fuchsia.posix.socket

PROTOCOLS

BaseSocket

Defined in fuchsia.posix.socket/socket.fidl

A network socket.

Once a socket has been retrieved from a Provider, this interface is then used to further configure and use the socket. This interface is essentially POSIX. Its implementation must support Linux-specific arguments to {Get,Set}SockOpt.

All methods on this type are nonblocking; their exact behaviors match their Linux counterparts.

Warning: This protocol is not yet ready for direct use by clients. Instead, clients should use the BSD sockets API to interact with sockets. We plan to change this protocol substantially and clients that couple directly to this protocol will make those changes more difficult.

Bind

Sets the local address used for the socket.

Request

Name	Type
addr	fuchsia.net/SocketAddress

Response

Name	Type
result	BaseSocket_Bind_Result

Clone

Create another connection to the same remote object.

flags may be any of:

• OPEN_RIGHT_*
• OPEN_FLAG_APPEND
• OPEN_FLAG_NO_REMOTE
• OPEN_FLAG_DESCRIBE
• CLONE_FLAG_SAME_RIGHTS

All other flags are ignored.

The OPEN_RIGHT_* bits in flags request corresponding rights over the resulting cloned object. The cloned object must have rights less than or equal to the original object. Alternatively, pass CLONE_FLAG_SAME_RIGHTS to inherit the rights on the source connection. It is invalid to pass any of the OPEN_RIGHT_* flags together with CLONE_FLAG_SAME_RIGHTS.

Request

Name	Type
flags	uint32
object	request<fuchsia.io/Node>

Close

Terminates connection with object.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
s	zx/status

Connect

Initiates a connection to a remote address.

Request

Name	Type
addr	fuchsia.net/SocketAddress

Response

Name	Type
result	BaseSocket_Connect_Result

Describe

Returns extra information about the type of the object. If the Describe operation fails, the connection is closed.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
info	fuchsia.io/NodeInfo

Disconnect

Clears connection information from this socket.

Request

Name	Type

Response

Name	Type
result	BaseSocket_Disconnect_Result

GetAttr

Acquires information about the node.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
s	zx/status
attributes	fuchsia.io/NodeAttributes

GetPeerName

Retrieves the remote socket address.

Request

Name	Type

Response

Name	Type
result	BaseSocket_GetPeerName_Result

GetSockName

Retrieves the local socket address.

Request

Name	Type

Response

Name	Type
result	BaseSocket_GetSockName_Result

GetSockOpt

Retrieves the value of a socket option.

Request

Name	Type
level	int16
optname	int16

Response

Name	Type
result	BaseSocket_GetSockOpt_Result

NodeGetFlags

Acquires the Directory.Open rights and flags used to access this file.

This method does not require any rights. This method has the same functionality as GetFlags for File and is meant as an in-progress replacement.

Request

Name	Type

Response

Name	Type
s	zx/status
flags	uint32

NodeSetFlags

Changes the Directory.Open flags used to access the file. Supported flags which can be turned on / off:

• OPEN_FLAG_APPEND

This method does not require any rights. This method has the same functionality as SetFlags for File and is meant as an in-progress replacement.

Request

Name	Type
flags	uint32

Response

Name	Type
s	zx/status

OnOpen

An event produced eagerly by a FIDL server if requested by OPEN_FLAG_DESCRIBE.

Indicates the success or failure of the open operation, and optionally describes the object. If the status is ZX_OK, info contains descriptive information about the object (the same as would be returned by Describe).

Response

Name	Type
s	zx/status
info	fuchsia.io/NodeInfo?

SetAttr

Updates information about the node. flags may be any of NODE_ATTRIBUTE_FLAG_*.

This method requires following rights: OPEN_RIGHT_WRITABLE.

Request

Name	Type
flags	uint32
attributes	fuchsia.io/NodeAttributes

Response

Name	Type
s	zx/status

SetSockOpt

Sets the value of a socket option.

Request

Name	Type
level	int16
optname	int16
optval	sockopt

Response

Name	Type
result	BaseSocket_SetSockOpt_Result

Sync

Synchronizes updates to the node to the underlying media, if it exists.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
s	zx/status

DatagramSocket

Defined in fuchsia.posix.socket/socket.fidl

A datagram socket.

This type's fuchsia.io.Node/Describe method returns an eventpair which is used to signal additional information about the state of the socket such as readiness or shutdown-ness.

All methods on this type are nonblocking; their exact behaviors match their Linux counterparts.

