Struct wasi::sockets::tcp::TcpSocket

pub struct TcpSocket { /* private fields */ }

A TCP socket resource.

The socket can be in one of the following states:

• unbound
• bind-in-progress
• bound (See note below)
• listen-in-progress
• listening
• connect-in-progress
• connected
• closed See https://github.com/WebAssembly/wasi-sockets/TcpSocketOperationalSemantics.md for a more information.

Note: Except where explicitly mentioned, whenever this documentation uses the term “bound” without backticks it actually means: in the bound state or higher. (i.e. bound, listen-in-progress, listening, connect-in-progress or connected)

In addition to the general error codes documented on the network::error-code type, TCP socket methods may always return error(invalid-state) when in the closed state.

Implementations

impl TcpSocket

pub fn start_bind( &self, network: &Network, local_address: IpSocketAddress ) -> Result<(), ErrorCode>

Bind the socket to a specific network on the provided IP address and port.

If the IP address is zero (0.0.0.0 in IPv4, :: in IPv6), it is left to the implementation to decide which network interface(s) to bind to. If the TCP/UDP port is zero, the socket will be bound to a random free port.

Bind can be attempted multiple times on the same socket, even with different arguments on each iteration. But never concurrently and only as long as the previous bind failed. Once a bind succeeds, the binding can’t be changed anymore.

Typical errors

• invalid-argument: The local-address has the wrong address family. (EAFNOSUPPORT, EFAULT on Windows)
• invalid-argument: local-address is not a unicast address. (EINVAL)
• invalid-argument: local-address is an IPv4-mapped IPv6 address. (EINVAL)
• invalid-state: The socket is already bound. (EINVAL)
• address-in-use: No ephemeral ports available. (EADDRINUSE, ENOBUFS on Windows)
• address-in-use: Address is already in use. (EADDRINUSE)
• address-not-bindable: local-address is not an address that the network can bind to. (EADDRNOTAVAIL)
• not-in-progress: A bind operation is not in progress.
• would-block: Can’t finish the operation, it is still in progress. (EWOULDBLOCK, EAGAIN)

Implementors note

When binding to a non-zero port, this bind operation shouldn’t be affected by the TIME_WAIT state of a recently closed socket on the same local address. In practice this means that the SO_REUSEADDR socket option should be set implicitly on all platforms, except on Windows where this is the default behavior and SO_REUSEADDR performs something different entirely.

Unlike in POSIX, in WASI the bind operation is async. This enables interactive WASI hosts to inject permission prompts. Runtimes that don’t want to make use of this ability can simply call the native bind as part of either start-bind or finish-bind.

References

• https://pubs.opengroup.org/onlinepubs/9699919799/functions/bind.html
• https://man7.org/linux/man-pages/man2/bind.2.html
• https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-bind
• https://man.freebsd.org/cgi/man.cgi?query=bind&sektion=2&format=html

impl TcpSocket

pub fn finish_bind(&self) -> Result<(), ErrorCode>

impl TcpSocket

pub fn start_connect( &self, network: &Network, remote_address: IpSocketAddress ) -> Result<(), ErrorCode>

Connect to a remote endpoint.

On success:

• the socket is transitioned into the connection state.
• a pair of streams is returned that can be used to read & write to the connection

After a failed connection attempt, the socket will be in the closed state and the only valid action left is to drop the socket. A single socket can not be used to connect more than once.

