我正在开发一个项目，需要将字符串转换为二进制格式并对二进制数据实施循环冗余校验（crc）。数据需要通过客户端-服务器通信进行传输。我需要提供两个文件 city.txt 和 Country.txt，这两个文件的数据需要首先转换为二进制并在其上实现 crc，然后将这些文件发送到服务器，服务器删除 crc 并将其再次更改回字符串，将其发送给客户。所有这些功能对于我通过网络发送的第一个文件（city.txt）运行良好，但对于第二个文件则不起作用。
客户端代码是
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#define SIZE 1024
// Function to run the CRC service and generate the CRC file
void runCRCService(const char *inputFile, const char *outputFile) {
pid_t pid = fork();
if (pid < 0) {
perror("[-]Error in fork");
exit(1);
} else if (pid == 0) {
FILE *fp = fopen(outputFile, "w");
if (!fp) {
perror("[-]Error in opening output file");
exit(1);
}
dup2(fileno(fp), STDOUT_FILENO);
fclose(fp);
execlp("./crcservice_v2", "./crcservice_v2", inputFile, NULL);
perror("[-]Error in execlp for CRC service");
exit(1);
} else {
wait(NULL);
}
}
// Function to receive a file from the server
void write_file(int sockfd, const char *filename) {
FILE *fp = fopen(filename, "w");
if (fp == NULL) {
perror("[-]Error in opening file");
exit(1);
}
char buffer[SIZE] = {0};
int n;
while (1) {
n = recv(sockfd, buffer, SIZE, 0);
if (n <= 0) break;
if (strncmp(buffer, "FILE_END", 8) == 0) break;
fwrite(buffer, 1, n, fp);
memset(buffer, 0, SIZE);
}
fclose(fp);
}
void send_file(FILE *fp, int sockfd) {
char data[SIZE] = {0};
int bytes_read, bytes_sent, total_sent = 0;
while ((bytes_read = fread(data, 1, SIZE, fp)) > 0) {
total_sent = 0;
while (total_sent < bytes_read) {
bytes_sent = send(sockfd, data + total_sent, bytes_read - total_sent, 0);
if (bytes_sent == -1) {
perror("[-]Error in sending file");
exit(1);
}
total_sent += bytes_sent;
}
bzero(data, SIZE);
}
// Send "FILE_END" delimiter
send(sockfd, "FILE_END", 8, 0);
}
int main() {
char *ip = "127.0.0.1";
int port = 8080;
int sockfd, e;
struct sockaddr_in server_addr;
FILE *fp;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) {
perror("[-]Error in socket");
exit(1);
}
printf("[+]Server socket created successfully.\n");
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(port);
server_addr.sin_addr.s_addr = inet_addr(ip);
e = connect(sockfd, (struct sockaddr*)&server_addr, sizeof(server_addr));
if (e == -1) {
perror("[-]Error in connecting to server");
exit(1);
}
printf("[+]Connected to Server.\n");
// Generate CRC for city.txt and store it in citycrc.txt
printf("[+]Generating CRC for city.txt\n");
runCRCService("city.txt", "citycrc.txt");
sleep(1);
// Generate CRC for country.txt and store it in countrycrc.txt
printf("[+]Generating CRC for country.txt\n");
runCRCService("country.txt", "countrycrc.txt");
// Send citycrc.txt to the server
fp = fopen("citycrc.txt", "r");
if (fp == NULL) {
perror("[-]Error in reading citycrc.txt");
exit(1);
}
printf("[+]Sending citycrc.txt to the server\n");
send_file(fp, sockfd);
fclose(fp);
printf("[+]citycrc.txt sent successfully.\n");
sleep(1);
// Send countrycrc.txt to the server
fp = fopen("countrycrc.txt", "r");
if (fp == NULL) {
perror("[-]Error in reading countrycrc.txt");
