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Top Forums Programming Store file into a buffer to send it through a socket Post 302347468 by achenle on Tuesday 25th of August 2009 07:20:02 PM
Old 08-25-2009
You can also use "sendfile()". That's a lot more efficient because it cuts the number of memory copies by half.

When you read data from a file into the address space of a process, usually the data is copied into a kernel buffer as it comes in off disk, and it get copied again from that kernel buffer into the process buffer. To send that data out a socket, the data is first copied into a kernel buffer, and the data in that buffer is copied out to the socket.

The sendfile() library call will bypass the copying of data into and out of the address space of the process.

For example (I left off all error checking for clarity):

Code:
    struct stat sb;
    off_t offset = 0L;
    int fd;

    fd = open( filename, O_RDONLY );
    fstat( fd, &sb );
    sendfile( socket_fd, fd, &offset, sb.st_size );
    close( fd );

 

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CLTP(4) 						   BSD Kernel Interfaces Manual 						   CLTP(4)

NAME
cltp -- ISO Connectionless Transport Protocol SYNOPSIS
#include <sys/socket.h> #include <netiso/iso.h> int socket(AF_ISO, SOCK_DGRAM, 0); DESCRIPTION
CLTP is a simple, unreliable datagram protocol which is accessed via the SOCK_DGRAM abstraction for the ISO protocol family. CLTP sockets are connectionless, and are normally used with the sendto(2) and recvfrom(2) calls, though the connect(2) call may also be used to fix the destination for future packets (in which case the recv(2) or read(2) and send(2) or write(2) system calls may be used). CLTP address formats are identical to those used by TP. In particular CLTP provides a service selector in addition to the normal ISO NSAP. Note that the CLTP selector space is separate from the TP selector space (i.e. a CLTP selector may not be ``connected'' to a TP selector). Options at the CLNP network level may be used with CLTP; see clnp(4). DIAGNOSTICS
A socket operation may fail with one of the following errors returned: [EISCONN] when trying to establish a connection on a socket which already has one, or when trying to send a datagram with the destina- tion address specified and the socket is already connected; [ENOTCONN] when trying to send a datagram, but no destination address is specified, and the socket hasn't been connected; [ENOBUFS] when the system runs out of memory for an internal data structure; [EADDRINUSE] when an attempt is made to create a socket with a selector which has already been allocated; [EADDRNOTAVAIL] when an attempt is made to create a socket with a network address for which no network interface exists. SEE ALSO
getsockopt(2), recv(2), send(2), socket(2), clnp(4), intro(4), iso(4) BSD
June 9, 1993 BSD
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