World imports

Import interface wasi:cli/environment@0.2.0


Functions

get-environment: func

Get the POSIX-style environment variables.

Each environment variable is provided as a pair of string variable names and string value.

Morally, these are a value import, but until value imports are available in the component model, this import function should return the same values each time it is called.

Return values

get-arguments: func

Get the POSIX-style arguments to the program.

Return values

initial-cwd: func

Return a path that programs should use as their initial current working directory, interpreting . as shorthand for this.

Return values

Import interface wasi:cli/exit@0.2.0


Functions

exit: func

Exit the current instance and any linked instances.

Params

Import interface wasi:io/error@0.2.0


Types

resource error

A resource which represents some error information.

The only method provided by this resource is to-debug-string, which provides some human-readable information about the error.

In the wasi:io package, this resource is returned through the wasi:io/streams/stream-error type.

To provide more specific error information, other interfaces may provide functions to further "downcast" this error into more specific error information. For example, errors returned in streams derived from filesystem types to be described using the filesystem's own error-code type, using the function wasi:filesystem/types/filesystem-error-code, which takes a parameter borrow<error> and returns option<wasi:filesystem/types/error-code>.

The set of functions which can "downcast" an error into a more concrete type is open.

Functions

[method]error.to-debug-string: func

Returns a string that is suitable to assist humans in debugging this error.

WARNING: The returned string should not be consumed mechanically! It may change across platforms, hosts, or other implementation details. Parsing this string is a major platform-compatibility hazard.

Params
Return values

Import interface wasi:io/poll@0.2.0

A poll API intended to let users wait for I/O events on multiple handles at once.


Types

resource pollable

pollable represents a single I/O event which may be ready, or not.

Functions

[method]pollable.ready: func

Return the readiness of a pollable. This function never blocks.

Returns true when the pollable is ready, and false otherwise.

Params
Return values

[method]pollable.block: func

block returns immediately if the pollable is ready, and otherwise blocks until ready.

This function is equivalent to calling poll.poll on a list containing only this pollable.

Params

poll: func

Poll for completion on a set of pollables.

This function takes a list of pollables, which identify I/O sources of interest, and waits until one or more of the events is ready for I/O.

The result list<u32> contains one or more indices of handles in the argument list that is ready for I/O.

If the list contains more elements than can be indexed with a u32 value, this function traps.

A timeout can be implemented by adding a pollable from the wasi-clocks API to the list.

This function does not return a result; polling in itself does not do any I/O so it doesn't fail. If any of the I/O sources identified by the pollables has an error, it is indicated by marking the source as being reaedy for I/O.

Params
Return values

Import interface wasi:io/streams@0.2.0

WASI I/O is an I/O abstraction API which is currently focused on providing stream types.

In the future, the component model is expected to add built-in stream types; when it does, they are expected to subsume this API.


Types

type error

error

#### `type pollable` [`pollable`](#pollable)

#### `variant stream-error`

An error for input-stream and output-stream operations.

Variant Cases

resource input-stream

An input bytestream.

input-streams are non-blocking to the extent practical on underlying platforms. I/O operations always return promptly; if fewer bytes are promptly available than requested, they return the number of bytes promptly available, which could even be zero. To wait for data to be available, use the subscribe function to obtain a pollable which can be polled for using wasi:io/poll.

resource output-stream

An output bytestream.

output-streams are non-blocking to the extent practical on underlying platforms. Except where specified otherwise, I/O operations also always return promptly, after the number of bytes that can be written promptly, which could even be zero. To wait for the stream to be ready to accept data, the subscribe function to obtain a pollable which can be polled for using wasi:io/poll.

Functions

[method]input-stream.read: func

Perform a non-blocking read from the stream.

When the source of a read is binary data, the bytes from the source are returned verbatim. When the source of a read is known to the implementation to be text, bytes containing the UTF-8 encoding of the text are returned.

This function returns a list of bytes containing the read data, when successful. The returned list will contain up to len bytes; it may return fewer than requested, but not more. The list is empty when no bytes are available for reading at this time. The pollable given by subscribe will be ready when more bytes are available.

This function fails with a stream-error when the operation encounters an error, giving last-operation-failed, or when the stream is closed, giving closed.

When the caller gives a len of 0, it represents a request to read 0 bytes. If the stream is still open, this call should succeed and return an empty list, or otherwise fail with closed.

The len parameter is a u64, which could represent a list of u8 which is not possible to allocate in wasm32, or not desirable to allocate as as a return value by the callee. The callee may return a list of bytes less than len in size while more bytes are available for reading.

Params
Return values

[method]input-stream.blocking-read: func

Read bytes from a stream, after blocking until at least one byte can be read. Except for blocking, behavior is identical to read.

