TCPConnection

[Source]

A TCP connection. When connecting, the Happy Eyeballs algorithm is used.

The following code creates a client that connects to port 8989 of the local host, writes "hello world", and listens for a response, which it then prints.

use "net"

class MyTCPConnectionNotify is TCPConnectionNotify
  let _out: OutStream

  new create(out: OutStream) =>
    _out = out

  fun ref connected(conn: TCPConnection ref) =>
    conn.write("hello world")

  fun ref received(
    conn: TCPConnection ref,
    data: Array[U8] iso,
    times: USize)
    : Bool
  =>
    _out.print("GOT:" + String.from_array(consume data))
    conn.close()
    true

  fun ref connect_failed(conn: TCPConnection ref) =>
    None

actor Main
  new create(env: Env) =>
    TCPConnection(TCPConnectAuth(env.root),
      recover MyTCPConnectionNotify(env.out) end, "", "8989")

Note: when writing to the connection data will be silently discarded if the connection has not yet been established.

Backpressure support

Write

The TCP protocol has built-in backpressure support. This is generally experienced as the outgoing write buffer becoming full and being unable to write all requested data to the socket. In TCPConnection, this is hidden from the programmer. When this occurs, TCPConnection will buffer the extra data until such time as it is able to be sent. Left unchecked, this could result in uncontrolled queuing. To address this, TCPConnectionNotify implements two methods throttled and unthrottled that are called when backpressure is applied and released.

Upon receiving a throttled notification, your application has two choices on how to handle it. One is to inform the Pony runtime that it can no longer make progress and that runtime backpressure should be applied to any actors sending this one messages. For example, you might construct your application like:

// Here we have a TCPConnectionNotify that upon construction
// is given a ApplyReleaseBackpressureAuth token. This allows the notifier
// to inform the Pony runtime when to apply and release backpressure
// as the connection experiences it.
// Note the calls to
//
// Backpressure.apply(_auth)
// Backpressure.release(_auth)
//
// that apply and release backpressure as needed

use "backpressure"
use "collections"
use "net"

class SlowDown is TCPConnectionNotify
  let _auth: ApplyReleaseBackpressureAuth
  let _out: OutStream

  new iso create(auth: ApplyReleaseBackpressureAuth, out: OutStream) =>
    _auth = auth
    _out = out

  fun ref throttled(connection: TCPConnection ref) =>
    _out.print("Experiencing backpressure!")
    Backpressure.apply(_auth)

  fun ref unthrottled(connection: TCPConnection ref) =>
    _out.print("Releasing backpressure!")
    Backpressure.release(_auth)

  fun ref closed(connection: TCPConnection ref) =>
    // if backpressure has been applied, make sure we release
    // when shutting down
    _out.print("Releasing backpressure if applied!")
    Backpressure.release(_auth)

  fun ref connect_failed(conn: TCPConnection ref) =>
    None

actor Main
  new create(env: Env) =>
    let c_auth = TCPConnectAuth(env.root)
    let bp_auth = ApplyReleaseBackpressureAuth(env.root)
    let socket = TCPConnection(c_auth,
      recover SlowDown(bp_auth, env.out) end, "", "7669")

Or if you want, you could handle backpressure by shedding load, that is, dropping the extra data rather than carrying out the send. This might look like:

use "net"

class ThrowItAway is TCPConnectionNotify
  var _throttled: Bool = false

  fun ref sent(conn: TCPConnection ref, data: ByteSeq): ByteSeq =>
    if not _throttled then
      data
    else
      ""
    end

  fun ref sentv(conn: TCPConnection ref, data: ByteSeqIter): ByteSeqIter =>
    if not _throttled then
      data
    else
      recover Array[String] end
    end

  fun ref throttled(connection: TCPConnection ref) =>
    _throttled = true

  fun ref unthrottled(connection: TCPConnection ref) =>
    _throttled = false

  fun ref connect_failed(conn: TCPConnection ref) =>
    None

actor Main
  new create(env: Env) =>
    TCPConnection(TCPConnectAuth(env.root),
      recover ThrowItAway end, "", "7669")

In general, unless you have a very specific use case, we strongly advise that you don't implement a load shedding scheme where you drop data.

Read

If your application is unable to keep up with data being sent to it over a TCPConnection you can use the builtin read backpressure support to pause reading the socket which will in turn start to exert backpressure on the corresponding writer on the other end of that socket.

The mute behavior allow any other actors in your application to request the cessation of additional reads until such time as unmute is called. Please note that this cessation is not guaranteed to happen immediately as it is the result of an asynchronous behavior call and as such will have to wait for existing messages in the TCPConnection's mailbox to be handled.