Bind

Sets the local address used for the socket.

Request

Name	Type
addr	fuchsia.net/SocketAddress

Response

Name	Type
result	BaseSocket_Bind_Result

Clone

Create another connection to the same remote object.

flags may be any of:

• OPEN_RIGHT_*
• OPEN_FLAG_APPEND
• OPEN_FLAG_NO_REMOTE
• OPEN_FLAG_DESCRIBE
• CLONE_FLAG_SAME_RIGHTS

All other flags are ignored.

The OPEN_RIGHT_* bits in flags request corresponding rights over the resulting cloned object. The cloned object must have rights less than or equal to the original object. Alternatively, pass CLONE_FLAG_SAME_RIGHTS to inherit the rights on the source connection. It is invalid to pass any of the OPEN_RIGHT_* flags together with CLONE_FLAG_SAME_RIGHTS.

Request

Name	Type
flags	uint32
object	request<fuchsia.io/Node>

Close

Terminates connection with object.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
s	zx/status

Connect

Initiates a connection to a remote address.

Request

Name	Type
addr	fuchsia.net/SocketAddress

Response

Name	Type
result	BaseSocket_Connect_Result

Describe

Returns extra information about the type of the object. If the Describe operation fails, the connection is closed.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
info	fuchsia.io/NodeInfo

Disconnect

Clears connection information from this socket.

Request

Name	Type

Response

Name	Type
result	BaseSocket_Disconnect_Result

GetAttr

Acquires information about the node.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
s	zx/status
attributes	fuchsia.io/NodeAttributes

GetPeerName

Retrieves the remote socket address.

Request

Name	Type

Response

Name	Type
result	BaseSocket_GetPeerName_Result

GetSockName

Retrieves the local socket address.

Request

Name	Type

Response

Name	Type
result	BaseSocket_GetSockName_Result

GetSockOpt

Retrieves the value of a socket option.

Request

Name	Type
level	int16
optname	int16

Response

Name	Type
result	BaseSocket_GetSockOpt_Result

NodeGetFlags

Acquires the Directory.Open rights and flags used to access this file.

This method does not require any rights. This method has the same functionality as GetFlags for File and is meant as an in-progress replacement.

Request

Name	Type

Response

Name	Type
s	zx/status
flags	uint32

NodeSetFlags

Changes the Directory.Open flags used to access the file. Supported flags which can be turned on / off:

• OPEN_FLAG_APPEND

This method does not require any rights. This method has the same functionality as SetFlags for File and is meant as an in-progress replacement.

Request

Name	Type
flags	uint32

Response

Name	Type
s	zx/status

OnOpen

An event produced eagerly by a FIDL server if requested by OPEN_FLAG_DESCRIBE.

Indicates the success or failure of the open operation, and optionally describes the object. If the status is ZX_OK, info contains descriptive information about the object (the same as would be returned by Describe).

Response

Name	Type
s	zx/status
info	fuchsia.io/NodeInfo?

RecvMsg

Receives a message from the socket.

Request

Name	Type
want_addr	bool
data_len	uint32
want_control	bool
flags	RecvMsgFlags

Response

Name	Type
result	DatagramSocket_RecvMsg_Result

SendMsg

Sends a message on the socket.

Request

Name	Type
addr	fuchsia.net/SocketAddress?
data	vector<uint8>
control	SendControlData
flags	SendMsgFlags

Response

Name	Type
result	DatagramSocket_SendMsg_Result

SetAttr

Updates information about the node. flags may be any of NODE_ATTRIBUTE_FLAG_*.

This method requires following rights: OPEN_RIGHT_WRITABLE.

Request

Name	Type
flags	uint32
attributes	fuchsia.io/NodeAttributes

Response

Name	Type
s	zx/status

SetSockOpt

Sets the value of a socket option.

Request

Name	Type
level	int16
optname	int16
optval	sockopt

Response

Name	Type
result	BaseSocket_SetSockOpt_Result

Shutdown

Shuts down part of the socket.

Request

Name	Type
mode	ShutdownMode

Response

Name	Type
result	DatagramSocket_Shutdown_Result

Sync

Synchronizes updates to the node to the underlying media, if it exists.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
s	zx/status

Provider

Defined in fuchsia.posix.socket/socket.fidl

Provider implements the POSIX sockets API.

DatagramSocket

Requests a datagram socket with the specified parameters.

