为什么我在用C编写的tcp客户端/服务器中没有正确接收非纯文本文件？

Question

我写了一个客户端/服务器程序，客户端将文件发送到服务器。

这里是代码：

macro.h

#ifndef MACRO_H
#define MACRO_H

#include <stdio.h>
#include <errno.h>
#include <stdint.h>


#define SERV_PORT 49312
#define MAXLINE   1400

#define END_FLAG "================END"

#define abort_on_error(cond, msg) do {                                          \
if (cond) {                                                                 \
    fprintf(stderr, "%s (errno=%d [%s])\n", msg, errno, strerror(errno));   \
    exit(EXIT_FAILURE);                                                     \
}                                                                           \
} while (0)

struct pkt {
    uint32_t seq_num;
    uint32_t status;
    uint8_t data[MAXLINE];
};

typedef struct pkt PACK;

#endif // MACRO_H

我需要struct pkt在未来的项目中发送它。

client.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <fcntl.h>

#include "macro.h"

int main(int argc, char **argv)
{
int sockfd, n, count = 0;
struct sockaddr_in servaddr;
// char buf[MAXLINE];
char *target, *path;
FILE *file;
PACK packet;
long filesize;

bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(SERV_PORT);
inet_pton(AF_INET, argv[1], &servaddr.sin_addr);

sockfd = socket(AF_INET, SOCK_STREAM, 0);

abort_on_error(connect(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0,
                "Error connect()");

path = argv[2];
target = argv[3];

packet.seq_num = 0;
packet.status = 0;
memset(packet.data, 0, sizeof(packet.data));
memcpy(packet.data, target, strlen(target));

abort_on_error(sendto(sockfd, (struct pkt *) &packet, sizeof(packet), 0, (struct sockaddr *) &servaddr, sizeof(servaddr)) == -1,
                "sendto() filename error");

memset(packet.data, 0, sizeof(packet.data));
abort_on_error(recvfrom(sockfd, &packet, sizeof(packet), 0, NULL, NULL) == -1, "recvfrom() ok error");
if (!strncmp((const char *) packet.data, "ok", 2)) {
    printf("Filename sent.\n");
}

file = fopen(path, "r");
abort_on_error(file == NULL, "fopen() error");

fseek(file, 0L, SEEK_END);
filesize = ftell(file);
printf("filesize: %ld\n", filesize);
fseek(file, 0L, SEEK_SET);
memset(packet.data, 0, sizeof(packet.data));
sprintf((char *) packet.data, "%ld", filesize);

abort_on_error(sendto(sockfd, (struct pkt *) &packet, sizeof(packet), 0, (struct sockaddr *) &servaddr, sizeof(servaddr)) == -1,
                    "sendto() data error");

memset(packet.data, 0, sizeof(packet.data));

while ((n = fread(packet.data, sizeof(char), MAXLINE, file))) {
    abort_on_error(ferror(file), "fread() error");
    abort_on_error(sendto(sockfd, (struct pkt *) &packet, sizeof(packet), 0, (struct sockaddr *) &servaddr, sizeof(servaddr)) == -1,
                    "sendto() data error");
    count = count + n;
    memset(packet.data, 0, sizeof(packet.data));
}
printf("Tot Bytes sent: %d\n", count);

memset(packet.data, 0, sizeof(packet.data));
memcpy(packet.data, END_FLAG, strlen(END_FLAG));
abort_on_error(sendto(sockfd, (struct pkt *) &packet, sizeof(packet), 0, (struct sockaddr *) &servaddr, sizeof(servaddr)) == -1,
                "sendto() end_flag error");

fclose(file);
return 0;
}

客户端将文件的文件名发送到服务器，等待服务器的响应，将文件大小发送到服务器并发送文件。

server.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#include "macro.h"

void run(int sockfd, struct sockaddr *cliaddr, socklen_t clilen)
{
int n = 0, count = 0, status = 0;
socklen_t len;
// char buf[MAXLINE*MUL];
FILE *file;
PACK packet;

len = clilen;
n = recvfrom(sockfd, &packet, sizeof(packet), 0, cliaddr, &len);
abort_on_error(n == -1, "recvfrom() filename error");
// buf[n] = 0;
printf("Received from client: [%s]\n", packet.data);

file = fopen((const char *) packet.data, "w+");
abort_on_error(file == NULL, "fopen() error");