On non-windows platforms, your TCPConnection will not notice if the other end of the connection closes until you unmute it. Unix type systems like FreeBSD, Linux and OSX learn about a closed connection upon read. On these platforms, you must call unmute on a muted connection to have it close. Without calling unmute the TCPConnection actor will never exit.

Proxy support

Using the proxy_via callback in a TCPConnectionNotify it is possible to implement proxies. The function takes the intended destination host and service as parameters and returns a 2-tuple of the proxy host and service.

The proxy TCPConnectionNotify should decorate another implementation of TCPConnectionNotify passing relevent data through.

Example proxy implementation

actor Main
  new create(env: Env) =>
    MyClient.create(
      "example.com", // we actually want to connect to this host
      "80",
      ExampleProxy.create("proxy.example.com", "80")) // we connect via this proxy

actor MyClient
  new create(host: String, service: String, proxy: Proxy = NoProxy) =>
    let conn: TCPConnection = TCPConnection.create(
      TCPConnectAuth(env.root),
      proxy.apply(MyConnectionNotify.create()),
      host,
      service)

class ExampleProxy is Proxy
  let _proxy_host: String
  let _proxy_service: String

  new create(proxy_host: String, proxy_service: String) =>
    _proxy_host = proxy_host
    _proxy_service = proxy_service

  fun apply(wrap: TCPConnectionNotify iso): TCPConnectionNotify iso^ =>
    ExampleProxyNotify.create(consume wrap, _proxy_service, _proxy_service)

class iso ExampleProxyNotify is TCPConnectionNotify
  // Fictional proxy implementation that has no error
  // conditions, and always forwards the connection.
  let _proxy_host: String
  let _proxy_service: String
  var _destination_host: (None | String) = None
  var _destination_service: (None | String) = None
  let _wrapped: TCPConnectionNotify iso

  new iso create(wrap: TCPConnectionNotify iso, proxy_host: String, proxy_service: String) =>
    _wrapped = wrap
    _proxy_host = proxy_host
    _proxy_service = proxy_service

  fun ref proxy_via(host: String, service: String): (String, String) =>
    // Stash the original host & service; return the host & service
    // for the proxy; indicating that the initial TCP connection should
    // be made to the proxy
    _destination_host = host
    _destination_service = service
    (_proxy_host, _proxy_service)

  fun ref connected(conn: TCPConnection ref) =>
    // conn is the connection to the *proxy* server. We need to ask the
    // proxy server to forward this connection to our intended final
    // destination.
    conn.write((_destination_host + "\n").array())
    conn.write((_destination_service + "\n").array())
    wrapped.connected(conn)

  fun ref received(conn, data, times) => _wrapped.received(conn, data, times)
  fun ref connect_failed(conn: TCPConnection ref) => None

actor tag TCPConnection is
  AsioEventNotify tag

Implements

• AsioEventNotify tag

---

Constructors

create

[Source]

Connect via IPv4 or IPv6. If from is a non-empty string, the connection will be made from the specified interface.

new tag create(
  auth: TCPConnectAuth val,
  notify: TCPConnectionNotify iso,
  host: String val,
  service: String val,
  from: String val = "",
  read_buffer_size: USize val = 16384,
  yield_after_reading: USize val = 16384,
  yield_after_writing: USize val = 16384)
: TCPConnection tag^

Parameters

• auth: TCPConnectAuth val
• notify: TCPConnectionNotify iso
• host: String val
• service: String val
• from: String val = ""
• read_buffer_size: USize val = 16384
• yield_after_reading: USize val = 16384
• yield_after_writing: USize val = 16384

Returns

• TCPConnection tag^

---

ip4

[Source]

Connect via IPv4.

new tag ip4(
  auth: TCPConnectAuth val,
  notify: TCPConnectionNotify iso,
  host: String val,
  service: String val,
  from: String val = "",
  read_buffer_size: USize val = 16384,
  yield_after_reading: USize val = 16384,
  yield_after_writing: USize val = 16384)
: TCPConnection tag^

Parameters

• auth: TCPConnectAuth val
• notify: TCPConnectionNotify iso
• host: String val
• service: String val
• from: String val = ""
• read_buffer_size: USize val = 16384
• yield_after_reading: USize val = 16384
• yield_after_writing: USize val = 16384

Returns

• TCPConnection tag^

---

ip6

[Source]

Connect via IPv6.

