### Socket service requirements

A socket service must meet the requirements for an I/O object service, as well as the additional requirements listed below.

In the table below, `X` denotes a socket service class for protocol `Protocol`, `a` denotes a value of type `X`, `b` denotes a value of type `X::implementation_type`, `p` denotes a value of type `Protocol`, `n` denotes a value of type `X::native_type`, `e` denotes a value of type `Protocol::endpoint`, `ec` denotes a value of type `error_code`, `s` denotes a value meeting `SettableSocketOption` requirements, `g` denotes a value meeting `GettableSocketOption` requirements, `i` denotes a value meeting `IoControlCommand` requirements, `h` denotes a value of type `socket_base::shutdown_type`, `ch` denotes a value meeting `ConnectHandler` requirements, and `u` and `v` denote identifiers.

Table 20. SocketService requirements

expression | return type | assertion/note pre/post-condition
--- | --- | ---
`X::native_type` |  | The implementation-defined native representation of a socket. Must satisfy the requirements of `CopyConstructible` types (C++ Std, 20.1.3), and the requirements of `Assignable` types (C++ Std, 23.1).
`a.construct(b);` |  | From IoObjectService requirements. post: `!a.is_open(b)`.
`a.destroy(b);` |  | From IoObjectService requirements. Implicitly cancels asynchronous operations, as if by calling `a.close(b, ec)`.
    a.open(b, p, ec);
| `error_code` | pre: `!a.is_open(b)`. post: `!!ec || a.is_open(b)`.
    a.assign(b, p, n, ec);
| `error_code` | pre: `!a.is_open(b)`. post: `!!ec || a.is_open(b)`.
    a.is_open(b);
| `bool` |
    const X& u = a;
    const X::implementation_type& v = b;
    u.is_open(v);
| `bool` |
    a.close(b, ec);
| `error_code` | If `a.is_open()` is true, causes any outstanding asynchronous operations to complete as soon as possible. Handlers for cancelled operations shall be passed the error code `error::operation_aborted`. post: `!a.is_open(b)`.
    a.native(b);
| `X::native_type` |
    a.cancel(b, ec);
| `error_code` | pre: `a.is_open(b)`. Causes any outstanding asynchronous operations to complete as soon as possible. Handlers for cancelled operations shall be passed the error code `error::operation_aborted`.
    a.set_option(b, s, ec);
| `error_code` | pre: `a.is_open(b)`.
    a.get_option(b, g, ec);
| `error_code` | pre: `a.is_open(b)`.
    const X& u = a;
    const X::implementation_type& v = b;
    u.get_option(v, g, ec);
| `error_code` | pre: `a.is_open(b)`.
    a.io_control(b, i, ec);
| `error_code` | pre: `a.is_open(b)`.
    a.at_mark(b, ec);
| `bool` | pre: `a.is_open(b)`.
    const X& u = a;
    const X::implementation_type& v = b;
    u.at_mark(v, ec);
| `bool` | pre: `a.is_open(b)`.
    a.available(b, ec);
| `size_t` | pre: `a.is_open(b)`.
    const X& u = a;
    const X::implementation_type& v = b;
    u.available(v, ec);
| `size_t` | pre: `a.is_open(b)`.
    const typename Protocol::endpoint& u = e;
    a.bind(b, u, ec);
| `error_code` | pre: `a.is_open(b)`.
    a.shutdown(b, h, ec);
| `error_code` | pre: `a.is_open(b)`.
    a.local_endpoint(b, ec);
| `Protocol::endpoint` | pre: `a.is_open(b)`.
    const X& u = a;
    const X::implementation_type& v = b;
    u.local_endpoint(v, ec);
| `Protocol::endpoint` | pre: `a.is_open(b)`.
    a.remote_endpoint(b, ec);
| `Protocol::endpoint` | pre: `a.is_open(b)`.
    const X& u = a;
    const X::implementation_type& v = b;
    u.remote_endpoint(v, ec);
| `Protocol::endpoint` | pre: `a.is_open(b)`.
    const typename Protocol::endpoint& u = e;
    a.connect(b, u, ec);
| `error_code` | pre: `a.is_open(b)`.
    const typename Protocol::endpoint& u = e;
    a.async_connect(b, u, ch);
|  | pre: `a.is_open(b)`. Initiates an asynchronous connect operation that is performed via the `io_service` object `a.io_service()` and behaves according to asynchronous operation requirements.