Request

Name	Type
domain	Domain
proto	DatagramSocketProtocol

Response

Name	Type
result	Provider_DatagramSocket_Result

GetInterfaceAddresses

Requests a list of fuchsia.posix.socket.InterfaceAddresses describing the network interfaces on the system.

Request

Name	Type

Response

Name	Type
interfaces	vector<InterfaceAddresses>

InterfaceIndexToName

Looks up an interface by its index and returns its name. Returns ZX_ERR_NOT_FOUND if the specified index doesn't exist.

Request

Name	Type
index	uint64

Response

Name	Type
result	Provider_InterfaceIndexToName_Result

InterfaceNameToFlags

Looks up an interface by its name and returns its flags. Returns ZX_ERR_NOT_FOUND if the specified name doesn't exist.

Request

Name	Type
name	interface_name

Response

Name	Type
result	Provider_InterfaceNameToFlags_Result

InterfaceNameToIndex

Looks up an interface by its name and returns its index. Returns ZX_ERR_NOT_FOUND if the specified name doesn't exist.

Request

Name	Type
name	interface_name

Response

Name	Type
result	Provider_InterfaceNameToIndex_Result

StreamSocket

Requests a stream socket with the specified parameters.

Request

Name	Type
domain	Domain
proto	StreamSocketProtocol

Response

Name	Type
result	Provider_StreamSocket_Result

StreamSocket

Defined in fuchsia.posix.socket/socket.fidl

A stream socket.

This type's fuchsia.io.Node/Describe method returns a socket which is used to transfer data to and from the caller. Signals are used to communicate additional information about the state of the socket such as connectedness and the presence of incoming connections in the case of a listening socket.

All methods on this type are nonblocking; their exact behaviors match their Linux counterparts.

Accept

Accepts a buffered incoming connection.

Request

Name	Type
want_addr	bool

Response

Name	Type
result	StreamSocket_Accept_Result

Bind

Sets the local address used for the socket.

Request

Name	Type
addr	fuchsia.net/SocketAddress

Response

Name	Type
result	BaseSocket_Bind_Result

Clone

Create another connection to the same remote object.

flags may be any of:

• OPEN_RIGHT_*
• OPEN_FLAG_APPEND
• OPEN_FLAG_NO_REMOTE
• OPEN_FLAG_DESCRIBE
• CLONE_FLAG_SAME_RIGHTS

All other flags are ignored.

The OPEN_RIGHT_* bits in flags request corresponding rights over the resulting cloned object. The cloned object must have rights less than or equal to the original object. Alternatively, pass CLONE_FLAG_SAME_RIGHTS to inherit the rights on the source connection. It is invalid to pass any of the OPEN_RIGHT_* flags together with CLONE_FLAG_SAME_RIGHTS.

Request

Name	Type
flags	uint32
object	request<fuchsia.io/Node>

Close

Terminates connection with object.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
s	zx/status

Connect

Initiates a connection to a remote address.

Request

Name	Type
addr	fuchsia.net/SocketAddress

Response

Name	Type
result	BaseSocket_Connect_Result

Describe

Returns extra information about the type of the object. If the Describe operation fails, the connection is closed.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
info	fuchsia.io/NodeInfo

Disconnect

Clears connection information from this socket.

Request

Name	Type

Response

Name	Type
result	BaseSocket_Disconnect_Result

GetAttr

Acquires information about the node.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
s	zx/status
attributes	fuchsia.io/NodeAttributes

GetPeerName

Retrieves the remote socket address.

Request

Name	Type

Response

Name	Type
result	BaseSocket_GetPeerName_Result

GetSockName

Retrieves the local socket address.

Request

Name	Type

Response

Name	Type
result	BaseSocket_GetSockName_Result

GetSockOpt

Retrieves the value of a socket option.

Request

Name	Type
level	int16
optname	int16

Response

Name	Type
result	BaseSocket_GetSockOpt_Result

Listen

Begins listening for new incoming connections. At most backlog connections will be buffered.

Request

Name	Type
backlog	int16

Response

Name	Type
result	StreamSocket_Listen_Result

NodeGetFlags

Acquires the Directory.Open rights and flags used to access this file.

This method does not require any rights. This method has the same functionality as GetFlags for File and is meant as an in-progress replacement.

Request

Name	Type

Response

Name	Type
s	zx/status
flags	uint32

NodeSetFlags

Changes the Directory.Open flags used to access the file. Supported flags which can be turned on / off:

• OPEN_FLAG_APPEND

This method does not require any rights. This method has the same functionality as SetFlags for File and is meant as an in-progress replacement.

