clientif.c

《Beginning Linux Programming》书的配置实例源代码。

// The file starts with #include files and constants.

#define _POSIX_SOURCE

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/types.h>
#include <sys/stat.h>

#include "cd_data.h"
#include "cliserv.h"

// The static variable mypid reduces the number of calls to getpid that would
// otherwise be required.
// We use a local function, read_one_response, to eliminate duplicated code.

static pid_t mypid;

static int read_one_response(message_db_t *rec_ptr);

// The database_initialize and close routines are still called, but are now used, respectively,
// for initializing the client-side of the pipes interface and for removing redundant named
// pipes when the client exits.

int database_initialize(const int new_database)
{
    if (!client_starting()) return(0);
    mypid = getpid();
    return(1);
    
} /* database_initialize */

void database_close(void) {
    client_ending();
}

// The get_cdc_entry routine is called to get a catalog entry from the database,
// given a CD catalog title.
// Here we encode the request in a message_db_t structure and pass it to the server.
// We then read the response back into a different message_db_t structure.
// If an entry is found, it's included inside the message_db_t structure as a cdc_entry
// structure, so we pass back the appropriate part of the structure.

cdc_entry get_cdc_entry(const char *cd_catalog_ptr)
{
    cdc_entry ret_val;
    message_db_t mess_send;
    message_db_t mess_ret;

    ret_val.catalog[0] = '\0';
    mess_send.client_pid = mypid;
    mess_send.request = s_get_cdc_entry;
    strcpy(mess_send.cdc_entry_data.catalog, cd_catalog_ptr);

    if (send_mess_to_server(mess_send)) {
        if (read_one_response(&mess_ret)) {
            if (mess_ret.response == r_success) {
                ret_val = mess_ret.cdc_entry_data;
            } else {
                fprintf(stderr, "%s", mess_ret.error_text);
            }
        } else {
            fprintf(stderr, "Server failed to respond\n");
        }
    } else {
        fprintf(stderr, "Server not accepting requests\n");
    }
    return(ret_val);
}

// Here's the source for the function read_one_response that we use to avoid duplicating code.

static int read_one_response(message_db_t *rec_ptr) {

    int return_code = 0;
    if (!rec_ptr) return(0);
    
    if (start_resp_from_server()) {
        if (read_resp_from_server(rec_ptr)) {
            return_code = 1;
        }
        end_resp_from_server();
    }
    return(return_code);
}
 
// The other get_xxx, del_xxx and add_xxx routines are implemented in a similar way to the
// get_cdc_entry function and are reproduced here for completeness.
// First, the function for retrieving CD tracks.

cdt_entry get_cdt_entry(const char *cd_catalog_ptr, const int track_no)
{
    cdt_entry ret_val;
    message_db_t mess_send;
    message_db_t mess_ret;

    ret_val.catalog[0] = '\0';
    mess_send.client_pid = mypid;
    mess_send.request = s_get_cdt_entry;
    strcpy(mess_send.cdt_entry_data.catalog, cd_catalog_ptr);
    mess_send.cdt_entry_data.track_no = track_no;

    if (send_mess_to_server(mess_send)) {
        if (read_one_response(&mess_ret)) {
            if (mess_ret.response == r_success) {
                ret_val = mess_ret.cdt_entry_data;
            } else {
                fprintf(stderr, "%s", mess_ret.error_text);
            }
        } else {
            fprintf(stderr, "Server failed to respond\n");
        }
    } else {
        fprintf(stderr, "Server not accepting requests\n");
    }
    return(ret_val);
}

// Next, two functions for adding data, first to the catalog and then to the tracks database.

int add_cdc_entry(const cdc_entry entry_to_add)
{
    message_db_t mess_send;
    message_db_t mess_ret;

    mess_send.client_pid = mypid;
    mess_send.request = s_add_cdc_entry;
    mess_send.cdc_entry_data = entry_to_add;

    if (send_mess_to_server(mess_send)) {
        if (read_one_response(&mess_ret)) {
            if (mess_ret.response == r_success) {
                return(1);
            } else {
                fprintf(stderr, "%s", mess_ret.error_text);
            }
        } else {
            fprintf(stderr, "Server failed to respond\n");
        }
    } else {
        fprintf(stderr, "Server not accepting requests\n");
    }
    return(0);
}

int add_cdt_entry(const cdt_entry entry_to_add)
{
    message_db_t mess_send;
    message_db_t mess_ret;

    mess_send.client_pid = mypid;
    mess_send.request = s_add_cdt_entry;
    mess_send.cdt_entry_data = entry_to_add;

    if (send_mess_to_server(mess_send)) {
        if (read_one_response(&mess_ret)) {
            if (mess_ret.response == r_success) {
                return(1);
            } else {
                fprintf(stderr, "%s", mess_ret.error_text);
            }
        } else {
            fprintf(stderr, "Server failed to respond\n");
        }
    } else {
        fprintf(stderr, "Server not accepting requests\n");
    }
    return(0);
}