Params
Return values

[method]input-stream.skip: func

Skip bytes from a stream. Returns number of bytes skipped.

Behaves identical to read, except instead of returning a list of bytes, returns the number of bytes consumed from the stream.

Params
Return values

[method]input-stream.blocking-skip: func

Skip bytes from a stream, after blocking until at least one byte can be skipped. Except for blocking behavior, identical to skip.

Params
Return values

[method]input-stream.subscribe: func

Create a pollable which will resolve once either the specified stream has bytes available to read or the other end of the stream has been closed. The created pollable is a child resource of the input-stream. Implementations may trap if the input-stream is dropped before all derived pollables created with this function are dropped.

Params
Return values

[method]output-stream.check-write: func

Check readiness for writing. This function never blocks.

Returns the number of bytes permitted for the next call to write, or an error. Calling write with more bytes than this function has permitted will trap.

When this function returns 0 bytes, the subscribe pollable will become ready when this function will report at least 1 byte, or an error.

Params
Return values

[method]output-stream.write: func

Perform a write. This function never blocks.

When the destination of a write is binary data, the bytes from contents are written verbatim. When the destination of a write is known to the implementation to be text, the bytes of contents are transcoded from UTF-8 into the encoding of the destination and then written.

Precondition: check-write gave permit of Ok(n) and contents has a length of less than or equal to n. Otherwise, this function will trap.

returns Err(closed) without writing if the stream has closed since the last call to check-write provided a permit.

Params
Return values

[method]output-stream.blocking-write-and-flush: func

Perform a write of up to 4096 bytes, and then flush the stream. Block until all of these operations are complete, or an error occurs.

This is a convenience wrapper around the use of check-write, subscribe, write, and flush, and is implemented with the following pseudo-code:

let pollable = this.subscribe();
while !contents.is_empty() {
  // Wait for the stream to become writable
  pollable.block();
  let Ok(n) = this.check-write(); // eliding error handling
  let len = min(n, contents.len());
  let (chunk, rest) = contents.split_at(len);
  this.write(chunk  );            // eliding error handling
  contents = rest;
}
this.flush();
// Wait for completion of `flush`
pollable.block();
// Check for any errors that arose during `flush`
let _ = this.check-write();         // eliding error handling
Params
Return values

[method]output-stream.flush: func

Request to flush buffered output. This function never blocks.

This tells the output-stream that the caller intends any buffered output to be flushed. the output which is expected to be flushed is all that has been passed to write prior to this call.

Upon calling this function, the output-stream will not accept any writes (check-write will return ok(0)) until the flush has completed. The subscribe pollable will become ready when the flush has completed and the stream can accept more writes.

Params
Return values

[method]output-stream.blocking-flush: func

Request to flush buffered output, and block until flush completes and stream is ready for writing again.

Params
Return values

[method]output-stream.subscribe: func

Create a pollable which will resolve once the output-stream is ready for more writing, or an error has occured. When this pollable is ready, check-write will return ok(n) with n>0, or an error.

If the stream is closed, this pollable is always ready immediately.

The created pollable is a child resource of the output-stream. Implementations may trap if the output-stream is dropped before all derived pollables created with this function are dropped.

Params
Return values

[method]output-stream.write-zeroes: func

Write zeroes to a stream.

This should be used precisely like write with the exact same preconditions (must use check-write first), but instead of passing a list of bytes, you simply pass the number of zero-bytes that should be written.

Params
Return values

[method]output-stream.blocking-write-zeroes-and-flush: func

Perform a write of up to 4096 zeroes, and then flush the stream. Block until all of these operations are complete, or an error occurs.

This is a convenience wrapper around the use of check-write, subscribe, write-zeroes, and flush, and is implemented with the following pseudo-code:

let pollable = this.subscribe();
while num_zeroes != 0 {
  // Wait for the stream to become writable
  pollable.block();
  let Ok(n) = this.check-write(); // eliding error handling
  let len = min(n, num_zeroes);
  this.write-zeroes(len);         // eliding error handling
  num_zeroes -= len;
}
this.flush();
// Wait for completion of `flush`
pollable.block();
// Check for any errors that arose during `flush`
let _ = this.check-write();         // eliding error handling
Params
Return values

[method]output-stream.splice: func

Read from one stream and write to another.

The behavior of splice is equivelant to:

  1. calling check-write on the output-stream
  2. calling read on the input-stream with the smaller of the check-write permitted length and the len provided to splice
  3. calling write on the output-stream with that read data.

Any error reported by the call to check-write, read, or write ends the splice and reports that error.

This function returns the number of bytes transferred; it may be less than len.

