Skip to content
Swift playground with a micro web server that replies "Hello world!" to every request
Branch: master
Clone or download
Latest commit e42d450 Apr 19, 2017
Type Name Latest commit message Commit time
Failed to load latest commit information.
Katan.playground Fix english Apr 19, 2017 Fix engish Apr 19, 2017


A micro web server that replies "Hello world!" to every request

The idea is to show the basics steps to create a web server in Swift.

A web server overview:

alt text

1. Create Socket 🐣

func startWebServer(){
   let socketDescriptor = Darwin.socket(AF_INET, SOCK_STREAM, 0)

socket -- creates an endpoint for communication and returns a descriptor.

domain: Communication domain, selects the protocol family, in our case ipv4 (AF_INET). AF_INET6 if we wanted to use ipv6.

type: Specifies semantics of communication. A SOCK_STREAM type provides sequenced, reliable, two-way connection based byte streams.

protocol: The protocol specifies a particular protocol to be used with the socket. Normally only a single protocol exists to support a particular socket type within a given protocol family

Returns -1 if there's an error otherwise the descriptor (a reference).

2. Set options 🎛

   var noSigPipe: Int32 = 1
   setsockopt(socketDescriptor, SOL_SOCKET, SO_NOSIGPIPE, &noSigPipe, socklen_t(MemoryLayout<Int32>.size))

setsockopt -- get and set options on sockets

socket: The socket descriptor

level: To manipulate options at the socket level

option_name: The name of our the option, in our case we do not generate SIGPIPE, instead return EPIPE A SIGPIPE is sent to a process if it tried to write to a socket that had been shutdown for writing or isn't connected (anymore).

socklen_t: the option length

3. Create adress and bind 🚪🔌

alt text

   let port: in_port_t = 9292
   var address = sockaddr_in(
       sin_len: UInt8(MemoryLayout<sockaddr_in>.stride),
       sin_family: UInt8(AF_INET),
       sin_port: port.bigEndian,
       sin_addr: in_addr(s_addr: in_addr_t(0)),
       sin_zero:(0, 0, 0, 0, 0, 0, 0, 0) // Add some padding, more info at:

   var bindResult: Int32 = -1
   bindResult = withUnsafePointer(to: &address) {
       bind(socketDescriptor, UnsafePointer<sockaddr>(OpaquePointer($0)), socklen_t(MemoryLayout<sockaddr_in>.size))

bind -- assigns a name to an unnamed socket.

When a socket is created with socket() it exists in a name space (address family) but has no name assigned. bind() requests that address be assigned to the socket.

   if bindResult == -1 {
       fatalError(String(cString: UnsafePointer(strerror(errno))))

4. Listen 📡

    listen(socketDescriptor, SOMAXCONN)

listen -- for connections on a socket

The backlog parameter defines the maximum length for the queue of pending connections. If a connection request arrives with the queue full, the client may receive an error with an indication of ECONNREFUSED.

5. Accept connection on socket

  print("Starting HTTP server on port \(port)")
  repeat {
      var address = sockaddr()
      var length: socklen_t = 0
      let clientSocket = accept(socketDescriptor, &address, &length)
      if clientSocket == -1 {
          fatalError(String(cString: UnsafePointer(strerror(errno))))

accept -- extracts the first connection request on the queue of pending connections,

Creates a new socket with the same properties of socket, and allocates a new file descriptor for the socket.

The argument address is a result parameter that is filled in with the address of the connecting entity, as known to the communications layer.

The address_len is a value-result parameter; it should initially contain the amount of space pointed to by address; on return it will contain the actual length (in bytes) of the address returned.

       var characters = ""
       var received: UInt8 = 0
       repeat {
           var buffer = [UInt8](repeatElement(0, count: 1))

6. Read socket 📖

recv -- receive a message from a socket

            let resp = recv(clientSocket, &buffer, Int(buffer.count), 0)
            if resp <= 0 {
                fatalError(String(cString: UnsafePointer(strerror(errno))))
            received = buffer.first!
            if received > 13 /* Carriage Return on ASCII table */ {
        } while received != 10 /* New Line on ASCII table */
        print("Received -> \(characters)")

7. Write response 📝

write -- write output

        let message = "HTTP/1.1 200 OK\r\n\r\n Hello World!"
        print("Response -> \(message)")
        let messageData = ArraySlice(message.utf8)
        _ = messageData.withUnsafeBytes {

            write(clientSocket, $0.baseAddress, messageData.count)

8. Close socket ⚰️

close -- delete a descriptor

    } while true


You can’t perform that action at this time.