problem with sockets on ubuntu.

[krimix]

Hello i am new on ubuntu and i coded on windows before. i wanted to code with sockets but i have a problem. i use this example: Minimaler TCP Server & TCP Client in C | Webmaster, Security und Technik Blog

at first everything works fine

patti@patti-pc:~/Arbeitsfläche/code/tcp$ ./client
Sende String: test
Es wurden 5 Bytes gesendet

but when i try to change the host and the port to the address of google.de:

inet_pton(AF_INET, "74.125.39.99", &serveraddr);
serveraddr.sin_family = AF_INET;
serveraddr.sin_port = htons(80);

it wont work. it does not print out anything probably because the program exits after send()
i think its because connect does not work properly.

patti@patti-pc:~/Arbeitsfläche/code/tcp$ ./client
patti@patti-pc:~/Arbeitsfläche/code/tcp$

sorry for my bad english and i am not a very experienced coder.

[anduril462]

We can't do much without seeing your code. First, make sure you're checking the return value of every IO and socket related function you call (e.g. socket(), send(), etc). Use the perror function to print out a useful error message if a function fails. Then, post your code and the error messages (if any) that your program outputs.

It's also worth noting that the Windows sockets and the Winsock library were based off of the BSD sockets, which is what Linux uses, so they're very similar. If you've worked with Windows sockets, then you should have a good understanding of what to do in Linux.

EDIT: I like this network programming guide, but I'm not sure if there's a German translation. And don't worry, your English is pretty good (much better than my German!)

[krimix]

i will read this tutorial in a second but first:

the code is 1:1 to the code of the tutorial both Client and Server only that i changed the ip and the port. but here i placed perror under every operation that could error:
codepaste

edit: sorry i forgot to place it under socket() now i did it but its still success

patti@patti-pc:~/Arbeitsfläche/code/tcp$ ./client
bzero error: Success
inet_pton error: Success
htons error: Success
error: Connection refused
patti@patti-pc:~/Arbeitsfläche/code/tcp$

as you can see it says connection refused after connect.
but when i try it with telnet> o 74.125.39.103 80 it works

[Salem]

> connect(socks, (struct sockaddr*) &serveraddr, sizeof(serveraddr));
This also returns a descriptor, and it is this you should be trying to send to.

[krimix]

if i got this right:
codepaste

nope still does not work. but now the program does not hang itself.

socket error: Success
bzero error: Success
inet_pton error: Success
htons error: Success
send:-1
error: Connection refused
Sende String: test
Es wurden -1 Bytes gesendet

[anduril462]

AF_INET
src points to a character string containing an IPv4 network address in dotted-decimal format, "ddd.ddd.ddd.ddd", where ddd is a decimal number of up to three digits
in the range 0 to 255. The address is converted to a struct in_addr and copied to dst, which must be sizeof(struct in_addr) (4) bytes (32 bits) long.

The tutorial is wrong. You need to call inet_pton like so:

inet_pton(AF_INET, "74.125.39.103", &(serveraddr.sin_addr));

Also, Salem was a little mixed up:

RETURN VALUE
If the connection or binding succeeds, zero is returned. On error, -1 is returned, and errno is set appropriately.

You want to send to your socks variable, like so:

int bytes = send(socks, buffer, sizeof(buffer), 0);

A couple other quick notes:
1. You need a perror after send()
2. Your printf statements need a new line at the end. Change the trailing n to a \n:

printf("Sende String: %s\n", buffer);

[anduril462]

Oh, and you probably ought to leave a comment on that tutorial page notifying the author of his/her mistake so they can correct it so nobody else has this problem. I would do it myself, but I don't speak German, and I don't trust an online translator to do a good enough job.

EDIT: Nevermind, I see a link to this thread in the comments section of the tutorial.

[krimix]

inet_pton(AF_INET, "74.125.39.103", &(serveraddr.sin_addr));
thats what i needed thanks man everything works perfect now.