exit(1);
}
printf("[+]Sending countrycrc.txt to the server\n");
send_file(fp, sockfd);
fclose(fp);
printf("[+]countrycrc.txt sent successfully.\n");
sleep(1);
// Receive crcascii.txt from the server
printf("[+]Receiving crcasciicity.txt from the server\n");
write_file(sockfd, "crcasciicity.txt");
printf("[+]crcasciicity.txt received successfully.\n");
sleep(1);
printf("[+]Receiving crcasciicountry.txt from the server\n");
write_file(sockfd, "crcasciicountry.txt");
printf("[+]crcasciicountry.txt received successfully.\n");
// Close the connection
close(sockfd);
printf("[+]Connection closed.\n");
return 0;
}
服务器端代码：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#define SIZE 1024
// Function to receive a file from the client
void write_file(int sockfd, const char *filename) {
FILE *fp = fopen(filename, "w");
if (fp == NULL) {
perror("[-]Error in opening file");
exit(1);
}
char buffer[SIZE];
int n;
while (1) {
n = recv(sockfd, buffer, SIZE, 0);
if (n <= 0) break;
// Check for "FILE_END" delimiter
if (strncmp(buffer, "FILE_END", 8) == 0) break;
fwrite(buffer, 1, n, fp);
memset(buffer, 0, SIZE);
}
fclose(fp);
fsync(fileno(fp));
}
void send_file(int sockfd, const char *filename) {
FILE *fp = fopen(filename, "r");
if (fp == NULL) {
perror("[-]Error in opening file");
exit(1);
}
char data[SIZE] = {0};
int bytes_read;
while ((bytes_read = fread(data, 1, SIZE, fp)) > 0) {
if (send(sockfd, data, bytes_read, 0) == -1) {
perror("[-]Error in sending file");
exit(1);
}
memset(data, 0, SIZE);
}
// Send "FILE_END" delimiter
send(sockfd, "FILE_END", 8, 0);
fclose(fp);
}
// Function to extract, flip MSB, convert to ASCII, and save to ASCII file
void extract_flip_and_save_ascii(const char *inputFile, const char *outputFile) {
FILE *fp = fopen(inputFile, "r");
if (fp == NULL) {
perror("[-]Error in opening input file");
return;
}
char buffer[SIZE * 8] = {0};
int bitCount = 0;
char ch;
while ((ch = fgetc(fp)) != EOF) {
if (ch == '0' || ch == '1') {
buffer[bitCount++] = ch;
}
}
buffer[bitCount] = '\0';
fclose(fp);
int totalBits = strlen(buffer);
if (totalBits <= 54) {
printf("[-]Error: Not enough bits to extract data part.\n");
return;
}
int dataStart = 24;
int dataEnd = totalBits - 31;
FILE *output_fp = fopen(outputFile, "w");
if (output_fp == NULL) {
perror("[-]Error in opening output file");
return;
}
for (int i = dataStart; i < dataEnd; i += 8) {
if (i + 7 < dataEnd) {
buffer[i] = (buffer[i] == '0') ? '1' : '0';
int asciiValue = 0;
for (int j = 0; j < 8; j++) {
asciiValue = (asciiValue << 1) | (buffer[i + j] - '0');
}
fputc(asciiValue, output_fp);
}
}
fclose(output_fp);
}
int main() {
char *ip = "127.0.0.1";
int port = 8080;
int sockfd, new_sock;
struct sockaddr_in server_addr, new_addr;
socklen_t addr_size;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) {
perror("[-]Error in socket");
exit(1);
}
printf("[+]Server socket created successfully.\n");
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(port);
