEXT_LEN 80/* We implement the commands as enumerated types, rather than #defines. This is a good way of allowing the compiler to do more type checking and also helps in debugging the application, as many debuggers are able to show the name of enumerated constants, but not the name defined by a #define directive. The first typedef gives the type of request being sent to the server, the second the server response to the client.*/typedef enum {    s_create_new_database = 0,    s_get_cdc_entry,    s_get_cdt_entry,    s_add_cdc_entry,    s_add_cdt_entry,    s_del_cdc_entry,    s_del_cdt_entry,    s_find_cdc_entry} client_request_e;typedef enum {    r_success = 0,    r_failure,    r_find_no_more} server_response_e;/*  Next, we declare a structure that will form the message passed in both directions between the two processes.Since we don't actually need to return both a cdc_entry and cdt_entry in the same response, we could have combined them in a union. For simplicity, we keep them separate.  This also makes the code easier to maintain.*/typedef struct {    pid_t               client_pid;    client_request_e    request;    server_response_e   response;    cdc_entry           cdc_entry_data;    cdt_entry           cdt_entry_data;    char                error_text[ERR_TEXT_LEN + 1];} message_db_t;/*  Finally, we get to the pipe interface functions that perform data transfer implemented *//*  in pipe_imp.c. These divide into server- and client-side functions, in the first and *//*  second blocks respectively. */int server_starting(void);void server_ending(void);int read_request_from_client(message_db_t *rec_ptr);int start_resp_to_client(const message_db_t mess_to_send);int send_resp_to_client(const message_db_t mess_to_send);void end_resp_to_client(void);int client_starting(void);void client_ending(void);int send_mess_to_server(message_db_t mess_to_send);int start_resp_from_server(void);int read_resp_from_server(message_db_t *rec_ptr);void end_resp_from_server(void);