我想實作的目標：一個客戶端知道托管完全相同檔案的不同服務器的多個 IP 地址。
客戶端應該能夠接收有關托管在服務器上的檔案/檔案夾的資訊（權限、大小等）。我被卡住了，因為我將緩沖區從 char* 移動到 struct 以控制損壞的資料包。現在我的客戶端沒有使用 send() 函式到達服務器。
它與 sendto 和 recvfrom 完美配合，但據我所知，它們不能用于結構，只能用于 char* 緩沖區。
謝謝！
服務器.c
// Server side implementation of UDP client-server model
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/stat.h> //Used to get file metadata
#include <time.h> //Used to format time-based metadata
#include <dirent.h> //User to list directory's content
#define PORT 8080
#define MAXLINE 65527 // 65535 is MAX and other 8 bytes are reserved for header
struct SPacket {
int len;
char msg[MAXLINE - sizeof(int)];
};
void GetFileMetadata(const char* szPath, char* Out)
{
if (access(szPath, F_OK) != 0 )
snprintf(Out, MAXLINE, "%s", szPath);
else
{
struct stat res;
stat(szPath, &res);
int length = 0;
length = snprintf(Out length, MAXLINE, "Filename:\t\t%s\n", szPath);
length = snprintf(Out length, MAXLINE, "Filesize:\t\t%d\n", res.st_size);
length = snprintf(Out length, MAXLINE, "Permissions:\t\t");
length = snprintf(Out length, MAXLINE, (S_ISDIR(res.st_mode)) ? "d" : "-");
length = snprintf(Out length, MAXLINE, (res.st_mode & S_IRUSR) ? "r" : "-");
length = snprintf(Out length, MAXLINE, (res.st_mode & S_IWUSR) ? "w" : "-");
length = snprintf(Out length, MAXLINE, (res.st_mode & S_IXUSR) ? "x" : "-");
length = snprintf(Out length, MAXLINE, (res.st_mode & S_IRGRP) ? "r" : "-");
length = snprintf(Out length, MAXLINE, (res.st_mode & S_IWGRP) ? "w" : "-");
length = snprintf(Out length, MAXLINE, (res.st_mode & S_IXGRP) ? "x" : "-");
length = snprintf(Out length, MAXLINE, (res.st_mode & S_IROTH) ? "r" : "-");
length = snprintf(Out length, MAXLINE, (res.st_mode & S_IWOTH) ? "w" : "-");
length = snprintf(Out length, MAXLINE, (res.st_mode & S_IXOTH) ? "x\n" : "-\n");
length = snprintf(Out length, MAXLINE, "Owner:\t\t\t%d\n", res.st_gid);
length = snprintf(Out length, MAXLINE, "Last status change:\t%s", ctime(&res.st_ctime));
length = snprintf(Out length, MAXLINE, "Last file access:\t%s", ctime(&res.st_atime));
length = snprintf(Out length, MAXLINE, "Last file modification:\t%s", ctime(&res.st_mtime));
DIR *d;
struct dirent *dir;
d = opendir(szPath);
if (d != NULL)
{
length = snprintf(Out length, MAXLINE, "Content of %s:\t", szPath);
while ((dir = readdir(d)) != NULL)
{
length = snprintf(Out length, MAXLINE, "%s\t", dir->d_name);
}
closedir(d);
}
length = snprintf(Out length, MAXLINE, "\n");
}
}
int main()
{
int sockfd;
struct SPacket toSend, toRecv;
struct sockaddr_in servaddr, cliaddr;
// Creating socket file descriptor
if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 )
{
perror("socket creation failed");
exit(EXIT_FAILURE);
}
memset(&servaddr, 0, sizeof(servaddr));
memset(&cliaddr, 0, sizeof(cliaddr));
// Filling server information
servaddr.sin_family = AF_INET; // IPv4
servaddr.sin_addr.s_addr = INADDR_ANY;
servaddr.sin_port = htons(PORT);
// Bind the socket with the server address
if (bind(sockfd, (const struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
{
perror("bind failed");
exit(EXIT_FAILURE);
}
int len, n;
len = sizeof(cliaddr); //len is value/resuslt
while(1)
{
n = recv(sockfd, &toRecv, sizeof(toRecv), 0);