Typical errors

• invalid-argument: The remote-address has the wrong address family. (EAFNOSUPPORT)
• invalid-argument: remote-address is not a unicast address. (EINVAL, ENETUNREACH on Linux, EAFNOSUPPORT on MacOS)
• invalid-argument: remote-address is an IPv4-mapped IPv6 address. (EINVAL, EADDRNOTAVAIL on Illumos)
• invalid-argument: The IP address in remote-address is set to INADDR_ANY (0.0.0.0 / ::). (EADDRNOTAVAIL on Windows)
• invalid-argument: The port in remote-address is set to 0. (EADDRNOTAVAIL on Windows)
• invalid-argument: The socket is already attached to a different network. The network passed to connect must be identical to the one passed to bind.
• invalid-state: The socket is already in the connected state. (EISCONN)
• invalid-state: The socket is already in the listening state. (EOPNOTSUPP, EINVAL on Windows)
• timeout: Connection timed out. (ETIMEDOUT)
• connection-refused: The connection was forcefully rejected. (ECONNREFUSED)
• connection-reset: The connection was reset. (ECONNRESET)
• connection-aborted: The connection was aborted. (ECONNABORTED)
• remote-unreachable: The remote address is not reachable. (EHOSTUNREACH, EHOSTDOWN, ENETUNREACH, ENETDOWN, ENONET)
• address-in-use: Tried to perform an implicit bind, but there were no ephemeral ports available. (EADDRINUSE, EADDRNOTAVAIL on Linux, EAGAIN on BSD)
• not-in-progress: A connect operation is not in progress.
• would-block: Can’t finish the operation, it is still in progress. (EWOULDBLOCK, EAGAIN)

Implementors note

The POSIX equivalent of start-connect is the regular connect syscall. Because all WASI sockets are non-blocking this is expected to return EINPROGRESS, which should be translated to ok() in WASI.

The POSIX equivalent of finish-connect is a poll for event POLLOUT with a timeout of 0 on the socket descriptor. Followed by a check for the SO_ERROR socket option, in case the poll signaled readiness.

References

• https://pubs.opengroup.org/onlinepubs/9699919799/functions/connect.html
• https://man7.org/linux/man-pages/man2/connect.2.html
• https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-connect
• https://man.freebsd.org/cgi/man.cgi?connect

impl TcpSocket

pub fn finish_connect(&self) -> Result<(InputStream, OutputStream), ErrorCode>

impl TcpSocket

pub fn start_listen(&self) -> Result<(), ErrorCode>

Start listening for new connections.

Transitions the socket into the listening state.

Unlike POSIX, the socket must already be explicitly bound.

Typical errors

• invalid-state: The socket is not bound to any local address. (EDESTADDRREQ)
• invalid-state: The socket is already in the connected state. (EISCONN, EINVAL on BSD)
• invalid-state: The socket is already in the listening state.
• address-in-use: Tried to perform an implicit bind, but there were no ephemeral ports available. (EADDRINUSE)
• not-in-progress: A listen operation is not in progress.
• would-block: Can’t finish the operation, it is still in progress. (EWOULDBLOCK, EAGAIN)

Implementors note

Unlike in POSIX, in WASI the listen operation is async. This enables interactive WASI hosts to inject permission prompts. Runtimes that don’t want to make use of this ability can simply call the native listen as part of either start-listen or finish-listen.

References

• https://pubs.opengroup.org/onlinepubs/9699919799/functions/listen.html
• https://man7.org/linux/man-pages/man2/listen.2.html
• https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-listen
• https://man.freebsd.org/cgi/man.cgi?query=listen&sektion=2

impl TcpSocket

pub fn finish_listen(&self) -> Result<(), ErrorCode>

impl TcpSocket

pub fn accept( &self ) -> Result<(TcpSocket, InputStream, OutputStream), ErrorCode>

Accept a new client socket.

The returned socket is bound and in the connected state. The following properties are inherited from the listener socket:

• address-family
• keep-alive-enabled
• keep-alive-idle-time
• keep-alive-interval
• keep-alive-count
• hop-limit
• receive-buffer-size
• send-buffer-size

On success, this function returns the newly accepted client socket along with a pair of streams that can be used to read & write to the connection.