Request

Name	Type
flags	uint32

Response

Name	Type
s	zx/status

OnOpen

An event produced eagerly by a FIDL server if requested by OPEN_FLAG_DESCRIBE.

Indicates the success or failure of the open operation, and optionally describes the object. If the status is ZX_OK, info contains descriptive information about the object (the same as would be returned by Describe).

Response

Name	Type
s	zx/status
info	fuchsia.io/NodeInfo?

SetAttr

Updates information about the node. flags may be any of NODE_ATTRIBUTE_FLAG_*.

This method requires following rights: OPEN_RIGHT_WRITABLE.

Request

Name	Type
flags	uint32
attributes	fuchsia.io/NodeAttributes

Response

Name	Type
s	zx/status

SetSockOpt

Sets the value of a socket option.

Request

Name	Type
level	int16
optname	int16
optval	sockopt

Response

Name	Type
result	BaseSocket_SetSockOpt_Result

Sync

Synchronizes updates to the node to the underlying media, if it exists.

This method does not require any rights.

Request

Name	Type

Response

Name	Type
s	zx/status

STRUCTS

BaseSocket_Bind_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default

BaseSocket_Connect_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default

BaseSocket_Disconnect_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default

BaseSocket_GetPeerName_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default
addr	fuchsia.net/SocketAddress		No default

BaseSocket_GetSockName_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default
addr	fuchsia.net/SocketAddress		No default

BaseSocket_GetSockOpt_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default
optval	sockopt		No default

BaseSocket_SetSockOpt_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default

DatagramSocket_RecvMsg_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default
addr	fuchsia.net/SocketAddress?		No default
data	vector<uint8>		No default
control	RecvControlData		No default
truncated	uint32		No default

DatagramSocket_SendMsg_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default
len	int64		No default

DatagramSocket_Shutdown_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default

Empty

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default

Provider_DatagramSocket_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default
s	DatagramSocket		No default

Provider_InterfaceIndexToName_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default
name	interface_name		No default

Provider_InterfaceNameToFlags_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default
flags	InterfaceFlags		No default

Provider_InterfaceNameToIndex_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default
index	uint64		No default

Provider_StreamSocket_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default
s	StreamSocket		No default

StreamSocket_Accept_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default
addr	fuchsia.net/SocketAddress?		No default
s	StreamSocket		No default

StreamSocket_Listen_Response

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description	Default

ENUMS

DatagramSocketProtocol

Type: uint32

Defined in fuchsia.posix.socket/socket.fidl

Protocols supported by DatagramSocket.

DatagramSocketProtocol enumerates the protocols supported by the network stack over datagram sockets.

Name	Value	Description
UDP	1	UDP (User Datagram Protocol). A UDP socket is equivalent to the POSIX API of SOCK_DGRAM with a protocol of 0 or IPPROTO_UDP.
ICMP_ECHO	2	ICMP (Internet Control Message Protocol) echo. An ICMP echo socket is equivalent to the POSIX API of SOCK_DGRAM with a protocol of IPPROTO_ICMP IPPROTO_ICMPV6 (depending on provided domain). Datagrams sent over an ICMP echo socket must have a valid ICMP or ICMPv6 echo header.

Domain

Type: int16

Defined in fuchsia.posix.socket/socket.fidl

A socket's domain.

Determines the addressing domain for a socket.

Name	Value	Description
IPV4	0	An IPv4 socket. Equivalent to AF_INET.
IPV6	1	An IPv6 socket. Equivalent to AF_INET6.

StreamSocketProtocol

Type: uint32

Defined in fuchsia.posix.socket/socket.fidl

Protocols supported by StreamSocket.

StreamSocketProtocol enumerates the protocols supported by the network stack over stream sockets.

Name	Value	Description
TCP	0	TCP (Transmission Control Protocol). A TCP socket is equivalent to the POSIX API of SOCK_STREAM with a protocol of 0 or IPPROTO_TCP.

TABLES

InterfaceAddresses

Defined in fuchsia.posix.socket/socket.fidl

Holds information about an interface and its addresses.

Ordinal	Name	Type	Description
1	id	uint64	ID of the interface.
2	name	interface_name	Name of the interface.
3	flags	uint32	Contains the interface flags, as returned by the SIOCGIFFLAGS ioctl operation. TODO(fxbug.dev/64758): remove this once all clients are transitioned to use more strongly-typed interface_flags.
4	addresses	vector<fuchsia.net/Subnet>	All addresses currently assigned to the interface.
5	interface_flags	InterfaceFlags	Contains the interface flags, as returned by the SIOCGIFFLAGS ioctl operation.