Params
Return values

[method]output-stream.blocking-splice: func

Read from one stream and write to another, with blocking.

This is similar to splice, except that it blocks until the output-stream is ready for writing, and the input-stream is ready for reading, before performing the splice.

Params
Return values

Import interface wasi:cli/stdin@0.2.0


Types

type input-stream

input-stream

----

Functions

get-stdin: func

Return values

Import interface wasi:cli/stdout@0.2.0


Types

type output-stream

output-stream

----

Functions

get-stdout: func

Return values

Import interface wasi:cli/stderr@0.2.0


Types

type output-stream

output-stream

----

Functions

get-stderr: func

Return values

Import interface wasi:cli/terminal-input@0.2.0

Terminal input.

In the future, this may include functions for disabling echoing, disabling input buffering so that keyboard events are sent through immediately, querying supported features, and so on.


Types

resource terminal-input

The input side of a terminal.

Import interface wasi:cli/terminal-output@0.2.0

Terminal output.

In the future, this may include functions for querying the terminal size, being notified of terminal size changes, querying supported features, and so on.


Types

resource terminal-output

The output side of a terminal.

Import interface wasi:cli/terminal-stdin@0.2.0

An interface providing an optional terminal-input for stdin as a link-time authority.


Types

type terminal-input

terminal-input

----

Functions

get-terminal-stdin: func

If stdin is connected to a terminal, return a terminal-input handle allowing further interaction with it.

Return values

Import interface wasi:cli/terminal-stdout@0.2.0

An interface providing an optional terminal-output for stdout as a link-time authority.


Types

type terminal-output

terminal-output

----

Functions

get-terminal-stdout: func

If stdout is connected to a terminal, return a terminal-output handle allowing further interaction with it.

Return values

Import interface wasi:cli/terminal-stderr@0.2.0

An interface providing an optional terminal-output for stderr as a link-time authority.


Types

type terminal-output

terminal-output

----

Functions

get-terminal-stderr: func

If stderr is connected to a terminal, return a terminal-output handle allowing further interaction with it.

Return values

Import interface wasi:clocks/monotonic-clock@0.2.0

WASI Monotonic Clock is a clock API intended to let users measure elapsed time.

It is intended to be portable at least between Unix-family platforms and Windows.

A monotonic clock is a clock which has an unspecified initial value, and successive reads of the clock will produce non-decreasing values.

It is intended for measuring elapsed time.


Types

type pollable

pollable

#### `type instant` `u64`

An instant in time, in nanoseconds. An instant is relative to an unspecified initial value, and can only be compared to instances from the same monotonic-clock.

type duration

u64

A duration of time, in nanoseconds.


Functions

now: func

Read the current value of the clock.

The clock is monotonic, therefore calling this function repeatedly will produce a sequence of non-decreasing values.

Return values

resolution: func

Query the resolution of the clock. Returns the duration of time corresponding to a clock tick.

Return values

subscribe-instant: func

Create a pollable which will resolve once the specified instant occured.

Params
Return values

subscribe-duration: func

Create a pollable which will resolve once the given duration has elapsed, starting at the time at which this function was called. occured.

Params
Return values

Import interface wasi:clocks/wall-clock@0.2.0

WASI Wall Clock is a clock API intended to let users query the current time. The name "wall" makes an analogy to a "clock on the wall", which is not necessarily monotonic as it may be reset.

It is intended to be portable at least between Unix-family platforms and Windows.

A wall clock is a clock which measures the date and time according to some external reference.

External references may be reset, so this clock is not necessarily monotonic, making it unsuitable for measuring elapsed time.

It is intended for reporting the current date and time for humans.


Types

record datetime

A time and date in seconds plus nanoseconds.

Record Fields

Functions

now: func

Read the current value of the clock.

This clock is not monotonic, therefore calling this function repeatedly will not necessarily produce a sequence of non-decreasing values.

The returned timestamps represent the number of seconds since 1970-01-01T00:00:00Z, also known as POSIX's Seconds Since the Epoch, also known as Unix Time.

The nanoseconds field of the output is always less than 1000000000.

Return values

resolution: func

Query the resolution of the clock.

The nanoseconds field of the output is always less than 1000000000.

Return values

Import interface wasi:filesystem/types@0.2.0

WASI filesystem is a filesystem API primarily intended to let users run WASI programs that access their files on their existing filesystems, without significant overhead.

It is intended to be roughly portable between Unix-family platforms and Windows, though it does not hide many of the major differences.

Paths are passed as interface-type strings, meaning they must consist of a sequence of Unicode Scalar Values (USVs). Some filesystems may contain paths which are not accessible by this API.

The directory separator in WASI is always the forward-slash (/).