Typical errors

• invalid-state: Socket is not in the listening state. (EINVAL)
• would-block: No pending connections at the moment. (EWOULDBLOCK, EAGAIN)
• connection-aborted: An incoming connection was pending, but was terminated by the client before this listener could accept it. (ECONNABORTED)
• new-socket-limit: The new socket resource could not be created because of a system limit. (EMFILE, ENFILE)

References

• https://pubs.opengroup.org/onlinepubs/9699919799/functions/accept.html
• https://man7.org/linux/man-pages/man2/accept.2.html
• https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-accept
• https://man.freebsd.org/cgi/man.cgi?query=accept&sektion=2

impl TcpSocket

pub fn local_address(&self) -> Result<IpSocketAddress, ErrorCode>

Get the bound local address.

POSIX mentions:

If the socket has not been bound to a local name, the value stored in the object pointed to by address is unspecified.

WASI is stricter and requires local-address to return invalid-state when the socket hasn’t been bound yet.

Typical errors

• invalid-state: The socket is not bound to any local address.

References

• https://pubs.opengroup.org/onlinepubs/9699919799/functions/getsockname.html
• https://man7.org/linux/man-pages/man2/getsockname.2.html
• https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-getsockname
• https://man.freebsd.org/cgi/man.cgi?getsockname

impl TcpSocket

pub fn remote_address(&self) -> Result<IpSocketAddress, ErrorCode>

Get the remote address.

Typical errors

• invalid-state: The socket is not connected to a remote address. (ENOTCONN)

References

• https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpeername.html
• https://man7.org/linux/man-pages/man2/getpeername.2.html
• https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-getpeername
• https://man.freebsd.org/cgi/man.cgi?query=getpeername&sektion=2&n=1

impl TcpSocket

pub fn is_listening(&self) -> bool

Whether the socket is in the listening state.

Equivalent to the SO_ACCEPTCONN socket option.

impl TcpSocket

pub fn address_family(&self) -> IpAddressFamily

Whether this is a IPv4 or IPv6 socket.

Equivalent to the SO_DOMAIN socket option.

impl TcpSocket

pub fn set_listen_backlog_size(&self, value: u64) -> Result<(), ErrorCode>

Hints the desired listen queue size. Implementations are free to ignore this.

If the provided value is 0, an invalid-argument error is returned. Any other value will never cause an error, but it might be silently clamped and/or rounded.

Typical errors

• not-supported: (set) The platform does not support changing the backlog size after the initial listen.
• invalid-argument: (set) The provided value was 0.
• invalid-state: (set) The socket is in the connect-in-progress or connected state.

impl TcpSocket

pub fn keep_alive_enabled(&self) -> Result<bool, ErrorCode>

Enables or disables keepalive.

The keepalive behavior can be adjusted using:

• keep-alive-idle-time
• keep-alive-interval
• keep-alive-count These properties can be configured while keep-alive-enabled is false, but only come into effect when keep-alive-enabled is true.

Equivalent to the SO_KEEPALIVE socket option.

impl TcpSocket

pub fn set_keep_alive_enabled(&self, value: bool) -> Result<(), ErrorCode>

impl TcpSocket

pub fn keep_alive_idle_time(&self) -> Result<Duration, ErrorCode>

Amount of time the connection has to be idle before TCP starts sending keepalive packets.

If the provided value is 0, an invalid-argument error is returned. Any other value will never cause an error, but it might be silently clamped and/or rounded. I.e. after setting a value, reading the same setting back may return a different value.

Equivalent to the TCP_KEEPIDLE socket option. (TCP_KEEPALIVE on MacOS)

Typical errors

• invalid-argument: (set) The provided value was 0.

impl TcpSocket

pub fn set_keep_alive_idle_time(&self, value: Duration) -> Result<(), ErrorCode>

impl TcpSocket

pub fn keep_alive_interval(&self) -> Result<Duration, ErrorCode>

The time between keepalive packets.

If the provided value is 0, an invalid-argument error is returned. Any other value will never cause an error, but it might be silently clamped and/or rounded. I.e. after setting a value, reading the same setting back may return a different value.

