在strcat()中编程segfaulting

Question

我正在尝试用C编写一个Web服务器,我的代码目前是segfaulting,我不知道为什么.它似乎与我的strcats有关,但就我能够得到的而言.我已经发布了代码和gdb输出.任何帮助是极大的赞赏.

*** 码 ***

    /*  web-server.c    */

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

    #define BUFLEN 1500
    #define BACKLOG 10

    static int server_socket(int port) {
int fd;
struct sockaddr_in servaddr;

if ((fd = socket(AF_INET, SOCK_STREAM, 0)) == -1){
    perror("Unable to create socket");
    return -1;
}
printf("created socket\n");
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = INADDR_ANY;
servaddr.sin_port = htons(port);

if (bind(fd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1) {
    perror("Unable to bind to port");
    return -1;
}
printf("binding completed\n");
if (listen(fd, BACKLOG) == -1){
    perror("Unable to listen for connections");
    return -1;
}
printf("socket setup\n");
return fd;

    }

    static char *html_request(char *request) {
char request_code[3], url[BUFLEN], http_code[BUFLEN];
printf(request);
printf("\n");
sscanf(request, "%3s %s %s", request_code, url, http_code);
return url;
    }


    int main() {
int connfd, servfd, rlen, i, eof;
int content_length = 0;
char buf[BUFLEN];
struct sockaddr_in saddr;
char *response;
char *read_buffer = malloc(1);
    char *response200 = "HTTP/1.1 200 OK\nContent-Type: text/html\nConnection: close\nConnection-Length: ";
char *response404 = "HTTP/1.1 404 Not Found\nContent-Type: text/html\nConnection: close\nConnection-Length: ";
FILE *in;
char buffer[1500], content_buffer[5];
char *headers = malloc(BUFLEN);
char *output = malloc(BUFLEN);
socklen_t saddr_len = sizeof(saddr);
servfd = server_socket(8080);
printf("before connection\n");
if ((connfd = accept(servfd, (struct sockaddr *)&saddr, &saddr_len)) == -1) {
    perror("Unable to accept connection");
    return -1;
}
else {
printf("Accept connection\n");

}
if ((rlen = read(connfd, buf, BUFLEN)) > 0) {
    realloc(read_buffer,rlen);
    for (i = 0; i < rlen; i++){
        printf("%c", buf[i]);
        read_buffer[i] = buf[i];
    }
    printf("\n");

}
printf("IMMA BEAST!\n");
response = html_request(read_buffer);
printf(response);

if (strcmp(response, "/index.html") == 0){
    printf("\nMatches!");
    in = fopen("index.txt", "r");
    if (in == NULL){
        printf("Read fail!");
    }
    while ((eof = fread(buffer, 1, 296, in )) > 0){
        content_length = content_length + 1;
    }
    snprintf(content_buffer, 5, "%d" ,content_length);
    headers = strcat(response200, content_buffer);
}
else{
    printf("\nFails!");
    in = fopen("index-error.txt", "r");
    if (in == NULL){
        printf("Read fail!");
    }
    while ((eof = fread(buffer, 1, 300, in )) > 0){
        content_length = content_length + 1;
    }
    snprintf(content_buffer, 5, "%d" ,content_length);
    headers = strcat(response404, content_buffer);
}
fclose(in);
output = strcat(headers, buffer);
write(connfd, output, BUFLEN);
close(connfd);
free(read_buffer);
free(headers);
free(output);

return 0;

}

*GDB输出*

Program received signal SIGSEGV, Segmentation fault.
0x0000003d4647eff0 in strcat () from /lib64/libc.so.6
(gdb) where
#0  0x0000003d4647eff0 in strcat () from /lib64/libc.so.6
#1  0x0000000000400ecd in main ()
(gdb) n
Single stepping until exit from function strcat,
which has no line number information.

Program terminated with signal SIGSEGV, Segmentation fault.
The program no longer exists.

Answer 1

这根本不行:

strcat("HTTP/1.1 404 Not Found\nContent-Type: text/html\nConnection: close\nConnection-Length: ", content_buffer);

strcat()将第二个参数附加到第一个参数.第一个参数是一个文字字符串,绝不能修改.C允许这种编译的唯一原因是遗漏的事实是旧代码依赖于文字字符串char[]而不是类型const char[].