How would you receive a file sent with 'sendfile'?

Question

I'm trying to implement a basic file server. I have been trying to use the sendfile command found here: http://linux.die.net/man/2/sendfile I'm using TCP.

I can have it send fine, but its sending in binary and I'm not sure if thats the hang up.

I am trying to receive the file with recv, but it isn't coming through correctly. Is there a special way to receive a binary file, and put it into a string?

EDIT: Asked to supply some code, here it is:

SENDFILE Call (from Server process)

FILE * file = fopen(filename,"rb"); if ( file != NULL) { /*FILE EXISITS*/ //Get file size (which is why we opened in binary) fseek(file, 0L, SEEK_END); int sz = ftell(file); fseek(file,0L,SEEK_SET); //Send the file sendfile(fd,(int)file,0,sz); //Cleanup fclose(file); }

RECIEVE Call (from Client process, even more basic than a loop, just want a single letter)

//recieve file char fileBuffer[1000]; recv(sockfd,fileBuffer,1,0); fprintf(stderr,"\nContents:\n"); fprintf(stderr,"%c",fileBuffer[0]);

EDIT: wrote some code for checking return values. sendfile is giving errno 9 - bad file number. Which im assuming is at my second file descriptor in the call (the one for the file i'm sending). I cast it as an int because sendfile was complaining it wasn't an int.

How should I use send file given the file pointer code I have used above in th sendfile call?

Can you supply some code, your sendfile call and your recv-loop? — ott--
– ott--, Commented Oct 1, 2011 at 18:42
Always, always, always check the return value of your system calls (fseek, sendfile, recv). And include the result(s) in your question. — Nemo
– Nemo, Commented Oct 1, 2011 at 19:12

BatchyX · Accepted Answer · 2011-10-01 19:50:29Z

You cannot use sendfile() with a FILE*, you need a file descriptor as given by open(), close() and friends. You cannot just cast a FILE* into an int and thinking it would work.

Maybe you should read the sendfile() manpage for more information.

thanks, i just had to use open instead of fopen. Did not realize the difference.

jpalecek · Accepted Answer · 2011-10-01 17:55:06Z

1

There is no special way. You just receive with read() or recv().

Probably, you've got your receiving code wrong.

answered Oct 1, 2011 at 17:55

jpalecek

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3 Comments

user974703 Over a year ago

so if I were to recv into a string, everything should turn out fine?

jpalecek Over a year ago

depends on how you do it. Don't expect any socket reading code to read whole file at once, though. Especially if it is big.

user974703 Over a year ago

Yea, i have it in a loop. But even if i could get the first few letters to know it was reading right. I'll have a look at it soon.

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