c sendfile doesn't works the 2nd time

Question

This is a snippet of the LIST ftp's cmd:

count = file_list("./", &files); if((fp_list = fopen("listfiles.txt", "w")) == NULL){ perror("Impossibile aprire il file per la scrittura LIST"); onexit(newsockd, sockd, 0, 2); } for(i=0; i < count; i++){ if(strcmp(files[i], "DIR ..") == 0 || strcmp(files[i], "DIR .") == 0) continue; else{ fprintf(fp_list, "%s\n", files[i]); } } fclose(fp_list); if((fpl = open("listfiles.txt", O_RDONLY)) < 0){ perror("open file with open"); onexit(newsockd, sockd, 0, 2); exit(1); } if(fstat(fpl, &fileStat) < 0){ perror("Errore fstat"); onexit(newsockd, sockd, fpl, 3); } fsize = fileStat.st_size; if(send(newsockd, &fsize, sizeof(fsize), 0) < 0){ perror("Errore durante l'invio grande file list"); onexit(newsockd, sockd, fpl, 3); } rc_list = sendfile(newsockd, fpl, &offset_list, fileStat.st_size); if(rc_list == -1){ perror("Invio file list non riuscito"); onexit(newsockd, sockd, fpl, 3); } if((uint32_t)rc_list != fsize){ fprintf(stderr, "Error: transfer incomplete: %d di %d bytes inviati\n", rc_list, (int)fileStat.st_size); onexit(newsockd, sockd, fpl, 3); } printf("OK\n"); close(fpl); if(remove( "listfiles.txt" ) == -1 ){ perror("errore cancellazione file"); onexit(newsockd, sockd, 0, 2); }

wher &files is declared as char **files and the function list_files is a function written by me that isn't relevant for my problem.
My problem: the first time LIST cmd it's called it works properly but if i call LIST another time it always give me "error, transfer incomplete" i don't understand why...

Is the "error, transfer incomplete" message seen from the code you posted in your question? When in that case? Otherwise, what does the code in the question report? — Some programmer dude
– Some programmer dude, Commented Aug 8, 2012 at 8:02
yes, it is what i've posted into the question :) it give me an error when the sendfile function doesn't send all the file... — polslinux
– polslinux, Commented Aug 8, 2012 at 8:38
What is offset_list and how do you initialize it? Remember that if sendfile can't send everything then it will return a value less than the requested size, and you will have to adjust the size and try again. — Some programmer dude
– Some programmer dude, Commented Aug 8, 2012 at 8:45
offset_list is initialized with offset_t...so i have to do this? send: if((uint32_t)rc_list != fsize){ fprintf(stderr, "Error: transfer incomplete: %d di %d bytes inviati\n", rc_list, (int)fileStat.st_size); goto send; } — polslinux
– polslinux, Commented Aug 8, 2012 at 8:51

Some programmer dude · Accepted Answer · 2019-10-22 06:40:49Z

The sendfile function may not send all data in one call, in which case it will return a number less than requested. You treat this as an error, but instead you should try again. One way is to use a loop similar to this:

// Offset into buffer, this is where sendfile starts reading the buffer off_t offset = 0; // Loop while there's still some data to send for (size_t size_to_send = fsize; size_to_send > 0; ) { ssize_t sent = sendfile(newsockd, fpl, &offset, size_to_send); if (sent <= 0) { // Error or end of file if (sent != 0) perror("sendfile"); // Was an error, report it break; } size_to_send -= sent; // Decrease the length to send by the amount actually sent }

oh thanks :) i've posted my answer without see yours! However i've found my problem but your solution is better :)
but if sent is <= 0 i have to exit and close the socket...why you do only a break??
@polslinux You can do whatever you want in your code. The break is just an example.
Will the sendfile not set offset propertly? Do we need to do offset += sent;

polslinux · Accepted Answer · 2012-08-08 09:01:28Z

I've found my problem.
When i call sendfile multiple times the variable off_t offset_list; remains "dirty".
If a call sendfile the 1st time offest_list will have a value that won't be deleted the 2nd time i call that function.
So if i have to write offset_list = 0; before rc_list = sendfile(newsockd, fpl, &offset_list, fileStat.st_size); and all work!

it also fixed my problem!!! and I was into it for entire days !!! I can't say how much I'm happy right now. THANKS

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