Socket - Bidirectional streaming IPC transport
Sockets are a bidirectional stream transport. Unlike channels, sockets only move data (not handles).
Data is written into one end of a socket via zx_socket_write and read from the opposing end via zx_socket_read.
Upon creation, both ends of the socket are writable and readable. Via the ZX_SOCKET_SHUTDOWN_READ and ZX_SOCKET_SHUTDOWN_WRITE options to zx_socket_shutdown, one end of the socket can be closed for reading and/or writing.
The following properties may be queried from a socket object:
ZX_PROP_SOCKET_RX_THRESHOLD size of the read threshold of a socket, in bytes. When the bytes queued on the socket (available for reading) is equal to or greater than this value, the ZX_SOCKET_READ_THRESHOLD signal is asserted. Read threshold signalling is disabled by default (and when set, writing a value of 0 for this property disables it).
ZX_PROP_SOCKET_TX_THRESHOLD size of the write threshold of a socket, in bytes. When the space available for writing on the socket is equal to or greater than this value, the ZX_SOCKET_WRITE_THRESHOLD signal is asserted. Write threshold signalling is disabled by default (and when set, writing a value of 0 for this property disables it).
From the point of view of a socket handle, the receive buffer contains the data that is readable via zx_socket_read() from that handle (having been written from the opposing handle), and the transmit buffer contains the data that is written via zx_socket_write() to that handle (and readable from the opposing handle).
The following signals may be set for a socket object:
ZX_SOCKET_READABLE data is available to read from the socket
ZX_SOCKET_WRITABLE data may be written to the socket
ZX_SOCKET_PEER_CLOSED the other endpoint of this socket has been closed.
ZX_SOCKET_PEER_WRITE_DISABLED writing is disabled permanently for the other endpoint either because of passing ZX_SOCKET_SHUTDOWN_READ to this endpoint or passing ZX_SOCKET_SHUTDOWN_WRITE to the peer. Reads on a socket endpoint with this signal raised will succeed so long as there is data in the socket that was written before writing was disabled.
ZX_SOCKET_WRITE_DISABLED writing is disabled permanently for this endpoint either because of passing ZX_SOCKET_SHUTDOWN_WRITE to this endpoint or passing ZX_SOCKET_SHUTDOWN_READ to the peer.
ZX_SOCKET_CONTROL_READABLE data is available to read from the socket control plane.
ZX_SOCKET_CONTROL_WRITABLE data may be written to the socket control plane.
ZX_SOCKET_SHARE a socket may be sent via zx_socket_share.
ZX_SOCKET_ACCEPT a socket may be received via zx_socket_accept.
ZX_SOCKET_READ_THRESHOLD data queued up on socket for reading exceeds the read threshold.
ZX_SOCKET_WRITE_THRESHOLD space available on the socket for writing exceeds the write threshold.