从Java服务器向C客户端发送文本文件

Question

I am trying to send a text file from a Java server to a C client. After I ran my code, the text file was received successfully but when i opened it, i found out that some random data had been inserted in the text file.

This is the server code for sending the file.

public void sendFile(Socket socket, String file) throws IOException 
{
    DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
    FileInputStream fis = new FileInputStream(file);
    byte[] buffer = new byte[256];

    while (fis.read(buffer) > 0) {
        dos.write(buffer);
    }

    fis.close();
    dos.close();    
}

And this is the client code for receiving the file.

int recv_file(int sock, char* file_name)
{
     char send_str [MAX_SEND_BUF]; 
     int fp; 
     int sent_bytes, rcvd_bytes, rcvd_file_size;
     int recv_count; 
     unsigned int recv_str[MAX_RECV_BUF];
     size_t send_strlen; 
     send_strlen = strlen(send_str); 
     if ( (fp = open(file_name, O_WRONLY|O_CREAT, 0644)) < 0 )
     {
           perror("error creating file");
           return -1;
     }
     recv_count = 0;
     rcvd_file_size = 0;
     while ( (rcvd_bytes = recv(sock, recv_str, MAX_RECV_BUF/*256*/, 0)) > 0 )
     {
           recv_count++;
           rcvd_file_size += rcvd_bytes;
           if (write(fp, recv_str, rcvd_bytes) < 0 )
           {
                  perror("error writing to file");
                  return -1;
           }
           printf("%dThe data received is %u\n", ++count, recv_str);
     }
     close(fp);
     printf("Client Received: %d bytes in %d recv(s)\n", rcvd_file_size,    recv_count);
     return rcvd_file_size;
}

And this is the text file received at the client side. Received text file

This gibberish is added to the text file, how do i resolve this issue?

Answer 1

while (fis.read(buffer) > 0) {
    dos.write(buffer);
}

Your copy loop is incorrect. You are writing junk at the end of the file, if not before. It should be:

int count;
while ((count = fis.read(buffer)) > 0) {
    dos.write(buffer, 0, count);
}

Answer 2

You should not use a DataOutputStream because it provides no benefit here. Just use the plain OutputStream from the socket.

Then, you must make sure you only write as much data as there is in the file.

So instead of

while (fis.read(buffer) > 0) {
    dos.write(buffer);
}

use

OutputStream os = socket.getOutputStream();
int len;
while ( (len = fis.read(buffer)) > 0) {
    os.write(buffer,0,len);
}

to make sure you only write as many bytes as there are in the file.