All paths in WASI are relative paths, and are interpreted relative to a descriptor referring to a base directory. If a path argument to any WASI function starts with /, or if any step of resolving a path, including .. and symbolic link steps, reaches a directory outside of the base directory, or reaches a symlink to an absolute or rooted path in the underlying filesystem, the function fails with error-code::not-permitted.

For more information about WASI path resolution and sandboxing, see WASI filesystem path resolution.


Types

type input-stream

input-stream

#### `type output-stream` [`output-stream`](#output_stream)

#### `type error` [`error`](#error)

#### `type datetime` [`datetime`](#datetime)

#### `type filesize` `u64`

File size or length of a region within a file.

enum descriptor-type

The type of a filesystem object referenced by a descriptor.

Note: This was called filetype in earlier versions of WASI.

Enum Cases

flags descriptor-flags

Descriptor flags.

Note: This was called fdflags in earlier versions of WASI.

Flags members

flags path-flags

Flags determining the method of how paths are resolved.

Flags members

flags open-flags

Open flags used by open-at.

Flags members

type link-count

u64

Number of hard links to an inode.

record descriptor-stat

File attributes.

Note: This was called filestat in earlier versions of WASI.

Record Fields

variant new-timestamp

When setting a timestamp, this gives the value to set it to.

Variant Cases

record directory-entry

A directory entry.

Record Fields

enum error-code

Error codes returned by functions, similar to errno in POSIX. Not all of these error codes are returned by the functions provided by this API; some are used in higher-level library layers, and others are provided merely for alignment with POSIX.

Enum Cases

enum advice

File or memory access pattern advisory information.

Enum Cases

record metadata-hash-value

A 128-bit hash value, split into parts because wasm doesn't have a 128-bit integer type.

Record Fields

resource descriptor

A descriptor is a reference to a filesystem object, which may be a file, directory, named pipe, special file, or other object on which filesystem calls may be made.

resource directory-entry-stream

A stream of directory entries.

Functions

[method]descriptor.read-via-stream: func

Return a stream for reading from a file, if available.

May fail with an error-code describing why the file cannot be read.

Multiple read, write, and append streams may be active on the same open file and they do not interfere with each other.

Note: This allows using read-stream, which is similar to read in POSIX.

Params
Return values

[method]descriptor.write-via-stream: func

Return a stream for writing to a file, if available.

May fail with an error-code describing why the file cannot be written.

Note: This allows using write-stream, which is similar to write in POSIX.

Params
Return values

[method]descriptor.append-via-stream: func

Return a stream for appending to a file, if available.

May fail with an error-code describing why the file cannot be appended.

Note: This allows using write-stream, which is similar to write with O_APPEND in in POSIX.

Params
Return values

[method]descriptor.advise: func

Provide file advisory information on a descriptor.

This is similar to posix_fadvise in POSIX.

Params
Return values

[method]descriptor.sync-data: func

Synchronize the data of a file to disk.

This function succeeds with no effect if the file descriptor is not opened for writing.

Note: This is similar to fdatasync in POSIX.

Params
Return values

[method]descriptor.get-flags: func

Get flags associated with a descriptor.

Note: This returns similar flags to fcntl(fd, F_GETFL) in POSIX.

Note: This returns the value that was the fs_flags value returned from fdstat_get in earlier versions of WASI.

Params
Return values

[method]descriptor.get-type: func

Get the dynamic type of a descriptor.

Note: This returns the same value as the type field of the fd-stat returned by stat, stat-at and similar.

Note: This returns similar flags to the st_mode & S_IFMT value provided by fstat in POSIX.

Note: This returns the value that was the fs_filetype value returned from fdstat_get in earlier versions of WASI.

Params
Return values

[method]descriptor.set-size: func

Adjust the size of an open file. If this increases the file's size, the extra bytes are filled with zeros.

Note: This was called fd_filestat_set_size in earlier versions of WASI.

Params
Return values

[method]descriptor.set-times: func

Adjust the timestamps of an open file or directory.

Note: This is similar to futimens in POSIX.

Note: This was called fd_filestat_set_times in earlier versions of WASI.

Params
Return values

[method]descriptor.read: func

Read from a descriptor, without using and updating the descriptor's offset.

This function returns a list of bytes containing the data that was read, along with a bool which, when true, indicates that the end of the file was reached. The returned list will contain up to length bytes; it may return fewer than requested, if the end of the file is reached or if the I/O operation is interrupted.

In the future, this may change to return a stream<u8, error-code>.

Note: This is similar to pread in POSIX.

Params
Return values

[method]descriptor.write: func

Write to a descriptor, without using and updating the descriptor's offset.

It is valid to write past the end of a file; the file is extended to the extent of the write, with bytes between the previous end and the start of the write set to zero.