// And lastly, two functions for data deletion.

int del_cdc_entry(const char *cd_catalog_ptr)
{
    message_db_t mess_send;
    message_db_t mess_ret;

    mess_send.client_pid = mypid;
    mess_send.request = s_del_cdc_entry;
    strcpy(mess_send.cdc_entry_data.catalog, cd_catalog_ptr);

    if (send_mess_to_server(mess_send)) {
        if (read_one_response(&mess_ret)) {
            if (mess_ret.response == r_success) {
                return(1);
            } else {
                fprintf(stderr, "%s", mess_ret.error_text);
            }
        } else {
            fprintf(stderr, "Server failed to respond\n");
        }
    } else {
        fprintf(stderr, "Server not accepting requests\n");
    }
    return(0);
}


int del_cdt_entry(const char *cd_catalog_ptr, const int track_no)
{
    message_db_t mess_send;
    message_db_t mess_ret;

    mess_send.client_pid = mypid;
    mess_send.request = s_del_cdt_entry;
    strcpy(mess_send.cdt_entry_data.catalog, cd_catalog_ptr);
    mess_send.cdt_entry_data.track_no = track_no;

    if (send_mess_to_server(mess_send)) {
        if (read_one_response(&mess_ret)) {
            if (mess_ret.response == r_success) {
                return(1);
            } else {
                fprintf(stderr, "%s", mess_ret.error_text);
            }
        } else {
            fprintf(stderr, "Server failed to respond\n");
        }
    } else {
        fprintf(stderr, "Server not accepting requests\n");
    }
    return(0);
}


// This function looks more complicated than it is because it calls three pipe functions
// that we'll be looking at in the next section, send_mess_to_server, start_resp_from_server
// and read_resp_from_server.

cdc_entry search_cdc_entry(const char *cd_catalog_ptr, int *first_call_ptr)
{
    message_db_t mess_send;
    message_db_t mess_ret;
    
    static FILE *work_file = (FILE *)0;
    static int entries_matching = 0;
    cdc_entry ret_val;

    ret_val.catalog[0] = '\0';

    if (!work_file && (*first_call_ptr == 0)) return(ret_val);

// Here's the first call to search, i.e. with *first_call_ptr set to true.
// It's set to false immediately, lest we forget. A work_file is created and the client
// message structure initialized.

    if (*first_call_ptr) {
        *first_call_ptr = 0;
        if (work_file) fclose(work_file);
        work_file = tmpfile();
        if (!work_file) return(ret_val);

        mess_send.client_pid = mypid;
        mess_send.request = s_find_cdc_entry;
        strcpy(mess_send.cdc_entry_data.catalog, cd_catalog_ptr);

// Now there's this three-deep condition test, which makes calls to functions in pipe_imp.c.
// If the message is successfully sent to the server, the client waits for the server's response.
// While reads from the server are successful, the search matches are returned to the client's
// work_file and the entries_matching counter is incremented.

        if (send_mess_to_server(mess_send)) {
            if (start_resp_from_server()) {
                while (read_resp_from_server(&mess_ret)) {
                    if (mess_ret.response == r_success) {
               fwrite(&mess_ret.cdc_entry_data, sizeof(cdc_entry), 1, work_file);
                        entries_matching++;
                    } else {
                        break;
                    }
                } /* while */
            } else {
                fprintf(stderr, "Server not responding\n");
            }
        } else {
            fprintf(stderr, "Server not accepting requests\n");
        }

// The next test checks whether the search had any luck.
// Then the fseek call sets the work_file to the next place for data to be written.

        if (entries_matching == 0) {
            fclose(work_file);
            work_file = (FILE *)0;
            return(ret_val);
        }      
        (void)fseek(work_file, 0L, SEEK_SET);

// If this is not the first call to the search function with this particular search term,
// the code checks whether there are any matches left. Finally, the next matching entry is
// read to the ret_val structure. The previous checks guarantee that a matching entry exists.

    } else {
            /* not *first_call_ptr */
        if (entries_matching == 0) {
            fclose(work_file);
            work_file = (FILE *)0;            
            return(ret_val);
        }
    }

    fread(&ret_val, sizeof(cdc_entry), 1, work_file);    
    entries_matching--;
    
    return(ret_val);
}