Socket Server Example with Swift - macos

Question

I tried to make an example of simple socket server.
Build and run successfully. However it doesn't work well.
Client couldn't connect to this server.
How to solve this problem? I need your help, thanks.
import Foundation
let BUFF_SIZE = 1024
func initStruct<S>() -> S {
let struct_pointer = UnsafePointer<S>.alloc(1)
let struct_memory = struct_pointer.memory
struct_pointer.destroy()
return struct_memory
}
func sockaddr_cast(p: ConstUnsafePointer<sockaddr_in>) -> UnsafePointer<sockaddr> {
return UnsafePointer<sockaddr>(p)
}
func socklen_t_cast(p: UnsafePointer<Int>) -> UnsafePointer<socklen_t> {
return UnsafePointer<socklen_t>(p)
}
var server_socket: Int32
var client_socket: Int32
var server_addr_size: Int
var client_addr_size: Int
var server_addr: sockaddr_in = initStruct()
var client_addr: sockaddr_in = initStruct()
var buff_rcv: Array<CChar> = []
var buff_snd: String
server_socket = socket(PF_INET, SOCK_STREAM, 0);
if server_socket == -1
{
println("[Fail] Create Server Socket")
exit(1)
}
else
{
println("[Success] Created Server Socket")
}
server_addr_size = sizeof(server_addr.dynamicType)
memset(&server_addr, 0, UInt(server_addr_size));
server_addr.sin_family = sa_family_t(AF_INET)
server_addr.sin_port = 4000
server_addr.sin_addr.s_addr = UInt32(0x00000000) // INADDR_ANY = (u_int32_t)0x00000000 ----- <netinet/in.h>
let bind_server = bind(server_socket, sockaddr_cast(&server_addr), socklen_t(server_addr_size))
if bind_server == -1
{
println("[Fail] Bind Port");
exit(1);
}
else
{
println("[Success] Binded Port");
}
if listen(server_socket, 5) == -1
{
println("[Fail] Listen");
exit(1);
}
else
{
println("[Success] Listening : \(server_addr.sin_port) Port ...");
}
var n = 0
while n < 1
{
client_addr_size = sizeof(client_addr.dynamicType)
client_socket = accept(server_socket, sockaddr_cast(&client_addr), socklen_t_cast(&client_addr_size))
if client_socket == -1
{
println("[Fail] Accept Client Connection");
exit(1);
}
else
{
println("[Success] Accepted Client : \(inet_ntoa(client_addr.sin_addr)) : \(client_addr.sin_port)");
}
read(client_socket, &buff_rcv, UInt(BUFF_SIZE))
println("[Success] Received : \(buff_rcv)")
buff_snd = "\(strlen(buff_rcv)) : \(buff_rcv)"
write(client_socket, &buff_snd, strlen(buff_snd) + 1)
close(client_socket)
}

Answer 1

The port number in the socket address must be in big-endian byte order:
server_addr.sin_port = UInt16(4000).bigEndian
So your program actually listens on port 40975 (hex 0xA00F) and not
on port 4000 (hex 0x0FA0).
Another problem is here:
var buff_rcv: Array<CChar> = []
// ...
read(client_socket, &buff_rcv, UInt(BUFF_SIZE))
Your buffer is an empty array, but recv() expects a buffer of size BUFF_SIZE.
The behaviour is undefined. To get a buffer of the required size, use
var buff_rcv = [CChar](count:BUFF_SIZE, repeatedValue:0)
// ...
read(client_socket, &buff_rcv, UInt(buff_rcv.count))
Remark: Here you cast the address of an Int to the address of an socklen_t
and pass that to the accept() function:
client_socket = accept(server_socket, sockaddr_cast(&client_addr), socklen_t_cast(&client_addr_size))
That is not safe. If Int and socklen_t have different sizes then the behaviour
will be undefined. You should declare server_addr_size and client_addr_size
as socklen_t and remove the socklen_t_cast() function:
client_socket = accept(server_socket, sockaddr_cast(&client_addr), &client_addr_size)

Answer 2

As Martin R commented before, the write command shouldn't be using the swift string as that. Something like this will work properly:
write(client_socket, buff_snd.cStringUsingEncoding(NSUTF8StringEncoding)!, countElements(buff_snd) + 1)