In the future, this may change to take a stream<u8, error-code>.

Note: This is similar to pwrite in POSIX.

Params
Return values

[method]descriptor.read-directory: func

Read directory entries from a directory.

On filesystems where directories contain entries referring to themselves and their parents, often named . and .. respectively, these entries are omitted.

This always returns a new stream which starts at the beginning of the directory. Multiple streams may be active on the same directory, and they do not interfere with each other.

Params
Return values

[method]descriptor.sync: func

Synchronize the data and metadata of a file to disk.

This function succeeds with no effect if the file descriptor is not opened for writing.

Note: This is similar to fsync in POSIX.

Params
Return values

[method]descriptor.create-directory-at: func

Create a directory.

Note: This is similar to mkdirat in POSIX.

Params
Return values

[method]descriptor.stat: func

Return the attributes of an open file or directory.

Note: This is similar to fstat in POSIX, except that it does not return device and inode information. For testing whether two descriptors refer to the same underlying filesystem object, use is-same-object. To obtain additional data that can be used do determine whether a file has been modified, use metadata-hash.

Note: This was called fd_filestat_get in earlier versions of WASI.

Params
Return values

[method]descriptor.stat-at: func

Return the attributes of a file or directory.

Note: This is similar to fstatat in POSIX, except that it does not return device and inode information. See the stat description for a discussion of alternatives.

Note: This was called path_filestat_get in earlier versions of WASI.

Params
Return values

[method]descriptor.set-times-at: func

Adjust the timestamps of a file or directory.

Note: This is similar to utimensat in POSIX.

Note: This was called path_filestat_set_times in earlier versions of WASI.

Params
Return values

[method]descriptor.link-at: func

Create a hard link.

Note: This is similar to linkat in POSIX.

Params
Return values

[method]descriptor.open-at: func

Open a file or directory.

The returned descriptor is not guaranteed to be the lowest-numbered descriptor not currently open/ it is randomized to prevent applications from depending on making assumptions about indexes, since this is error-prone in multi-threaded contexts. The returned descriptor is guaranteed to be less than 2**31.

If flags contains descriptor-flags::mutate-directory, and the base descriptor doesn't have descriptor-flags::mutate-directory set, open-at fails with error-code::read-only.

If flags contains write or mutate-directory, or open-flags contains truncate or create, and the base descriptor doesn't have descriptor-flags::mutate-directory set, open-at fails with error-code::read-only.

Note: This is similar to openat in POSIX.

Params
Return values

[method]descriptor.readlink-at: func

Read the contents of a symbolic link.

If the contents contain an absolute or rooted path in the underlying filesystem, this function fails with error-code::not-permitted.

Note: This is similar to readlinkat in POSIX.

Params
Return values

[method]descriptor.remove-directory-at: func

Remove a directory.

Return error-code::not-empty if the directory is not empty.

Note: This is similar to unlinkat(fd, path, AT_REMOVEDIR) in POSIX.

Params
Return values

[method]descriptor.rename-at: func

Rename a filesystem object.

Note: This is similar to renameat in POSIX.

Params
Return values

[method]descriptor.symlink-at: func

Create a symbolic link (also known as a "symlink").

If old-path starts with /, the function fails with error-code::not-permitted.

Note: This is similar to symlinkat in POSIX.

Params
Return values

[method]descriptor.unlink-file-at: func

Unlink a filesystem object that is not a directory.

Return error-code::is-directory if the path refers to a directory. Note: This is similar to unlinkat(fd, path, 0) in POSIX.

Params
Return values

[method]descriptor.is-same-object: func

Test whether two descriptors refer to the same filesystem object.

In POSIX, this corresponds to testing whether the two descriptors have the same device (st_dev) and inode (st_ino or d_ino) numbers. wasi-filesystem does not expose device and inode numbers, so this function may be used instead.

Params
Return values

[method]descriptor.metadata-hash: func

Return a hash of the metadata associated with a filesystem object referred to by a descriptor.

This returns a hash of the last-modification timestamp and file size, and may also include the inode number, device number, birth timestamp, and other metadata fields that may change when the file is modified or replaced. It may also include a secret value chosen by the implementation and not otherwise exposed.

Implementations are encourated to provide the following properties:

However, none of these is required.

Params
Return values

[method]descriptor.metadata-hash-at: func

Return a hash of the metadata associated with a filesystem object referred to by a directory descriptor and a relative path.

This performs the same hash computation as metadata-hash.

Params
Return values

[method]directory-entry-stream.read-directory-entry: func

Read a single directory entry from a directory-entry-stream.

Params
Return values

filesystem-error-code: func

Attempts to extract a filesystem-related error-code from the stream error provided.

