while loop for recv and send to get all data doesn't work

Hi,

I'm trying to put recv and send in a while(1) loop to ensure i get all
data from the client and from the server. Within the loop i check for <=0
, if it occurs, i do a break.

However, it does not work. It seems to keep sending data and never breaks!

I use the following loop for send:

while(1) {
if(send(sockfd,buffer,strlen(buffer),0)<=0)
break;
}

and for recv

while(1) {
if (recv(sockfd,buffer,sizeof(buffer),0)<=)
break;
}
because recv gets the entire buffer, i terminate
the buffer like this buffer[strlen(buffer)-1]='\0';

Apart from the above problem, i also realize what would happen
if the buffer did not get sent completetly,iwould get double
data because the buffer would get sent twice.

What am i doing wrong,
Alef

Alef T Veld wrote:
> Hi,
>
> I'm trying to put recv and send in a while(1) loop to ensure i get all
> data from the client and from the server. Within the loop i check for <=0
> , if it occurs, i do a break.
>
> However, it does not work. It seems to keep sending data and never breaks!
>
> I use the following loop for send:
>
> while(1) {
> if(send(sockfd,buffer,strlen(buffer),0)<=0)
> break;
> }
>
> and for recv
>
> while(1) {
> if (recv(sockfd,buffer,sizeof(buffer),0)<=)
> break;
> }
> because recv gets the entire buffer, i terminate
> the buffer like this buffer[strlen(buffer)-1]='\0';
>
> Apart from the above problem, i also realize what would happen
> if the buffer did not get sent completetly,iwould get double
> data because the buffer would get sent twice.
>
> What am i doing wrong,

Implementation.


Use this one:

int already_read = 0;

while(1) {
int rd = recv(sockfd, buffer + already_read, sizeof(buffer) -
already_read, 0);
switch(rd) {
case 0: return already_read;
case -1:
switch(errno) {
case EINTR:
case EAGAIN:
continue; /* Safe one */
}
return -1; /* Hard error */
}
already_read += rd;
}


--
Lev Walkin
vlm@lionet.info

Alef T Veld <alef@xs2.xs4all.nl> writes:

> Hi,
>
> I'm trying to put recv and send in a while(1) loop to ensure i get all
> data from the client and from the server. Within the loop i check for <=0
> , if it occurs, i do a break.
>
> However, it does not work. It seems to keep sending data and never breaks!
>
> I use the following loop for send:
>
> while(1) {
> if(send(sockfd,buffer,strlen(buffer),0)<=0)
> break;
> }
>
> and for recv
>
> while(1) {
> if (recv(sockfd,buffer,sizeof(buffer),0)<=)
> break;
> }
> because recv gets the entire buffer, i terminate
> the buffer like this buffer[strlen(buffer)-1]='\0';
>
> Apart from the above problem, i also realize what would happen
> if the buffer did not get sent completetly,iwould get double
> data because the buffer would get sent twice.
>
> What am i doing wrong,

Here's how to do it (unless I've made some silly mistake):

#include <sys/types.h>
#include <sys/socket.h>
#include <errno.h>

size_t sendall(int fd, const void *buf, size_t len, int flags)
{
while(len > 0){
ssize_t r = send(s, buf, len, flags);
if(r >= 0){
buf += r;
len -= r;
} else if(errno != EINTR){
break;
}
}

return len;
}

This will send all the data in the buffer, if possible.  It returns
the number of bytes not sent.  The caller can examine errno to find
out what went wrong if this is not zero.

--
Måns Rullgård
mru@mru.ath.cx

Alef T Veld wrote:
> because recv gets the entire buffer, i terminate
> the buffer like this buffer[strlen(buffer)-1]='\0';
The other has told you what to do for send,
note that the above is total nonsense though, strlen
would expect a nul terminated string in the first place.
You need do do similar things on the recieve side as
on the send side, possible send the nul terminator as well and
check for that if you just send C strings, or send the
length first, and read until you got lenght bytes.

Måns Rullgård <mru@mru.ath.cx> writes:

> Here's how to do it (unless I've made some silly mistake):

For receiving, just replace send() with recv().

--
Måns Rullgård
mru@mru.ath.cx

Alef T Veld wrote:
> Hi,
>
> I'm trying to put recv and send in a while(1) loop to ensure i get all
> data from the client and from the server. Within the loop i check for <=0
> , if it occurs, i do a break.
>
> However, it does not work. It seems to keep sending data and never breaks!
>
> I use the following loop for send:
>
> while(1) {
> if(send(sockfd,buffer,strlen(buffer),0)<=0)
> break;
> }
>
> and for recv
>
> while(1) {
> if (recv(sockfd,buffer,sizeof(buffer),0)<=)
> break;
> }
> because recv gets the entire buffer, i terminate
> the buffer like this buffer[strlen(buffer)-1]='\0';
>
> Apart from the above problem, i also realize what would happen
> if the buffer did not get sent completetly,iwould get double
> data because the buffer would get sent twice.
>
> What am i doing wrong,
> Alef

You are aware that your send loop has no condition for termination.  The
only time that it would quit sending is if you got an error, or the
system send buffer was temporarily full.  If you were trying to overcome
partial sends, then you have to do your own pointer and count control.

--

Fletcher Glenn

>
> You are aware that your send loop has no condition for termination.  The
> only time that it would quit sending is if you got an error, or the
> system send buffer was temporarily full.  If you were trying to overcome
> partial sends, then you have to do your own pointer and count control.

I thought that it would break upon receiving 0, indicating the server has
closed connection or that there was no more data to send.

>
> --
>
> Fletcher Glenn

--
new

>
>
> Use this one:

I will, thanks, but why doesn't mine work? Should'nt it break on receiving
0 or -1?

>
> int already_read = 0;

"Bjorn Reese" <breese@see.signature> wrote:
 
>
> Minor point, but send() returns -1 on error, not some arbitrary
> negative number, so it may be more correct to use "r != -1".

Mmm, but that's not very defensive, is it? Imagine a broken socket lib whose
recv() sometimes returns -3. I wouldn't want to ignore this.

"Martin Carpenter" <mcarpenter@free.fr> writes:

> "Bjorn Reese" <breese@see.signature> wrote:
> 
>
> Mmm, but that's not very defensive, is it? Imagine a broken socket lib who
se
> recv() sometimes returns -3. I wouldn't want to ignore this.

And < 0 is quicker to type than == -1.

--
Måns Rullgård
mru@mru.ath.cx