Sending and receiving file size successfully in C - c

Question

I want to be able to send a file from the client to the server. I'm using TCP. I'm trying to use fseek and etc to get the size of the file because I want to be able to handle large files, and then send that amount of bytes of data as well as the files contents to the server. So far, according to my printf messages everything goes through and the file is created. However, the file created on the server is empty. There's obviously something wrong with the way I am sending it and receiving it via parameters or something, but I can't figure it out. Can someone please show me where I've gone wrong and how I can fix it because I'm so close!
Server part:
if(getFile){
char *tmp = buf + 9;
char filename2[MAX_BLOCK_SIZE];
int length, x;
long file_size = 0;
FILE *fp;
strcpy(filename2, tmp);
printf("Server receiving file name...\n");
//first 'read' receives the file name
fp = fopen(filename2, "wb");
if(fp == NULL){
printf("File could not be opened.\n");
exit(1);
}
printf("Server receiving file...\n");
while((x = read(sd, buf, sizeof(buf)) > 0)){ //second read now retrieving the file
printf("Server creating new file...\n");
fwrite(buf, 1, file_size, fp);
}
fclose(fp);
printf("The server has received the requested document.\n");
}
Client side:
else if(putCommand){
char *tmp = buf + 4;
char filename[MAX_BLOCK_SIZE];
long file_size;
strcpy(filename, "filename ");
strcat(filename, tmp);
FILE *fp;
printf("File name: %s\n", tmp);
fp = fopen(tmp, "rb");
if(fp == NULL){
printf("ERROR: Requested file does not exist.\n");
}
else{
printf("Client sending filename...\n");
if ((nw = write(sd, filename, sizeof(filename)) < nr)){ //sending the file name to the client first
printf("Error sending client's filename.\n");
}
//size_t file_size;
printf("Client sending file...\n");
fseek(fp, 0, SEEK_END);
long filesize = ftell(fp);
fseek(fp, 0, SEEK_SET);
while((file_size = fread(buf, 1, MAX_BLOCK_SIZE, fp)) > 0){ //sending the file
if ((x = write(sd, buf, filesize) < 0)){
printf("Error sending client file.\n");
}
}
fclose(fp);
}

Answer 1

It is close to a typo. On the receiver side, you have:
long file_size = 0;
...
while(...)
...
fwrite(buf, 1, file_size, fp);
So you consistently write 0 byte.
The standard way is:
while((x = read(sd, buf, sizeof(buf)) > 0)){ //second read now retrieving the file
printf("Server creating new file...\n");
fwrite(buf, 1, x, fp); // write the number of bytes returned by previous read
}
Last remark, I hope that buf is a true array and not a pointer...