Datagram socket service requirements

A datagram socket service must meet the requirements for a socket service, as well as the additional requirements listed below.

In the table below, X denotes a datagram socket service class for protocol Protocol, a denotes a value of type X, b denotes a value of type X::implementation_type, e denotes a value of type Protocol::endpoint, ec denotes a value of type error_code, f denotes a value of type socket_base::message_flags, mb denotes a value satisfying mutable buffer sequence requirements, rh denotes a value meeting ReadHandler requirements, cb denotes a value satisfying constant buffer sequence requirements, and wh denotes a value meeting WriteHandler requirements.

Table 8. DatagramSocketService requirements

expression	return type	assertion/note pre/post-condition
`a.receive(b, mb, f, ec);`	`size_t`	pre: `a.is_open(b)`. Reads one or more bytes of data from a connected socket `b`. The mutable buffer sequence `mb` specifies memory where the data should be placed. The operation shall always fill a buffer in the sequence completely before proceeding to the next. If successful, returns the number of bytes read. Otherwise returns `0`.
`a.async_receive(b, mb, f, rh);`	`void`	pre: `a.is_open(b)`. Initiates an asynchronous operation to read one or more bytes of data from a connected socket `b`. The operation is performed via the `io_service` object `a.get_io_service()` and behaves according to asynchronous operation requirements. The mutable buffer sequence `mb` specifies memory where the data should be placed. The operation shall always fill a buffer in the sequence completely before proceeding to the next. The implementation shall maintain one or more copies of `mb` until such time as the read operation no longer requires access to the memory specified by the buffers in the sequence. The program must ensure the memory is valid until: — the last copy of `mb` is destroyed, or — the handler for the asynchronous operation is invoked, whichever comes first. If the operation completes successfully, the `ReadHandler` object `rh` is invoked with the number of bytes transferred. Otherwise it is invoked with `0`.
`a.receive_from(b, mb, e, f, ec);`	`size_t`	pre: `a.is_open(b)`. Reads one or more bytes of data from an unconnected socket `b`. The mutable buffer sequence `mb` specifies memory where the data should be placed. The operation shall always fill a buffer in the sequence completely before proceeding to the next. If successful, returns the number of bytes read. Otherwise returns `0`.
`a.async_receive_from(b, mb, e, f, rh);`	`void`	pre: `a.is_open(b)`. Initiates an asynchronous operation to read one or more bytes of data from an unconnected socket `b`. The operation is performed via the `io_service` object `a.get_io_service()` and behaves according to asynchronous operation requirements. The mutable buffer sequence `mb` specifies memory where the data should be placed. The operation shall always fill a buffer in the sequence completely before proceeding to the next. The implementation shall maintain one or more copies of `mb` until such time as the read operation no longer requires access to the memory specified by the buffers in the sequence. The program must ensure the memory is valid until: — the last copy of `mb` is destroyed, or — the handler for the asynchronous operation is invoked, whichever comes first. The program must ensure the object `e` is valid until the handler for the asynchronous operation is invoked. If the operation completes successfully, the `ReadHandler` object `rh` is invoked with the number of bytes transferred. Otherwise it is invoked with `0`.
`a.send(b, cb, f, ec);`	`size_t`	pre: `a.is_open(b)`. Writes one or more bytes of data to a connected socket `b`. The constant buffer sequence `cb` specifies memory where the data to be written is located. The operation shall always write a buffer in the sequence completely before proceeding to the next. If successful, returns the number of bytes written. Otherwise returns `0`.
`a.async_send(b, cb, f, wh);`	`void`	pre: `a.is_open(b)`. Initiates an asynchronous operation to write one or more bytes of data to a connected socket `b`. The operation is performed via the `io_service` object `a.get_io_service()` and behaves according to asynchronous operation requirements. The constant buffer sequence `cb` specifies memory where the data to be written is located. The operation shall always write a buffer in the sequence completely before proceeding to the next. The implementation shall maintain one or more copies of `cb` until such time as the write operation no longer requires access to the memory specified by the buffers in the sequence. The program must ensure the memory is valid until: — the last copy of `cb` is destroyed, or — the handler for the asynchronous operation is invoked, whichever comes first. If the operation completes successfully, the `WriteHandler` object `wh` is invoked with the number of bytes transferred. Otherwise it is invoked with `0`.
const typename Protocol::endpoint& u = e; a.send_to(b, cb, u, f, ec);	`size_t`	pre: `a.is_open(b)`. Writes one or more bytes of data to an unconnected socket `b`. The constant buffer sequence `cb` specifies memory where the data to be written is located. The operation shall always write a buffer in the sequence completely before proceeding to the next. If successful, returns the number of bytes written. Otherwise returns `0`.
const typename Protocol::endpoint& u = e; a.async_send(b, cb, u, f, wh);	`void`	pre: `a.is_open(b)`. Initiates an asynchronous operation to write one or more bytes of data to an unconnected socket `b`. The operation is performed via the `io_service` object `a.get_io_service()` and behaves according to asynchronous operation requirements. The constant buffer sequence `cb` specifies memory where the data to be written is located. The operation shall always write a buffer in the sequence completely before proceeding to the next. The implementation shall maintain one or more copies of `cb` until such time as the write operation no longer requires access to the memory specified by the buffers in the sequence. The program must ensure the memory is valid until: — the last copy of `cb` is destroyed, or — the handler for the asynchronous operation is invoked, whichever comes first. If the operation completes successfully, the `WriteHandler` object `wh` is invoked with the number of bytes transferred. Otherwise it is invoked with `0`.