Send and Receive a file in socket programming in Linux with C C GCC G

Question

I would like to implement a client-server architecture running on Linux using sockets and C C   language that is capable of sending and receiving files  Is there any library that makes this task easy  Could anyone please provide an example

User · Answer

Do aman 2 sendfile   You only need to open the source file on the client and destination file on the server  then call sendfile and the kernel will chop and move the data

User · Answer

Minimal runnable POSIX read   write example  Usage    get two computers on a LAN   For example  this will work if both computers are connected to your home router in most cases  which is how I tested it  On the server computer    Find the server local IP with ifconfig  e g  192 168 0 10 Run     server output tmp 12345   On the client computer   printf  ab ncd n   gt  input tmp   client input tmp 192 168 0 10 12345  Outcome  a file output tmp is created on the sever computer containing  ab ncd n     server c     Receive a file over a socket   Saves it to output tmp by default   Interface         executable   lt output file gt    lt port gt     Defaults   - output file  output tmp - port  12345      define  XOPEN SOURCE 700   include  lt stdio h gt   include  lt stdlib h gt    include  lt arpa inet h gt   include  lt fcntl h gt   include  lt netdb h gt     getprotobyname     include  lt netinet in h gt   include  lt sys stat h gt   include  lt sys socket h gt   include  lt unistd h gt   int main int argc  char   argv        char  file path    output tmp       char buffer BUFSIZ       char protoname      tcp       int client sockfd      int enable   1      int filefd      int i      int server sockfd      socklen t client len      ssize t read return      struct protoent  protoent      struct sockaddr in client address  server address      unsigned short server port   12345u       if  argc  gt  1            file path   argv 1           if  argc  gt  2                server port   strtol argv 2   NULL  10                           Create a socket and listen to it          protoent   getprotobyname protoname       if  protoent    NULL            perror  getprotobyname            exit EXIT FAILURE             server sockfd   socket          AF INET          SOCK STREAM          protoent- gt p proto            if  server sockfd    -1            perror  socket            exit EXIT FAILURE             if  setsockopt server sockfd  SOL SOCKET  SO REUSEADDR   amp enable  sizeof enable    lt  0            perror  setsockopt SO REUSEADDR  failed            exit EXIT FAILURE             server address sin family   AF INET      server address sin addr s addr   htonl INADDR ANY       server address sin port   htons server port       if  bind              server sockfd               struct sockaddr   amp server address              sizeof server address               -1                 perror  bind            exit EXIT FAILURE             if  listen server sockfd  5     -1            perror  listen            exit EXIT FAILURE             fprintf stderr   listening on port  d n   server port        while  1            client len   sizeof client address           puts  waiting for client            client sockfd   accept              server sockfd               struct sockaddr   amp client address               amp client len                    filefd   open file path                  O WRONLY   O CREAT   O TRUNC                  S IRUSR   S IWUSR           if  filefd    -1                perror  open                exit EXIT FAILURE                     do               read return   read client sockfd  buffer  BUFSIZ               if  read return    -1                    perror  read                    exit EXIT FAILURE                             if  write filefd  buffer  read return     -1                    perror  write                    exit EXIT FAILURE                           while  read return  gt  0           close filefd           close client sockfd             return EXIT SUCCESS      client c     Send a file over a socket   Interface         executable   lt input path gt    lt sever hostname gt    lt port gt      Defaults   - input path  input tmp - server hostname  127 0 0 1 - port  12345      define  XOPEN SOURCE 700   include  lt stdio h gt   include  lt stdlib h gt    include  lt arpa inet h gt   include  lt fcntl h gt   include  lt netdb h gt     getprotobyname     include  lt netinet in h gt   include  lt sys stat h gt   include  lt sys socket h gt   include  lt unistd h gt   int main int argc  char   argv        char protoname      tcp       struct protoent  protoent      char  file path    input tmp       char  server hostname    127 0 0 1       char  server reply   NULL      char  user input   NULL      char buffer BUFSIZ       in addr t in addr      in addr t server addr      int filefd      int sockfd      ssize t i      ssize t read return      struct hostent  hostent      struct sockaddr in sockaddr in      unsigned short server port   12345       if  argc  gt  1            file path   argv 1           if  argc  gt  2                server hostname   argv 2               if  argc  gt  3                    server port   strtol argv 3   NULL  10                                      filefd   open file path  O RDONLY       if  filefd    -1            perror  open            exit EXIT FAILURE                 Get socket         protoent   getprotobyname protoname       if  protoent    NULL            perror  getprotobyname            exit EXIT FAILURE             sockfd   socket AF INET  SOCK STREAM  protoent- gt p proto       if  sockfd    -1            perror  socket            exit EXIT FAILURE                Prepare sockaddr in         hostent   gethostbyname server hostname       if  hostent    NULL            fprintf stderr   error  gethostbyname    s    n   server hostname           exit EXIT FAILURE             in addr   inet addr inet ntoa   struct in addr    hostent- gt h addr list         if  in addr     in addr t -1            fprintf stderr   error  inet addr    s    n     hostent- gt h addr list            exit EXIT FAILURE             sockaddr in sin addr s addr   in addr      sockaddr in sin family   AF INET      sockaddr in sin port   htons server port          Do the actual connection         if  connect sockfd   struct sockaddr   amp sockaddr in  sizeof sockaddr in      -1            perror  connect            return EXIT FAILURE             while  1            read return   read filefd  buffer  BUFSIZ           if  read return    0              break          if  read return    -1                perror  read                exit EXIT FAILURE                        TODO use write loop  https   stackoverflow com questions 24259640 writing-a-full-buffer-using-write-system-call            if  write sockfd  buffer  read return     -1                perror  write                exit EXIT FAILURE                       free user input       free server reply       close filefd       exit EXIT SUCCESS       GitHub upstream   Further comments  Possible improvements    Currently output tmp gets overwritten each time a send is done   This begs for the creation of a simple protocol that allows to pass a filename so that multiple files can be uploaded  e g   filename up to the first newline character  max filename 256 chars  and the rest until socket closure are the contents  Of course  that would require sanitation to avoid a path transversal vulnerability   Alternatively  we could make a server that hashes the files to find filenames  and keeps a map from original paths to hashes on disk  on a database   Only one client can connect at a time   This is specially harmful if there are slow clients whose connections last for a long time  the slow connection halts everyone down   One way to work around that is to fork a process   thread for each accept  start listening again immediately  and use file lock synchronization on the files  Add timeouts  and close clients if they take too long  Or else it would be easy to do a DoS   poll or select are some options  How to implement a timeout in read function call    A simple HTTP wget implementation is shown at  How to make an HTTP get request in C without libcurl   Tested on Ubuntu 15 10

