### Buffer-oriented synchronous read stream requirements

A type `X` meets the `SyncReadStream` requirements if it satisfies the requirements listed below.

In the table below, `a` denotes a value of type `X`, `mb` denotes a (possibly const) value satisfying the `MutableBufferSequence` requirements, and `ec` denotes an object of type `error_code`.

Table 31. SyncReadStream requirements

operation | type | semantics, pre/post-conditions
--- | --- | ---
`a.read_some(mb)` `a.read_some(mb,ec)` | `size_t` | Meets the requirements for a read operation. If `buffer_size(mb) > 0`, reads one or more bytes of data from the stream `a` into the buffer sequence `mb`. If successful, sets `ec` such that `!ec` is `true`, and returns the number of bytes read. If an error occurred, sets `ec` such that `!!ec` is `true`, and returns 0. If all data has been read from the stream, and the stream performed an orderly shutdown, sets `ec` to `stream_errc::eof` and returns 0. If `buffer_size(mb) == 0`, the operation shall not block. Sets `ec` such that `!ec` is `true`, and returns 0.