// abort_on_error(setvbuf(file, buf, _IOFBF, MAXLINE*MUL), "setvbuf() error");

packet.seq_num = 0;
packet.status = 0;
memset(packet.data, 0, sizeof(packet.data));
memcpy(packet.data, "ok", strlen("ok"));
abort_on_error(sendto(sockfd, (struct pkt *) &packet, sizeof(packet), 0, cliaddr, len) == -1,
                "sendto() ok error");

memset(packet.data, 0, sizeof(packet.data));
abort_on_error(recvfrom(sockfd, &packet, sizeof(packet), 0, cliaddr, &len) == -1,
                "recvfrom() error");
long filesize = strtol((const char *) packet.data, NULL, 0);
printf("filesize: %ld\n", filesize);

while ((n = recvfrom(sockfd, &packet, sizeof(packet), 0, cliaddr, &len))) {
    abort_on_error(n == -1, "recvfrom() data error");

    if (!(strcmp((const char *) packet.data, END_FLAG))) {
        break;
    }

    int num_packet = filesize / n;
    int packet_header_size = sizeof(packet) - sizeof(packet.data);
    // printf("num_packet: %d\n", num_packet);

    count += n;
    if(!num_packet){
        fwrite(packet.data, sizeof(char), filesize, file);
        // printf("byte to write: %ld\n", filesize);
    }
    else {
        if(count <= filesize) {
            fwrite(packet.data, sizeof(char), n-packet_header_size, file);
            // printf("byte to write: %ld\n", n-packet_header_size);
        }
        else if ((count > filesize) && (filesize-num_packet*(n-packet_header_size)) &&!status) {
            fwrite(packet.data, sizeof(char), filesize-num_packet*(n-packet_header_size), file);
            // printf("byte to write: %ld\n", filesize-num_packet*(n-packet_header_size));
            status = 1;
        }
    }
}
printf("Tot Bytes received: %d\n", count);
fclose(file);
}

int main(int argc, char **argv)
{
int sockfd, newsockfd;
struct sockaddr_in servaddr, cliaddr;

sockfd = socket(AF_INET, SOCK_STREAM, 0);
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
servaddr.sin_port = htons(SERV_PORT);

bind(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr));

listen(sockfd, 5);

int clilen = sizeof(cliaddr);
newsockfd = accept(sockfd, (struct sockaddr *) &cliaddr, (unsigned int *) &clilen);

abort_on_error(newsockfd == -1, "Error accept()");

run(newsockfd, (struct sockaddr *) &cliaddr, sizeof(cliaddr));

return 0;
}

在while循环中，ifs用于正确处理文件的文件大小。

它适用于纯文本文件，但对于其他文件（大文件，例如jpg，zip，iso），它会丢失一些字节而且它不起作用！ 我无法理解为什么!!!？

Answer 1

当您使用非明文（也就是二进制数据）时，您需要更改打开文件的方式。

您目前正在执行此操作：

 file = fopen(path, "r");

相反，改为：

 file = fopen(path, "rb");

显然，你需要使用"rb"打开写作。如果您不这样做，您将无法正确读取某些字符（例如，空值）。

Answer 2

现在一切正常。我在 server.c 中的while循环中弄乱了ifs。

client.c ：

int main(int argc, char **argv)
{
int sockfd, n, sent;
long count = 0;
struct sockaddr_in servaddr;
// char buf[MAXLINE];
char *target, *path;
FILE *file;
PACK packet;
long filesize;

bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(SERV_PORT);
inet_pton(AF_INET, argv[1], &servaddr.sin_addr);

sockfd = socket(AF_INET, SOCK_STREAM, 0);

abort_on_error(connect(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0,
                "Error connect()");

path = argv[2];
target = argv[3];

packet.seq_num = 0;
packet.status = 0;
memset(packet.data, 0, sizeof(packet.data));
memcpy(packet.data, target, strlen(target));

abort_on_error(sendto(sockfd, (struct pkt *) &packet, sizeof(packet), 0, (struct sockaddr *) &servaddr, sizeof(servaddr)) == -1,
                "sendto() filename error");

memset(packet.data, 0, sizeof(packet.data));
abort_on_error(recvfrom(sockfd, &packet, sizeof(packet), 0, NULL, NULL) == -1, "recvfrom() ok error");
if (!strncmp((const char *) packet.data, "ok", 2)) {
    printf("Filename sent.\n");
}

file = fopen(path, "r");
abort_on_error(file == NULL, "fopen() error");