User · Answer

This file will serve you as a good sendfile example   http   tldp org LDP LGNET 91 misc tranter server c txt

User · Answer

The most portable solution is just to read the file in chunks  and then write the data out to the socket  in a loop  and likewise  the other way around when receiving the file   You allocate a buffer  read into that buffer  and write from that buffer into your socket  you could also use send and recv  which are socket-specific ways of writing and reading data   The outline would look something like this   while  1           Read data into buffer   We may not have enough to fill up buffer  so we        store how many bytes were actually read in bytes read      int bytes read   read input file  buffer  sizeof buffer        if  bytes read    0     We re done reading from the file         break       if  bytes read  lt  0               handle errors               You need a loop for the write  because not all of the data may be written        in one call  write will return how many bytes were written  p keeps        track of where in the buffer we are  while we decrement bytes read        to keep track of how many bytes are left to write      void  p   buffer      while  bytes read  gt  0            int bytes written   write output socket  p  bytes read           if  bytes written  lt   0                   handle errors                   bytes read -  bytes written          p    bytes written            Make sure to read the documentation for read and write carefully  especially when handling errors  Some of the error codes mean that you should just try again  for instance just looping again with a continue statement  while others mean something is broken and you need to stop   For sending the file to a socket  there is a system call  sendfile that does just what you want  It tells the kernel to send a file from one file descriptor to another  and then the kernel can take care of the rest  There is a caveat that the source file descriptor must support mmap  as in  be an actual file  not a socket   and the destination must be a socket  so you can t use it to copy files  or send data directly from one socket to another   it is designed to support the usage you describe  of sending a file to a socket  It doesn t help with receiving the file  however  you would need to do the loop yourself for that  I cannot tell you why there is a sendfile call but no analogous recvfile   Beware that sendfile is Linux specific  it is not portable to other systems  Other systems frequently have their own version of sendfile  but the exact interface may vary  FreeBSD  Mac OS X  Solaris    In Linux 2 6 17  the splice system call was introduced  and as of 2 6 23 is used internally to implement sendfile  splice is a more general purpose API than sendfile  For a good description of splice and tee  see the rather good explanation from Linus himself  He points out how using splice is basically just like the loop above  using read and write  except that the buffer is in the kernel  so the data doesn t have to transferred between the kernel and user space  or may not even ever pass through the CPU  known as  zero-copy I O

[c++] Send and Receive a file in socket programming in Linux with C/C++ (GCC/G++)

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