server_addr.sin_addr.s_addr = inet_addr(ip);
if (bind(sockfd, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0) {
perror("[-]Error in bind");
exit(1);
}
printf("[+]Binding successful.\n");
if (listen(sockfd, 10) == 0) {
printf("[+]Listening...\n");
} else {
perror("[-]Error in listening");
exit(1);
}
addr_size = sizeof(new_addr);
new_sock = accept(sockfd, (struct sockaddr*)&new_addr, &addr_size);
if (new_sock < 0) {
perror("[-]Error in accepting connection");
exit(1);
}
printf("[+]Connection accepted.\n");
// Receive citycrc.txt from the client
write_file(new_sock, "citycrc.txt");
printf("[+]citycrc.txt received successfully.\n");
// Receive countrycrc.txt from the client
write_file(new_sock, "countrycrc.txt");
printf("[+]countrycrc.txt received successfully.\n");
// Generate crcasciicity.txt from citycrc.txt
extract_flip_and_save_ascii("citycrc.txt", "crcasciicity.txt");
printf("[+]crcasciicity.txt generated successfully.\n");
// Send crcasciicity.txt to the client
printf("[+]Sending crcasciicity.txt to the client.\n");
send_file(new_sock, "crcasciicity.txt");
printf("[+]crcasciicity.txt sent successfully.\n");
sleep(1);
// Generate crcasciicountry.txt from countrycrc.txt
extract_flip_and_save_ascii("countrycrc.txt", "crcasciicountry.txt");
printf("[+]crcasciicountry.txt generated successfully.\n");
// Send crcasciicountry.txt to the client
printf("[+]Sending crcasciicountry.txt to the client.\n");
send_file(new_sock, "crcasciicountry.txt");
printf("[+]crcasciicountry.txt sent successfully.\n");
// Close the connection
close(new_sock);
close(sockfd);
printf("[+]Connection closed.\n");
return 0;
}
city.txt 包含克林顿、格林维尔等数据......
county.txt 有加拿大、巴西等数据...
citycrc.txt 保存 city.txt 文件的二进制表示形式，如“10”格式。
countrycrc.txt 保存country.txt 文件的二进制表示形式，如“10”格式。
cityasciicrc.txt 以 citycrc.txt 作为输入，对其进行 extract_flip_save_ascii() 操作并返回 Clinton、Greenvile。 Countryasciicrc.txt 将countrycrc.txt 作为输入，对其进行extract_flip_save_ascii() 操作并返回加拿大、巴西。
上述代码的问题是当我运行服务器可执行文件时它首先执行
Server socket created successfully
Binding successful.
Listening ...
客户端可执行文件：
[+]Server socket created successfully.
[+]Connected to Server.
[+]Generating CRC for city.txt
[+]Generating CRC for country.txt
[+]Sending citycrc.txt to the server
[+]citycrc.txt sent successfully.
[+]Sending countrycrc.txt to the server
[+]countrycrc.txt sent successfully.
[+]Receiving crcasciicity.txt from the server
然后停止执行。在这种情况下，如果我从工作目录打开 citycrc.txt 和 Countrycrc.txt，我可以看到正确生成的二进制结果。那么他们的crcservice_v2就没有问题了。我等待了 5/6 分钟代码完全执行，然后我按 ctrl+c 终止了客户端的代码。
现在，如果我检查countrycrc.txt，我发现它是空的。我还发现有时（当我重复运行处理后）会生成 crcasciicountry.txt 但是一个空文件。有时crcasciicountry.txt没有生成，有时crcasciicity.txt实际上同时具有city.txt和country.txt的内容。如果我收到 crcasciicountry.txt 的空文件，则 crcasciicity 的输出是正确的，没有合并两个文件的内容。
我使用的是Ubuntu 20.04，一台电脑，两个终端，实现客户端服务器通信。
谢谢你。任何帮助将不胜感激。
您似乎对
read()为了能够将两个文件识别为单独的单元，您需要在原始字节流之上分层某种应用程序协议。 这可能就像在每个文件的数据前面放置一个字节计数一样简单，这样接收器就知道它已经通过读取了那么多（附加）字节而到达了该文件的末尾。 当然，更复杂的方案也是可能的。