package wasi:io@0.2.0;
interface 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, `error`s 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.
resource error {
/// 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.
to-debug-string: func() -> string;
}
}
/// A poll API intended to let users wait for I/O events on multiple handles
/// at once.
interface poll {
/// `pollable` represents a single I/O event which may be ready, or not.
resource pollable {
/// Return the readiness of a pollable. This function never blocks.
///
/// Returns `true` when the pollable is ready, and `false` otherwise.
ready: func() -> bool;
/// `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.
block: 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.
poll: func(in: list<borrow<pollable>>) -> list<u32>;
}
/// 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.
interface streams {
use error.{error};
use poll.{pollable};
/// An error for input-stream and output-stream operations.
variant stream-error {
/// The last operation (a write or flush) failed before completion.
///
/// More information is available in the `error` payload.
last-operation-failed(error),
/// The stream is closed: no more input will be accepted by the
/// stream. A closed output-stream will return this error on all
/// future operations.
closed
}
/// An input bytestream.
///
/// `input-stream`s 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 input-stream {
/// 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.
read: func(
/// The maximum number of bytes to read
len: u64
) -> result<list<u8>, stream-error>;
/// Read bytes from a stream, after blocking until at least one byte can
/// be read. Except for blocking, behavior is identical to `read`.
blocking-read: func(
/// The maximum number of bytes to read
len: u64
) -> result<list<u8>, stream-error>;
/// 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.
skip: func(
/// The maximum number of bytes to skip.
len: u64,
) -> result<u64, stream-error>;
/// Skip bytes from a stream, after blocking until at least one byte
/// can be skipped. Except for blocking behavior, identical to `skip`.
blocking-skip: func(
/// The maximum number of bytes to skip.
len: u64,
) -> result<u64, stream-error>;
/// 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 `pollable`s created with this function are dropped.
subscribe: func() -> pollable;
}
/// An output bytestream.
///
/// `output-stream`s 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`.
resource output-stream {
/// 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.
check-write: func() -> result<u64, stream-error>;
/// 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.
write: func(
contents: list<u8>
) -> result<_, stream-error>;
/// 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:
///
/// ```text
/// 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
/// ```
blocking-write-and-flush: func(
contents: list<u8>
) -> result<_, stream-error>;
/// 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.
flush: func() -> result<_, stream-error>;
/// Request to flush buffered output, and block until flush completes
/// and stream is ready for writing again.
blocking-flush: func() -> result<_, stream-error>;
/// 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 `pollable`s created with this function are dropped.
subscribe: func() -> pollable;
/// 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.
write-zeroes: func(
/// The number of zero-bytes to write
len: u64
) -> result<_, stream-error>;
/// 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:
///
/// ```text
/// 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
/// ```
blocking-write-zeroes-and-flush: func(
/// The number of zero-bytes to write
len: u64
) -> result<_, stream-error>;
/// 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`.
splice: func(
/// The stream to read from
src: borrow<input-stream>,
/// The number of bytes to splice
len: u64,
) -> result<u64, stream-error>;
/// 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`.
blocking-splice: func(
/// The stream to read from
src: borrow<input-stream>,
/// The number of bytes to splice
len: u64,
) -> result<u64, stream-error>;
}
}
world imports {
import streams;
import poll;
}