new tag ip6(
  auth: TCPConnectAuth val,
  notify: TCPConnectionNotify iso,
  host: String val,
  service: String val,
  from: String val = "",
  read_buffer_size: USize val = 16384,
  yield_after_reading: USize val = 16384,
  yield_after_writing: USize val = 16384)
: TCPConnection tag^

Parameters

• auth: TCPConnectAuth val
• notify: TCPConnectionNotify iso
• host: String val
• service: String val
• from: String val = ""
• read_buffer_size: USize val = 16384
• yield_after_reading: USize val = 16384
• yield_after_writing: USize val = 16384

Returns

• TCPConnection tag^

---

Public Behaviours

write

[Source]

Write a single sequence of bytes. Data will be silently discarded if the connection has not yet been established though.

be write(
  data: (String val | Array[U8 val] val))

Parameters

• data: (String val | Array[U8 val] val)

---

writev

[Source]

Write a sequence of sequences of bytes. Data will be silently discarded if the connection has not yet been established though.

be writev(
  data: ByteSeqIter val)

Parameters

• data: ByteSeqIter val

---

mute

[Source]

Temporarily suspend reading off this TCPConnection until such time as unmute is called.

be mute()

---

unmute

[Source]

Start reading off this TCPConnection again after having been muted.

be unmute()

---

set_notify

[Source]

Change the notifier.

be set_notify(
  notify: TCPConnectionNotify iso)

Parameters

• notify: TCPConnectionNotify iso

---

dispose

[Source]

Close the connection gracefully once all writes are sent.

be dispose()

---

Public Functions

local_address

[Source]

Return the local IP address. If this TCPConnection is closed then the address returned is invalid.

fun box local_address()
: NetAddress val

Returns

• NetAddress val

---

remote_address

[Source]

Return the remote IP address. If this TCPConnection is closed then the address returned is invalid.

fun box remote_address()
: NetAddress val

Returns

• NetAddress val

---

expect

[Source]

A received call on the notifier must contain exactly qty bytes. If qty is zero, the call can contain any amount of data. This has no effect if called in the sent notifier callback.

Errors if qty exceeds the max buffer size as indicated by the read_buffer_size supplied when the connection was created.

fun ref expect(
  qty: USize val = 0)
: None val ?

Parameters

• qty: USize val = 0

Returns

• None val ?

---

set_nodelay

[Source]

Turn Nagle on/off. Defaults to on. This can only be set on a connected socket.

fun ref set_nodelay(
  state: Bool val)
: None val

Parameters

• state: Bool val

Returns

• None val

---

set_keepalive

[Source]

Sets the TCP keepalive timeout to approximately secs seconds. Exact timing is OS dependent. If secs is zero, TCP keepalive is disabled. TCP keepalive is disabled by default. This can only be set on a connected socket.

fun ref set_keepalive(
  secs: U32 val)
: None val

Parameters

• secs: U32 val

Returns

• None val

---

write_final

[Source]

Write as much as possible to the socket. Set _writeable to false if not everything was written. On an error, close the connection. This is for data that has already been transformed by the notifier. Data will be silently discarded if the connection has not yet been established though.

fun ref write_final(
  data: (String val | Array[U8 val] val))
: None val

Parameters

• data: (String val | Array[U8 val] val)

Returns

• None val

---

close

[Source]

Attempt to perform a graceful shutdown. Don't accept new writes. If the connection isn't muted then we won't finish closing until we get a zero length read. If the connection is muted, perform a hard close and shut down immediately.

fun ref close()
: None val

Returns

• None val

---

hard_close

[Source]

When an error happens, do a non-graceful close.

fun ref hard_close()
: None val

Returns

• None val

---

getsockopt

[Source]

General wrapper for TCP sockets to the getsockopt(2) system call.

The caller must provide an array that is pre-allocated to be at least as large as the largest data structure that the kernel may return for the requested option.

In case of system call success, this function returns the 2-tuple: 1. The integer 0. 2. An Array[U8] of data returned by the system call's void * 4th argument. Its size is specified by the kernel via the system call's sockopt_len_t * 5th argument.

In case of system call failure, this function returns the 2-tuple: 1. The value of errno. 2. An undefined value that must be ignored.