fseek(file, 0L, SEEK_END);
filesize = ftell(file);
printf("filesize: %ld\n", filesize);
fseek(file, 0L, SEEK_SET);
memset(packet.data, 0, sizeof(packet.data));
sprintf((char *) packet.data, "%ld", filesize);

abort_on_error(sendto(sockfd, (struct pkt *) &packet, sizeof(packet), 0, (struct sockaddr *) &servaddr, sizeof(servaddr)) == -1,
                    "sendto() data error");

memset(packet.data, 0, sizeof(packet.data));

while ((n = fread(packet.data, sizeof(char), MAXLINE, file))) {
    abort_on_error(ferror(file), "fread() error");
    abort_on_error((sent = sendto(sockfd, (struct pkt *) &packet, sizeof(packet), 0, (struct sockaddr *) &servaddr, sizeof(servaddr))) == -1,
                    "sendto() data error");

    count += sent;
    printf("Bytes sent: %d\n", sent);
    memset(packet.data, 0, sizeof(packet.data));
}
printf("Tot Bytes sent: %ld\n", count);

memset(packet.data, 0, sizeof(packet.data));
memcpy(packet.data, END_FLAG, strlen(END_FLAG));
abort_on_error(sendto(sockfd, (struct pkt *) &packet, sizeof(packet), 0, (struct sockaddr *) &servaddr, sizeof(servaddr)) == -1,
                "sendto() end_flag error");

fclose(file);
return 0;
}

server.c上的 run（）功能：

void run(int sockfd, struct sockaddr *cliaddr, socklen_t clilen)
{
int n = 0, count = 0, w = 0;
long received = 0, writed = 0;
socklen_t len;
// char buf[MAXLINE];
FILE *file;
PACK packet;

len = clilen;
n = recvfrom(sockfd, &packet, sizeof(packet), 0, cliaddr, &len);
abort_on_error(n == -1, "recvfrom() filename error");
// buf[n] = 0;
printf("Received from client: [%s]\n", packet.data);

file = fopen((const char *) packet.data, "w+");
abort_on_error(file == NULL, "fopen() error");

// abort_on_error(setvbuf(file, buf, _IOFBF, MAXLINE*MUL), "setvbuf() error");

packet.seq_num = 0;
packet.status = 0;
memset(packet.data, 0, sizeof(packet.data));
memcpy(packet.data, "ok", strlen("ok"));
abort_on_error(sendto(sockfd, (struct pkt *) &packet, sizeof(packet), 0, cliaddr, len) == -1,
                "sendto() ok error");

memset(packet.data, 0, sizeof(packet.data));
abort_on_error(recvfrom(sockfd, &packet, sizeof(packet), 0, cliaddr, &len) == -1,
                "recvfrom() error");
long filesize = strtol((const char *) packet.data, NULL, 0);
printf("filesize: %ld\n", filesize);

int num_packet = filesize / sizeof(packet.data);
int packet_header_size = sizeof(packet) - sizeof(packet.data);
int last_size = filesize-num_packet*(n-packet_header_size);

while ((n = recvfrom(sockfd, &packet, sizeof(packet), 0, cliaddr, &len))) {
    abort_on_error(n == -1, "recvfrom() data error");

    if (!(strcmp((const char *) packet.data, END_FLAG))) {
        printf("END_FLAG received. Stopping receiving data.\n");
        break;
    }

    received += n;
    count += 1;
    // memset(buf, (int) packet.data, sizeof(packet.data));
    printf("Bytes received: %d\n", n);

    // printf("num_packet: %d\n", num_packet);

    if (!num_packet) {
        printf("byte to write: %ld\n", filesize);
        w = fwrite(packet.data, sizeof(char), filesize, file);
        printf("byte writed: %d\n", w);
        writed += w;
    }
    else {
        if (count <= num_packet) {
            printf("byte to write: %d\n", n-packet_header_size);
            w = fwrite(packet.data, sizeof(char), n-packet_header_size, file);
            printf("byte writed: %d\n", w);
            writed += w;
        }
        else {
            printf("byte to write: %d\n", last_size);
            w = fwrite(packet.data, sizeof(char), last_size, file);
            printf("byte writed: %d\n", w);
            writed += w;
        }
    }
}
printf("Tot Bytes writed: %ld\n", writed);
printf("Tot Bytes received: %ld\n", received);
fclose(file);
}

其他代码（ macro.h 和 server.c ）是相同的。