Equivalent to the TCP_KEEPINTVL socket option.

Typical errors

• invalid-argument: (set) The provided value was 0.

impl TcpSocket

pub fn set_keep_alive_interval(&self, value: Duration) -> Result<(), ErrorCode>

impl TcpSocket

pub fn keep_alive_count(&self) -> Result<u32, ErrorCode>

The maximum amount of keepalive packets TCP should send before aborting the connection.

If the provided value is 0, an invalid-argument error is returned. Any other value will never cause an error, but it might be silently clamped and/or rounded. I.e. after setting a value, reading the same setting back may return a different value.

Equivalent to the TCP_KEEPCNT socket option.

Typical errors

• invalid-argument: (set) The provided value was 0.

impl TcpSocket

pub fn set_keep_alive_count(&self, value: u32) -> Result<(), ErrorCode>

impl TcpSocket

pub fn hop_limit(&self) -> Result<u8, ErrorCode>

Equivalent to the IP_TTL & IPV6_UNICAST_HOPS socket options.

If the provided value is 0, an invalid-argument error is returned.

Typical errors

• invalid-argument: (set) The TTL value must be 1 or higher.

impl TcpSocket

pub fn set_hop_limit(&self, value: u8) -> Result<(), ErrorCode>

impl TcpSocket

pub fn receive_buffer_size(&self) -> Result<u64, ErrorCode>

The kernel buffer space reserved for sends/receives on this socket.

If the provided value is 0, an invalid-argument error is returned. Any other value will never cause an error, but it might be silently clamped and/or rounded. I.e. after setting a value, reading the same setting back may return a different value.

Equivalent to the SO_RCVBUF and SO_SNDBUF socket options.

Typical errors

• invalid-argument: (set) The provided value was 0.

impl TcpSocket

pub fn set_receive_buffer_size(&self, value: u64) -> Result<(), ErrorCode>

impl TcpSocket

pub fn send_buffer_size(&self) -> Result<u64, ErrorCode>

impl TcpSocket

pub fn set_send_buffer_size(&self, value: u64) -> Result<(), ErrorCode>

impl TcpSocket

pub fn subscribe(&self) -> Pollable

Create a pollable which can be used to poll for, or block on, completion of any of the asynchronous operations of this socket.

When finish-bind, finish-listen, finish-connect or accept return error(would-block), this pollable can be used to wait for their success or failure, after which the method can be retried.

The pollable is not limited to the async operation that happens to be in progress at the time of calling subscribe (if any). Theoretically, subscribe only has to be called once per socket and can then be (re)used for the remainder of the socket’s lifetime.

See https://github.com/WebAssembly/wasi-sockets/TcpSocketOperationalSemantics.md#Pollable-readiness for a more information.

Note: this function is here for WASI Preview2 only. It’s planned to be removed when future is natively supported in Preview3.

impl TcpSocket

pub fn shutdown(&self, shutdown_type: ShutdownType) -> Result<(), ErrorCode>

Initiate a graceful shutdown.

• receive: The socket is not expecting to receive any data from the peer. The input-stream associated with this socket will be closed. Any data still in the receive queue at time of calling this method will be discarded.
• send: The socket has no more data to send to the peer. The output-stream associated with this socket will be closed and a FIN packet will be sent.
• both: Same effect as receive & send combined.

This function is idempotent. Shutting a down a direction more than once has no effect and returns ok.

The shutdown function does not close (drop) the socket.

Typical errors

• invalid-state: The socket is not in the connected state. (ENOTCONN)

References

• https://pubs.opengroup.org/onlinepubs/9699919799/functions/shutdown.html
• https://man7.org/linux/man-pages/man2/shutdown.2.html
• https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-shutdown
• https://man.freebsd.org/cgi/man.cgi?query=shutdown&sektion=2

Trait Implementations

impl Debug for TcpSocket

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.