Stream operations which return stream-error::last-operation-failed have a payload with more information about the operation that failed. This payload can be passed through to this function to see if there's filesystem-related information about the error to return.

Note that this function is fallible because not all stream-related errors are filesystem-related errors.

Params
Return values

Import interface wasi:filesystem/preopens@0.2.0


Types

type descriptor

descriptor

----

Functions

get-directories: func

Return the set of preopened directories, and their path.

Return values

Import interface wasi:sockets/network@0.2.0


Types

resource network

An opaque resource that represents access to (a subset of) the network. This enables context-based security for networking. There is no need for this to map 1:1 to a physical network interface.

enum error-code

Error codes.

In theory, every API can return any error code. In practice, API's typically only return the errors documented per API combined with a couple of errors that are always possible:

See each individual API for what the POSIX equivalents are. They sometimes differ per API.

Enum Cases

enum ip-address-family

Enum Cases

tuple ipv4-address

Tuple Fields

tuple ipv6-address

Tuple Fields

variant ip-address

Variant Cases

record ipv4-socket-address

Record Fields

record ipv6-socket-address

Record Fields

variant ip-socket-address

Variant Cases

Import interface wasi:sockets/instance-network@0.2.0

This interface provides a value-export of the default network handle..


Types

type network

network

----

Functions

instance-network: func

Get a handle to the default network.

Return values

Import interface wasi:sockets/udp@0.2.0


Types

type pollable

pollable

#### `type network` [`network`](#network)

#### `type error-code` [`error-code`](#error_code)

#### `type ip-socket-address` [`ip-socket-address`](#ip_socket_address)

#### `type ip-address-family` [`ip-address-family`](#ip_address_family)

#### `record incoming-datagram`

A received datagram.

Record Fields

record outgoing-datagram

A datagram to be sent out.

Record Fields

resource udp-socket

A UDP socket handle.

resource incoming-datagram-stream

resource outgoing-datagram-stream


Functions

[method]udp-socket.start-bind: func

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 port is zero, the socket will be bound to a random free port.

Typical errors

Implementors note

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

Params
Return values

[method]udp-socket.finish-bind: func

Params
Return values

[method]udp-socket.stream: func

Set up inbound & outbound communication channels, optionally to a specific peer.

This function only changes the local socket configuration and does not generate any network traffic. On success, the remote-address of the socket is updated. The local-address may be updated as well, based on the best network path to remote-address.

When a remote-address is provided, the returned streams are limited to communicating with that specific peer:

This method may be called multiple times on the same socket to change its association, but only the most recently returned pair of streams will be operational. Implementations may trap if the streams returned by a previous invocation haven't been dropped yet before calling stream again.

The POSIX equivalent in pseudo-code is:

if (was previously connected) {
  connect(s, AF_UNSPEC)
}
if (remote_address is Some) {
  connect(s, remote_address)
}

Unlike in POSIX, the socket must already be explicitly bound.

Typical errors

References

Params
Return values

[method]udp-socket.local-address: func

Get the current bound 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

References

Params
Return values

[method]udp-socket.remote-address: func

Get the address the socket is currently streaming to.

Typical errors

References

Params
Return values

[method]udp-socket.address-family: func

Whether this is a IPv4 or IPv6 socket.

Equivalent to the SO_DOMAIN socket option.

Params
Return values

[method]udp-socket.unicast-hop-limit: func

Equivalent to the IP_TTL & IPV6_UNICAST_HOPS socket options.

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

Typical errors

Params
Return values

[method]udp-socket.set-unicast-hop-limit: func

Params
Return values

[method]udp-socket.receive-buffer-size: func

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

Params
Return values

[method]udp-socket.set-receive-buffer-size: func

Params
Return values

[method]udp-socket.send-buffer-size: func

Params
Return values

[method]udp-socket.set-send-buffer-size: func

Params
Return values

[method]udp-socket.subscribe: func

Create a pollable which will resolve once the socket is ready for I/O.

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

Params
Return values

[method]incoming-datagram-stream.receive: func

Receive messages on the socket.

This function attempts to receive up to max-results datagrams on the socket without blocking. The returned list may contain fewer elements than requested, but never more.

This function returns successfully with an empty list when either:

Typical errors

References

Params
Return values

[method]incoming-datagram-stream.subscribe: func

Create a pollable which will resolve once the stream is ready to receive again.

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

Params
Return values

[method]outgoing-datagram-stream.check-send: func

Check readiness for sending. This function never blocks.

Returns the number of datagrams permitted for the next call to send, or an error. Calling send with more datagrams than this function has permitted will trap.

When this function returns ok(0), the subscribe pollable will become ready when this function will report at least ok(1), or an error.

