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Module Udp

A grab-bag of performance-oriented, UDP-oriented network tools. These provide some convenience, but they are more complex than basic applications require.

Defaults are chosen for typical UDP applications. Buffering is via Iobuf conventions, where a typical packet-handling loop iteration is read-flip_lo-process-reset.

While these functions are oriented toward UDP, they work with any files that satisfy Fd.supports_nonblock.

For zero-copy Bigstring.t transfers, we must ensure no buffering between the receive loop and caller. So, an interface like Tcp.connect, with something like (Bigstring.t * Socket.Address.Inet.t) Pipe.Reader.t, won't work.

Instead, we use synchronous callbacks.

Signature

val default_capacity : int

The default buffer capacity for UDP-oriented buffers is 1472, determined as the typical Ethernet MTU (1500 octets) less the typical UDP header length (28). Using buffers of this size, one avoids accidentally creating messages that will be dropped on send because they exceed the MTU, and can receive the largest corresponding UDP message.

While this number is merely typical and not guaranteed to work in all cases, defining it in one place makes it easy to share and change. For example, another MTU in common use is 9000 for Jumbo frames, so the value of default_capacity might change to 8972 in the future.

module Config : sig .. end
A typical receive loop implicitly calls Iobuf.flip_lo before calling its callback to prepare a packet buffer for reading by the callback and Iobuf.reset afterward to prepare for the next iteration.
val sendto_sync : unit -> (Import.Fd.t -> ([>
| Core.Std.read
], Core.Std.Iobuf.seek) Core.Std.Iobuf.t -> Import.Socket.Address.Inet.t -> Import.Unix.Syscall_result.Unit.t) Core.Std.Or_error.t
ERROR: udp.mli:73:11-73:12
10:11-10:12 :
expected identifier
val send_sync : unit -> (Import.Fd.t -> ([>
| Core.Std.read
], Core.Std.Iobuf.seek) Core.Std.Iobuf.t -> Import.Unix.Syscall_result.Unit.t) Core.Std.Or_error.t
ERROR: udp.mli:90:11-90:12
8:11-8:12 :
expected identifier
val sendto : unit -> (Import.Fd.t -> ([>
| Core.Std.read
], Core.Std.Iobuf.seek) Core.Std.Iobuf.t -> Import.Socket.Address.Inet.t -> unit Import.Deferred.t) Core.Std.Or_error.t
ERROR: udp.mli:99:11-99:12
3:11-3:12 :
expected identifier
val send : unit -> (Import.Fd.t -> ([>
| Core.Std.read
], Core.Std.Iobuf.seek) Core.Std.Iobuf.t -> unit Import.Deferred.t) Core.Std.Or_error.t
ERROR: udp.mli:111:11-111:12
3:11-3:12 :
expected identifier
val bind : ?ifname:string -> Import.Socket.Address.Inet.t -> ([
| `Bound
], Import.Socket.Address.Inet.t) Import.Socket.t Import.Deferred.t

bind address creates a socket bound to address, and, if address is a multicast address, joins the multicast group.

val bind_any : unit -> ([
| `Bound
], Import.Socket.Address.Inet.t) Import.Socket.t Import.Deferred.t
val recvfrom_loop : ?config:Config.t -> Import.Fd.t -> (write_buffer -> Import.Socket.Address.Inet.t -> unit) -> unit Import.Deferred.t

recvfrom_loop_with_buffer_replacement callback calls callback synchronously on each message received. callback returns the packet buffer for subsequent iterations, so it can replace the initial packet buffer when necessary. This enables immediate buffer reuse in the common case and fallback to allocation if we want to save the packet buffer for asynchronous processing.

val recvfrom_loop_with_buffer_replacement : ?config:Config.t -> Import.Fd.t -> (write_buffer -> Import.Socket.Address.Inet.t -> write_buffer) -> write_buffer Import.Deferred.t

recvfrom_loop_with_buffer_replacement callback calls callback synchronously on each message received. callback returns the packet buffer for subsequent iterations, so it can replace the initial packet buffer when necessary. This enables immediate buffer reuse in the common case and fallback to allocation if we want to save the packet buffer for asynchronous processing.

val read_loop : ?config:Config.t -> Import.Fd.t -> (write_buffer -> unit) -> unit Import.Deferred.t
val read_loop_with_buffer_replacement : ?config:Config.t -> Import.Fd.t -> (write_buffer -> write_buffer) -> write_buffer Import.Deferred.t
val recvmmsg_loop : (?config:Config.t -> ?max_count:int -> ?on_wouldblock:(unit -> unit) -> Import.Fd.t -> (write_buffer array -> count:int -> unit) -> unit Import.Deferred.t) Core.Std.Or_error.t

recvmmsg_loop ~socket callback iteratively receives up to max_count packets at a time on socket and passes them to callback. Each packet is up to Iobuf.capacity bytes.

callback bufs ~count processes count packets synchronously.

Config.init config is used as a prototype for bufs and as one of the elements.

val default_recvmmsg_loop_max_count : int