Usage example:

// connected() is a callback function for class TCPConnectionNotify
fun ref connected(conn: TCPConnection ref) =>
  match conn.getsockopt(OSSockOpt.sol_socket(), OSSockOpt.so_rcvbuf(), 4)
    | (0, let gbytes: Array[U8] iso) =>
      try
        let br = Reader.create().>append(consume gbytes)
        ifdef littleendian then
          let buffer_size = br.u32_le()?
        else
          let buffer_size = br.u32_be()?
        end
      end
    | (let errno: U32, _) =>
      // System call failed
  end

fun ref getsockopt(
  level: I32 val,
  option_name: I32 val,
  option_max_size: USize val = 4)
: (U32 val , Array[U8 val] iso^)

Parameters

• level: I32 val
• option_name: I32 val
• option_max_size: USize val = 4

Returns

• (U32 val , Array[U8 val] iso^)

---

getsockopt_u32

[Source]

Wrapper for TCP sockets to the getsockopt(2) system call where the kernel's returned option value is a C uint32_t type / Pony type U32.

In case of system call success, this function returns the 2-tuple: 1. The integer 0. 2. The *option_value returned by the kernel converted to a Pony U32.

In case of system call failure, this function returns the 2-tuple: 1. The value of errno. 2. An undefined value that must be ignored.

fun ref getsockopt_u32(
  level: I32 val,
  option_name: I32 val)
: (U32 val , U32 val)

Parameters

• level: I32 val
• option_name: I32 val

Returns

• (U32 val , U32 val)

---

setsockopt

[Source]

General wrapper for TCP sockets to the setsockopt(2) system call.

The caller is responsible for the correct size and byte contents of the option array for the requested level and option_name, including using the appropriate machine endian byte order.

This function returns 0 on success, else the value of errno on failure.

Usage example:

// connected() is a callback function for class TCPConnectionNotify
fun ref connected(conn: TCPConnection ref) =>
  let sb = Writer

  sb.u32_le(7744)             // Our desired socket buffer size
  let sbytes = Array[U8]
  for bs in sb.done().values() do
    sbytes.append(bs)
  end
  match conn.setsockopt(OSSockOpt.sol_socket(), OSSockOpt.so_rcvbuf(), sbytes)
    | 0 =>
      // System call was successful
    | let errno: U32 =>
      // System call failed
  end

fun ref setsockopt(
  level: I32 val,
  option_name: I32 val,
  option: Array[U8 val] ref)
: U32 val

Parameters

• level: I32 val
• option_name: I32 val
• option: Array[U8 val] ref

Returns

• U32 val

---

setsockopt_u32

[Source]

General wrapper for TCP sockets to the setsockopt(2) system call where the kernel expects an option value of a C uint32_t type / Pony type U32.

This function returns 0 on success, else the value of errno on failure.

fun ref setsockopt_u32(
  level: I32 val,
  option_name: I32 val,
  option: U32 val)
: U32 val

Parameters

• level: I32 val
• option_name: I32 val
• option: U32 val

Returns

• U32 val

---

get_so_error

[Source]

Wrapper for the FFI call getsockopt(fd, SOL_SOCKET, SO_ERROR, ...)

fun ref get_so_error()
: (U32 val , U32 val)

Returns

• (U32 val , U32 val)

---

get_so_rcvbuf

[Source]

Wrapper for the FFI call getsockopt(fd, SOL_SOCKET, SO_RCVBUF, ...)

fun ref get_so_rcvbuf()
: (U32 val , U32 val)

Returns

• (U32 val , U32 val)

---

get_so_sndbuf

[Source]

Wrapper for the FFI call getsockopt(fd, SOL_SOCKET, SO_SNDBUF, ...)

fun ref get_so_sndbuf()
: (U32 val , U32 val)

Returns

• (U32 val , U32 val)

---

get_tcp_nodelay

[Source]

Wrapper for the FFI call getsockopt(fd, SOL_SOCKET, TCP_NODELAY, ...)

fun ref get_tcp_nodelay()
: (U32 val , U32 val)

Returns

• (U32 val , U32 val)

---

set_so_rcvbuf

[Source]

Wrapper for the FFI call setsockopt(fd, SOL_SOCKET, SO_RCVBUF, ...)

fun ref set_so_rcvbuf(
  bufsize: U32 val)
: U32 val

Parameters

• bufsize: U32 val

Returns

• U32 val

---

set_so_sndbuf

[Source]

Wrapper for the FFI call setsockopt(fd, SOL_SOCKET, SO_SNDBUF, ...)

fun ref set_so_sndbuf(
  bufsize: U32 val)
: U32 val

Parameters

• bufsize: U32 val

Returns

• U32 val

---

set_tcp_nodelay

[Source]

Wrapper for the FFI call setsockopt(fd, SOL_SOCKET, TCP_NODELAY, ...)

fun ref set_tcp_nodelay(
  state: Bool val)
: U32 val

Parameters

• state: Bool val

Returns

• U32 val

---