套接字程序文件傳輸

Question

當我使用下面的代碼傳輸二進制文件時，只傳輸了一半的文件。 當我使用具有相同二進制文件的環回地址檢查相同的代碼時，它正常工作，即整個文件被傳輸。

以下代碼或我的網絡有任何問題嗎？

Client.c：

#include<stdlib.h>
#include<stdio.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<sys/wait.h>
#include<sys/socket.h>
#include<signal.h>
#include<ctype.h>          
#include<arpa/inet.h>
#include<netdb.h>
#define PORT 20000
#define LENGTH 512

void error(const char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc, char *argv[])
{
    /* Variable Definition */
    int sockfd, nsockfd;
    char revbuf[LENGTH]; 
    struct sockaddr_in remote_addr;

    /* Get the Socket file descriptor */
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        fprintf(stderr, "ERROR: Failed to obtain Socket Descriptor! (errno = %d)\n",errno);
        exit(1);
    }

    /* Fill the socket address struct */
    remote_addr.sin_family = AF_INET; 
    remote_addr.sin_port = htons(PORT); 
    inet_pton(AF_INET, "192.168.103.190", &remote_addr.sin_addr); 
    //inet_pton(AF_INET, "192.168.103.179", &remote_addr.sin_addr);
    bzero(&(remote_addr.sin_zero), 8);

    /* Try to connect the remote */
    if (connect(sockfd, (struct sockaddr *)&remote_addr, sizeof(struct sockaddr)) == -1) {
        fprintf(stderr, "ERROR: Failed to connect to the host! (errno = %d)\n",errno);
        exit(1);
    }
    else
        printf("[Client] Connected to server at port %d...ok!\n", PORT);

    /*send to server*/
    char* fs_name = "/usr/local/context.2848";
    char sdbuf[LENGTH]; 
    printf("[Client] Sending %s to the Server... ", fs_name);
    FILE *fs = fopen(fs_name, "r");
    if(fs == NULL) {
        printf("ERROR: File %s not found.\n", fs_name);
        exit(1);
    }
    bzero(sdbuf, LENGTH); 
    int fs_block_sz,i=0; 
    while((fs_block_sz = fread(sdbuf, sizeof(char), LENGTH, fs)) > 0) {
        printf("Data Sent %d = %d\n",i,fs_block_sz);
        if(send(sockfd, sdbuf, fs_block_sz, 0) < 0) {
            fprintf(stderr, "ERROR: Failed to send file %s. (errno = %d)\n", fs_name,     errno);
            exit(1);
        }
        bzero(sdbuf, LENGTH);
        i++;
    }
    close (sockfd);
    printf("[Client] Connection lost.\n");
    return (0);
}

Server.c

#include<stdlib.h>
#include<stdio.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<sys/wait.h>
#include<sys/socket.h>
#include<signal.h>
#include<ctype.h>          
#include<arpa/inet.h>
#include<netdb.h>
#define PORT 20000 
#define BACKLOG 5
#define LENGTH 512 

void error(const char *msg)
{
    perror(msg);
    exit(1);
}

int main ()
{
    /* Defining Variables */
    int sockfd, nsockfd; 
    int num;
    int sin_size; 
    struct sockaddr_in addr_local; /* client addr */
    struct sockaddr_in addr_remote; /* server addr */
    char revbuf[LENGTH]; // Receiver buffer

    /* Get the Socket file descriptor */
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1 ) {
        fprintf(stderr, "ERROR: Failed to obtain Socket Descriptor. (errno = %d)\n", errno);
        exit(1);
    }
    else 
        printf("[Server] Obtaining socket descriptor successfully.\n");

    /* Fill the client socket address struct */
    addr_local.sin_family = AF_INET; // Protocol Family
    addr_local.sin_port = htons(PORT); // Port number
    addr_local.sin_addr.s_addr = INADDR_ANY; // AutoFill local address
    bzero(&(addr_local.sin_zero), 8); // Flush the rest of struct

    /* Bind a special Port */
    if( bind(sockfd, (struct sockaddr*)&addr_local, sizeof(struct sockaddr)) == -1 ) {
        fprintf(stderr, "ERROR: Failed to bind Port. (errno = %d)\n", errno);
        exit(1);
    }
    else 
        printf("[Server] Binded tcp port %d in addr 127.0.0.1 sucessfully.\n",PORT);

    /* Listen remote connect/calling */
    if(listen(sockfd,BACKLOG) == -1) {
        fprintf(stderr, "ERROR: Failed to listen Port. (errno = %d)\n", errno);
        exit(1);
    }
    else
        printf ("[Server] Listening the port %d successfully.\n", PORT);

    int success = 0;
    while(success == 0)
    {
        sin_size = sizeof(struct sockaddr_in);

        /* Wait a connection, and obtain a new socket file despriptor for single connection */
        if ((nsockfd = accept(sockfd, (struct sockaddr *)&addr_remote, &sin_size)) == -1) {
            fprintf(stderr, "ERROR: Obtaining new Socket Despcritor. (errno = %d)\n", errno);
            exit(1);
        }
        else 
            printf("[Server] Server has got connected from %s.\n", inet_ntoa(addr_remote.sin_addr));
        /*Receive File from Client */
        char* fr_name = "/home/ankita/context.2848";
        FILE *fr = fopen(fr_name, "a");
        if(fr == NULL)
            printf("File %s Cannot be opened file on server.\n", fr_name);
        else {
            bzero(revbuf, LENGTH); 
            int fr_block_sz = 0;
            int i=0;
            while((fr_block_sz = recv(nsockfd, revbuf, LENGTH, 0)) > 0) {
                printf("Data Received %d = %d\n",i,fr_block_sz);
                int write_sz = fwrite(revbuf, sizeof(char), fr_block_sz, fr);
                if(write_sz < fr_block_sz)
                    error("File write failed on server.\n");
                bzero(revbuf, LENGTH);
                i++;
            }
            if(fr_block_sz < 0) {
                if (errno == EAGAIN)
                    printf("recv() timed out.\n");
                else {
                    fprintf(stderr, "recv() failed due to errno = %d\n", errno);
                    exit(1);
                }
            }
            printf("Ok received from client!\n");
            fclose(fr); 
        }
        success = 1;
    }
}   

Answer 1

發送不保證發送您要求的所有數據，它可能發送更少。 您只檢查發送時的錯誤，而不是發送的數據少於預期。 recv是一樣的。 因此，在實現的兩個方面都存在相同的錯誤。 你可能會為localhost僥幸逃脫，因為內核可以聰明地將數據傳輸給自己。

Answer 2

您應該查看recv循環中的if語句。 首先，條件是

fr_block_sz == 0

因為while循環檢查> 0，所以永遠不會發生。其次，如果recv沒有得到512字節，我不明白為什么要中斷。 （如果你真的需要它，你應該把它改為LENGTH。）你應該繼續recv直到返回代碼為0（在這種情況下套接字關閉）或否定（在這種情況下你有一個錯誤）。 使用流套接字時，接收方不一定會收到發送方為每個請求的IO發送的相同數據量。

Answer 3

正如Joe在回​​答中指出的那樣， send並不總是發送所有數據。 您可以按照此指南正確使用send 。

只有當您嘗試發送到另一台計算機上的服務器時才會注意到此行為，因為您正在達到MTU （即物理介質可以處理的最大數據大小）。 如果我沒記錯的話，使用環回地址時，MTU為8K - 16K。 我猜你的二進制文件大小恰好小於這個，這就是為什么你在嘗試發送到真實服務器之后才觀察到這一點。 然而，以太網介質的MTU是1500字節，相對低得多。