Never returns would-block.

Params
Return values

[method]outgoing-datagram-stream.send: func

Send messages on the socket.

This function attempts to send all provided datagrams on the socket without blocking and returns how many messages were actually sent (or queued for sending). This function never returns error(would-block). If none of the datagrams were able to be sent, ok(0) is returned.

This function semantically behaves the same as iterating the datagrams list and sequentially sending each individual datagram until either the end of the list has been reached or the first error occurred. If at least one datagram has been sent successfully, this function never returns an error.

If the input list is empty, the function returns ok(0).

Each call to send must be permitted by a preceding check-send. Implementations must trap if either check-send was not called or datagrams contains more items than check-send permitted.

Typical errors

References

Params
Return values

[method]outgoing-datagram-stream.subscribe: func

Create a pollable which will resolve once the stream is ready to send again.

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

Params
Return values

Import interface wasi:sockets/udp-create-socket@0.2.0


Types

type network

network

#### `type error-code` [`error-code`](#error_code)

#### `type ip-address-family` [`ip-address-family`](#ip_address_family)

#### `type udp-socket` [`udp-socket`](#udp_socket)

----

Functions

create-udp-socket: func

Create a new UDP socket.

Similar to socket(AF_INET or AF_INET6, SOCK_DGRAM, IPPROTO_UDP) in POSIX. On IPv6 sockets, IPV6_V6ONLY is enabled by default and can't be configured otherwise.

This function does not require a network capability handle. This is considered to be safe because at time of creation, the socket is not bound to any network yet. Up to the moment bind is called, the socket is effectively an in-memory configuration object, unable to communicate with the outside world.

All sockets are non-blocking. Use the wasi-poll interface to block on asynchronous operations.

Typical errors

References:

Params
Return values

Import interface wasi:sockets/tcp@0.2.0


Types

type input-stream

input-stream

#### `type output-stream` [`output-stream`](#output_stream)

#### `type pollable` [`pollable`](#pollable)

#### `type duration` [`duration`](#duration)

#### `type network` [`network`](#network)

#### `type error-code` [`error-code`](#error_code)

#### `type ip-socket-address` [`ip-socket-address`](#ip_socket_address)

#### `type ip-address-family` [`ip-address-family`](#ip_address_family)

#### `enum shutdown-type`

Enum Cases

resource tcp-socket

A TCP socket resource.

The socket can be in one of the following states:

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.

Functions

[method]tcp-socket.start-bind: func

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

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

Params
Return values

[method]tcp-socket.finish-bind: func

Params
Return values

[method]tcp-socket.start-connect: func

Connect to a remote endpoint.

On success:

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

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

Params
Return values

[method]tcp-socket.finish-connect: func

Params
Return values

[method]tcp-socket.start-listen: func

Start listening for new connections.

Transitions the socket into the listening state.

Unlike POSIX, the socket must already be explicitly bound.

Typical errors

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

Params
Return values

[method]tcp-socket.finish-listen: func

Params
Return values

[method]tcp-socket.accept: func

Accept a new client socket.

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

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

References

Params
Return values

[method]tcp-socket.local-address: func

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

References

Params
Return values

[method]tcp-socket.remote-address: func

Get the remote address.

Typical errors

References

Params
Return values

[method]tcp-socket.is-listening: func

Whether the socket is in the listening state.

Equivalent to the SO_ACCEPTCONN socket option.

Params
Return values

[method]tcp-socket.address-family: func

Whether this is a IPv4 or IPv6 socket.

Equivalent to the SO_DOMAIN socket option.

Params
Return values

[method]tcp-socket.set-listen-backlog-size: func

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

Params
Return values

[method]tcp-socket.keep-alive-enabled: func

Enables or disables keepalive.

The keepalive behavior can be adjusted using:

Equivalent to the SO_KEEPALIVE socket option.

Params
Return values

[method]tcp-socket.set-keep-alive-enabled: func

Params
Return values

[method]tcp-socket.keep-alive-idle-time: func

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

Params
Return values

[method]tcp-socket.set-keep-alive-idle-time: func

Params
Return values

[method]tcp-socket.keep-alive-interval: func

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

Params
Return values

[method]tcp-socket.set-keep-alive-interval: func

Params
Return values

[method]tcp-socket.keep-alive-count: func

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

Params
Return values

[method]tcp-socket.set-keep-alive-count: func

Params
Return values

[method]tcp-socket.hop-limit: func

Equivalent to the IP_TTL & IPV6_UNICAST_HOPS socket options.