RecvControlData

Defined in fuchsia.posix.socket/socket.fidl

Ancillary data for received datagram sockets.

Ordinal	Name	Type	Description

SendControlData

Defined in fuchsia.posix.socket/socket.fidl

Ancillary data for sending datagram sockets.

Ordinal	Name	Type	Description

UNIONS

BaseSocket_Bind_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	BaseSocket_Bind_Response
err	fuchsia.posix/Errno

BaseSocket_Connect_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	BaseSocket_Connect_Response
err	fuchsia.posix/Errno

BaseSocket_Disconnect_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	BaseSocket_Disconnect_Response
err	fuchsia.posix/Errno

BaseSocket_GetPeerName_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	BaseSocket_GetPeerName_Response
err	fuchsia.posix/Errno

BaseSocket_GetSockName_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	BaseSocket_GetSockName_Response
err	fuchsia.posix/Errno

BaseSocket_GetSockOpt_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	BaseSocket_GetSockOpt_Response
err	fuchsia.posix/Errno

BaseSocket_SetSockOpt_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	BaseSocket_SetSockOpt_Response
err	fuchsia.posix/Errno

DatagramSocket_RecvMsg_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	DatagramSocket_RecvMsg_Response
err	fuchsia.posix/Errno

DatagramSocket_SendMsg_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	DatagramSocket_SendMsg_Response
err	fuchsia.posix/Errno

DatagramSocket_Shutdown_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	DatagramSocket_Shutdown_Response
err	fuchsia.posix/Errno

Provider_DatagramSocket_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	Provider_DatagramSocket_Response
err	fuchsia.posix/Errno

Provider_InterfaceIndexToName_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	Provider_InterfaceIndexToName_Response
err	zx/status

Provider_InterfaceNameToFlags_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	Provider_InterfaceNameToFlags_Response
err	zx/status

Provider_InterfaceNameToIndex_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	Provider_InterfaceNameToIndex_Response
err	zx/status

Provider_StreamSocket_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	Provider_StreamSocket_Response
err	fuchsia.posix/Errno

StreamSocket_Accept_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	StreamSocket_Accept_Response
err	fuchsia.posix/Errno

StreamSocket_Listen_Result

Defined in fuchsia.posix.socket/socket.fidl

Name	Type	Description
response	StreamSocket_Listen_Response
err	fuchsia.posix/Errno

BITS

InterfaceFlags

Type: uint16

Defined in fuchsia.posix.socket/socket.fidl

Bits representing the interface flags as returned by the SIOCGIFFLAGS ioctl operation. These bitmasks are intended to track the C API definition. For example, InterfaceFlags.UP corresponds to IFF_UP, etc.

Name	Value	Description
UP	1
BROADCAST	2
DEBUG	4
LOOPBACK	8
POINTTOPOINT	16
NOTRAILERS	32
RUNNING	64
NOARP	128
PROMISC	256
ALLMULTI	512
LEADER	1024
FOLLOWER	2048
MULTICAST	4096
PORTSEL	8192
AUTOMEDIA	16384
DYNAMIC	32768

RecvMsgFlags

Type: uint16

Defined in fuchsia.posix.socket/socket.fidl

Flags controlling RecvMsg behavior.

Name	Value	Description
PEEK	2	Returns data from the receive queue without removing from it. Equivalent to MSG_PEEK.

SendMsgFlags

Type: uint16

Defined in fuchsia.posix.socket/socket.fidl

Name	Value	Description
RESERVED	32768

ShutdownMode

Type: uint16

Defined in fuchsia.posix.socket/socket.fidl

Socket shutdown mode.

Name	Value	Description
READ	1	Shutdown socket read endpoint.
WRITE	2	Shutdown socket write endpoint.

CONSTANTS

Name	Value	Type	Description
INTERFACE_NAME_LENGTH	15	uint8	The maximum length of an interface name.

TYPE ALIASES

Name	Value	Description
interface_name	string[INTERFACE_NAME_LENGTH]	An interface name as a sequence of bytes.
sockopt	vector[900]	Chosen to be large enough to hold whatever we might want to cram in it. So long as we support socket options, we don't have a good sense of what we might want to send as payload.