读取系统调用返回垃圾并读取比写入系统调用在套接字中写入的次数更多

Question

我想实现一个 fork 并执行一个新进程的程序。然后，父进程将多次写入套接字，子进程（执行）将从套接字读取写入发送的全部数据。问题是有时当我运行程序时，子进程读取 4501 次或更多并打印垃圾，而父进程只写入 4500。 这不会一直发生，所以我怀疑某处可能有一个统一变量。

父进程：

#include <stdio.h>
#include <sys/wait.h>        
#include <sys/types.h>       
#include <sys/socket.h>      
#include <netinet/in.h>      
#include <netdb.h>           
#include <unistd.h>          
#include <stdlib.h>         
#include <ctype.h>           
#include <signal.h>
#include <string.h>

typedef char * String;

void perror_exit(char *message);


int getSocketWrite(int portWrite){
    struct hostent *remWrite;
    struct sockaddr *serverptrWrite = NULL;
    struct sockaddr_in serverWrite;
    int sockWrite;
    serverptrWrite = (struct sockaddr*)&serverWrite;

    if ((sockWrite = socket(AF_INET, SOCK_STREAM, 0)) < 0)
        perror_exit("socket");

    if (setsockopt(sockWrite, SOL_SOCKET, SO_REUSEADDR, &(int){1}, sizeof(int)) < 0)             //To reuse port if program exits.
        perror("setsockopt(SO_REUSEADDR) failed");


    char hostname[256];
    gethostname(hostname, 256);
    if ((remWrite = gethostbyname(hostname)) == NULL) { 
       herror("gethostbyname"); 
       exit(1);
    }
    serverWrite.sin_family = AF_INET;       
    memcpy(&serverWrite.sin_addr, remWrite->h_addr, remWrite->h_length);
    serverWrite.sin_port = htons(portWrite);    

    while (connect(sockWrite, serverptrWrite, sizeof(serverWrite)) < 0);
    return sockWrite;
}

void main(int argc, char *argv[]) {
    int             portWrite, sockWrite, i;
    int buffsize = 256;
    char            buf[buffsize];

    struct sockaddr_in serverWrite;
    struct sockaddr *serverptrWrite = NULL;
    struct hostent *remWrite = NULL;

    portWrite = 8080;

    pid_t pid = fork();
    if(pid == 0){
        execl("./server", "server");
        exit(1);
    }   
    else if(pid < 0){
        perror("error in fork");
    }
    
    sockWrite = getSocketWrite(portWrite);

    printf("Connecting to %s port %d\n", "Lenovo", portWrite);
    for(int i = 0; i < 4500; i++){
        memset(buf, 0, buffsize);
        strcpy(buf,"Test");
        write(sockWrite, buf, buffsize);
    }
    close(sockWrite);

}                

void perror_exit(char *message){
    perror(message);
    exit(EXIT_FAILURE);
}

server.c:

#include <stdio.h>
#include <sys/wait.h>        
#include <sys/types.h>       
#include <sys/socket.h>      
#include <netinet/in.h>      
#include <netdb.h>           
#include <unistd.h>          
#include <stdlib.h>         
#include <ctype.h>           
#include <signal.h>
#include <string.h>

typedef char * String;

void perror_exit(char *message);

int getSocketRead(int portRead){
    struct sockaddr_in serverRead;
    struct sockaddr *serverptrRead;
    int sockRead;
    serverptrRead = (struct sockaddr*)&serverRead;


    if ((sockRead = socket(AF_INET, SOCK_STREAM, 0)) < 0){
        perror("socket");
        exit(1);
    }
    if (setsockopt(sockRead, SOL_SOCKET, SO_REUSEADDR, &(int){1}, sizeof(int)) < 0)             //To reuse port if program exits.
        perror("setsockopt(SO_REUSEADDR) failed");


    serverRead.sin_family = AF_INET;       
    serverRead.sin_addr.s_addr = htonl(INADDR_ANY);
    serverRead.sin_port = htons(portRead);      
    if (bind(sockRead, serverptrRead, sizeof(serverRead)) < 0){
        perror("bind");
        exit(1);
    }

    if (listen(sockRead, 5) < 0) {
        perror("listen"); 
        exit(1);
    }
    printf("Listening for connections to port %d\n", portRead);

    return sockRead;
}


int main(int argc, char *argv[]) {
    int buffsize = 256;
    char buffer[buffsize];

    int portRead, sockRead, newsock;
    struct sockaddr_in serverRead, clientRead;
    socklen_t clientlen = 0;

    struct sockaddr *serverptrRead = NULL;
    struct sockaddr *clientptrRead = NULL;


// //////////////////////////////////////////////////////////////////////////////////////////

    portRead = 8080;

    sockRead = getSocketRead(portRead);

    if ((newsock = accept(sockRead, clientptrRead, &clientlen)) < 0) {
        perror("accept");
        exit(1);
    }
    int count = 0;
    int bytes = 0;
    memset(buffer, 0, buffsize);

    while ((bytes = read(newsock, buffer, buffsize)) > 0){
        count++;
        buffer[bytes] = '\0';
        printf("%s %d bytes\n", buffer, bytes);
    }
    close(sockRead);

    printf("Count = %d\n",count);
}



void perror_exit(char *message){
    perror(message);
    exit(EXIT_FAILURE);
}

我在运行程序的 5 次中大约有 1 次出现错误。 奇怪的是，当我每 500 次使用 sleep(1) 时，我写了大约 该程序似乎运行良好。

Answer 1

我终于找到了问题，但我不太明白为什么会发生这种情况。 有时 read 返回的字节数少于参数中给出的字节数，当它返回时，我读取其余字节并将它们附加到我的变量中。 我的问题是，为什么 read() 读取的字节数少于给定的字节数。我也试过这个 管道和 read() 总是返回预期的结果（给读取的字节）

还有为什么 write() 总是写入预期的字节数？