How should I do to check if the service running on a remote host?

Question

I'm writing a port scanner and I want to verify if a specific port is running the standard service expected on that port, such as SSH and HTTP. I know one of the methods is to send a query to that port and analyze the returned information. For example, SSH sends me the version information immediately upon connection. However, when I did connect() to port 22 on an ip address, I only got Error number: 110. Error message: Connection timed out. Any idea will be appreciated.

The whole code is a long story. I paste some excerpt here.

struct sockaddr_in dest_addr;
dest_addr.sin_family = AF_INET;
dest_addr.sin_port = htons(22);
dest_addr.sin_addr.s_addr = inet_addr("8.8.8.8");

int service_sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (service_sock < 0) {
    printf("Error creating service socket. Error number: %d. Error message: %s\n", errno, strerror(errno));
    exit(0);
}

int dest_addr_len = sizeof(dest_addr);
if (connect(service_sock, (struct sockaddr *)&dest_addr, dest_addr_len) < 0) { // stuck here
    printf("Error connection. Error number: %d. Error message: %s\n", errno, strerror(errno));
    exit(0);
}

To clarify this question, I need to show an example. I just figured out a method to verify HTTP service. That is to send a string "GET / HTTP\n\n" to destination address. Then call recv() function to read the returned message. I can get something like this.

HTTP/1.0 400 Bad Request
Content-Type: text/html; charset=UTF-8
Content-Length: 1419
Date: Tue, 02 Dec 2014 05:56:25 GMT
Server: GFE/2.0
...

I can read the HTTP version is 1.0 from the first line.

Here I want to check many services on the remote host including but not limited to SSH, HTTP. I don't think guessing is a good idea. So I need a general method to retrieve those information from dest_addr.

doesn't `connection time out` mean that remote host is not responding on that port? — Ubica, Dec 02 '14 at 01:25
@Ubica It does. I just don't know what kind of query I should send, or, how could I get response from that remote host. — Old Panda, Dec 02 '14 at 01:29
check out this question http://stackoverflow.com/questions/11547082/fastest-way-to-scan-ports-with-java — Ubica, Dec 02 '14 at 06:01
@Ubica Thank you, but that link doesn't help. I already implemented how to check if a port is open or closed. Here I want to verify if a specific service is running on that port. — Old Panda, Dec 02 '14 at 15:50
you can't check a port for services unless the port is responsive... it's as simple as that :) try this link http://nmap.org/nmap_doc.html — Ubica, Dec 02 '14 at 22:20
@Ubica Yes, `connect()` won't work when the port is closed or filtered. The problem I met is a normal response. Thank you! — Old Panda, Dec 03 '14 at 01:35

score 0 · Accepted Answer · answered Dec 03 '14 at 18:14

0

OK, finally I need to answer my own question. I just got this verification work and wrote a post for it.

answered Dec 03 '14 at 18:14

Old Panda

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How should I do to check if the service running on a remote host?

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