toRecv.msg[n] = '\0';
// printf("[DEBUG] Client request: %s\n", InMsg);
GetFileMetadata(toRecv.msg, toSend.msg);
// printf("[DEBUG] Server answer: %s (len = %d)\n", OutMsg, strlen(OutMsg));
send(sockfd, &toSend, sizeof(toSend), 0);
memset(&toRecv, 0, MAXLINE); //We're preparing buffer for next request
memset(&toSend, 0, MAXLINE); //We're preparing buffer for next request
}
return 0;
}
客戶端
// Client side implementation of UDP client-server model
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdbool.h> //So retarded, need this for bool functions because we compile with C99 standard
#define PORT 8080
#define MAXLINE 65527 // 65535 is MAX and other 8 bytes are reserved for header
struct SPacket {
int len;
char msg[MAXLINE - sizeof(int)];
};
bool isValidIpAddress(char *ipAddress)
{
struct sockaddr_in sa;
int result = inet_pton(AF_INET, ipAddress, &(sa.sin_addr)); //Convert IP address from string to binary
return result != 0;
}
bool ReadIPsList(char** iplist, int maxLines, int maxLen, int* ipCount)
{
FILE *fp = fopen("Servers.txt", "r");
size_t len = 255;
char *line = malloc(sizeof(char) * len);
if (fp == NULL)
{
printf("Can't open file Servers.txt!\n");
return false;
}
while(fgets(line, len, fp) != NULL)
{
line[strlen(line)-1]='\0'; //Remove newline
if (*ipCount < maxLines && strlen(line) < maxLen && isValidIpAddress(line))
{
iplist[*ipCount] = (char *)malloc(16);
strncpy(iplist[*ipCount], line, maxLen);
printf("\"%s\" added to IP list\n", iplist[*ipCount]);
}
else
{
printf("Invalid IP address (%s), line (%d).\n", line, *ipCount);
return false;
}
(*ipCount) = 1;
}
if (*ipCount == 0)
{
printf("Servers.txt is empty ?!?\n");
return false;
}
fclose(fp);
free(line);
printf("\n");
return true;
}
bool AskAppendNewServer(char** iplist, int maxLines, int maxLen, int* ipCount)
{
printf("Do you want to add a new server? (Y/N)\n");
char ans = getchar();
if (ans == 'y' || ans == 'Y')
{
if (*ipCount >= maxLines)
{
printf("ERROR! Maximum number of IP addresses has been reached!\n");
return false;
}
FILE *fp = fopen("Servers.txt", "a");
if (fp == NULL)
{
printf("Can't open file Servers.txt!\n");
return false;
}
bool is_ok = false;
char IP[16 1];
do {
printf("\nEnter IP address: ");
scanf("%s", IP);
if (isValidIpAddress(IP))
{
is_ok = true;
fprintf(fp, "%s\n", IP);
iplist[*ipCount] = (char *)malloc(16);
strncpy(iplist[*ipCount], IP, maxLen);
printf("\"%s\" added to IP list\n", iplist[*ipCount]);
}
else
printf("ERROR! %s is not a valid IP address!", IP);
} while (is_ok != true);
fclose(fp);
(*ipCount) = 1;
return true;
}
return false;
}
int main()
{
int sockfd, ipCount = 0, selIp = 0;
struct SPacket toSend, toRecv;
struct sockaddr_in servaddr;
char* ipList[255];
if (ReadIPsList(ipList, 255, 16, &ipCount) == 0)
return -1;
// Creating socket file descriptor
if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
memset(&servaddr, 0, sizeof(servaddr));
// Filling server information
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(PORT);
servaddr.sin_addr.s_addr = inet_addr(ipList[selIp]); //Trying 1st server then we move to a new one if this become unavailable
int n, len;
//If we don't receive any answer in less than 1 second then is a problem..
