struct sockaddr_un serverUNIXAddress;
The following code works under Mac OS 10.9, but not under Linux. It doesn't die on either, but writing from the client to the server, only works under Mac OS. I fully understand that it shouldn't work on either. Why does it work under Mac OS? Is this a bug in the socket implementation, or just a peculiarity that makes it difficult to port, if the bug is not caught?
client.c
//Server domain
serverUNIXAddress.sun_family = AF_UNIX;
//Server name
strcpy(serverUNIXAddress.sun_path, "rockPaperScissors");
server.c
strcpy(serverUNIXAddress.sun_path, "RockPaperScissors");
//Create file
bind(serverFd, serverSockAddrPtr, serverLen);
//Maximum pending connection length
listen (serverFd, 5);
////[...]
A Unix domain socket file is created in the file system. The default file system on OS X is case-insensitive. Therefore, the client finds the server's socket using a case-insensitive match.
You can use case-sensitive file systems on OS X. If you did and created your socket file there, then the matching would be case-sensitive, too.
I assume Linux supports case-insensitive file systems. If you used one of those and created your socket file on it, then the matching would be case-insensitive.
Related
I'm writing a BitTorrent client to learn some more about networking, and I've got something that I'm struggling to Google for. As part of the BT spec, I need a server to listen for peer connections to my computer. In the win32 port, I have code like this to setup my server
struct sockaddr_in saServer;
struct hostent* localHost;
char* localIP;
// Get the local host information
localHost = gethostbyname("");
localIP = inet_ntoa(*(struct in_addr *)*localHost->h_addr_list);
saServer.sin_family = AF_INET;
saServer.sin_addr.s_addr = inet_addr(localIP);
saServer.sin_port = htons(6881);
struct evconnlistener *listener = evconnlistener_new_bind(base, accept_conn_cb, NULL,
LEV_OPT_CLOSE_ON_FREE | LEV_OPT_REUSEABLE, -1, (SOCKADDR*)&saServer, sizeof(saServer));
That seems to work, but if I look at netstat, I see the following,
BitTorrentClient.exe 6092 TCP hostname 50216 localhost 50217 ESTABLISHED
BitTorrentClient.exe 6092 TCP hostname 50217 localhost 50216 ESTABLISHED
BitTorrentClient.exe 6092 TCP hostname.home 6881 hostname 0 LISTENING
Why are there two other connections, one from port 50216->50217 and one looping back from 50217->50216? I was expected to have just one listening connection on port 6881. Is this a libevent quirk, or something more fundamental related to networking?
What can I search for to understand what the other two ports are used for?
This is most likely a result of libevent calling evutil_make_internal_pipe_ internally.
Libevent creates internal "pipes" for inter-thread communication and signal delivery using socketpair(2) on POSIX-compliant systems, whereas on Windows libevent has to resort to manually connecting two sockets together instead.
So, after I got this error, I've been looking for an answer in here, almost everyone had a difficult way to fix this error but no one explained why this error occurs at all, so I don't find this question to be exactly duplicate.
I wrote a TCP socket in C and I used "getaddrinfo" function to make the socket work with hostnames, well it worked perfectly! you can find my codes on github.
but when I tried to create a UDP socket by "getaddrinfo" I got this error:
Servname not supported for ai_socktype
client.c
const char *host = argv[1];
const char *service = argv[2];
const char *string = argv[3];
struct addrinfo addrCriteria;
memset(&addrCriteria, 0, sizeof(addrCriteria));
addrCriteria.ai_family = AF_UNSPEC;
addrCriteria.ai_socktype = SOCK_DGRAM;
addrCriteria.ai_protocol = IPPROTO_UDP;
struct addrinfo *servAddr;
int ret = getaddrinfo(host, service, &addrCriteria, &servAddr);
if(ret != 0)
sysError(gai_strerror(ret));
I realized that when I give "service" a numeric input like 8080, no errors would return but when I use a string as service name like "tproxy" which points to port/8081, 'gai_strerror' returns mentioned error.
Obviously, gai_strerror says: "service names not supported for 'SOCK_DGRAM' socket types", but why? I mean the exact reason for "getaddrinfo" not supporting name services over UDP sockets?
Is there any other way to use service names with UDP sockets instead of port numbers? how?
TL;DR: There is no tproxy UDP port.
If you look up the tproxy service for UDP sockets in your service database,
getent services tproxy/udp
You get no output, because tproxy is not an UDP service. If you look at all tproxy services regardless of the protocol, getent services | grep -e tproxy, you'll see
tproxy 8081/tcp
which means that tproxy service is only defined for TCP protocol.
This means that if you ask getaddrinfo() for an UDP socket for service 8081, you will not find anything, because tproxy is only defined for TCP and not UDP.
Compare to the case where you ask for and UDP socket for xmpp-client service. At least my service database (getent services xmpp-client/udp) responds with
xmpp-client 5222/udp jabber-client
and indeed, getaddrinfo() happily provides the socket description for such UDP sockets (using xmpp-client or jabber-client as the service).
So, there are services like xmpp-client that do have both TCP and UDP ports defined. On my system, getent services | grep -e xmpp-client shows
xmpp-client 5222/tcp jabber-client
xmpp-client 5222/udp jabber-client
Because TCP and UDP are different protocols over IP, it makes sense that a service could use a different port number for TCP and UDP communications. So, it is unreasonable to assume that the service database should just return the same port numbers for TCP and UDP sockets.
