wstd 0.5.0-draft2

An async standard library for Wasm Components and WASI 0.2
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125

use super::{AsyncPollable, AsyncRead, AsyncWrite};
use std::cell::RefCell;
use std::io::Result;
use wasi::io::streams::{InputStream, OutputStream, StreamError};

#[derive(Debug)]
pub struct AsyncInputStream {
    // Lazily initialized pollable, used for lifetime of stream to check readiness.
    // Field ordering matters: this child must be dropped before stream
    subscription: RefCell<Option<AsyncPollable>>,
    stream: InputStream,
}

impl AsyncInputStream {
    pub fn new(stream: InputStream) -> Self {
        Self {
            subscription: RefCell::new(None),
            stream,
        }
    }
    async fn ready(&self) {
        // Lazily initialize the AsyncPollable
        if self.subscription.borrow().is_none() {
            self.subscription
                .replace(Some(AsyncPollable::new(self.stream.subscribe())));
        }
        // Wait on readiness
        self.subscription
            .borrow()
            .as_ref()
            .expect("populated refcell")
            .wait_for()
            .await;
    }
}

impl AsyncRead for AsyncInputStream {
    async fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        self.ready().await;
        // Ideally, the ABI would be able to read directly into buf. However, with the default
        // generated bindings, it returns a newly allocated vec, which we need to copy into buf.
        let read = match self.stream.read(buf.len() as u64) {
            Ok(r) => r,
            Err(StreamError::Closed) => return Ok(0),
            Err(StreamError::LastOperationFailed(err)) => {
                return Err(std::io::Error::other(err.to_debug_string()))
            }
        };
        let len = read.len();
        buf[0..len].copy_from_slice(&read);
        Ok(len)
    }
}

#[derive(Debug)]
pub struct AsyncOutputStream {
    // Lazily initialized pollable, used for lifetime of stream to check readiness.
    // Field ordering matters: this child must be dropped before stream
    subscription: RefCell<Option<AsyncPollable>>,
    stream: OutputStream,
}

impl AsyncOutputStream {
    pub fn new(stream: OutputStream) -> Self {
        Self {
            subscription: RefCell::new(None),
            stream,
        }
    }
    async fn ready(&self) {
        // Lazily initialize the AsyncPollable
        if self.subscription.borrow().is_none() {
            self.subscription
                .replace(Some(AsyncPollable::new(self.stream.subscribe())));
        }
        // Wait on readiness
        self.subscription
            .borrow()
            .as_ref()
            .expect("populated refcell")
            .wait_for()
            .await;
    }
}
impl AsyncWrite for AsyncOutputStream {
    // Required methods
    async fn write(&mut self, buf: &[u8]) -> Result<usize> {
        // Loops at most twice.
        loop {
            match self.stream.check_write() {
                Ok(0) => {
                    self.ready().await;
                    // Next loop guaranteed to have nonzero check_write, or error.
                    continue;
                }
                Ok(some) => {
                    let writable = some.try_into().unwrap_or(usize::MAX).min(buf.len());
                    match self.stream.write(&buf[0..writable]) {
                        Ok(()) => return Ok(writable),
                        Err(StreamError::Closed) => return Ok(0),
                        Err(StreamError::LastOperationFailed(err)) => {
                            return Err(std::io::Error::other(err.to_debug_string()))
                        }
                    }
                }
                Err(StreamError::Closed) => return Ok(0),
                Err(StreamError::LastOperationFailed(err)) => {
                    return Err(std::io::Error::other(err.to_debug_string()))
                }
            }
        }
    }
    async fn flush(&mut self) -> Result<()> {
        match self.stream.flush() {
            Ok(()) => {
                self.ready().await;
                Ok(())
            }
            Err(StreamError::Closed) => Ok(()),
            Err(StreamError::LastOperationFailed(err)) => {
                Err(std::io::Error::other(err.to_debug_string()))
            }
        }
    }
}