struct timeval tv;
tv.tv_sec = 0;
tv.tv_usec = 100000;
if (setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO,&tv,sizeof(tv)) < 0) {
perror("Error");
}
connect(sockfd, (const struct sockaddr *) &servaddr, sizeof(servaddr));
while(1)
{
char c;
while((c= getchar()) != '\n' && c != EOF); // Remove any unwanted character from stdin (scanf from AskAppendNewServer created this issue)
printf("Enter filename:\t");
fgets(toSend.msg, MAXLINE, stdin);
toSend.msg[strcspn(toSend.msg, "\n")] = '\0'; //Remove newline
toSend.len = strlen(toSend.msg);
if (strlen(toSend.msg) == 0)
continue;
send(sockfd, &toSend, sizeof(toSend), 0);
if (n = recv(sockfd, &toRecv, sizeof(toRecv), 0) > 0)
{
if (strcmp(toSend.msg, toRecv.msg) == 0) // Yep, this file does not exists on host.
{
if (AskAppendNewServer(ipList, 255, 16, &ipCount) == true)
{
selIp = ipCount - 1; //We append always at the end of the array
printf("Server (%s) has been added successfully. Now you can send your request from it.\n", ipList[selIp]);
servaddr.sin_addr.s_addr = inet_addr(ipList[selIp]);
}
}
else
printf("%s\n", toRecv.msg);
// printf("[DEBUG] Received msg len: %d\n", strlen(toRecv.msg));
}
else
{
int counter = 1, foundValidServer = 0;
while (counter < ipCount && foundValidServer == 0)
{
printf("Timeout reached :: server (%s) not available, trying next server available (%s)\n", ipList[selIp], ipList[(selIp 1) % ipCount]);
counter = 1;
selIp = (selIp 1) % ipCount;
servaddr.sin_addr.s_addr = inet_addr(ipList[selIp]); // Try next available server
sendto(sockfd, (const char *)toSend.msg, strlen(toSend.msg), MSG_CONFIRM, (const struct sockaddr *) &servaddr, sizeof(servaddr));
if (n = recvfrom(sockfd, (char *)toRecv.msg, MAXLINE, MSG_WAITALL, (struct sockaddr *) &servaddr, &len) > 0)
{
if (strcmp(toSend.msg, toRecv.msg) == 0)
AskAppendNewServer(ipList, 255, 16, &ipCount);
else
printf("%s\n", toRecv.msg);
foundValidServer = 1;
}
}
}
memset(&toSend.msg, 0, MAXLINE); //We're preparing buffer for next request
memset(&toRecv.msg, 0, MAXLINE); //We're preparing buffer for next request
}
free(ipList); //No memory leaks, please.
close(sockfd);
return 0;
}
uj5u.com熱心網友回復：
它不適用于 struct ，因為它不是故意的。您需要在單獨的引數中提供指向 char 緩沖區（而不是緩沖區本身）的指標和緩沖區的長度。請參閱此recv()檔案。
如果您想要使用套接字發送結構體資料，請嘗試在緩沖區中創建字串表示形式，然后在接收時對其進行決議。
uj5u.com熱心網友回復：
我的英語不是很好，所以請理解。
sendto() 和 recvfrom() 可以使用結構體資料。因為 sendto() 訊息型別是 const void* 而 recvfrom() 緩沖區型別是 void*。請參閱此 sendto() 檔案和此 recvfrom() 檔案。
發送至（）
sendto(sockfd, &toSend, sizeof(toSend), MSG_CONFIRM, (const struct sockaddr *) &servaddr, sizeof(servaddr));
接收（）
recvfrom(sockfd, &toRecv, sizeof(toRecv), MSG_WAITALL, (struct sockaddr *) &servaddr, &len);
如果recv資料損壞，請看下面的代碼。
char buf[sizeof(toRecv)];
memset(buf, 0x00, sizeof(buf));
recvfrom(sockfd, buf, sizeof(buf), MSG_WAITALL, (struct sockaddr *) &servaddr, &len);
memcpy(&toRecv, buf, sizeof(toRecv));
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