In other words, you encounter the error because you mistakenly assume that because some service uses a TCP port, with a name registered in the service database, you should be able to use that name to specify an UDP port number, too.
TCP and UDP are separate protocols, and their port number spaces are separate. For example, TCP port 512 is used by the Unix exec r-service, whereas UDP port 512 is used by the biff mail notification service.
When a non-numeric value is given for the service parameter, it is looked up (on Linux) in the /etc/services file. This file maps a service name to a port/protocol. Below are some sample entries:
ssh 22/tcp
telnet 23/tcp
domain 53/tcp # name-domain server
domain 53/udp
The reason you're getting an error is because there is no UDP entry in your /etc/services file for "tproxy". Take a look at this file and look for an entry that does specify a UDP port such as "domain". That should have entries for both 53/tcp and 53/udp. If you pass in "domain" as the service name you should get a result back.
I want to use pcap to capture packets
and then send the captured packets to another host
my source code snippets are like:
for(;;){
pcap_packet = pcap_next(pcap_handler, &pcap_header);
if(pcap_packet !=NULL)
printf("capture a packet with length of %d\n", pcap_header.len);
// send the packet as payload to the sender, excluding the Ethernet Header
n = send(sd_proxy, pcap_packet+ETHERNET_HDR_LEN, pcap_header.len-ETHERNET_HDR_LEN, 0);
if(n<0){
shutdown(connfd, SHUT_RDWR);
close(connfd);
break;
} new
}
so basically, I want program to be blocked by the pcap_next, once a
the socket sd_proxy establishes a TCP connection with the other host,
if the other host initiate an active TCP close, I want to detect this
active close. Ideally, I should use a select and a n=recv(rd_fd, ...)
if the other host initiates a active close, select will notice there is something with rd_fd and then I see whether 'n=0' or not.
but with pcap, select can't cooperate with pcap
so how to finish my task?
thanks!
select can't cooperate with pcap
Why not? Have you tried using pcap_get_selectable_fd() on pcap_handler and adding the resulting file descriptor to the file descriptor set in your select() call?
You're working on Linux, so that should Just Work.
(If you were running on a system that uses BPF, such as *BSD or OS X, you might have problems with this, at least with older versions of those OSes; various *BSDs have had their select-with-BPF bugs fixed for a while; on OS X, I fixed it in Lion, so it could have problems on Snow Leopard and earlier.)
I want to use RSA_generate_key() on HP-UX 11.11. But hp-ux 11.11 does not provide /dev/random or /dev/urandom, so I need to use openssl prngd.
Please let me know how to use it by default in C code. I have openssl installed and prngd is available.
$ ls /opt/openssl/prngd/prngd
/opt/openssl/prngd/prngd
Let me know if you need more information.
Noting that prngd uses the same interface that EGD does, checkout the instructions found here. A quote of interest is:
On systems without /dev/*random devices providing entropy from the kernel
Alternatively, the EGD-interface compatible daemon PRNGD can be used.
OpenSSL automatically queries EGD when entropy is requested via RAND_bytes() or the status is checked via RAND_status() for the first time, if the socket is located at /var/run/egd-pool, /dev/egd-pool or /etc/egd-pool.
So when you run prngd, run it as prngd /dev/egd-pool or one of the other alternatives
prngd simulates "/dev/random" and "/dev/urandom" over a network connection. It supports either a Unix stream-based domain socket ("/var/run/egd-pool") or (if configured to) or IP using TCP ports 708 or 4840 (default values---can be changed).
So, in using the Unix domain socket, it would look something like:
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
int devrandom(void)
{
union
{
struct sockaddr sa;
struct sockaddr_un path;
} location;
int sock;
memset(&location,0,sizeof(location));
location.path.sun_family = AF_UNIX;
strcpy(location.path.sun_path,"/var/run/egd-pool");
sock = socket(AF_UNIX,SOCK_STREAM,0);
if (sock < 0)
return -1;
if (connect(sock,&location.sa,sizeof(struct sockaddr_un)) < 0)
return -1;
return sock;
}
This will return a file descriptor you can pass to read() in order to obtain the random data (note: this code is untested). A TCP/IP based connection is a bit more involved, requiring binding the socket to a local address and connecting to the remote address but there are plenty of examples on the Internet for that type of code.
I've gone through many posts and forums and I'm new to socket programming. Major parts of my code are similar to
BIND ERROR : Address already in use
but then i changed my code so that i include "setsockopt" function like so:
const char* port="5555";
int opt=1;
portno=atoi(port);
//parameters for server address
serv_addr.sin_family=AF_INET;
serv_addr.sin_port=htons(portno);
serv_addr.sin_addr.s_addr=INADDR_ANY;
//bind the socket to the address
setsockopt(sockfd,SOL_SOCKET,SO_REUSEADDR,(const char *)&opt,sizeof(int));
if(bind(sockfd,(struct sockaddr*)&serv_addr,sizeof(serv_addr))<0)
{close(sockfd);
error("error in binding port!");
}
But still i get the error. I have to close the terminal and restart it in order to use the port again. I want to use a hardcoded port (like i mentioned in the code above)
Thanks a lot in advance
Check to see if the port is in use. Either telnet to that port or use netstat -a. It should be in use (as the error indicates) and kill the appropriate process. Perhaps using ps to find the process.
A port number can only be used by one application at a time. That means you can not start the same program twice expecting both to bind to the same port.
The SO_REUSEADDR is for when the socket bound to an address has already been closed, the same address (ip-address/port pair) can be used again directly.