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

Typical errors

Params
Return values

[method]tcp-socket.set-hop-limit: func

Params
Return values

[method]tcp-socket.receive-buffer-size: func

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

Params
Return values

[method]tcp-socket.set-receive-buffer-size: func

Params
Return values

[method]tcp-socket.send-buffer-size: func

Params
Return values

[method]tcp-socket.set-send-buffer-size: func

Params
Return values

[method]tcp-socket.subscribe: func

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.

Params
Return values

[method]tcp-socket.shutdown: func

Initiate a graceful shutdown.

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

References

Params
Return values

Import interface wasi:sockets/tcp-create-socket@0.2.0


Types

type network

network

#### `type error-code` [`error-code`](#error_code)

#### `type ip-address-family` [`ip-address-family`](#ip_address_family)

#### `type tcp-socket` [`tcp-socket`](#tcp_socket)

----

Functions

create-tcp-socket: func

Create a new TCP socket.

Similar to socket(AF_INET or AF_INET6, SOCK_STREAM, IPPROTO_TCP) in POSIX. On IPv6 sockets, IPV6_V6ONLY is enabled by default and can't be configured otherwise.

This function does not require a network capability handle. This is considered to be safe because at time of creation, the socket is not bound to any network yet. Up to the moment bind/connect is called, the socket is effectively an in-memory configuration object, unable to communicate with the outside world.

All sockets are non-blocking. Use the wasi-poll interface to block on asynchronous operations.

Typical errors

References

Params
Return values

Import interface wasi:sockets/ip-name-lookup@0.2.0


Types

type pollable

pollable

#### `type network` [`network`](#network)

#### `type error-code` [`error-code`](#error_code)

#### `type ip-address` [`ip-address`](#ip_address)

#### `resource resolve-address-stream`


Functions

resolve-addresses: func

Resolve an internet host name to a list of IP addresses.

Unicode domain names are automatically converted to ASCII using IDNA encoding. If the input is an IP address string, the address is parsed and returned as-is without making any external requests.

See the wasi-socket proposal README.md for a comparison with getaddrinfo.

This function never blocks. It either immediately fails or immediately returns successfully with a resolve-address-stream that can be used to (asynchronously) fetch the results.

Typical errors

References:

Params
Return values

[method]resolve-address-stream.resolve-next-address: func

Returns the next address from the resolver.

This function should be called multiple times. On each call, it will return the next address in connection order preference. If all addresses have been exhausted, this function returns none.

This function never returns IPv4-mapped IPv6 addresses.

Typical errors

Params
Return values

[method]resolve-address-stream.subscribe: func

Create a pollable which will resolve once the stream is ready for I/O.

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

Params
Return values

Import interface wasi:random/random@0.2.0

WASI Random is a random data API.

It is intended to be portable at least between Unix-family platforms and Windows.


Functions

get-random-bytes: func

Return len cryptographically-secure random or pseudo-random bytes.

This function must produce data at least as cryptographically secure and fast as an adequately seeded cryptographically-secure pseudo-random number generator (CSPRNG). It must not block, from the perspective of the calling program, under any circumstances, including on the first request and on requests for numbers of bytes. The returned data must always be unpredictable.

This function must always return fresh data. Deterministic environments must omit this function, rather than implementing it with deterministic data.

Params
Return values

get-random-u64: func

Return a cryptographically-secure random or pseudo-random u64 value.

This function returns the same type of data as get-random-bytes, represented as a u64.

Return values

Import interface wasi:random/insecure@0.2.0

The insecure interface for insecure pseudo-random numbers.

It is intended to be portable at least between Unix-family platforms and Windows.


Functions

get-insecure-random-bytes: func

Return len insecure pseudo-random bytes.

This function is not cryptographically secure. Do not use it for anything related to security.

There are no requirements on the values of the returned bytes, however implementations are encouraged to return evenly distributed values with a long period.

Params
Return values

get-insecure-random-u64: func

Return an insecure pseudo-random u64 value.

This function returns the same type of pseudo-random data as get-insecure-random-bytes, represented as a u64.

Return values

Import interface wasi:random/insecure-seed@0.2.0

The insecure-seed interface for seeding hash-map DoS resistance.

It is intended to be portable at least between Unix-family platforms and Windows.


Functions

insecure-seed: func

Return a 128-bit value that may contain a pseudo-random value.

The returned value is not required to be computed from a CSPRNG, and may even be entirely deterministic. Host implementations are encouraged to provide pseudo-random values to any program exposed to attacker-controlled content, to enable DoS protection built into many languages' hash-map implementations.

This function is intended to only be called once, by a source language to initialize Denial Of Service (DoS) protection in its hash-map implementation.

Expected future evolution

This will likely be changed to a value import, to prevent it from being called multiple times and potentially used for purposes other than DoS protection.

Return values